Abstract:
A system and method of perforating by stacking a perforating string within a wellbore, then deploying the perforating string to a designated depth for detonating shaped charges in the perforating string. The string can be formed by anchoring a single perforating gun in the wellbore, then landing subsequent guns on one another atop the anchored gun. Wet connects on the ends of the perforating guns enable mechanical engagement of each adjacent gun as well as signal communication through the connections.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a system and method for stacking perforating guns to form a perforating string. 
         [0003]    2. Description of Prior Art 
         [0004]    Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore. The casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore. 
         [0005]    Perforating systems typically comprise one or more perforating guns strung together, these strings of guns can sometimes surpass a thousand feet of perforating length. In  FIG. 1  a prior art perforating system  11  is shown having a perforating gun string  4  with perforating guns  6 . The gun string  4  is shown disposed within a wellbore  1  on a wireline  5 . The perforating guns  6  in the gun string  4  are usually coupled together by connector subs  13 . A service truck  7  on the surface  9  generally accompanies perforating systems  11  for handling the upper end of the wireline  5 . The wireline  5  typically is used for raising and lowering the gun string  4 , as well as a communication means and control signal path between the truck  7  and the perforating gun  6 . The wireline  5  is generally threaded through pulleys  3  supported above the wellbore  1 . As is known, derricks, slips and other similar systems may be used in lieu of a surface truck for inserting and retrieving the perforating system into and from a wellbore. Moreover, perforating systems are also disposed into a wellbore via tubing, drill pipe, slick line, and/or coiled tubing. 
         [0006]    Included with the perforating gun  6  are shaped charges  8  that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the high explosive is detonated, the force of the detonation collapses the liner and ejects it from one end of the charge  8  at very high velocity in a pattern called a “jet”  12 . The jet  12  perforates the casing and the cement and creates a perforation  10  that extends into the surrounding formation  2 . 
         [0007]    Typically the gun string  4  is inserted within a lubricator that is then mounted on a wellhead assembly for deployment into a wellbore. The lubricator provides a pressure seal around the string  4  so the gun string  4  can be pressure equalized with the usually higher pressure wellbore prior to being deployed therein. In some instances space constraints at the well site may limit the height of the lubricator thereby in turn limiting the length of the gun string  4 . 
       SUMMARY OF INVENTION 
       [0008]    Disclosed herein is an example method and apparatus for perforating a wellbore. In one example method a string of perforating guns is formed by inserting a perforating gun into a wellbore and then anchoring the perforating gun to a wall of the wellbore. Another perforating gun is then inserted into the wellbore and lowered onto the anchored perforated gun. These guns are then coupling to one another to form a string of perforating guns. Alternatively, the anchor on the perforating gun is removed and the string is lowered deeper into the wellbore. Optionally, a plurality of perforating guns is added into the wellbore that are coupled to each adjacent perforating gun. In an example embodiment, each perforating gun is lowered via wireline into the wellbore. Optionally, wet connections are provided on each of the perforating guns, so that when the perforating guns are disposed in liquid and coupled to one another, the perforating guns are in electrical communication through the wet connectors. Optionally, an anchor can be added onto the perforating gun, so that by deploying the anchor from the perforating gun into contact with the wall of the wellbore the perforating gun is anchored in the wellbore. Further, the method can include resetting the anchor, decoupling the another perforating gun from the perforating gun, and removing the another perforating gun and the perforating gun from the wellbore. 
         [0009]    An alternate method of perforating a wellbore is provided herein that includes anchoring a perforating gun to a wall of the wellbore and coupling another perforating gun to the perforating gun anchored to the wellbore wall to form a perforating gun string. The perforating gun is released from the wall of the wellbore and the perforating string is lowered to a designated depth within the wellbore where the wellbore is perforated by detonating shaped charges disposed within the perforating string. Communication may occur between the perforating gun and the another perforating gun. As the shaped charges in either of the perforating gun or the another perforating gun may be detonated at different times, the method may further include moving the perforating string to a depth different from the designated depth of the initial step of detonation, and detonating shaped charges not already detonated. Optionally, a plurality of additional perforating guns may be provided, where the additional perforating guns are coupled to the upper end of the another perforating gun. The perforating string can be re-anchored in the wellbore, and each of the guns selectively decoupled. A connector for connecting each adjacent gun may optionally be provided, wherein each connector is assigned an address, so that by directing a signal to the address each of the guns are selectively decoupled. 
         [0010]    Also described herein is a perforating system, that in one embodiment is made up of a lower perforating gun, a selectively deployable anchoring device on the lower perforating gun, an upper connector on an upper end of the lower perforating gun, and a contact on an end of the upper connector distal from the lower perforating gun. The contact is in signal communication with the lower perforating gun. Also included is an upper perforating gun with a lower connector on its lower end, where the lower connector automatically connects to the upper connector when the lower connector lands on the upper connector. In an example embodiment, a receptacle is on an end of the lower connector distal from the upper perforating gun. An opening in the receptacle is in signal communication with the upper perforating gun, so that when the upper and lower perforating guns are coupled the upper and lower connector are mated such that the contact inserts into the opening and the upper and lower perforating guns are in signal communication. In an example embodiment, a selectively releasable coupling is provided that is disposed in at least one of the lower connector or lower connector. In an example embodiment, a communications module is provided in the upper perforating gun in signal communication with a communications module in the lower perforating gun. In an example embodiment, signal communication between the communications modules in the upper and lower perforating guns is routed through the connectors. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0012]      FIG. 1  is a side partial sectional view of a prior art perforating system used for perforating a wellbore. 
           [0013]      FIGS. 2A through 2C  are side partial sectional views of a perforating string being stacked together in a wellbore in accordance with the present invention. 
           [0014]      FIG. 3  is a perspective side sectional view of an example embodiment of a connector for perforating guns in accordance with the present invention. 
           [0015]      FIG. 4  is a side partial sectional view of a method of perforating a wellbore in accordance with the present invention. 
           [0016]      FIGS. 5 through 7  are perspective side sectional views of alternate example embodiments of connectors for perforating guns in accordance with the present invention. 
           [0017]      FIG. 8  is a side partial sectional view of an example of removing a perforating string from a wellbore in accordance with the present invention. 
       
    
    
       [0018]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF INVENTION 
       [0019]    The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. 
         [0020]    It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the improvements herein described are therefore to be limited only by the scope of the appended claims. 
         [0021]      FIGS. 2A through 2C  illustrate an example method of forming a perforating gun string within a wellbore. More specifically and with reference to  FIG. 2A , a perforating gun  20   1  is shown being lowered into a wellbore  22  by attachment on its upper end to a cablehead  24 . A wireline  26  mounts on a side of the cablehead  24  opposite a side where it couples to the upper end of the perforating gun  20   1 . The wireline  26 , which inserts into the wellbore  22  through a wellhead assembly  28 , may be spooled from a service truck (not shown), derrick (not shown), or other deployment means disposed on the surface. Shaped charges  30  are provided with the perforating gun  20   1  and shown positioned to direct a jet radially outward from the perforating  20   1 . Also included with the perforating gun  20   1  of  FIG. 2A  is an anchor  22  in a retracted mode and circumscribing the outer surface of the perforating gun  20   1 . In the example embodiment of  FIG. 2B , the anchor  32 A is deployed and extends across the annulus between the perforating gun  20   1  and an inner wall of the wellbore  22 . The anchor  32 A exerts opposing forces against the perforating gun  20   1  in the wall of the wellbore  22  thereby suspending the perforating gun  20   1  at a designated location within the wellbore  22 . Once supported within the wellbore  22  by the anchor  32 A, the cablehead  24  can be released from the perforating gun  20   1  and drawn up the wellbore  22  for optional attachment of a subsequent perforating gun  20   2  ( FIG. 2C ) and lowered on the wireline  26  and onto the anchored perforating gun  20   1 . This process is repeated until a string of perforating guns is formed. When a string of designated or desired length is formed, the anchor  32 A can be released thereby allowing the string to be deployed to a depth or depths for perforating operations. 
         [0022]    Attachment between perforating guns may occur upon landing a perforating gun on an adjacent lower perforating gun. Shown in a perspective and side section view in  FIG. 3  is one example of a connector  33  for coupling adjacent guns. In the example of  FIG. 3 , the connector  33  includes an upper connector  34  and lower connector  36 . The lower connector  34  of  FIG. 3  is a generally annular member shown having a set of slips  38  whose outer radius increases with distance away from the upper end of the upper connector  34 . The slips  38  mount on a mandrel  40 , that as will be described in more detail below, is selectively movable in an axial direction within the upper connector  34 . Collet like ribs  41  are provided on a lower end of the lower connector  36  that in the example of  FIG. 3  are raised profiles shown circumscribing the outer surface of the lower end of the lower connector  36 . In one example embodiment, the upper connector  34  mounts on an upper end of a lower positioned perforating gun, and the lower connector  36  mounts on a lower end of an upper positioned perforating gun. Such that when the upper perforating gun lands on the lower gun, the surface of the lower connector  36  having the ribs  41  inserts into the upper end of the upper connector  34  and into the annular space between the slips  38  and inner surface of the upper connector  34 . The contour of the slips  38  outwardly urges the ribs  41  into engaging contact with the inner wall of the connector  34  as the lower connecter  36  inserts into the upper connector  34 ; thereby coupling the adjacent perforating guns attached on opposing ends of the connector  33 . By axially moving the mandrel  40  in a direction downward, i.e. away from the lower connector  36 , the slips  38  move away from the ribs  41  thereby allowing the upper and lower connectors  34 ,  36  to be disengaged. 
         [0023]      FIG. 4  provides in a side partial sectional view one schematic example of perforating within the wellbore  22 . A perforating string  42  is shown made up of perforating guns  20   1 ,  20   2 , . . .  20   n  and connectors  33  for coupling each of the adjacent perforating guns. The perforating string  42  may be constructed by landing the guns  20   1 ,  20   2 , . . .  20   n  sequentially in series top to bottom. Attachment between adjacent guns is not limited to the connector of  FIG. 3 , but can include any type of connection that provides for latching upon landing that may be later selectively released. Components of the gun string  42  are shown in communication via a communication link  44 . The communication link  44  includes a main bus  46  from which individual lead buses  48 ,  50 ,  52 ,  54  communicate directly with one of the perforating guns as well as the cablehead  24 . Modules provided in each of the perforating guns  20   1 ,  20   2 , . . .  20   n  are equipped with communication devices enabling communication with any of the other guns, the cablehead  24 , or the surface via the wireline  26 . Moreover, communication may occur through hard links, such as wires that extend along the length of the perforating string  42  as well as wireless links that extend along the wellbore  22 . Examples of wireless communication include radio waves, mud pulses, acoustic signals and the like. Further illustrated in the example of  FIG. 4  is that the shaped charges  30  within perforating gun  20   1  are being detonated to form jets  56  that project radially outward from the perforating string  42  and form perforations  58  into the formation  60  surrounding the wellbore  22 . The control modules within the perforating guns enables selective detonation within a single gun and so that a subsequent detonation of a different one or more of the guns in the perforating string  42  can occur while at the same position within the wellbore  22 , or at a different depth and at a later time. 
         [0024]    Schematically presented in a side view in  FIG. 5  is an alternate example of a connector  33 A used to connect adjacent perforating guns  20   i ,  20   i+1 . An upper connector  34 A is shown that includes a firing head  62  that can be used to control detonation of shape charges within the connected perforating gun  20   i . In the example of  FIG. 5 , an initiator  64  is shown for initiating a detonation wave within the perforating cord  65  for detonating charges  30  within the perforating gun  20   i . Also illustratively shown within the firing head  62  is a transmitter/receiver  66  that is used for receiving signals within the firing head  62  for controlling operation of the associated perforating gun  20   i . The signals may be provided to the transmitter receiver  66  via hardwire (not shown) or wireless signals as discussed above. The use of the term signals herein includes discrete and analog signals that represent or contain information, such as data or commands, as well as an electrical flow of power. A controller  68  is further optionally provided within the firing head  62  for processing signals received from the transmitter receiver  66  and controlling operation of the initiator  64  as well as controlling operation of any data signals that may be transmitted from the transmitter receiver  66 . In an optional embodiment, a latching actuator  70  is shown within the lower connector  36 A for automating actuation, release, or both of an actuating mechanism (not shown) for coupling together the upper and lower connectors  34 A,  36 A of the connector  33 A. Alternatively, the latching actuator  70  may be provided within the upper connector  34 A as well as the lower connector  36 A, or instead of being within the lower connector  36 A. 
         [0025]      FIGS. 6 and 7  provide in perspective view examples of alternate connectors  33 B,  33 C and that may be useful for a wet connect. For the purposes of discussion herein, a wet connect is a connection formed submerged or in the presence of a fluid, such as wellbore fluid, and when formed provides a pathway for signal travel therethrough. The connector  33 B embodiment of  FIG. 6  includes a lower connector  34 B in which connector pins  72 ,  74  are provided on an upper end shown projecting towards a lower end of the lower connector  36 B. The connector pins  72 ,  74 , which may be formed from a conductive material, are in signal communication with leads  76 ,  78  shown depending within the upper connector  34 B. Examples of the leads  76 ,  78  include wire, cable, as well as fiber optic material. Receptacles  80 ,  82  are shown fitted within the lower end of the lower connector  36 B and have openings therein shown facing in the direction of the pins  72 ,  74 . Leads  84 ,  86  are shown provided in the lower connector  36 B that connect to and are in electrical and signal communication with the receptacles  80 ,  82 . As such, by inserting the pins  72 ,  74  into the openings within the receptacles  80 ,  82  a line of electrical and/or signal communication is created from leads  84 ,  86  through leads  76 ,  78 . Alignment of the receptacles  80 ,  82  with the pins  72 ,  74  may be accomplished via a post  88  shown protruding from an outer surface of the lower connector  36 B and a profile  90  that is formed along the inner surface of the upper end of the upper connector  34 B. In one example the post  88  lands on the profile  90  and as the lower connector  36  is urged further downward, the post  88  slides to a low point within the profile  90  thereby rotating the lower connector  36 B to align the pins  72 ,  74  with the receptacles  80 ,  82  for ready insertion therein. 
         [0026]    In the embodiment of  FIG. 7 , the connector  33 C includes upper and lower connectors  34 C,  36 C wherein the upper connector  34 C has a single connector pin  92 . Contacts  94 ,  96  are shown provided on the outer circumference of the connector pin  92  that are separated from one another at distinct spaced apart axial locations. The leads  76 ,  78  connect respectively with the contacts  94 ,  96  so that electrical and signal communication exists between the contacts,  94 ,  96  and leads  76 ,  78 . Similarly, a single receptacle  97  is shown set within the lower end of the lower connector  36 C and having an opening facing the connector pin  92 ; thereby when the upper and lower connectors  34 C,  36 C are substantially coaxially aligned, the connector pin  92  is readily inserted into the receptacle  97 . Corresponding contacts  98 ,  100  are provided within the inner surface of the receptacle  97  that engage the contacts  94 ,  96  when the pin  92  inserts into the receptacle  97 , so that electrical and signal communication extends from the leads  76 ,  78  and to the leads  84 ,  86  shown connected to the contacts  98 ,  100 . 
         [0027]    As discussed above the perforating string  42  may be dismantled in a manner similar to its construction illustrated in  FIGS. 2A through 2C . In an example embodiment of dismantling provided in side partial sectional view in  FIG. 8 , the string  42  is shown deployed on wireline  26  at a depth relatively proximate to the wellhead housing  28  with the anchor  32 A deployed thereby supporting the string  42  within the wellbore  22 . The signaling sequence of  FIG. 4  may be utilized, i.e. through lines extending through the perforating string  42  or wireless signals, to address each of the connectors  33  within the string  42 . Providing a specific address to each of the guns or each specific connector  33  enables selective delatching of the individual perforating guns for retrieval from within the wellbore  22 . Stacking and destacking the string  42  proximate the wellhead housing  28  allows for a perforating gun string to have a sufficient number of guns so that wellbore perforating can be accomplished with a single trip into a wellbore; which significantly reduces the time required for multiple trips in and out of a wellbore with shorter gun strings. 
         [0028]    The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.