Patent Publication Number: US-11661824-B2

Title: Autonomous perforating drone

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority (e.g. as a continuation application) to U.S. patent application Ser. No. 16/542,890 filed Aug. 16, 2019, and thereby to all priority claims therein. 
     Specifically, U.S. patent application Ser. No. 16/542,890 claims priority to U.S. patent application Ser. No. 16/537,720, filed Aug. 12, 2019, which claims the benefit of U.S. Provisional Patent Application No. 62/831,215, filed Apr. 9, 2019 and U.S. Provisional Patent Application No. 62/823,737, filed Mar. 26, 2019, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 also claims priority to U.S. Provisional Application No. 62/720,638, filed Aug. 21, 2018, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 also claims priority to U.S. patent application Ser. No. 16/455,816, filed Jun. 28, 2019 (now issued as U.S. Pat. No. 10,844,696), which claims priority to U.S. patent application Ser. No. 16/272,326 filed Feb. 11, 2019 (now issued as U.S. Pat. No. 10,458,213), which claims the benefit of U.S. Provisional Patent Application No. 62/780,427 filed Dec. 17, 2018 and U.S. Provisional Patent Application No. 62/699,484 filed Jul. 17, 2018, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 claims priority to U.S. application Ser. No. 16/451,440, filed Jun. 25, 2019 (now issued as U.S. Pat. No. 10,794,159), which claims the benefit of U.S. Provisional Patent Application No. 62/842,329, filed May 2, 2019, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 also claims priority to International Patent Application No. PCT/EP2019/066919, filed Jun. 25, 2019, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 also claims the benefit of U.S. Provisional Patent Application No. 62/816,649, filed Mar. 11, 2019, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 also claims priority to International Patent Application No. PCT/IB2019/000526, filed Apr. 12, 2019, which claims priority to International Patent Application No. PCT/IB2019/000537, filed Mar. 18, 2019, which claims the benefit of U.S. Provisional Patent Application No. 62/678,636 filed May 31, 2018, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 also claims priority to International Patent Application No. PCT/IB2019/000530 filed Mar. 29, 2019, which claims the benefit of U.S. Provisional Patent Application No. 62/690,314 filed Jun. 26, 2018, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 also claims the benefit of U.S. Provisional Patent Application No. 62/765,185 filed Aug. 20, 2018, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 also claims priority to U.S. patent application Ser. No. 16/272,326 filed Feb. 11, 2019 (now issued as U.S. Pat. No. 10,458,213), which claims the benefit of U.S. Provisional Patent Application No. 62/780,427 filed Dec. 17, 2018 and U.S. Provisional Patent Application No. 62/699,484 filed Jul. 17, 2018, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 also claims the benefit of U.S. Provisional Patent Application No. 62/823,737 filed Mar. 26, 2019, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 also claims the benefit of U.S. Provisional Patent Application No. 62/827,468 filed Apr. 1, 2019, to which this application also claims the benefit. 
     U.S. patent application Ser. No. 16/542,890 also claims the benefit of U.S. Provisional Patent Application No. 62/831,215 filed Apr. 9, 2019, to which this application also claims the benefit. The entire contents of each application listed above are incorporated herein by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Hydraulic Fracturing (or, “fracking”) is a commonly-used method for extracting oil and gas from geological formations (i.e., “hydrocarbon bearing formations”) such as shale and tight-rock formations. Fracking typically involves, among other things, drilling a wellbore into a hydrocarbon bearing formation; installing casing(s) and tubing; deploying a perforating gun including shaped explosive charges in the wellbore via a wireline or other methods; positioning the perforating gun within the wellbore at a desired area; perforating the wellbore and the hydrocarbon formation by detonating the shaped charges; pumping high hydraulic pressure fracking fluid into the wellbore to force open perforations, cracks, and imperfections in the hydrocarbon formation; delivering a proppant material (such as sand or other hard, granular materials) into the hydrocarbon formation to hold open the perforations, fractures, and cracks (giving the tight-rock formation permeability) through which hydrocarbons flow out of the hydrocarbon formation; and, collecting the liberated hydrocarbons via the wellbore. 
     Perforating the wellbore and the hydrocarbon formations is typically done using one or more perforating guns. For example, as shown in  FIG.  1   , a conventional perforating gun string  1100  may have two or more perforating guns  1110 . Each perforating gun  1110  may have a substantially cylindrical gun barrel  1120  housing a charge carrier  1130  including, among other things, one more shaped charges  1140 , a detonating cord  1150  for detonating the shaped charges  1140 , and a conductive line  1160  for relaying an electrical signal between connected perforating guns  1110 . 
     Shaped charges  1140  in the perforating gun  1110  are typically detonated in a “top-fire” sequence from a topmost shaped charge  1141  to a bottommost shaped charge  1142 . For purposes of this disclosure, “topmost” means furthest “upstream,” or towards the well surface, and “bottommost” means furthest “downstream,” or further from the surface within the well. The top-fire sequence is initiated by a detonator  1145  positioned nearest the topmost shaped charge  1141 . The top-fire sequence may be problematic for any perforating gun or wellbore tool that is detonated while traveling at high speed, because the velocity of the tool and the wellbore fluid combined with the force from detonating a topmost explosive charge may separate and scatter different portions of the tool. This may decrease accuracy in perforating at particular locations, cause failure of explosive charges or other components, result in greater amounts of debris, and the like. In addition, it is generally more favorable for the deployment and physical conveyance for pump down operations of the wellbore tool if most of the weight of the tool (i.e., the detonator and associated control components) is at the front (downstream end) of the tool in relation to its direction of movement. 
       FIG.  1 B  shows a cross-sectional view of a wellbore and wellhead according to the prior art use of a wireline cable  2012  to place drones in a wellbore  2016 . In oil and gas wells, the wellbore  2016 , as illustrated in  FIG.  1 B  is a narrow shaft drilled in the ground, vertically and/or horizontally deviated. A wellbore  2016  can include a substantially vertical portion as well as a substantially horizontal portion and a typical wellbore may be over a mile in depth (e.g., the vertical portion) and several miles in length (e.g., the horizontal portion). The wellbore  2016  is usually fitted with a wellbore casing that includes multiple segments (e.g., about 40-foot segments) that are connected to one another by couplers. A coupler (e.g., a collar), may connect two sections of wellbore casing. 
     In the oil and gas industry, the wireline cable  2012 , electric line or e-line are cabling technology used to lower and retrieve equipment or measurement devices into and out of the wellbore  2016  of an oil or gas well for the purpose of delivering an explosive charge, evaluation of the wellbore  2016  or other well-related tasks. Other methods include tubing conveyed (i.e., TCP for perforating) slickline or coil tubing conveyance. A speed of unwinding the wireline cable  2012  and winding the wireline cable  2012  back up is limited based on a speed of the wireline equipment  2062  and forces on the wireline cable  2012  itself (e.g., friction within the well). Because of these limitations, it typically can take several hours for a wireline cable  2012  and a toolstring  2031  to be lowered into a well and another several hours for the wireline cable  2012  to be wound back up and the expended toolstring retrieved. The wireline equipment  2062  feeds wireline  2012  through wellhead  2060 . When detonating explosives, the wireline cable  2012  will be used to position the toolstring  2031  of perforating guns  2018  containing the explosives into the wellbore  2016 . After the explosives are detonated, the wireline cable  2012  will have to be extracted or retrieved from the well. 
     Wireline cables and TCP systems have other limitations such as becoming damaged after multiple uses in the wellbore due to, among other issues, friction associated with the wireline cable rubbing against the sides of the wellbore. Location within the wellbore is a simple function of the length of wireline cable that has been sent into the well. Thus, the use of wireline may be a critical and very useful component in the oil and gas industry yet also presents significant engineering challenges and is typically quite time consuming. It would therefore be desirable to provide a system that can minimize or even eliminate the use of wireline cables for activity within a wellbore while still enabling the position of the downhole equipment, e.g., the toolstring  2031 , to be monitored. 
     During many critical operations utilizing equipment disposed in a wellbore, it is important to know the location and depth of the equipment in the wellbore at a particular time. When utilizing a wireline cable for placement and potential retrieval of equipment, the location of the equipment within the well is known or, at least, may be estimated depending upon how much of the wireline cable has been fed into the wellbore. Similarly, the speed of the equipment within the wellbore is determined by the speed at which the wireline cable is fed into the wellbore. As is the case for a toolstring  2031  attached to a wireline, determining depth, location and orientation of a toolstring  2031  within a wellbore  2016  is typically a prerequisite for proper functioning. 
     One known means of locating a toolstring  2031 , whether tethered or untethered, within a wellbore involves a casing collar locator (“CCL”) or similar arrangement, which utilizes a passive system of magnets and coils to detect increased thickness/mass in a wellbore casing  1580  ( FIG.  7   ) at portions where coupling collars  1590  ( FIG.  7   ) connect two sections of wellbore casing  1582 ,  1584  ( FIG.  7   ). A toolstring  2031  equipped with a CCL may be moved through a portion of the wellbore casing  1580  having the collar  1590 . The increased wellbore wall thickness/mass the collar  1590  results in a distortion of the magnetic field (flux) around the CCL magnet. This magnetic field distortion, in turn, results in a small current being induced in a coil; this induced current is detected by a processor/onboard computer which is part of the CCL. In a typical embodiment of known CCL, the computer ‘counts’ the number of coupling collars  1590  detected and calculates a location along the wellbore  2016  based on the running count. 
     Another known means of locating a toolstring  2031  within a wellbore  2016  involves tags attached at known locations along the wellbore casing  1580 . The tags, e.g., radio frequency identification (“RFID”) tags, may be attached on or adjacent to casing collars but placement unrelated to casing collars is also an option. Electronics for detecting the tags are integrated with the toolstring  2031  and the onboard computer may ‘count’ the tags that have been passed. Alternatively, each tag attached to a portion of the wellbore may be uniquely identified. The detecting electronics may be configured to detect the unique tag identifier and pass this information along to the computer, which can then determine current location of the toolstring  2031  along the wellbore  2016 . 
     Similar operations and challenges may be encountered with downhole delivery, deployment, and/or initiation of a variety of wellbore tools besides perforating guns. For example, a wellbore tool may be a puncher gun, logging tool, jet cutter, plug, frac plug, bridge plug, setting tool, self-setting bridge plug, self-setting frac plug, mapping/positioning/orientating tool, bailer/dump bailer tool, or other ballistic tool. For purposes of this disclosure, a wellbore tool is any such tool, listed or otherwise, that is delivered, deployed, or initiated in a wellbore, and the disclosed exemplary embodiments are not limited to any particular wellbore tool. 
     Accordingly, current wellbore operations and system(s) require substantial amounts of onsite personnel and equipment. Even with large gun strings, a substantial amount of time, equipment, and labor may be required to deploy the perforating gun or wellbore tool string, position the perforating gun or wellbore tool string at the desired location(s), and retrieve the fired perforating gun assemblies post perforating. Further, current perforating devices and systems may be made from materials that remain in the wellbore after detonation of the shaped charges and leave a large amount of debris that must either be removed from the wellbore or left within. Accordingly, devices, systems, and methods that may reduce the time, equipment, labor, and debris associated with downhole operations would be beneficial. 
     Knowledge of the location, depth and velocity of the toolstring in the absence of a wireline cable would be essential. The present disclosure is further associated with systems and methods of determining location along a wellbore  2016  that do not necessarily rely on the presence of casing collars or any other standardized structural element, e.g., tags, associated with the wellbore casing  1580 . 
     BRIEF DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     In an aspect, the disclosure relates to an autonomous perforating drone for downhole delivery of one or more wellbore tools. The autonomous perforating drone may comprise a perforating assembly section including at least one aperture configured for receiving a shaped charge; a control module section positioned upstream of the perforating assembly section relative to an orientation of the drone when deployed in the wellbore, the control module section including a hollow interior portion; a ballistic channel open to and extending from the hollow interior portion to the at least one aperture in the perforating assembly section; and, a control module positioned within the hollow interior portion of the control module section. The control module may include a housing enclosing a donor charge within an inner area of the control module, the donor charge being positioned adjacent to the ballistic channel. A receiver booster may be positioned within the ballistic channel, at the portion of the ballistic channel that extends to the at least one aperture, such that the receiver booster may be configured to directly initiate a shaped charge received in the aperture. 
     In another aspect, the disclosure relates to a method for perforating a wellbore casing or hydrocarbon formation. The method may include arming an autonomous perforating drone according to the exemplary embodiments, e.g., including a perforating assembly section including at least one shaped charge received in an aperture, wherein at least a portion of the shaped charge and the aperture extend into a body of the drone, a control module section positioned upstream of the perforating assembly section relative to an orientation of the drone when deployed in the wellbore, the control module section including a hollow interior portion, a ballistic channel open to and extending from the hollow interior portion to the at least one aperture in the perforating assembly section, and a control module positioned within the hollow interior portion of the control module section. The control module may include a housing enclosing a detonator and a donor charge, the detonator being configured for initiating the donor charge which is positioned adjacent to the ballistic channel. A receiver booster may be positioned within the ballistic channel, at the portion of the ballistic channel that extends to the at least one aperture, and a ballistic interrupt may be positioned within the ballistic channel between the donor charge and the receiver booster in a spaced apart configuration from the donor charge and the receiver booster. The ballistic interrupt may be movable between a closed state and an open state and arming the autonomous perforating drone may include moving the ballistic interrupt from the closed state to the open state. The method may further include deploying the drone into the wellbore and detonating the at least one shaped charge. 
     In a further aspect, the disclosure relates to an autonomous perforating drone for downhole delivery of one or more wellbore tools, comprising: a perforating assembly section; a control module section positioned upstream of the perforating assembly section relative to an orientation of the drone when deployed in the wellbore, the control module section including a hollow interior portion; a ballistic channel open to and extending from the hollow interior portion into at least a portion of the perforating assembly section; a control module positioned within the hollow interior portion of the control module section, and a donor charge housed within the control module and substantially aligned with the ballistic channel; a receiver booster positioned at least in part within the portion of the ballistic channel within the perforating assembly section; a first plurality of shaped charges received in a first plurality of shaped charge apertures in the body portion of the drone positioned at the perforating assembly section. In the exemplary embodiment(s), the first plurality of shaped charge apertures are arranged in a first single radial plane and an initiation end of each of the first plurality of shaped charges is substantially adjacent to the receiver booster when the respective shaped charges are received in the respective shaped charge apertures, and a second plurality of shaped charges received in a second plurality of shaped charge apertures in the body portion of the drone may be positioned at the perforating assembly section, and the second plurality of shaped charge apertures are arranged in a second single radial plane. The second single radial plane is positioned upstream of the first single radial plane, and an initiation end of each of the second plurality of shaped charges is substantially adjacent to the receiver booster when the respective shaped charges are received in the respective shaped charge apertures, such that the receiver booster may be configured to directly initiate a shaped charge received in the aperture. 
     For purposes of this disclosure, a “drone” is a self-contained, autonomous or semi-autonomous vehicle for downhole delivery of a wellbore tool. For purposes of this disclosure and without limitation, “autonomous” means without a physical connection or manual control and “semi-autonomous” means without a physical connection. An “autonomous perforating drone” according to some embodiments is a drone in which, e.g., shaped charges carried by the drone are detonated within the wellbore; however, as the disclosure makes clear, an “autonomous perforating drone” is not limited to a drone for downhole delivery of shaped charges and may include any known or later-developed wellbore tools consistent with this disclosure. Further, the use of the word “drone” throughout this disclosure may be used interchangeably and/or for brevity with the phrase “autonomous perforating drone” without limitation, except where the specification otherwise makes clear. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more particular description will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments thereof and are not therefore to be considered to be limiting of its scope, exemplary embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG.  1 A  is a cross-sectional view of a perforating gun string according to the prior art; 
         FIG.  1 B  is a cross-sectional view of a wellbore and wellhead showing the prior art use of a wireline to place drones in a wellbore; 
         FIG.  2 A  is a side perspective view of an autonomous perforating drone according to an exemplary embodiment; 
         FIG.  2 B  is a side view with partial cross-sectional view taken along the planes by view ‘B’ of the autonomous perforating drone according to  FIG.  2 A ; 
         FIG.  3 A  is a side view with cross-sectional view of the exemplary embodiment according to  FIG.  2 B , with a ballistic interrupt in a closed state; 
         FIG.  3 B  is a side view with cross-sectional view of the exemplary embodiment according to  FIG.  2 B , with a ballistic interrupt in an open state; 
         FIG.  4    is a perspective view with an exploded, cross-sectional view of a control module section of the exemplary embodiment according to  FIG.  2 B ; 
         FIG.  5 A  is a perspective view with an exploded view of a shaped charge and a fixation connector of the exemplary embodiment according to  FIG.  2 B ; 
         FIG.  5 B  shows the exemplary shaped charge for use with the exemplary fixation connector according to  FIG.  5 A ; 
         FIG.  5 C  shows the exemplary fixation connector according to  FIG.  5 A , in a first state of assembly; 
         FIG.  5 D  shows the exemplary fixation connector according to  FIG.  5 A , in a second state of assembly; 
         FIG.  5 E  shows the exemplary fixation connector according to  FIG.  5 A , in a third state of assembly; 
         FIG.  6 A  is a cross-sectional, side plan view of an ultrasonic transceiver utilized in an embodiment; 
         FIG.  6 B  is a cross-sectional, side plan view of an ultrasonic transceiver utilized in an embodiment; 
         FIG.  7    is a cross-sectional plan view of a two ultrasonic transceiver based navigation system of an embodiment; 
         FIG.  8    is a plan view of a navigation system of an embodiment; 
         FIG.  9    is a block diagram, cross sectional view of a drone in accordance with an embodiment; 
         FIG.  10 A  is a perspective view of an autonomous perforating drone according to an exemplary embodiment; 
         FIG.  10 B  is a lateral cross-sectional view of the autonomous perforating drone shown in  FIG.  10 A ; 
         FIG.  11    is a lateral cross-sectional view of an autonomous perforating drone according to an exemplary embodiment; 
         FIG.  12    is a cross-sectional view of an autonomous perforating drone according to an exemplary embodiment; 
         FIG.  13 A  is a plan view from the tip section of the exemplary autonomous perforating drone according to claim  12 ; 
         FIG.  13 B  is a cross-sectional view of the autonomous perforating drone according to  FIG.  12   , taken along the plane by view ‘A’ according to  FIG.  13 A ; 
         FIG.  14 A  shows an exemplary shaped charge for use with the exemplary autonomous perforating drone shown in  FIG.  12   ; 
         FIG.  14 B  shows a non-cross-sectional view of the exemplary shaped charge according to  FIG.  14 A ; 
         FIG.  15    shows a blown-up view of the shaped charges received in the exemplary perforating gun assembly section according to  FIG.  12   ; 
         FIG.  16    shows a perspective view of an autonomous perforating drone according to an exemplary embodiment; 
         FIG.  17    shows a reverse perspective view of the autonomous perforating drone shown in  FIG.  16   ; 
         FIG.  18    shows a rear plan view of the autonomous perforating drone shown in  FIG.  16   ; 
         FIG.  19    shows a front plan view of the autonomous perforating drone shown in  FIG.  16   ; 
         FIG.  20    shows a partial cutaway view of the autonomous perforating drone shown in the perspective of  FIG.  17   ; 
         FIG.  21    shows a side cross-sectional view taken longitudinally through the autonomous perforating drone shown in  FIG.  16   ; 
         FIG.  22    shows a perspective view of an exemplary control module for use with the exemplary embodiments described herein; 
         FIG.  23    shows an exemplary Control Interface Unit for use with the exemplary embodiments described herein; 
         FIG.  23 A  shows an exemplary detonator and integrated donor charge for use with the exemplary embodiments described herein; 
         FIG.  24    shows a front cross-sectional view of the control module shown in  FIG.  22    housing the Control Interface Unit shown in  FIG.  23   ; 
         FIG.  25    shows a side view of the Control Interface Unit shown in  FIG.  23   ; and, 
         FIG.  26    shows an exemplary arrangement of a ballistic interrupt retention mechanism according to some embodiments. 
     
    
    
     Various features, aspects, and advantages of the embodiments will become more apparent from the following detailed description, along with the accompanying figures in which like numerals represent like components throughout the figures and text. The various described features are not necessarily drawn to scale but are drawn to emphasize specific features relevant to some embodiments. 
     The headings used herein are for organizational purposes only and are not meant to limit the scope of the description or the claims. To facilitate understanding, reference numerals have been used, where possible, to designate like elements common to the figures. 
     DETAILED DESCRIPTION 
     This application incorporates by reference each of the following pending patent applications in their entireties: International Patent Application No. PCT/US2019/063966, filed May 29, 2019; U.S. patent application Ser. No. 16/423,230, filed May 28, 2019; U.S. Provisional Patent Application No. 62/841,382, filed May 1, 2019; U.S. Provisional Patent Application No. 62/720,638, filed Aug. 21, 2018; U.S. Provisional Patent Application No. 62/719,816, filed Aug. 20, 2018; and U.S. Provisional Patent Application No. 62/678,654, filed May 31, 2018. 
     Reference will now be made in detail to various exemplary embodiments. Each example is provided by way of explanation and is not meant as a limitation and does not constitute a definition of all possible embodiments. 
     Turning now to  FIG.  2 A  and  FIG.  2 B , an exemplary embodiment of an autonomous perforating drone  100  according to this disclosure is shown. The exemplary autonomous perforating drone  100  is a generally (though not literally or limitingly) torpedo-shaped assembly or module with a circumferential aspect c formed about a longitudinal axis x. The autonomous perforating drone  100  includes a tip section  195  at a front (downstream) end  101  of the autonomous perforating drone  100  and a tail section  180  at a rear (upstream) end  102 , opposite the front end  101 , of the autonomous perforating drone  100 . A perforating assembly section  110  and a control module section  130  are respectively positioned between the tail section  180  and the tip section  195 . The control module section  130  is connected at a first end  135  of the control module section  130  to the tip section  195  and at a second end  136 , opposite the first end  135 , of the control module section  130  to a downstream end  111  of the perforating assembly section  110 . The perforating assembly section  110  includes an upstream end  112  opposite the downstream end  111  and in the exemplary embodiment shown in  FIG.  2 A  and  FIG.  2 B  the upstream end  112  of the perforating assembly section  110  is connected to the tail section  180 . 
     The tail section  180  may include guiding fins  181  for providing radial stability as the autonomous perforating drone  100  is traveling through a wellbore fluid within a wellbore. In various embodiments, one or more of the tip section  195 , the control module section  130 , the perforating assembly section  110 , and the tail section  180  may have features such as guiding fins, a curved topology, etc. for providing one or more of rotational speed, radial stability, and reduced friction to the autonomous perforating drone  100 . 
     For purposes of this disclosure, each of the “tip section”, “control module section”, “perforating assembly section”, and “tail section” is defined with respect and reference to, and to aid in the description of, the position and configuration of certain structures and componentry of the exemplary embodiments of an autonomous perforating drone as described throughout this disclosure. None of the terms “tip section”, “control module section”, “perforating assembly section”, or “tail section” is limited to any particular assembly, configuration, or delineation points of, or along, an autonomous perforating drone according to this disclosure. For example, any or all of the “tip section”, “control module section”, “perforating assembly section”, and “tail section” may be integrally formed by injection molding, casting, 3D printing, 3D milling from bar stock, etc. For purposes of this disclosure, “integral” or “integrally formed” respectively means a single piece or formed as a single piece. 
     Further, for purposes of this disclosure, the term “connected” generally means joined, such as by mechanical features, adhesives, welding, friction fit, or other known techniques for joining separate components, and may also mean “integrally formed” as that term is used in this disclosure, except where otherwise indicated. 
     Moreover, for purposes of this disclosure, “upstream” means in a direction towards the wellbore entrance or surface and “downstream” means in a direction deeper or further into the wellbore. For example, as the autonomous perforating drone  100  travels downstream, the tip section  195  is positioned first in the wellbore fluid, the tip section  195  being positioned downstream of the tail section  180 . The autonomous perforating drone  100  is deployed and conveyed through the wellbore fluid via known techniques including, but not limited to, pump down conveyance. 
     With continuing reference to  FIG.  2 A  and  FIG.  2 B , the exemplary perforating assembly section  110  is generally defined by a perforating assembly section body  119  that is configured for, among other things, retaining one or more shaped charges  113  and a detonating cord  160  for delivery downhole in a wellbore. The perforating assembly section  110  is generally cylindrically-shaped and is formed about the longitudinal axis x. In the exemplary embodiment shown in  FIG.  2 A  and  FIG.  2 B , the perforating assembly section  110  includes a plurality of shaped charges  113 , and each shaped charge  113  is positioned and retained, in part, in a first opening  115  of an aperture  114  that extends laterally through the perforating assembly section  110  along an axis y. The aperture extends between the first opening  115  on a first side  117  of the perforating assembly section  110  and a second opening  116  on a second side  118 , opposite the first side  117 , of the perforating assembly section  110 . The first side  117  of the perforating assembly section  110  and the second side  118  of the perforating assembly section  110  are defined separately for each of the plurality of apertures  114 , according to the respective opposing portions of the perforating assembly section  110  through which a particular aperture  114  passes. As described in detail with respect to  FIGS.  3 A,  3 B,  5 A, and  5 C- 5 E , a fixation assembly  200  of the exemplary embodiment shown in  FIG.  2 A  and  FIG.  2 B  is positioned about the second opening  116  of each aperture  114  and secures the shaped charge  113  within the aperture  114 . The fixation assembly  200  may also secure the detonating cord  160  in place at each shaped charge  113  along a length L of the perforating assembly section  110 , as described in detail with respect to  FIGS.  5 A- 5 E . 
     With reference specifically to  FIG.  2 A , the exemplary autonomous perforating drone  100  also includes, among other things, features such as charging/programming contacts  1800  for charging a power source and/or programming onboard circuitry contained in a control module  137  ( FIG.  2 B ) of the autonomous perforating drone  100  and a ballistic interrupt actuator  460  for moving a ballistic interrupt  140  ( FIG.  2 B ) between a closed state  143  ( FIG.  3 A ) and an open state  144  ( FIG.  3 B ) within the autonomous perforating drone  100 . Aspect of these features are variously shown and described throughout this disclosure and in the figures, as follows. 
     With reference now to  FIGS.  3 A and  3 B , each of those figures shows, among other things, a cross-section of the exemplary control module section  130  of the autonomous perforating drone  100  as generally described with respect to  FIG.  2 A  and  FIG.  2 B . However, as explained in greater detail further below,  FIG.  3 A  shows the exemplary autonomous perforating drone  100  with the ballistic interrupt  140  in a closed state  143  and  FIG.  3 B  shows the exemplary autonomous perforating drone  100 ′ with the ballistic interrupt in an open state  144 . 
     In an aspect, and with reference to  FIG.  26   , at least a portion of the ballistic interrupt  140  may include a detent  3001  for seating against a corresponding protrusion  3000  on a surface within the drone body, for example within the cavity (not numbered) in which the ballistic interrupt  140  sits. The seating contributes to maintaining a position (relative to rotation) of the ballistic interrupt  140 . In addition, a stop notch  3002  may extend from, for example and without limitation, a surface of the cavity and have a size and geometry configured to resist over-rotation of the ballistic interrupt  140  within the cavity, for example, when the ballistic interrupt  140  is moved between the on and off states. 
     With continuing reference to  FIGS.  2 A- 3 B , and further reference to  FIG.  4   , the exemplary control module section  130  is generally defined by a control module section body  191  and is circumferentially-shaped and formed about the longitudinal axis x. The control module section  130  defined by the control module section body  191  has a profile including, among other things, a large diameter portion  193  with a diameter d 1 , a reduced diameter portion  194  with a diameter d 2 , a transition region  197  positioned between the large diameter portion  193  and the reduced diameter portion  194 , and a tapered portion  196  with a diameter d 3  at a position  196 ′ representing any particular point along the varying-diameter tapered portion  196  at which the diameter d 3  is measured. The diameter d 1  of the large diameter portion  193  is greater than the diameter d 2  of the reduced diameter portion  194 . In the exemplary embodiments shown in  FIGS.  3 A and  3 B , the diameter d 2  of the reduced diameter portion  194  is substantially equal to a diameter d 7  of the perforating assembly section  110 . 
     The transition region  197  is connected to each of the large diameter portion  193  and the reduced diameter portion  194  and spans a space therebetween. The presence and profile of the transition region  197  is not limited by the disclosed embodiments and may take any shape or configuration as particular applications dictate. The tapered portion  196  is positioned and spans a gap between the large-diameter portion  194  of the control module section  130  and the tip section  195 , and the diameter d 3  at the position  196 ′ on the tapered portion  196  gradually decreases in a direction v from the large-diameter portion  194  of the control module section  130  towards the tip section  195 . The exemplary profile of the control module section  130  shown in, e.g.,  FIG.  3 B  helps to reduce impacts and friction on the shaped charges  113  as the autonomous perforating drone  100 ,  100 ′ travels through a wellbore fluid, whereby the large diameter portion  193  absorbs impacts against a wellbore casing and pushes wellbore fluid out and around the perforating assembly section  110 . In other embodiments, the tip section  195  may have a different profile, for example and without limitation, an arrow-like or pointed tip. 
     For purposes of this disclosure, each of the “large diameter portion  193 ”, “reduced diameter portion  194 ”, “transition region  197 ”, and “tapered portion  196 ” is defined with respect and reference to, and to aid in the description of, the profile of the exemplary control module section  130  shown in, e.g.,  FIGS.  3 A and  3 B . None of the terms “large diameter portion  193 ”, “reduced diameter portion  194 ”, “transition region  197 ”, or “tapered portion  196 ” is limited to any particular assembly, configuration, or delineation points of, or along, an autonomous perforating drone according to this disclosure, nor is a control module section according to this disclosure limited to a profile including one or more diameters. For example and without limitation, the control module section  130  may be cylindrically shaped with a constant diameter, or may have a non-circumferential profile. 
     With continuing reference specifically to  FIGS.  3 A and  4    (and further shown and described with respect to  FIG.  13 B ), the control module section  130  defined by the control module section body  191  includes, among other things, a hollow interior portion  132  and a ballistic channel  141  respectively positioned within the control module section  130  defined by the control module section body  191 . The ballistic channel  141  is open to the hollow interior portion  132  and extends from the hollow interior portion  132  in a direction v′ from the hollow interior portion  132  towards the perforating assembly section  110 /tail section  180 . In the exemplary embodiments shown in  FIGS.  3 A- 4   , the ballistic channel  141  is surrounded by a portion  192  of increased thickness of the control module section body  191  and has a diameter d 4  that is smaller than a diameter d 5  of the hollow interior portion  132 . The diameter d 4  of the ballistic channel  141  is sized to receive a receiver booster  150  which, as shown in  FIGS.  3 A- 4   , is positioned within the ballistic channel  141 , and the ballistic interrupt  140  is positioned within the ballistic channel  141  in a ballistic interrupt cavity  146  that is formed as an area of the ballistic channel  141  with a diameter d 8  which is larger than the diameter d 4  of the ballistic channel  141 . The ballistic interrupt  140  and the receiver booster  150  are positioned in a spaced apart relationship within the ballistic channel  141  such that the ballistic interrupt  140  is nearer the hollow interior portion  132  and the receiver booster  150  is nearer the perforating assembly section  110 . The receiver booster  150  is connected to the detonating cord  160 , for example by crimping, within the ballistic channel  141 , and the exemplary ballistic channel  141  shown in, e.g.,  FIGS.  3 A- 4   , is sized to receive at least a portion of the detonating cord  160 . The detonating cord  160  extends away from the receiver booster  150  in the direction v′ towards the perforating assembly section  110 /tail section  180 , and opposite the direction v towards the ballistic interrupt  140 . 
     In some embodiments, a set of stackable pellets may be used in conjunction with, or in place of, the receiver booster  150  for initiating the detonating cord  160  by ballistic force. 
     The control module section  130  and the hollow interior portion  132  are sized to receive the control module  137  which is positioned within the hollow interior portion  132  of the control module section  130 . The control module  137  includes a housing  138  that defines an inner area  320  of the control module  137  and encloses, for example and without limitation, a detonator  133 , a donor charge  134 , and a control assembly  131 . The control module  137  and the control assembly  131  are further shown and described with respect to  FIG.  12   . With continuing reference to  FIGS.  3 A- 4   , the control assembly  131  may include controlling and operational components of the autonomous perforating drone  100 , such as, without limitation, a power source/battery, sensors, depth correlation device, programmable electronic circuit, trigger circuit, detonator fuse, etc. A power source/battery may also be positioned within the hollow interior portion  132 , itself, as may other components that do not necessarily need the isolation or component assemblies within the inner area  320  of the control module  137 . These and other components are discussed in additional detail with respect to the operation of the autonomous perforating drone  100 , especially in  FIGS.  22 - 25   , with respect to the exemplary embodiments of drone shown and described with respect to  FIGS.  16 - 21   . 
     The modular, i.e., self-contained, nature of the control module  137  allows it to be removed/removable from the autonomous perforating drone  100  during transport, e.g., to comply with regulatory requirements, and quickly loaded into the autonomous perforating drone  100  at a wellsite. The inner area  320  of the control module  137  can be completely or partially hollow, or not hollow at all, depending on the layout of the control module components and the requirements for sealing the control module  137 . For example, in an exemplary embodiment the control module  137  is pressure sealed to protect the components within the control module  137  from environmental conditions both outside of and within the wellbore. In other embodiments one or more of the control module  137 , control module section  130 , and hollow interior portion  132  may include various known seals to protect the control module  137  and the components within the control module  137 , components within the hollow interior portion  132 , or other components within the control module section  130  generally. 
     According to a further aspect, an electrical selective sequence signal may be sent from, e.g., the programmable electronic circuit to the detonator  133  to initiate the detonator when the autonomous perforating drone  100  reaches at least one of a threshold pressure, temperature, horizontal orientation, inclination angle, depth, distance traveled, rotational speed, and position within the wellbore. The threshold conditions may be measured by any known devices consistent with this disclosure including a temperature sensor, a pressure sensor, a positioning device as a gyroscope and/or accelerometer (for horizontal orientation, inclination angle, and rotational speed), and a correlation device such as a casing collar locator (CCL) or position determining system (for depth, distance traveled, and position within the wellbore) as discussed below with respect to  FIGS.  6 A- 9    and  FIG.  12   . The electrical selective sequence signal may include one or more of an addressing signal for activating one or more power components of the detonator  133 , an arming signal for activating a detonator firing assembly such as a trigger circuit or capacitor, and a detonating signal for detonating the detonator  133 . The threshold values and other instructions for addressing, arming, and/or detonating the detonator  133  may be taught to the programmable electronic circuit by, for example and without limitation, a control unit at a factory or assembly location or at the surface of the wellbore prior to deploying the autonomous perforating drone  100  into the wellbore. In an aspect, the selective sequence signal may be one or more digital codes including or more digital codes uniquely configured for the detonator  133  of each particular autonomous perforating drone  100 . 
       FIG.  6 A  is a cross-section of an ultrasonic transducer  1400  that may be used in a system and method of determining location along a wellbore  2016 . The transducer  1400  may include a housing  1410  and a connector  1402 ; the connector  1402  is the portion of the housing  1410  allowing for connections to, e.g., the programmable electronic circuit that may generate and interpret the ultrasound signals. The key elements of the transducer  1400  are a transmitting element  1404  and a receiving element  1406  that are contained in the housing  1410 . In the transducer shown in  FIG.  6 A , the transmitting element  1404  and the receiving element  1406  are integrated into a single active element  1414 . That is, the active element  1414  is configured to both transmit an ultrasound signal and receive an ultrasound signal. Electrical leads  1408  are connected to electrodes on the active element  1414  and convey electrical signals to/from the programmable electronic circuit. An electrical network  1420  may be connected between the electrical leads  1408 . Optional elements of a transducer include a sleeve  1412 , a backing  1416  and a cover/wearplate  1422  protecting the active element  1414 . 
       FIG.  6 B  is a cross-section of an alternative version of an ultrasonic transducer  1400 ′ that may be used in a system and method of determining location along a wellbore  2016 . The transducer  1400 ′ may include a housing  1410 ′ and a connector  1402 ′; the connector  1402 ′ is the portion of the housing  1410 ′ allowing for connections to, e.g., the programmable electronic circuit that may generate and interpret the ultrasound signals. The key elements of the transducer  1400 ′ are a transmitting element  1404 ′ and a receiving element  1406 ′ that are contained in the housing  1410 ′. A delay material  1418  and an acoustic barrier  1417  are provided for improving sound transmission and receipt in the context of a separate transmitting element  1404 ′ and receiving element  1406 ′ apparatus. 
     With additional reference to  FIG.  7   , an exemplary autonomous perforating drone  1510  as part of an ultrasonic transducer system  1500  for determining the speed of the autonomous perforating drone  1510  traveling down a wellbore  2016  by identifying ultrasonic waveform changes is shown. As depicted in  FIG.  7   , the autonomous perforating drone  1510  may be equipped with one or more ultrasonic transducers  1530 ,  1532 . In an embodiment, the autonomous perforating drone  1510  has a first transducer  1530  (also marked T 1 ) and a second transducer  1532  (also marked T 2 ), one at each end of the autonomous perforating drone  1510 . The distance separating the first transducer  1530  from the second transducer  1532  is a constant and may be referred to as distance ‘Z’. Each of the first transducer  1530  and the second transducer  1532  may have a transmitting element  1404  and a receiving element  1406  (as shown in  FIGS.  6 A and  6 B ) that sends/receives signals radially from the autonomous perforating drone  1510 . In an embodiment, each transmitting element  1404  and receiving element  1406  may be disposed about an entire radius of the autonomous perforating drone  1510 ; such an arrangement permits the transmitting element  1404  and the receiving element  1406  respectively to send and receive signals about essentially the entire radius of the autonomous perforating drone  1510 . 
     The exemplary autonomous perforating drone  1510  shown in  FIG.  7    includes the first ultrasonic transceiver  1530  and the second ultrasonic transceiver  1532 . Each of the first ultrasonic transceiver  1530  and the second ultrasonic transceiver  1532  is capable of detecting alterations in the medium through which the autonomous perforating drone  1510  is traversing by transmitting an ultrasound signal  1526 ,  1526 ′ and receiving a return ultrasound signal  1528 ,  1528 ′. Changes in the material and geometry of the wellbore casing  1580  and other material external to wellbore casing  1580  will often result in a substantial change in the return ultrasound signal  1528 ,  1528 ′ received by receiving element  1406  and conveyed to autonomous perforating drone  1510 , e.g., by the programmable electronic circuit. 
     With continuing reference to  FIG.  7   , because T 2   1532  is axially displaced from T 1   1530  along the long axis of the autonomous perforating drone  1510 , T 2   1532  passes through an anomaly in the wellbore  2016  at a different time than T 1   1530  as the autonomous perforating drone  1510  traverses the wellbore  2016 . Put another way, assuming the existence of an anomalous point  1506  along the wellbore, T 1   1530  and T 2   1532  pass the anomalous point  1506  in wellbore  1070  at slightly different times. In the event that T 1   1530  and T 2   1532  both register a sufficiently strong and identical, i.e., repeatable, modified return signal as a result of an anomaly at the anomalous point  1506 , it is possible to determine the time difference between T 1   1530  registering the anomaly at the anomalous point  1506  and T 2   1532  registering the same anomaly. The distance Z between T 1   1530  and T 2   1532  being known, a sufficiently precise measurement of time between T 1   1530  and T 2   1532  passing a particular anomaly provides a measure of the velocity of the autonomous perforating drone  1510 , i.e., velocity equals change in position divided by change in time. Utilizing the typically safe presumption that an anomaly is stationary, the velocity of the autonomous perforating drone  1510  through the wellbore  2016  is available every time the autonomous perforating drone  1510  passes an anomaly that returns a sufficient change in amplitude of a return signal for each of T 1   1530  and T 2   1532 . 
     The potential exists for locating ultrasonic transceiver T 1   1530  and ultrasonic transceiver T 2   1532  in different portions of the autonomous perforating drone  1510  and connecting them electrically to the programmable electronic circuit. As such, it is possible to increase the axial distance Z between T 1   1530  and T 2   1532  almost to the limit of the total length of the autonomous perforating drone  1510 . Placing T 1   1530  and T 2   1532  further away from one another achieves a more precise measure of velocity and retains precision more effectively as higher drone velocities are encountered, especially where sample rates for T 1   1530  and T 2   1532  reach an upper limit. 
     In an exemplary embodiment of a navigation system  1600  such as used in the ultrasonic transducer system  1500  shown in  FIG.  7   , two wire coils  1632 ,  1634  are respectively used with the transceivers  1530 ,  1532 . As seen in  FIG.  8   , a signal generating and processing unit  1640  is attached to both ends of a first coil  1632  wrapped around a first core  1622  of high magnetic permeability material and a second coil  1634  wrapped around a second core  1624  of high magnetic permeability material. As discussed previously, although the cores  1622 ,  1624  and the coils  1632 ,  1634  are presented in  FIG.  8    as toroidal in shape, other shapes are possible. The first coil  1632  and the second coil  1634  of the exemplary embodiment shown in  FIG.  7    and  FIG.  8    are configured coplanar to one another. Since a toroidal coil defines a plane, the magnetic field established by such a coil possesses a structure related to this plane. Changes in magnetic permeability occurring coplanar to the plane of the toroidal coil will have greater effect on the coil&#39;s inductance than changes that are not coplanar. Changes in magnetic permeability in a plane perpendicular to the plane of the coil may have little to no impact on the coil&#39;s inductance value. As previously described, the exemplary ultrasonic transducer system  1500  may register the same anomaly, i.e., change in magnetic permeability, once for each coil  1632 ,  1634 . In this configuration, having the coils  1632 ,  1634  disposed on the same plane may achieve this result. 
     The processing unit  1640  may include an oscillator circuit  1644  and a capacitor  1642 . An oscillating signal is generated by the oscillator circuit  1644 , and sent to the wire coils  1632 ,  1634 . With the wire coils  1632 ,  1634  acting as inductors, a magnetic field is established around the wire coils  1632 ,  1634  when charge flows through the wire coils  1632 ,  1634 . Insertion of the capacitor  1642  in the processing unit  1640  results in constant transfer of electrons between the wire coils/inductors  1632 ,  1634  and the capacitor  1642 , i.e., in a sinusoidal flow of electricity between the wire coils  1632 ,  1634  and the capacitor  1642 . The frequency of this sinusoidal flow will depend upon the capacitance value of the capacitor  1642  and the magnetic field generated around the wire coils  1632 ,  1634 , i.e., the inductance value of the wire coils  1632 ,  1634 . The peak strength of the sinusoidal magnetic field around the wire coils  1632 ,  1634  will depend on the materials immediately external to the wire coils  1632 ,  1634 . With the capacitance of the capacitor  1642  being constant and the peak strength of the magnetic field around the wire coils  1632 ,  1634  being constant, the circuit will resonate at a particular frequency. That is, current in the circuit will flow in a sinusoidal manner having a frequency, referred to as a resonant frequency, and a constant peak current. 
     With reference to  FIG.  9   , a schematic cross-sectional view of an autonomous perforating drone  1700  as generally described throughout this disclosure is shown. For example, the autonomous perforating drone  1700  may take the form of the autonomous perforating drone  100  shown in  FIGS.  2 A- 3 B . For example, the body portion  1710  of the autonomous perforating drone  1700  may bear one or more shaped charges. As is well-known in the art, detonation of the shaped charges is typically initiated with an electrical pulse or signal supplied to a detonator. The detonator of the autonomous perforating drone embodiment  1700  shown in  FIG.  9    and generally with respect to the exemplary embodiments of an autonomous perforating drone as described throughout this disclosure—e.g., in  FIGS.  2 A- 3 B —may be located in the control module section  130 , the perforating assembly section  110 , or at a position or intersection therebetween. The detonator  133  may initiate the shaped charges either directly or through an intermediary structure such as a detonating cord. 
     As would be understood by one of ordinary skill in the art, electrical power typically supplied via the wireline cable  2012  to wellbore tools, such as a tethered drone or typical perforating gun, would not be available to an autonomous perforating drone as described herein and shown in  FIG.  9   . In order for all components of the autonomous perforating drone  1700  to be supplied with electrical power, a power supply  1792  may be included generally as part of the autonomous perforating drone  1700  in any portion such as configurations dictate. It is contemplated that the power supply  1792  may be disposed so that it is adjacent any components of the autonomous perforating drone  1700  that require electrical power (such as an onboard computer  390 ). 
     The on-board power supply  1792  for the autonomous perforating drone  1700  may take the form of an electrical battery; the battery may be a primary battery or a rechargeable battery. Whether the power supply  1792  is a primary or rechargeable battery, it may be inserted into the autonomous perforating drone  1700  at any point during construction of the autonomous perforating drone  1700  or immediately prior to insertion of the autonomous perforating drone  1700  into the wellbore  2016 . If a rechargeable battery is used, it may be beneficial to charge the battery immediately prior to insertion of the autonomous perforating drone  1700  into the wellbore  2016 . Charge times for rechargeable batteries are typically on the order of minutes to hours. 
     In an embodiment, another option for the power supply  1792  is the use of a capacitor or a supercapacitor. A capacitor is an electrical component that consists of a pair of conductors separated by a dielectric. When an electric potential is placed across the plates of a capacitor, electrical current enters the capacitor, the dielectric stops the flow from passing from one plate to the other plate and a charge builds up. The charge of a capacitor is stored as an electric field between the plates. Each capacitor is designed to have a particular capacitance (energy storage). In the event that the capacitance of a chosen capacitor is insufficient, a plurality of capacitors may be used. When a capacitor is connected to a circuit, a current will flow through the circuit in the same way as a battery. That is, when electrically connected to elements that draw a current the electrical charge stored in the capacitor will flow through the elements. Utilizing a DC/DC converter or similar converter, the voltage output by the capacitor will be converted to an applicable operating voltage for the circuit. Charge times for capacitors are on the order of minutes, seconds or even less. 
     A supercapacitor operates in a similar manner to a capacitor except there is no dielectric between the plates. Instead, there is an electrolyte and a thin insulator such as cardboard or paper between the plates. When a current is introduced to the supercapacitor, ions build up on either side of the insulator to generate a double layer of charge. Although the structure of supercapacitors allows only low voltages to be stored, this limitation is often more than outweighed by the very high capacitance of supercapacitors compared to standard capacitors. That is, supercapacitors are a very attractive option for low voltage/high capacitance applications as will be discussed in greater detail hereinbelow. Charge times for supercapacitors are only slightly greater than for capacitors, i.e., minutes or less. 
     A battery typically charges and discharges more slowly than a capacitor due to latency associated with the chemical reaction to transfer the chemical energy into electrical energy in a battery. A capacitor is storing electrical energy on the plates so the charging and discharging rate for capacitors are dictated primarily by the conduction capabilities of the capacitors plates. Since conduction rates are typically orders of magnitude faster than chemical reaction rates, charging and discharging a capacitor is significantly faster than charging and discharging a battery. Thus, batteries provide higher energy density for storage while capacitors have more rapid charge and discharge capabilities, i.e., higher power density, and capacitors and supercapacitors may be an alternative to batteries especially in applications where rapid charge/discharge capabilities are desired. 
     Thus, the on-board power supply  1792  for the autonomous perforating drone  1700  may take the form of a capacitor or a supercapacitor, particularly for rapid charge and discharge capabilities. A capacitor may also be used to provide additional flexibility regarding when the power supply is inserted into the autonomous perforating drone  1700 , particularly because the capacitor will not provide power until it is charged. Thus, shipping and handling of the autonomous perforating drone  1700  containing shaped charges or other explosive materials presents low risks where an uncharged capacitor is installed as the power supply  1792 . This is contrasted with shipping and handling of an autonomous perforating drone  1700  with a battery, which can be an inherently high risk activity and frequently requires a separate safety mechanism to prevent accidental detonation. Further, and as discussed previously, the act of charging a capacitor is very fast. Thus, the capacitor or supercapacitor being used as a power supply  1792  for the autonomous perforating drone  1700  can be charged immediately prior to deployment of the autonomous perforating drone  1700  into the wellbore  2016 . 
     In an aspect, magnetic sensors such as Hall effect magnetic sensors or magnetometers may be used in combination with a super capacitor as a depth correlation sensor in the exemplary autonomous perforating drones described herein. Such a system may be used with a magnetic ring (e.g., a plastic with flexible magnetic tape or film secured thereto) between adjacent wellbore casings, for example, at a collar between casing ends, wherein the magnetic ring includes beacons or magnets for detection by the drone sensors. In another aspect, casing collars may be painted with high temperature paint or adhesives including magnetic material such as metal fillings, powder, or flakes. 
     While the option exists to ship the autonomous perforating drone  1700  preloaded with a rechargeable battery which has not been charged, i.e., the electrochemical potential of the rechargeable battery is zero, this option comes with some significant drawbacks. The goal must be kept in mind of assuring that no electrical charge is capable of inadvertently accessing any and all explosive materials in the autonomous perforating drone  1700 . Electrochemical potential is often not a simple, convenient or failsafe thing to measure in a battery. It may be the case that the potential that a ‘charged’ battery may be mistaken for an ‘uncharged’ battery simply cannot be reduced sufficiently to allow for shipping the autonomous perforating drone  1700  with an uncharged battery. In addition, as mentioned previously, the time for charging a rechargeable battery having adequate power for the autonomous perforating drone  1700  could be on the order of an hour or more. Currently, fast recharging batteries of sufficient charge capacity are uneconomical for the ‘one-time-use’ or ‘several-time-use’ that would be typical for batteries used in the autonomous perforating drone  1700 . 
     In an embodiment, electrical components of an exemplary autonomous perforating drone as described throughout this disclosure including the control module  137 , an oscillator circuit  1644 , one or more wire coils  1632 ,  1634 , and one or more ultrasonic transceivers  1530 ,  1532  may be battery powered while explosive elements like the detonator for initiating detonation of the shaped charges are capacitor powered. Such an arrangement would take advantage of the possibility that some or all of the control module  137 , the oscillator circuit  1644 , the wire coils  1632 ,  1634 , and the ultrasonic transceivers  1530 ,  1532  may benefit from a high density power supply having higher energy density, i.e., a battery, while initiating elements such as detonators typically benefit from a higher power density, i.e., capacitor/supercapacitor. A very important benefit for such an arrangement is that the battery is completely separate from the explosive materials, affording the potential to ship the autonomous perforating drone  1700  preloaded with a charged or uncharged battery. The power supply that is connected to the explosive materials, i.e., the capacitor/supercapacitor, may be very quickly charged immediately prior to dropping the autonomous perforating drone  1700  into wellbore  2016 . 
     In an aspect, a capacitor used as a power supply in the exemplary autonomous drones described throughout this disclosure may be charged to 30-40 Amps, and/or charged for approximately 15-40 minutes per autonomous perforating drone and provide approximately 1 hour of active power. 
     As shown in the exemplary embodiment of  FIG.  3 A , when the control module  137  is received within the hollow interior portion  132  of the control module section  130 , the donor charge  134  is adjacent to and substantially aligned with the ballistic channel  141 , and a portion  139  of the control module housing  138  is positioned between the donor charge  134  and the ballistic channel  141 . For purposes of this disclosure, “adjacent” means next to or near, but is not limited to directly abutting and does not exclude the presence of intervening structures. Thus, when the control module  137  is received within the hollow interior portion  132  of the control module section  130 , the ballistic interrupt  140  within the ballistic channel  141  is positioned in a spaced apart relationship between the donor charge  134  and the receiver booster  150 . 
     In an aspect, the donor charge  134  is positioned within a detonator channel  145  within the control module  137 , and the detonator  133  is positioned adjacent to the donor charge  134  within the detonator channel  145  and substantially aligned with the donor charge  134  along the longitudinal axis x. The detonator  133  may be, for example and without limitation, an explosive charge or any other device as is well known in the art for causing a detonation, ignition, or ballistic initiation. In an aspect, the detonator  133  may be a selective detonator. For purposes of this disclosure, “selective” means that the detonator  133  is initiated only when it receives a specific initiating signal or selective sequence signal, as discussed above, from the control module  137  (i.e., the programmable electronic circuit), e.g., to cause a capacitive discharge to a fuse of the detonator  133 . One benefit of a selective detonator is that it is radio-frequency (RF)-safe—i.e., it will not be initiated by stray RF signals in the proximity of the detonator  133 . 
     The donor charge  134  is also an explosive shaped charge, but the donor charge  134  may include, for example, an explosive material within a casing (not numbered), designed to create a directed perforating jet upon detonation, as is well known in the art. According to the exemplary configuration, detonating the detonator  133  will cause the donor charge  134  to detonate. In an aspect, the donor charge  134  may be designed, for example and without limitation, to have an explosive power for contributing to breaking apart the drone upon detonation. In another aspect, the donor charge  134  may be explosive and/or explosive/liner assembly as in a typical shaped charge but may be pressed into a plastic housing instead of contained within a metal casing. 
     The ballistic interrupt  140  is thus an important safety and operational feature of the autonomous perforating drone  100 . For example, in operation, when the donor charge  134  is detonated it produces the perforating jet that pierces the portion  139  of the control module housing  138  between the donor charge  134  and the ballistic channel  141 , and travels into the ballistic channel  141 . When the ballistic interrupt  140  is in the closed state  143  shown in FIG.  3 A, it provides a physical barrier and thereby prevents the perforating jet created by the donor charge  134  from reaching the receiver booster  150  and thereby initiating detonation (as explained further below) of the autonomous perforating drone  100 . Specifically, with continuing reference to the exemplary embodiment shown in  FIGS.  3 A and  4   , the ballistic interrupt  140  includes a through-bore  142  that extends through the ballistic interrupt  140  between a first opening  142   a  of the through-bore  142  and a second opening  142   b  of the through-bore  142 . When the ballistic interrupt  140  is in the closed state  143 , the through-bore  142  is substantially perpendicular to the longitudinal axis x and the ballistic interrupt  140  otherwise prevents ballistic communication between the donor charge  134  and the receiver booster  150  by shielding the receiver booster  150  from the perforating jet created by the donor charge  134 . Accordingly, the ballistic interrupt  140  in the closed state  143  does not provide a path through which the perforating jet created by the donor charge  134  may reach the receiver booster  150  and thus is no longer ballistically aligned with the donor charge  134 . In a further aspect of the exemplary closed state  143 , the first opening  142   a  and the second opening  142   b  of the through-bore  142  may be positioned within an area of the ballistic interrupt cavity  146  at the diameter d 8  which is beyond the diameter of the ballistic channel  141  and may enhance the shielding effect of the ballistic interrupt  140 . In another aspect, the ballistic interrupt  140  may include additional holes therethrough and/or in communication with the through-bore  142 , for preventing failure or collapse of the autonomous perforating drone  100  due to a pressure differential across the ballistic interrupt  140 . 
     In some embodiments, the detonator  133  may be spaced apart from the donor charge  134 . For example, a donor charge may be positioned in the ballistic channel  141  or in the through-bore  142  of the ballistic interrupt  140 . In such embodiments, the detonator  133  would provide sufficient ballistic energy to reach the spaced-apart donor charge, which may include, e.g., penetrating the portion  139  of the control module housing  138  between the detonator channel  145  and the ballistic channel  141 . In embodiments in which a donor charge is positioned in the through-bore  142 , the ballistic energy of the detonator  133  would be insufficient to initiate the donor charge through the ballistic interrupt  140  in the closed state  143 . Thus, the safety control provided by the ballistic interrupt  140  would not be compromised. 
     On the other hand, when the autonomous perforating drone  100  is ready for arming, e.g., after passing a safety check and a function test at a wellbore site and immediately before or while being deployed into the wellbore, the ballistic interrupt  140  is moved to the open state  144  as shown in  FIG.  3 B . In the open state  144 , the through-bore  142  is substantially parallel to the longitudinal axis x and coaxial with the ballistic channel  141 . The through-bore  142  in the open state  144  allows ballistic communication via the through-bore  142  between the donor charge  134  and the receiver booster  150  such that the perforating jet created by the donor charge  134  may reach the receiver booster  150 , causing the receiver booster  150  to detonate when subject to the perforating jet. The receiver booster  150  is generally an explosive charge or any other device, as is well known in the art, for causing an explosion, initiation, or ballistic force, including encapsulated receiver boosters and receiver boosters in a pressure sealed housing  151 . Detonation of the receiver booster  150  initiates the detonating cord  160  which is further connected to and configured for detonating the shaped charges  113 , as is generally known and explained in additional detail with respect to  FIG.  5 A . 
     The pressure sealed housing  151  of the receiver booster  150  may further extend to, or a separate pressure sealed housing may be used for, the connection between the receiver booster  150  and the detonating cord  160 . In an aspect, the pressure sealed housing  151  may be rated to at least 10,000 psi and, for exemplary uses, to at least between 15,000 psi and 20,000 psi to enhance waterproof capability. In another aspect, a small amount of grease may be used at a crimp connection between the receiver booster  150  and the detonating cord  160  to prevent water invasion into the connection. As fluid ingression could potentially desensitize the explosives in the detonating cord  160 , other techniques for sealing the receiver booster  150  onto the detonating cord  160 , and/or sealing the detonating cord  160 , are contemplated and include, without limitation, housing the receiver booster  150  and/or the detonating cord  160  in a cap that may include a grommet (or the like) for passing or fitting the detonating cord  160  therethrough, and may further include additional sealing mechanisms such as internal O-rings (or the like) for preventing fluid from seeping into the explosives at certain junctions. In addition, internal contours of the autonomous perforating drone  100 , e.g., the configuration of the ballistic channel  141 , may be conformed closely to the contour(s) of the receiver booster  150  and the detonating cord  160 , including any housings, caps, or sealing mechanisms thereon, to decrease the area through which fluid may encounter the components/connections. 
     In a further aspect, the receiver booster  150  may be enlarged relative to the detonating cord  160  to prevent an initial bend or curve in the detonating cord  160  which may interfere with assembly of the detonating cord  160  to the receiver booster  150  and result in nicks or crimps in the detonating cord  160 . In still a further aspect, the detonating cord  160  may be energetically coupled to the receiver booster  150  by engaging a lower end of the receiver booster  150  or being placed in a side-by-side configuration with the receiver booster  150 . 
     The ballistic interrupt  140  is movable between the closed state  143  and the open state  144  using, for example, a mechanical key as part of a control system at the surface of the wellbore. With reference to the exemplary embodiment shown in  FIG.  5 A , the ballistic interrupt  140  includes a ballistic interrupt actuator  460  that is part of or in operable connection with the ballistic interrupt  140 , for example when the ballistic interrupt  140  is cylindrical and extends laterally through the autonomous perforating drone  100 , and is received in an opening  462  in the control module section body  191 . The ballistic interrupt actuator  460  includes a keyway  461  for receiving the mechanical key (not shown). The mechanical key may rotate the keyway  461  using a rotational force, thereby rotating the ballistic interrupt  140  between the closed state  143  and the open state  144  (or vice versa). In the exemplary embodiments, the ballistic interrupt  140  is substantially cylindrically-shaped or spherically shaped and is rotatable between the closed state  143  and the open state  144  (and vice versa). The ballistic interrupt  140  including the ballistic interrupt actuator  460  is further shown and described with respect to  FIG.  12   . In other embodiments, the ballistic interrupt  140  may take any shape or configuration consistent with this disclosure, i.e., movable between a closed state and an open state. The ballistic interrupt  140  may also be moved by other mechanical techniques and using other configurations of a ballistic interrupt actuator and mechanical engagement or otherwise, such as a socket-nut engagement or pin-slot engagement, or may be movable via a magnetic engagement, or via a tool that extends through the control module section body  191  and directly engages the ballistic interrupt  140 . 
       FIG.  4    shows, among other things, an exploded, cross-sectional view of the control module section  130  of the exemplary autonomous perforating drone  100 . For example, the control module  137  is shown removed from the hollow interior  132  of the control module section  130  and an opening  147  from the ballistic channel  141  into the hollow interior portion  132  is visible. It is through the opening  147  that a perforating jet created by the donor charge  134  travels into the ballistic channel  141  and, if the ballistic interrupt  140  is in the open state  144 , through the through-bore  142 , and ultimately arrives at the receiver booster  150  to initiate the detonating cord  160  that is attached to the receiver booster  150 . 
     The detonating cord  160  extends away from the receiver booster  150  in the direction v′ towards, e.g., the perforating assembly section  110  and the shaped charges  113  positioned therein. The detonating cord  160  may be any known detonating cord that is pressure and temperature resistant to downhole conditions. A conversion region  330  guides the detonating cord  160  to a connecting portion  410  ( FIGS.  5 A,  5 B, and  5 E ) including a detonating cord slot  411  of a first shaped charge  113 , i.e., the shaped charge  113  nearest the control module section  130 , via a guiding slot  310  formed as a radial cutaway in the conversion region  330 . The conversion region  330  in the exemplary embodiment shown in  FIG.  4    is positioned between, and is integral with, each of the perforating assembly section  110  and the control module section  130 . As noted previously in this disclosure, the perforating assembly section  110  and the control module section  130  are generally defined with respect and reference to the position and configuration of certain structures and componentry and for aiding the description of an exemplary autonomous perforating drone according to this disclosure. For example, the perforating assembly section  110  in the exemplary embodiment shown in  FIG.  4    is generally the length L of the autonomous perforating drone  100  along which the shaped charges  113  are positioned and the control module section  130  is the length M of the autonomous perforating drone  100  along or within which, without limitation, control components (e.g., the control module  137 ) and initiation components (e.g., the detonator  133 , the donor charge  134 , the ballistic interrupt  140 , and the receiver booster  150 ) are positioned. The conversion region  330  in the exemplary embodiment shown in  FIG.  4    joins and transitions a configuration of the control module section  130  on a first side  331  of the conversion region  330  to a configuration of the perforating assembly section  110  on a second side  332  of the conversion region  330 . 
     With reference now to  FIGS.  5 A- 5 E , a shaped charge  400  and the fixation assembly  200  for retaining the shaped charge  400  in the perforating assembly section  110  according to an exemplary embodiment are shown.  FIG.  5 A  shows a breakout of the shaped charge  400  and a fixation connector  120  (described below) from the exemplary autonomous perforating drone  100  and fixation assembly  200  as shown and described with respect to  FIGS.  2 A- 4   .  FIG.  5 B  shows the exemplary shaped charge  400  for use in the embodiment shown in  FIG.  5 A .  FIGS.  5 C- 5 E  show blown-up views of the exemplary fixation assemblies  200  in various stages of assembly with the exemplary shaped charge  400  and detonating cord  160 . 
     With particular reference to  FIG.  5 A  and  FIG.  5 B , the exemplary shaped charge  400  includes, among other things, an initiation side  401  at which the detonating cord  160 , for example, will attach to detonate the shaped charge  400 , and an encapsulated side  402  opposite the initiation side  401  and including a cap  403  for enclosing explosive and/or kinetic materials (not shown) within a casing  404  of the shaped charge  400 , as is well known in the art. The exemplary shaped charges  400  include a cap  403  because the shaped charges  113 ,  400  in the disclosed exemplary embodiments of an autonomous perforating drone  100  are exposed—i.e., they are not otherwise isolated from wellbore conditions by a structure of the autonomous perforating drone  100 . Wellbore fluids and conditions may be corrosive, excessively hot and high pressure, turbulent, and/or otherwise damaging to the shaped charges  113 ,  400 , especially in the event that wellbore fluid or high pressures permeate into the shaped charge casing  404 . Encapsulated shaped charges are generally known for such exposed applications. However, in various embodiments consistent with this disclosure, an autonomous perforating drone may have a configuration for enclosing associated shaped charges and thereby obviating the need for encapsulated shaped charges. 
     Continuing with reference to  FIG.  5 A  and  FIG.  5 B , the connecting portion  410  of the exemplary shaped charge  400  is positioned at the initiation side  401  of the shaped charge  400  and may be integrally formed with the casing  404  as a projection therefrom. The exemplary connecting portion  410  shown in  FIG.  5 A  and  FIG.  5 B  is configured generally as a cylinder with the detonating cord slot  411 , i.e., a parabolic void, extending between a bottom surface  121  of the connecting portion  410  and a detonating cord seat  415  within the cylinder. The detonating cord slot  411  and the detonating cord seat  415  may be shaped complimentarily to the detonating cord  160  or may include any configuration consistent with retaining and guiding the detonating cord  160  between shaped charges  400  along the length L of the autonomous perforating drone  100 , as described herein. 
     With additional reference now to  FIGS.  5 C- 5 E , the shaped charge  400  and the connecting portion  410  are configured and sized such that the connecting portion  410  and an external threaded portion  412  of the connecting portion  410  protrude from a central aperture  171  of the fixation assembly  200  when the shaped charge  400  is received in the aperture  114  through the perforating assembly section  110 . In the exemplary embodiments shown in  FIGS.  5 A and  5 C- 5 E , the central aperture  171  defines, in part, the second opening  116  of the aperture  114  through the perforating assembly section  110 . This configuration provides a connection area for the fixation connector  120  to engage the connecting portion  410  of the shaped charge  400  and clamp, compress, or otherwise secure the connecting portion  410  at the second opening  116 , thereby securing, at least in part, the shaped charge  400  in the aperture  114 . In the exemplary embodiment shown in  FIGS.  5 A,  5 D, and  5 E , the fixation connector  120  is an annular, female connector with a threaded inner surface  420  and an annular opening  421 . The threaded inner surface  420  of the fixation connector  120  is complimentary to the external threaded portion  412  of the connecting portion  410  of the shaped charge  400 , for threadingly engaging the external threaded portion  412  of the connecting portion  410  when the connecting portion  410  is received within the annular opening  421  of the fixation connector  120 . The fixation connector  120  may then be threadingly advanced along the external threaded portion  412  of the connecting portion  410  until, e.g., it reaches and begins to compress against an opposing surface or structure of the fixation assembly  200 . In the exemplary embodiment shown in  FIGS.  5 A and  5 C- 5 E , the opposing structure includes a plurality of teeth  450  extending outwardly from a star-shaped plate  170  that will be further described with respect to the fixation assembly  200 . However, the fixation assembly  200  is not limited by the disclosed geometries or configurations. In various embodiments (see, e.g.,  FIGS.  10 B- 15   ), other known compression, connection, or retention devices and techniques including, without limitation, clamps, clasps, screws, nuts, ratcheting connectors, straps, bands, tape, rubber rings and the like may be used to fixate various exemplary shaped charges, in various exemplary autonomous perforating drone assemblies. Further, the mechanisms, structures, and components of a particular fixation assembly may be separate or may be integrally formed with each other and/or the perforating assembly section body  119  as, for example, features of a single injection-molded piece. 
     With continuing reference to  FIGS.  5 A and  5 C- 5 E , the star-shaped plate  170  in the exemplary fixation assembly  200  is integrally formed with the perforating assembly section body  119 , as a feature thereof. For example, the star-shaped plate  170  is a generally circularly-shaped surface feature on the second side  118  of the perforating assembly section body  119  with respect to, and opposite, the first opening  115  of a corresponding aperture  114  through the perforating assembly section  110 , with which the star-shaped plate  170  is concentrically aligned. In an aspect, the star-shaped plate  170  may be a terminus of the aperture  114 . 
     The star-shaped plate  170  is defined in part by an outer ring portion  174  from which a plurality of fingers  172  extend radially inwardly between the outer ring portion  174  and respective end portions  440  of each finger  172 . The end portions  440  are collectively positioned about the central aperture  171  in the star-shaped plate  170  and thereby define the central aperture  171 . The central aperture  171  extends laterally (e.g., along the axis y) through the star-shaped plate  170  between an outside of the autonomous perforating drone  100  and an interior (not numbered) of the aperture  114  through the perforating assembly section  110 . A plurality of gaps  173  extend radially outwardly from the central aperture  171  such that the fingers  172  and the gaps  173  are alternatingly arranged about a circumference of the central aperture  171 , thus creating the so-called “star-shaped” feature. 
     The end portions  440  of some of the fingers  172  collectively include the plurality of teeth  450  that form a compression surface for the fixation connector  120  as described further herein with respect to an exemplary practice of the autonomous perforating drone  100 . Each of the teeth  450  is a projection that is connected to, or integral with, a respective end portion  440  and extends away from the end portion  440  at about a 90-degree angle to the finger  172 , in a direction away from the longitudinal axis x of the autonomous perforating drone  100 . Thus, the plurality of teeth  450  will extend along at least a portion of the connecting portion  410  of the shaped charge  400  that protrudes from the central aperture  171  of the star-shaped plate  170  when the shaped charge  400  is retained in the aperture  114  through the perforating assembly section  110 . 
     In an exemplary practice of the autonomous perforating drone  100 , each shaped charge  400  may be connected to the exemplary autonomous perforating drone  100  by inserting the shaped charge  400  into the corresponding aperture  114  through the perforating assembly section  110 . When the shaped charge  400  is fully received in the aperture  114  the connecting portion  410  including the external threaded portion  412  and the detonating cord slot  411  protrudes from the central aperture  171  in the star-shaped plate  170 , as described. The detonating cord  160  may then be inserted into the detonating cord slot  411 , down to the detonating cord seat  415 , and the fixation connector  120  may be threaded onto and advanced along the connecting portion  410  until it reaches the plurality of teeth  450 , against which it will compress and retain the shaped charge  400  and the detonating cord  160 . The exemplary configuration of the plurality of teeth  450  shown in  FIGS.  5 A and  5 C- 5 E  elevates the fixation connector  120  above the detonating cord  160  within the detonating cord slot  411  such that the fixation connector  120  may be sufficiently compressed against the plurality of teeth  450  to secure the shaped charge  400  without crushing the detonating cord  160 . Further, the compression is enhanced because the teeth  450  are positioned on the fingers  172  which have additional resiliency and may conform to oppose specific forces created by the fixation connector  120 . 
     The configuration also allows the detonating cord  160  to extend along the length L of the perforating assembly section  110  through spaces (not numbered) created between the plurality of teeth  450  by end portions  440  that do not include teeth  450 . In addition, the shaped charge  400  may be oriented (e.g., turned) within the aperture  114  such that the detonating cord slot  411  is oriented to direct the detonating cord  160  towards a subsequent shaped charge  400  on the perforating assembly section  110 . In the exemplary embodiment shown in  FIG.  5 A , the shaped charges  400  are arranged in a helical pattern along the length L, and the detonating cord  160  follows the helical pattern and connects to each of the shaped charges  400 . The detonating cord  160  in the assembled fixation assembly  200  is held in sufficient contact, communication, or proximity with the initiation end  401  of the shaped charges  400  such that the detonating cord  160  is energetically coupled to the initiation end  401  of each shaped charge  400  so as to detonate the explosive charge within the casing  404 , as is well known in the art. 
     While the shaped charge apertures  114  (and correspondingly, the shaped charges  113 ,  400 ) are shown in a typical helical arrangement about the perforating assembly section  110  in the exemplary embodiment shown in  FIGS.  2 A- 5 E , the disclosure is not so limited and it is contemplated that any arrangement of one or more shaped charges may be accommodated, within the spirit and scope of this disclosure, by the exemplary autonomous perforating drone  100 . For example, a single shaped charge aperture or a plurality of shaped charge apertures for respectively receiving a shaped charge may be positioned at any phasing (i.e., circumferential angle) on the body portion, and a plurality of shaped charge apertures may be included, arranged, and aligned in any number of ways. For example, and without limitation, the shaped charge apertures  114  may be arranged, with respect to the body portion, along a single longitudinal axis, within a single radial plane, in a staggered or random configuration, spaced apart along a length of the body portion, pointing in opposite directions, and the like. 
     In the exemplary embodiments, the autonomous perforating drone  110  including the perforating assembly section body  119 , the control module section body  191 , the tip section  195 , and the tail section  180  may be formed from a material that will substantially disintegrate upon detonation of the shaped charges  113 . In an exemplary embodiment, the material may be an injection-molded plastic that will substantially dissolve into a proppant when the shaped charges  113  are detonated, and the autonomous perforating drone  100  may be an integral unit. In the same or other embodiments, one or more portions of the autonomous perforating drone  100  may be formed from a variety of techniques and/or materials including, for example and without limitation, injection molding, casting (e.g., plastic casting and resin casting), metal casting, 3D printing, and 3D milling from a solid plastic bar stock. Reference to the exemplary embodiments including injection-molded plastics is thus not limiting. Further, as noted herein, the description of particular sections and portions of an autonomous perforating drone  100  are for aiding the disclosure with respect and reference to the position of various components, and forming the autonomous perforating drone  100 , for example, with one or a combination of integral and separate elements, may be done as applications dictate, without limitation based on the disclosed sections and portions of an autonomous perforating drone  100 . 
     For example, the autonomous perforating drone  100  may be formed as an integral unit, and a portion such as the tip section  195  according to this disclosure may then be removed and adapted for re-securing to the autonomous perforating drone  100 , to allow the autonomous perforating drone  100  to, e.g., be transported without a detonator assembly (such as in the control module  137 ) according to applicable regulations. Once on site, the control module  137  may be inserted into, e.g., the control module section  130  according to this disclosure, and the tip section  195  re-secured thereto. The tip section  195  may be adapted for re-securing to the control module section  130  by milling, turning or injection molding complementary threaded portions, click slots or a bayonet key-turn in each, or using other techniques as known. The connection between the tip section  195  and the control module section is further shown and discussed with respect to  FIG.  12   . In another aspect, the control module  137  may be preassembled in the control module section  130 , before transport, as applicable regulations and applications allow. 
     An autonomous perforating drone  100  formed according to this disclosure leaves a relatively small amount of debris in the wellbore post perforation. In some embodiments, at least a portion of the autonomous perforating drone  100  may be formed from plastic that is substantially depleted of other components including metals. Substantially depleted may mean, for example and without limitation, lacking entirely or including only nominal or inconsequential amounts. In some embodiments, the plastic may be combined with any other materials consistent with this disclosure. For example, the materials may include metal powders, glass beads or particles, known proppant materials, and the like that may serve as a proppant material when the shaped charges  113  are detonated. In addition, the materials may include, for example, oil or hydrocarbon-based materials that may combust and generate pressure when one or more of the detonator  133 , the donor charge  134 , and the shaped charges  113  are detonated, synthetic materials potentially including a fuel material and an oxidizer to generate heat and pressure by an exothermic reaction, and materials that are dissolvable in a hydraulic fracturing fluid. 
     In some embodiments, the exemplary autonomous perforating drone  100  may be connected at the tail portion  180  to a wireline that extends to the surface of the wellbore. The wireline may be connected to the autonomous perforating drone by any known technique for connecting a wireline to a wellbore tool. The wireline may further assist in retrieving any components of the autonomous perforating drone, including, without limitation, a control module, data collection device, or other portions that remain in the wellbore post detonation/perforation. The remaining components may be retracted to the surface along with the wireline. 
     The exemplary drones described throughout this disclosure, for example and without limitation, with particular reference to  FIGS.  16 - 25   , may also be configured for connecting in series as a drone string. In an aspect of a drone string, a single control assembly and/or ballistic interrupt assembly may be used for every drone in the drone string and the drone string would detonate upon a single initiation. 
     In an exemplary operation, one or more autonomous perforating drones  100  according to the disclosed embodiments are connected to a control system at the surface of a wellbore. The autonomous perforating drones  100  may be manually connected to the control system, or loaded into, for example and without limitation, a deployment vehicle, pressure equalization chamber, or other system for deploying the autonomous perforating drones  100  into the wellbore and including an appropriate connection to the control system. The control system may perform, among other things, a safety check and function test on each autonomous perforating drone  100 . Upon a successful result from any test for safety, function, compliance, and/or otherwise, the control system or an operator may “arm” the autonomous perforating drone  100  by moving the ballistic interrupt  140  to an open state  144 , as described. The control system may also record which autonomous perforating drones  100  have been armed and determine the order in which the respective autonomous perforating drones  100  will be deployed. The control system may communicate the order, and other instructions, to the autonomous perforating drone  100  via an electrical connection to the control assembly  131 , e.g., the programmable electronic circuit, of each autonomous perforating drone  100  as described. Other instructions may include, without limitation, a threshold depth at which to send a detonation signal to the detonator  133 , a time delay or other instructions for arming a trigger circuit, desired data to transmit to the wellbore surface, or other instructions that a control system may provide as discussed in U.S. Provisional Patent Application. Nos. 62/690,314 filed Jun. 26, 2018 and 62/765,185 filed Aug. 20, 2018, both of which are incorporated herein by reference in their entirety. 
     In the exemplary embodiments, the control assembly  131  includes, without limitation, a depth correlation device, and the programmable electronic circuit is either pre-programmed, or programmed via the control system, to receive from the depth correlation device data regarding the current depth of the autonomous perforating drone  100  within the wellbore and send a detonation signal to the detonator  133  when the autonomous perforating drone  100  reaches a predetermined depth. The depth correlation device may be, for example, an electromagnetic sensor, an ultrasonic transducer, or other known depth correlation devices consistent with this disclosure. The autonomous perforating drone  100  may also include a velocity sensor for measuring a current velocity of the autonomous perforating drone  100  within the wellbore, or the depth correlation device may include a velocity sensor or calculate a velocity based on sequential depth readings, and the programmable electronic circuit may be programmed to receive such velocity data as part of a criteria for transmitting the detonation signal. 
     In some embodiments, the autonomous perforating drone  100  may work with other systems, such as radio-frequency (RF) transducers, casing collar locators (CCL), or other known systems for determining a position of a wellbore tool within the wellbore. 
     With reference again to the exemplary embodiments, after being deployed into the wellbore the depth correlation device measures the depth of the autonomous perforating drone  100  within the wellbore. When the autonomous perforating drone  100  reaches the predetermined depth, the programmable electronic circuit sends a detonation signal to the detonator  133 , which initiates detonation of the donor charge  134  and ultimately the shaped charges  113 , as described. The programmable electronic circuit may be in wired, wireless, or contactable electrical communication with the detonator  133  by various known techniques, or may send the detonation signal via, or after activating, e.g., a trigger circuit or other intervening detonation component. The detonation signal may be, without limitation, a selective sequence signal, as previously discussed, that is unique to the detonator  133  of the particular autonomous perforating drone  100 . The selective detonation signal may provide a safety measure against accidental firing by, for example, external RF signals. 
     As described, the autonomous perforating drone  100  travels through the wellbore with the tip section  195  downstream, and the detonating cord  160  is initiated by the receiver booster  150  at the downstream end  111  of the perforating assembly section  110 . Accordingly, the ballistic/thermal release from the detonating cord  160  propagates along the length L of the perforating assembly section  110  in a direction from the downstream end  111  of the perforating assembly section  110  to the upstream end of the perforating assembly section  110 , and the shaped charges  113  are correspondingly detonated (by the detonating cord  160 ) in a bottom-up, i.e., downstream to upstream, sequence. This bottom-up sequence for detonating the shaped charges  113  prevents downstream shaped charges and portions of the autonomous perforating drone  100  from being separated and blown away from the rest of the assembly, as may happen if an upstream shaped charge is detonated while a drone is traveling at high velocity in a wellbore fluid. Accordingly, the bottom-up detonation sequence may prevent downstream shaped charges from failing to detonate or detonating at an undesired location, and leaving unexploded shaped charges and extra debris in the wellbore. 
     With reference now to  FIGS.  10 A and  10 B ,  FIG.  10 A  shows an autonomous perforating drone  1200  according to an exemplary embodiment in which a plurality of shaped charges  1240  are arranged within one or more single radial planes R around a perforating assembly section body  1210  of the autonomous perforating drone  1200 . Each of the shaped charges  1240  is received and retained in a corresponding shaped charge aperture  1213  at least in part within an interior  1214  of the perforating assembly section body  1210 .  FIG.  10 B  is a cross-sectional view showing the arrangement of the shaped charges  1240  and the shaped charge apertures  1213 , among other things, within the interior  1214  of the perforating assembly section body  1210  of the exemplary autonomous perforating drone  1200  shown in  FIG.  10 A . In particular,  FIG.  10 B  is a lateral cross-sectional view of the perforating assembly section body  1210  of the autonomous perforating drone  1200  shown in  FIG.  10 A  taken along the radial plane R. For purposes of this disclosure, a radial plane is a plane generally containing each of a plurality of radii (e.g., shaped charges  1240 ) extending from a common center. The exemplary autonomous perforating drone  1200  shown in  FIGS.  10 A and  10 B  includes three shaped charges  1240  arranged in the same radial plane R and spaced apart by about a 120-degree phasing around the perforating assembly section body  1210 . The type(s) of shaped charges used with an autonomous perforating drone as described throughout this disclosure are not limited and may include any shaped charges as are well-known and/or would be understood in the art and consistent with this disclosure. Exemplary embodiments of shaped charges for use with embodiments of an autonomous perforating drone and arrangement of shaped charges/shaped charge holders according to this disclosure, but not limited thereto, are shown and described with respect to  FIGS.  10 B- 13 B . 
       FIG.  10 B  also shows a detonator or booster  1271  positioned within the interior  1214  of the perforating assembly section body  1210  and adjacent to the shaped charges  1240  such that the shaped charges  1240  extend radially from the detonator  1271 . In an aspect, the detonator  1271  may directly initiate detonation of the shaped charges  1240  upon detonation of the detonator  1271 . In some embodiments, a detonation extender, such as a detonating cord or a booster device may also be secured in the interior  1214  of the perforating assembly section body  1210 . The detonator extender may abut an end of the detonator  1271  or may be in side-by-side contact with at least a portion of the detonator  1271 . The detonation extender may be in communication with the detonator  1271  such that upon activation of the detonator  1271  a detonation energy from the detonator  1271  simultaneously detonates the shaped charges in a first radial plane R and then initiates the detonation extender such that the detonation extender transfers a ballistic energy to detonate shaped charges arranged in a second, third, etc. radial plane R+1, R+2 ( FIG.  12   ). 
     With reference now to  FIG.  11   , an exemplary autonomous perforating drone  1300  according to some embodiments may include a threaded connection between a shaped charge  1340  and a shaped charge aperture  1313  in which the shaped charge  1340  is received. For example,  FIG.  11    shows a lateral cross-sectional view taken along a radial plane of a body portion  1310  of the exemplary autonomous perforating drone  1300 , similar to the lateral cross-sectional view shown in  FIG.  10 B . As shown in  FIG.  11   , the exemplary autonomous perforating drone  1300  includes three shaped charges  1340  arranged in the same radial plane and spaced apart by about a 120-degree phasing around the perforating assembly section body  1310 . The shaped charges  1340  are respectively received and retained in the shaped charge apertures  1313  at least in part within an interior  1314  of the perforating assembly section body  1310 . According to an aspect, the shaped charge apertures  1313  include an internal thread  1320  for threadingly securing the shaped charge  1340  therein. The internal thread  1320  may be a continuous thread or interrupted threads that mate or engage with corresponding threads  1332  formed on a back wall protrusion  1330  of the shaped charge  1340 . Other aspects of a configuration of a shaped charge for use with an autonomous perforating drone as described throughout this disclosure are not limited by this disclosure and may include a shaped charge having any configuration as is well-known and/or would be understood in the art and consistent with this disclosure. For example, a shaped charge configuration in which a shaped charge casing houses one or more explosive loads and a liner atop the explosive loads for containing the explosive load(s) within the shaped charge and forming a perforating jet upon detonating the shaped charge. 
     In the exemplary configuration shown in  FIG.  11   , a detonator  1371  (and/or optionally, a detonating cord) is positioned within the interior  1314  of the perforating assembly section body  1310  and adjacent to the shaped charges  1340  such that the shaped charges  1340  extend radially from the detonator  1371 . In an aspect, the detonator  1371  may directly initiate detonation of the shaped charges  1340  upon detonation of the detonator  1371 . It is contemplated that at least one of the shaped charge apertures  1313  may be in open communication with a hollow portion of the interior  1314  of the perforating assembly section body  1310  in which the detonator  1371  and/or the detonating cord is positioned. 
     The arrangement of shaped charges within a single radial plane as shown in  FIGS.  10 A- 11    is not limited to the embodiments depicted in those figures, nor is the disclosure of such arrangements limiting. For example, any number of charges capable of fitting around a circumference of a portion of an autonomous perforating drone according to this disclosure may be arranged within a single radial plane and respectively spaced apart at any desired phasing. In another non-limiting example, shaped charges in separate radial planes may be arranged in a staggered fashion such that the shaped charges overlap along a single radial plane. In addition, one or more of a detonator, selective detonator, detonating cord, and other internal components of an autonomous perforating drone may be included and configured as particular applications consistent with this disclosure dictate. 
     With reference now to  FIG.  12   , a partial cross-section view of an exemplary autonomous drone  1200  with charges arranged in a series of respective radial planes R, R+1, in accordance, at least in part, with the embodiment shown in  FIG.  10 A , is shown. As discussed throughout this disclosure, autonomous drone  1200  includes a control module section  130  positioned between and connected to each of a tip section  195  and a perforating assembly section  110 . The control module section  130  in the exemplary embodiment shown in  FIG.  12    is connected to the tip section  195  via complimentary engagement structures including a lip  1835  extending away from a first end  135  of the control module section  130  and a corresponding lip  199  formed on the tip section  195 . The lip  1835  of the control module section  130  includes a tab  1835   a  extending inwardly (i.e., towards axis x) and a concave surface  1835   b  positioned between and connected to each of the tab  1835   a  and the control module section body  191 . The lip  199  of the tip section  195  includes a notch  199   a  and a tongue  199   b  configured respectively to receive the tab  1835   a  of the lip  1835  of the control module section  130  and be received against the concave surface  1835   b  of the lip of the control module section  130 . Tab  1835   a  thereby prevents lateral movement or disengagement of the tip section  195  by engaging each of the notch  199   a  and the tongue  199   b.    
     In an aspect, one or both of the control module section body  191  (including the lip  1835 ) and the lip  199  of the tip section  195  may be formed from a material with sufficient flexibility and resiliency to allow engagement of the lip  1835  of the control module section  130  and the lip  199  of the tip section  195  to move under a force of pushing the tip section  195  and the control module section  130  together, thereby bringing the respective engagement structures into position, before returning the complimentary engagement portions into their set position providing engagement as described above. In an aspect, the tip section  195  may be formed from a material such as, but not limited to, a hard rubber. In a further aspect, the material is abrasion-resistant. The separable aspect of the tip section  195  and the control module section  130  may allow selective insertion of the control module  137  into the hollow interior  132  of the control module section  130 . Other techniques and configurations for removably securing the tip section  195  to the control module section  130  include, without limitation, threaded engagements, dovetail arrangements, or other techniques as are known for removably securing structures. 
     In another aspect, the tip section  195  may be configured as a “frac ball” for sealing a corresponding “frac plug” downhole in the wellbore. For example, frac plugs are well known for isolating zones of a wellbore during perforation. One style of known frac plugs are configured as sealing elements with an open channel through the center of the plug such that the plug may be completely sealed by a frac ball that sets within the open channel. Sealing a zone currently undergoing perforation and fracking from downstream portions of the wellbore allows the fracking fluid to more efficiently achieve the pressures required for cracking hydrocarbon formations in the current zone because the fracking fluid does not lose pressure required to fill downstream portions of the wellbore. However, once the wellbore is ready for production, the frac balls must be drilled out of the frac plug openings to allow hydrocarbons to flow through the wellbore and to the surface. 
     In an aspect, the tip section  195  of the autonomous perforating drone may be configured dimensionally for use as a frac ball and formed from one or more materials such that the frac ball tip section will not be destroyed upon detonation of the autonomous perforating drone. The frac ball tip section may be retained to the control module section  130  by any known techniques including a threaded portion, clips, straps, friction fits, adhesives, retention in a cavity, or other techniques as described in or consistent with this disclosure. Upon detonation of the autonomous perforating drone, the frac ball tip section will release and travel downstream until it encounters and seals a frac plug. A drone for use with a frac ball tip section may be an autonomous perforating drone as described throughout this disclosure or may be a “dummy” drone, i.e., that does not carry perforating charges or other wellbore tools for performing a separate function in the wellbore. In either case, the control module  137  of the autonomous perforating (or dummy) drone may be made from standard metal and drilled out with the frac ball/plug, and the shaped charges may be formed at least in part from zinc to reduce debris. In addition, an autonomous perforating drone incorporating a tip section as a frac ball may be used in conjunction with an autonomous drone for deploying a frac plug, such that the frac plug drone is sent downhole, sets the plug, and the frac ball drone is sent in thereafter to provide the frac ball seal and potentially perforate the wellbore casing/hydrocarbon formation with shaped charges as discussed throughout this disclosure. 
     Continuing with reference to  FIG.  12   , an exemplary arrangement of components in the control module  137  is shown. In an aspect, the control module  137  includes a power source  1792  such as a battery or a capacitor as previously discussed. The power source  1792  may be used to power one or more of, among other things, an onboard computer  390  (i.e., control circuit(s)), sensors  1820  such as depth or velocity sensors, among others, as previously discussed, and detonator control electronics  1810  for, e.g., receiving and responding to selective detonation signals. Charging/programming contacts  1800  are electrically connected to one or more of, e.g., the power source  1792  and the onboard circuitry/sensors  390 ,  1820 ,  1810  and extend through the control module section body  191  for connecting to an external power/control source and respectively charging or programming components of the control module  137 . In an aspect, the contacts  1800  may be a combination of various seals and electrical contacts configured for, without limitations, isolating a relay between an electrical contact on an outside of the drone and a programmable electronic circuit or a power supply. The seals and connections may include, without limitation, o-rings, gaskets, face seals, sealing tape, contact pins, shafts, surfaces extending from the drone body, and the like. 
     In an aspect, the components of the control module  137  in the exemplary embodiment shown in  FIG.  12    are potted in material  1830  in the control module  137  to further pressure-isolate the components from potentially detrimental influence of surrounding environmental conditions, such as those of the wellbore. Other pressure-isolation techniques for the components include, without limitation, covering, embedding, and/or encasing the components in an injection-molded or 3D-printed material, and the like. Exemplary materials may include, without limitation, polyethylene-, polypropylene-, and/or polyamide-compounds. 
     The control module section  137 , as previously discussed, further includes a detonator  133  and a donor charge  134  positioned within a detonator channel  145  of the control module  137 . The donor charge  134  is substantially aligned with a ballistic channel  141  in which a ballistic interrupt  140  is positioned in a spaced apart relationship between the donor charge  134  and a receiver booster  150 . In the embodiment shown in  FIG.  12   , the receiver booster  150  extends along a length of the ballistic channel  141  that is adjacent to a plurality of shaped charges  113  arranged in respective single radial planes R, R+1 and thereby directly initiates the shaped charges  113  upon detonation of the receiver booster  150  in a manner as previously discussed with respect to, e.g., a detonator or a detonating cord. 
     The exemplary ballistic interrupt  140  is cylindrically-shaped and functions as previously described. For example, the ballistic interrupt  140  in  FIG.  12    is shown in an open state, i.e., where the autonomous drone  1200  would be considered armed in the sense that the donor charge  134  and the receiver booster  150  are in ballistic communication through the through-bore  142 . The ballistic interrupt  140  may be movable, as previously described, between a closed state and an open state by, e.g., rotating ballistic interrupt actuator  460  approximately 90 degrees in a direction a, or opposite direction, such that the through-bore  142  shown in  FIG.  12    as concentric with ballistic channel  141  would resultingly have a configuration perpendicular to the ballistic channel  141  (or, into the page as in the view of  FIG.  12   ), i.e., a closed state of the ballistic interrupt  140 . 
       FIG.  13 B  shows a cross-section of the exemplary autonomous drone  1200  shown in  FIG.  12    taken, according to  FIG.  13 A , along line A-A from the first end  135  of the control module section  130 , and without the various internal components such that the internal configuration alone, including the hollow interior  132  of the control module section  130 , the ballistic channel  141 , the opening  462  for the ballistic actuator  460 , and others as explained below, are illustrated. 
     With continuing reference to  FIG.  12   , and further reference to  FIGS.  13 B- 15   , an exemplary shaped charge  1240  as shown in  FIG.  12    and for use in the arrangement of, e.g.,  FIG.  10 B , although not limited thereto or restricted for use in that embodiment, is shown. As is well known for shaped charges, generally, and applicable commonly throughout this disclosure, the exemplary shaped charge includes a liner  1241  disposed adjacent an explosive load  1242 . The liner  1241  is configured for retaining the explosive load  1242  within a cavity  1243  defined at least in part by a cylindrical sidewall  1244  including a first sidewall portion  1245  and a second sidewall portion  1246 . A cap  1247  closes the shaped charge cavity  1243  from a surrounding environment as previously discussed with respect to known encapsulated shaped charges. In an aspect, the cap  1247  may not need to be crimped onto the sidewall  1244 , due, for example, to the protection that the control module section  130  and tail section  180  provide against the shaped charges  1240  (i.e., caps  1247 ) impacting the wellbore casing. In another aspect, the cap  1247  may be formed from, without limitation, zinc, aluminum, steel, plastic, or other materials consistent with this disclosure. 
     In an aspect, the explosive load  1242  includes at least one of pentaerythritol tetranitrate (PETN), cyclotrimethylenetrinitramine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine/cyclotetramethylene-tetranitramine (HMX), 2,6-Bis(picrylamino)-3,5-dinitropyridine/picrylaminodinitropyridin (PYX), hexanitrostibane (HNS), triaminotrinitrobenzol (TATB), and PTB (mixture of PYX and TATB). According to an aspect, the explosive load  1242  includes diamino-3,5-dinitropyrazine-1-oxide (LLM-105). The explosive load may include a mixture of PYX and triaminotrinitrobenzol (TATB). The type of explosive material used may be based at least in part on the operational conditions in the wellbore and the temperature downhole to which the explosive may be exposed. 
     In the exemplary embodiment shown in  FIG.  14 A , the liner  1241  has a conical configuration, however, it is contemplated that the liner  1241  may be of any known configuration consistent with this disclosure. The liner  1241  may be made of a material selected based on the target to be penetrated and may include, for example and without limitation, a plurality of powdered metals or metal alloys that are compressed to form the desired liner shape. Exemplary powdered metals and/or metal alloys include copper, tungsten, lead, nickel, bronze, molybdenum, titanium and combinations thereof. In some embodiments, the liner  1241  is made of a formed solid metal sheet, rather than compressed powdered metal and/or metal alloys. In another embodiment, the liner  1241  is made of a non-metal material, such as glass, cement, high-density composite or plastic. Typical liner constituents and formation techniques are further described in commonly-owned U.S. Pat. No. 9,862,027, which is incorporated by reference herein in its entirety to the extent that it is consistent with this disclosure. When the shaped charge  1240  is initiated, the explosive load  1242  detonates and creates a detonation wave that causes the liner  1241  to collapse and be expelled from the shaped charge  1240 . The expelled liner  1241  produces a forward-moving perforating jet that moves at a high velocity. 
     With continuing reference to  FIGS.  12  and  14 A- 14 B , an engagement member  1248  outwardly extends from an external surface  1249  of the side wall  1244  at a position substantially between the first sidewall portion  1245  and the second sidewall portion  1246 . In an aspect, the engagement member  1248  may be configured for coupling the shaped charge  1240  within a shaped charge holder  1840  within an aperture  1213  at least partially within an interior  1214  of the perforating assembly section body  1210 . In the exemplary embodiment, the engagement member  1248  at least in part defines a groove  1250  circumferentially extending around the side wall  1244 . The groove  1250  defines a seat  1251  for engaging a retention device, such as one or more clips  1850  within the shaped charge holder  1840  for retaining the shaped charge  1240  within the shaped charge holder  1840 . When the shaped charges  1240  are retained in the shaped charge holders  1840 , an initiation point  1252  of each shaped charge  1240  is adjacent the ballistic channel  141  including, e.g., the receiver booster  150  for initiating detonation of the shaped charges  1240  in the exemplary embodiments. 
     With reference now to  FIG.  15   , a blown-up view of the shaped charges  1240  received in the shaped charge holders  1840  according to  FIGS.  12 - 14 B  is shown. When a shaped charge  1240  is received in a corresponding shaped charge holder  1840 , clips  1850  engage against the seat  1251  formed on the groove  1250  defined by the engagement member  1248  extending outwardly from the external surface  1249  of the side wall  1244 . As shown in  FIG.  12   , a receiver booster  150  is positioned within the ballistic channel  141  of the autonomous perforating gun  1200 , adjacent to an initiation point  1252  of each shaped charge. 
     In an aspect, shaped charges arranged according to any of the exemplary embodiment(s) shown in  FIGS.  10 A- 15    in which shaped charges are arranged adjacent to a detonator, receiver booster, donor charge, etc. in the absence or optional absence of a detonating cord, may be directly initiated by one or more of the adjacent detonator, receiver booster, donor charge, etc. 
     With reference now to the exemplary embodiment shown in  FIG.  16   , an autonomous perforating drone  1200  includes a perforating assembly section  110  positioned between and connected to each of a head portion  1285  at a first end  101  of the drone  1200  and a control module section  130  at a second end of the drone  1200 . Except where otherwise noted, various aspects of the exemplary drones  100 ,  1200  disclosed herein are common to the embodiment shown in  FIG.  16    and for brevity will not be repeated here. Further, as previously noted, references to portions such as the head portion  1285 , perforating assembly section  110 , and control module section  130  are to aid generally in describing the location of certain components and do not imply any particular assembly, delineation between sections, or other limits on the configuration of the structures and components. In an aspect, the exemplary drone  1200  shown in  FIG.  16    may be an integrally formed piece, as additionally shown in  FIGS.  17 ,  20  and  21   , and a drone body  1255  is referenced for simplicity to identify the structure(s) that define, house, or retain the various features of the drone  1200 , except where otherwise indicated. 
     The control module section  130  in the exemplary embodiment shown in  FIG.  16    and  FIG.  20    is notably located upstream of the perforating assembly section  110  with respect to an orientation of the drone  1200  as it travels down a wellbore—that is, the control module section  130  is above the perforating assembly section  110  in the tail section  180  of the drone  1200 . With additional reference to  FIG.  20   , the control module section  130  includes a hollow interior portion  132  (as previously discussed) within which a control assembly, referred to interchangeably for purposes of this embodiment but without limitation and not implying a difference between the various embodiments, as a Control Interface Unit (CIU)  1804  is positioned and housed, as discussed below. As described below, the exemplary drone  1200  shown in  FIGS.  16 - 21    includes a configuration in which, e.g., shaped charges carried by the drone are detonated in a top-down sequence, while still addressing problems in the existing art in an alternative approach from embodiments of a drone in which shaped charges are detonated in a bottom-up sequence, as disclosed herein. 
     As previously described, both the head portion  1285  and the tail section  180  of the drone  1200  may be formed with fins  181 . Particularly pronounced fins  1281  may be present on one or both of the head portion  1285  and the tail section  180  and may be used, for example, to further lessen impacts against critical components of the drone  1200  and/or provide an engagement means for a mechanical implement to grip and move the drone as part of a management and/or launcher system for drones, for example as described in co-owned U.S. patent application Ser. No. 16/423,230, incorporated herein by reference. 
     Tail section  180 /control module section  130  may further include pass-through holes  1260  in a rear area of the tail section  180 /control module section  130 . The pass-through holes  1260  may, without limitation, provide a channel for fluid running through fins  181  to flow through, thus reducing friction on the drone  1200 , and may also be part of an engagement structure by which a mechanical implement for moving the drones, as mentioned above, may engage the drone  1200  for moving it as part of moving, making an electrical connection to, and/or launching the drone  1200 , or other operations of the like. With additional reference to  FIGS.  17  and  20 - 21   , the control module section  130  may further include a passage  1265  through the drone body  1255  for accessing a sealing access plate  1275  that encloses, seals, and protects the components within the hollow interior  132  of the control module section  130 . The passage  1265  is discussed further below. 
     As previously described with respect to other embodiments, the perforating assembly section  110  includes at least one aperture  1213  configured for receiving a shaped charge  140  at least in part within the body  1255  of the drone  1200 . For purposes of the embodiment(s) shown in  FIGS.  16 - 21   , retaining the shaped charges  1240  within the apertures  1213  may be accomplished by any known means. In the exemplary embodiment of  FIG.  16   , retaining the shaped charges  1240  within the apertures  1213  may be accomplished according to the shaped charges and associated assemblies shown and described with respect to  FIGS.  12 - 15   . For purposes of convenience and not limitation, such description or labeling is not repeated here. 
     The exemplary embodiment(s) shown in  FIGS.  16 ,  17 ,  20 , and  21    include opposing apertures  1213  and thus shaped charges  1240 , such that the charges will ideally fire at 180 degrees to each other. The ballistic interrupt  140 , as previously described, is retained within the drone body  1255  through an opening  462  in the drone body  1255 . The ballistic interrupt  140  in the exemplary embodiment and for purposes of preventing accidental or unintended detonation of the shaped charges is positioned, in any event, between an initiator within the control module section  130  and a shaped charge initiator configured for being initiated by the initiator in the control module (as discussed with respect to other embodiment(s) and further described below). 
     The head portion  1285  of the drone  1200  is sized and shaped, as previously discussed, to help reduce impacts between the drone  1200  and the wellbore casing as the drone  1200  travels down the well. The exemplary head portion  1285  shown in  FIG.  16    is defined by a generally circularly-shaped outer body portion  1287  of the head portion  1285 . A concavity  1286  is formed substantially in the center of the head portion  1285  and an upper ledge  1288  ( FIG.  19   ) of the concavity  1286  is defined by the outer body portion  1287 . As described below with additional reference to  FIGS.  19  and  20   , a series of slopes  1291  extend inward into the head portion  1285 , between the outer body portion  1287  and a bottom surface  1289  of the concavity  1286 , in a direction towards the perforating assembly section  110 . The series of slopes  1291  taper inward towards a common center that is substantially aligned with a booster  150  within the drone body  1255  (as discussed with respect to  FIGS.  20  and  21   ) and are interposed with slits  1290 , resulting in the star-shaped profile of the concavity  1286  seen in the straight-on view of the exemplary embodiment of  FIG.  19   . 
     As mentioned throughout this disclosure, the head portion  1285 , perforating assembly section  110 , and tail section  180  may take any form consistent with this disclosure. For example, an embodiment of a head portion may be torpedo or arrow shaped, have fins including a curved profile, or any other configuration consistent with the application(s). The exemplary head portion  1285  shown in  FIG.  16    may help with any or all, and without limitation, of increasing rotational speed of the drone  1200  or slowing a forward speed of the drone  1200  when it is traveling through a wellbore fluid, funneling the wellbore fluid through which it travels to help centralize the drone in the wellbore, and enhance the destructibility or break-up of the head portion  1285  when the drone  1200  is detonated. The shaped charges  1240  of a drone  1200  as in the exemplary embodiment shown in  FIG.  16    will detonate in a top-down sequence—i.e., upstream to downstream—when the drone is detonated, due to the configuration of the drone as described with respect to  FIGS.  16 - 21   . 
     With reference to  FIG.  17   , the exemplary embodiment of the drone  1200  shown in  FIG.  16    is illustrated from a reverse perspective such that the second end  102  and rear of the control module section  130  may be seen. The control module section  130  at the second end  102  includes the sealing access plate  1275  that seals the internal components of the control module section  130 . The sealing access plate  1275  includes the charging and programming contacts  1800  as discussed above. The charging and programming contacts  1800  are further described below especially with respect to  FIGS.  18  and  20 - 25   . The sealing access plate  1275  is set back within a recess  1270  of the tail section  180 , the recess defined by the body portion  1255  of the drone  1200  extending outwardly from the tail section  180 . This may provide additional protection to the sealing access plate  1275  and allow for the inclusion of different structures that will now be described. 
     For example, the annular portion of the tail section  180  extending beyond the sealing access plate  1275  defines a wall  1271  around the recess  1270 . The wall has an interior surface  1272  on which engagement structures may be formed. In the exemplary embodiment shown in  FIG.  17   , the engagement structures include receiving slots  1273  extending longitudinally through the wall as cut-outs between the second end  102  and towards the sealing access plate  1275 . The slots  1273  terminate at retaining channels  1274  that are open to and extend from the slots in a circumferential direction around the interior surface  1272  of the wall  1271 . The slot  1273 /channel  1274  configuration may receive a complimentary connecting element through the slot  1273  and into the channel  1274 , and thereby be securely yet removable retained to the second end  102  of the drone  1200 . The connection may be, without limitation, to another autonomous perforating drone having a complementary connecting structure on its head portion, to a mechanical implement for engaging and holding the drone  1200  such that the drone  1200  may be moved and/or loaded into a wellbore, or may be an attachment means for other wellbore tools, such as data collection devices, to connect to the drone  1200 . In a case where a series of drones or wellbore tools are connected in series as a string, an aspect of the string may be that a single drone or tool, for example the most upstream drone or tool, contains a single CIU for controlling each drone or tool in the string. 
       FIG.  18    shows a rear plan view of the exemplary drone  1200  shown in  FIG.  17   . As previously discussed, the rear plan view shows the relationship between the different components, including the passages  1260 , slots  1273 , and pronounced fins  1281 , of which one or more may be used to engage with a mechanical implement for moving the drone  1200  as discussed above. Charging and programming contacts  1800  are accessible through the sealing access plate  1275 . Sealing access plate  1275  additionally includes a plurality of slits  1276  formed in the sealing access plate  1275  for providing the sealing access plate  1275  with additional manipulability such that the sealing access plate  1275  may be attached to and removed from the drone  1200  as discussed below with respect to  FIGS.  20  and  21   . 
       FIG.  19    shows a front plan view of the exemplary drone  1200  as shown in  FIG.  16   , wherein passages  1260  are visible through spaces between the fins  181  of the head portion  1285 . As previously discussed,  FIG.  19    illustrates the star-shaped configuration of the concavity  1286  in the head portion  1285 . Also visible in  FIG.  19    is an aperture  1292  that opens certain areas of the drone body  1255  to a surrounding environment. The aperture  1292  may provide benefits in forming the drone body  1255  or in a flow profile as the drone  1200  travels through a wellbore. As discussed herein, the CIU  1804  may be provided in, e.g., a sealed control module housing  138 , and the CIU  1804  and/or other components may be sealed against the environmental aspects by known techniques, or those disclosed herein, such as for providing sealed boosters, detonators, shaped charges, and the like. 
     With reference now to  FIG.  20   , a partial cutaway of the exemplary drone  1200  is shown. The CIU  1804  is housed within a control module housing  138  positioned within the hollow interior portion  132  of the control module section  130 . The cross section shown in  FIG.  20    depicts that charging and programming contacts  1800  include pin contact leads  1802  electrically connected to the CIU  1804 , for example, to a programmable electronic circuit which may be contained on a Printed Circuit Board (PCB)  1805  ( FIG.  23   ). The pin contact leads  1802  may be exposed through, and sealed within, apertures  1801  through the sealing access plate  1275 . As previously discussed, a number of known techniques exist for sealing the CIU  1804  and, e.g., the pin contact leads  1802 , from external conditions. 
     As further shown in  FIG.  20   , and with further reference to  FIG.  21   , sealing access plate  1275  includes sealing portions  1276  on a periphery of the sealing access plate  1275 . The sealing portions  1276  in the exemplary embodiment are formed from a material and configured with a geometry to form a seal within the passages  1265  through the drone body  1255 . This technique both seals the internal components of the control module section  130  from external conditions and allows the sealing access plate  1275  to be removed and re-secured within the control module section  130 , although other techniques as known and consistent with this disclosure may be used. 
     With continuing reference to  FIG.  20   , the CIU  1804  may contain such electronic systems such as power supplies, programmable circuits, sensors, processors, and the like, as described throughout this disclosure. In an exemplary embodiment, the CIU  1804  further includes capacitor  1803  power supplies, a detonator  133 , and the donor charge  134 . According to previous embodiments, the detonator  133  is configured for initiating the donor charge  134  upon receiving a signal to detonate the drone  1200 . As further shown and discussed, below, with respect to  FIGS.  23 - 25   , the detonator  133  in the exemplary configuration may be surrounded by the one or more capacitors  1803  for powering the CIU  1804  and associated components. The detonator  133  may include a Non-Mass Explosive (NME) body and the donor charge  134  may be integrated with the explosive load of the detonator  133 . In an aspect of integrating the donor charge  134  with the explosive load of the detonator  133 , the amount of explosive may be adjusted to accommodate the donor charge  134  and the size and spacing of components such as a ballistic channel  141  along which the jet from the donor charge propagates, and the ballistic interrupt  140  and a receiver booster  150  positioned within the ballistic channel. 
     In an aspect, the CIU  1804  may include the PCB  1805  and a fuse for initiating the detonator  133  may be attached directly to the PCB  1805 . In an aspect of those embodiments, the detonator  133  may be connected to a non-charged firing panel—for example, a selective detonator may be attached to the PCB  1805  such that upon receiving a selective detonation signal the firing sequence, controls, and power may be supplied by components of the PCB or CIU via the PCB. This can enhance safety and potentially allow shipping the fully assembled drone in compliance with transportation regulations if the ballistic interrupt is in the closed position. Connections for the detonator/detonator components on the PCB board may be, without limitation, sealed contact pins or concentric rings with o-ring/groove seals to prevent the introduction of moisture, debris, and other undesirable materials. 
     In an aspect, the CIU  1804  may be configured without a control module housing  138 . For example, the CIU  1804  may be contained within the hollow interior portion  132  of the control module section  130  and sealed from external conditions by the drone body  1255  itself. Alternatively, the CIU  1804  may be housed within an injection molded case and sealed within the body  1255 . The injection molded case may be potted on the inside to add additional stability. In addition, or alternatively, the control module housing  138  or other volume in which the CIU  1804  is positioned may be filled with a fluid to serve as a buffer. An exemplary fluid is a non-conductive oil, such as mineral insulating oil, that will not compromise the CIU components including, e.g., the detonator. The control module housing  138  may also be a plastic carrier or housing to reduce weight versus a metal casing. In any configuration including a control module housing  138  the CIU components may be potted in place within the control module housing  138 , or alternatively potted in place within whatever space the CIU  1804  occupies. 
     With continuing reference to  FIGS.  20  and  21   , and the exemplary embodiment, the detonator  133  and donor charge  134  are contained within a control module housing  138  and the donor charge  134  is substantially aligned with the ballistic channel  141 . Upon detonation of the detonator  133 , the donor charge  134  is initiated and the jet from the donor charge  134  will pierce a portion  139  of the control module housing  138  that is positioned between the donor charge  134  and the ballistic channel  141 , according to operation as described throughout this disclosure. The ballistic interrupt  140  and receiver booster  150  are positioned in a spaced apart relationship within the ballistic channel  141 , and the ballistic interrupt  140  lies between the donor charge  134  and the receiver booster  150  such that, in the closed position, the ballistic interrupt  140  prevents the jet from the donor charge  134  from reaching and initiating the receiver booster  150 , as has been described herein. The ballistic interrupt  140  in the exemplary embodiments shown in each of  FIGS.  20  and  21    is shown in the open position—i.e., the through-bore  142  of the ballistic interrupt  140  is parallel and coaxial with the longitudinal axis of the ballistic channel  141 . As has been discussed herein, the ballistic interrupt  140  is movable between a closed and an open state by, for example and without limitation, rotating the ballistic interrupt  140  between open and closed states via the keyway  461 . 
     The ballistic channel  141  is open to and extends from the hollow interior portion  132  of the control module section  130  towards the perforating assembly section  110 . As shown in  FIGS.  20  and  21   , the receiver booster  150  extends, within the ballistic channel  141 , through a length of the perforating assembly section  110  adjacent the shaped charges  140  retained in the shaped charge apertures  1213  extending into a portion of the drone body  1255 . The shaped charges  1240  in the exemplary embodiments shown in  FIGS.  20  and  21    are received and secured in the shaped charge apertures  1213  in substantially the same was as has been described with respect to  FIGS.  12 - 15    and will not be repeated here. Accordingly, an initiation end  1252  of the shaped charges  1240  within the shaped charge apertures  1213  are, by the exemplary configuration, directly initiated by detonation of the receiver booster  150 . In alternative embodiments, the configuration may be applied with one or more of a detonator, detonating cord, or other initiation device consistent with the receiver booster  150  in the ballistic channel  141 , in place of or in combination with the receiver booster  150 . 
       FIGS.  22 - 25    illustrate exemplary CIU  1804  assemblies for use in the exemplary embodiments. For example,  FIG.  22    shows the control module  137  including control module housing  138  in which the CIU  1804  and related and/or other components may be housed within the control module section  130 . The control module housing  138  includes portion  139  positioned between the donor charge  134  and the ballistic channel  141  when the drone  1200  is assembled. Control module  137  additionally includes openings  1806  for pin contact leads  1802  from the CIU  1804  to pass into the apertures  1801  of the sealing access plate  1275  and remain exposed and available for an electrical or power connection to an outside control unit. In the event that the exemplary drone(s) is being moved or loaded into a wellbore using a mechanical implement for gripping, holding, engaging to the drone, the exemplary embodiment(s) shown in  FIGS.  16 - 21    provide the benefit of the charging and programming contacts  1800  being positioned and exposed in the area of engaging structures on the drone where a mechanical tool is likely to engage the drone. Thus, the connection to charge a power source of the drone or program the drone may be accomplished when the drone is engaged for moving/loading. The charging and programming contacts  1800  may also be used as part of a function test, safety test, arming procedure, data retrieval, and the like. 
       FIG.  23    shows the exemplary CIU  1804  for use with certain exemplary embodiments of the drone. As discussed previously, the CIU  1804  includes a PCB  1805  to which a detonator  133  is directly attached and in which the donor charge  134  is integrated with the explosive load  133   b  ( FIG.  23 A ) of the detonator  133 .  FIG.  23 A  shows the arrangement in which a detonator fuse  133   a , which may be directly attached to the PCB  1805 , is connected to initiate the detonator  133 , namely the explosive load  133   b  of the detonator  133 . The donor charge  134  being integrated with the detonator  133  configures the donor charge  134  to use the explosive load  133   b  of the detonator directly, instead of to initiate a separate, or full, explosive load of the donor charge  134 . Capacitors  1803  surround the detonator. Pin contact leads  1802  extend from, and are electrically connected to, e.g., a programmable electronic circuit on the PCB  1805  and/or the capacitors  1803 , for charging the capacitors  1803 . 
       FIG.  24    shows a cross section of the control module  137  with the exemplary CIU  1804  contained within an inner area  320  of the control module  137  defined by the control module housing  138 . From this vantage, taken along line ‘F’ of  FIG.  23   , the capacitors  1803  are seen surrounding at least a portion of each of the detonator  133  and the donor charge  134 , while the PCB  1805  and pin contact leads  1802  extend in a direction out of the page. 
       FIG.  25    is another vantage of the exemplary CIU  1804 , taken along the line ‘S’ of  FIG.  23   . Here, again, capacitors  1803  surround at least a portion of the detonator  133  and the donor charge  134 . Fuse  133   a  may be connected directly to the PCB  1805  and electrically connected to a programmable electronic circuit for receiving a selective detonation command for the detonator  133  and initiating detonation in response. Pin contact leads  1802  are connected to and extend from the PCT  1805  for connection/use as part of the charging and programming contacts  1800 . 
     With respect to the exemplary embodiment(s) presented in  FIGS.  16 - 26   , uses, methods, and variations as have been discussed throughout this disclosure remain applicable and are not repeated here. 
     The exemplary embodiments presented herein may be used for deploying a variety of wellbore tools downhole, as previously discussed. Thus, neither the description nor the claims necessarily excludes the use of the autonomous perforating drone described throughout this disclosure of deploying a variety of wellbore tools for activation. 
     The present disclosure, in various embodiments, configurations and aspects, includes components, methods, processes, systems and/or apparatus substantially developed as depicted and described herein, including various embodiments, sub-combinations, and subsets thereof. Those of skill in the art will understand how to make and use the present disclosure after understanding the present disclosure. The present disclosure, in various embodiments, configurations and aspects, includes providing devices and processes in the absence of items not depicted and/or described herein or in various embodiments, configurations, or aspects hereof, including in the absence of such items as may have been used in previous devices or processes, e.g., for improving performance, achieving ease and/or reducing cost of implementation. 
     The phrases “at least one”, “one or more”, and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C”, “at least one of A, B, or C”, “one or more of A, B, and C”, “one or more of A, B, or C” and “A, B, and/or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together. 
     In this specification and the claims that follow, reference will be made to a number of terms that have the following meanings. The terms “a” (or “an”) and “the” refer to one or more of that entity, thereby including plural referents unless the context clearly dictates otherwise. As such, the terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein. Furthermore, references to “one embodiment”, “some embodiments”, “an embodiment” and the like are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term such as “about” is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Terms such as “first,” “second,” “upper,” “lower” etc. are used to identify one element from another, and unless otherwise specified are not meant to refer to a particular order or number of elements. 
     As used herein, the terms “may” and “may be” indicate a possibility of an occurrence within a set of circumstances; a possession of a specified property, characteristic or function; and/or qualify another verb by expressing one or more of an ability, capability, or possibility associated with the qualified verb. Accordingly, usage of “may” and “may be” indicates that a modified term is apparently appropriate, capable, or suitable for an indicated capacity, function, or usage, while taking into account that in some circumstances the modified term may sometimes not be appropriate, capable, or suitable. For example, in some circumstances an event or capacity can be expected, while in other circumstances the event or capacity cannot occur—this distinction is captured by the terms “may” and “may be.” 
     As used in the claims, the word “comprises” and its grammatical variants logically also subtend and include phrases of varying and differing extent such as for example, but not limited thereto, “consisting essentially of” and “consisting of.” Where necessary, ranges have been supplied, and those ranges are inclusive of all sub-ranges therebetween. It is to be expected that variations in these ranges will suggest themselves to a practitioner having ordinary skill in the art and, where not already dedicated to the public, the appended claims should cover those variations. 
     The terms “determine”, “calculate” and “compute,” and variations thereof, as used herein, are used interchangeably and include any type of methodology, process, mathematical operation or technique. 
     The foregoing discussion of the present disclosure has been presented for purposes of illustration and description. The foregoing is not intended to limit the present disclosure to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the present disclosure are grouped together in one or more embodiments, configurations, or aspects for the purpose of streamlining the disclosure. The features of the embodiments, configurations, or aspects of the present disclosure may be combined in alternate embodiments, configurations, or aspects other than those discussed above. This method of disclosure is not to be interpreted as reflecting an intention that the present disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, the claimed features lie in less than all features of a single foregoing disclosed embodiment, configuration, or aspect. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of the present disclosure. 
     Advances in science and technology may make equivalents and substitutions possible that are not now contemplated by reason of the imprecision of language; these variations should be covered by the appended claims. This written description uses examples to disclose the method, machine and computer-readable medium, including the best mode, and also to enable any person of ordinary skill in the art to practice these, including making and using any devices or systems and performing any incorporated methods. The patentable scope thereof is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.