Patent Publication Number: US-7913603-B2

Title: Device and methods for firing perforating guns

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     None. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to devices and methods for selective actuation of wellbore tools. More particularly, the present invention is in the field of control devices and methods for selective firing of a gun assembly. 
     2. Description of the Related Art 
     Hydrocarbons, such as oil and gas, are produced from cased wellbores intersecting one or more hydrocarbon reservoirs in a formation. These hydrocarbons flow into the wellbore through perforations in the cased wellbore. Perforations are usually made using a perforating gun loaded with shaped charges. The gun is lowered into the wellbore on electric wireline, slickline, tubing, coiled tubing, or other conveyance device until it is adjacent the hydrocarbon producing formation. Thereafter, a surface signal actuates a firing head associated with the perforating gun, which then detonates the shaped charges. Projectiles or jets formed by the explosion of the shaped charges penetrate the casing to thereby allow formation fluids to flow through the perforations and into a production string. 
     Tubing conveyed perforating (TCP) is a common method of conveying perforating guns into a wellbore. TCP includes the use of standard threaded tubulars as well as endless tubing also referred to as coiled tubing. 
     For coiled tubing perforating systems, the perforating guns loaded with explosive shaped charges are conveyed down hole into the well connected to the end of a tubular work string made up of coiled tubing. One advantage of this method of perforating is that long zones of interest (areas of gas or oil) can be perforated with a single trip into the well. The perforating guns are of a certain length each and are threaded together using a tandem sub. With an explosive booster transfer system placed in the tandem sub, the detonation of one gun can be transferred to the next. This detonation can be initiated from either the top of the gun string or the bottom of the gun string. 
     TCP can be particularly effective for perforating multiple and separate zones of interest in a single trip. In such situations, the TCP guns are arranged to form perforations in selected zones but not perforate the gap areas separating the zones. If the gap distance is short, the gap area is usually incorporated in the gun string by leaving out a certain number of shaped charges or using blanks. However, the detonating cord carries the explosive transfer to the next loaded area of the gun string. 
     In wells that have long or substantial gaps between zones, an operator must consider the efficiency and cost of perforating the zones. The zones can be perforated separately via multiple trips into the well, which requires running the work string in and out of the well for each zone to be perforated. This increases rig and personnel time and can be costly. 
     Referring now to  FIG. 1 , there is shown another conventional system for perforating multiple zones that includes perforating guns  12  that are connected to each other by tubular work strings  14 . Devices such as circulation subs  16  can be used to equalize pressure in the work strings  14 . The guns  12  are fired using a detonator body  18  that is actuated by a pressure activated firing head  20 . During operation, the operator increases the pressure of the wellbore fluid in the well by energizing devices such as surface pumps. The firing heads  20 , which are exposed to the wellbore fluids, sense wellbore fluid pressure, i.e., the pressure of the fluid in the annulus formed by the gun and the wellbore wall. Once a pre-set value of the annulus fluid pressure is reached, the firing heads  20  initiate a firing sequence for its associated gun  12 . The firing heads  20  usually incorporate a pyrotechnic time delay  21  to allow operators to exceed the activation pressure of each firing head  20  in the TCP string  10  to ensure each firing head  20  is activated. If the operator cannot increase the pressure in the well, or if one of the firing heads or time delays fails and a zone is not perforated another round trip in the well is required to perforate the zone that was missed on the initial run. Each trip in the well costs time and money. 
     These conventional firing systems for various reasons, such as capacity, reliability, cost, and complexity, have proven inadequate for certain applications. The present invention addresses these and other drawbacks of the prior art. 
     SUMMARY OF THE INVENTION 
     In aspects, the present invention can be advantageously used in connection with a perforating gun train adapted to perforate two or more zones of interest. In an exemplary system, the gun train can include two or more gun sets made up of guns, detonators, and other associated equipment. In one embodiment, the gun sets making up the gun train are connected with connectors that can convey activation signals between the gun sets. The activation signals are created, either directly or indirectly, by the firing of the gun sets. For example, the firing of a first gun set can create an activation signal that is conveyed via a connector to a second gun set, which fires upon receiving the activation signal. The firing of the second gun set, in turn, can cause, either directly or indirectly, an activation signal that is conveyed via a connector to a third gun set, which fires upon receiving the activation signal, and so on. Thus, while the firing of the first gun set is initiated by a surface signal, subsequent firings are initiated by firing of the gun sets making up the gun train. 
     In one arrangement, the connector includes a signal transmission medium for transferring activation signals between the gun sets. For example, the connector can have a bore filled with fluid that transmits pressure changes caused by firing of the first gun set to the second gun set in a manner similar to a hydraulic line. The connector can be pre-filled with fluid from the surface. Also, a flow control unit can be used to selectively fill the connector with fluid from the wellbore. The flow control unit can include a fill valve that allows the bore to be flooded with wellbore fluid and a vent valve that allows fluid to exit the connector. The fill valve and vent valve can be configured to at least temporarily isolate the fluid in the connector from the fluid in the wellbore to provide the hydraulic connection. 
     For arrangements using pressure changes as an activation signal between the first gun set and the second gun set, the second gun set can include a pressure activated detonator assembly for initiating firing of the second gun set. The first gun set can be firing by using a pressure signal transmitted by via the fluid in the wellbore, an electrical signal transmitted via a conductor coupled to the detonator of the first gun set, a projectile dropped from the surface, or other suitable method. 
     In another arrangement, an activator is coupled to the first gun set to produce the activation signal. In one embodiment, the activator includes an energetic material that detonates upon firing of the first gun set. The detonating energetic material causes a pressure change in the fluid in the connector that acts as the activation signal for the detonator of the second gun set. In another embodiment, the activator includes a projectile retained by a retaining device. The retaining device releases the projectile through the connector upon firing of the first gun set. The projectile acts as the activation signal for the detonator of the second gun set. 
     It should be understood that examples of the more important features of the invention have been summarized rather broadly in order that detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For detailed understanding of the present invention, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein: 
         FIG. 1  schematically illustrates a conventional perforating gun train; 
         FIG. 2  schematically illustrates a deployment of a perforating gun train utilizing one embodiment of the present invention; 
         FIG. 3  schematically illustrates one embodiment of the present invention that is adapted to selectively permit transmission of signals to a downhole tool; 
         FIG. 4A  schematically illustrates another embodiment of the present invention that is adapted to selectively permit transmission of signals to a downhole tool; 
         FIG. 4B  schematically illustrates another embodiment of the present invention that is adapted to selectively permit transmission of signals to a downhole tool; 
         FIG. 5  schematically illustrates another embodiment of the present invention that is adapted to selectively permit transmission of signals to a downhole tool; and 
         FIG. 6  schematically illustrates another embodiment of the present invention that that is adapted for use in a non-vertical wellbore. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The present invention relates to devices and methods for firing two or more downhole tools. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. 
     Referring initially to  FIG. 2 , there is shown a well construction and/or hydrocarbon production facility  30  positioned over subterranean formations of interest  32 ,  34  separated by a gap section  36 . The facility  30  can be a land-based or offshore rig adapted to drill, complete, or service a wellbore  38 . The wellbore  38  can include a wellbore fluid WF that is made up of formation fluids such as water or hydrocarbons and/or man-made fluids such as drilling fluids. The facility  30  can include known equipment and structures such as a platform  40  at the earth&#39;s surface  42 , a wellhead  44 , and casing  46 . A work string  48  suspended within the well bore  38  is used to convey tooling into and out of the wellbore  38 . The work string  48  can include coiled tubing  50  injected by a coiled tubing injector  52 . Other work strings can include tubing, drill pipe, wire line, slick line, or any other known conveyance means. The work string  48  can include telemetry lines or other signal/power transmission mediums that establish one-way or two-way telemetric communication from the surface to a tool connected to an end of the work string  48 . A suitable telemetry system (not shown) can be known types as mud pulse, electrical signals, acoustic, or other suitable systems. A surface control unit (e.g., a power source and/or firing panel)  54  can be used to monitor and/or operate tooling connected to the work string  48 . 
     In one embodiment of the present invention, a perforating gun train  60  is coupled to an end of the work string  48 . An exemplary gun train includes a plurality of guns or gun sets  62   a - b , each of which includes perforating shaped charges  64   a - b , and detonators or firing heads  66   a - b . The guns  62   a - b  are connected to one another by a connector  68 . Other equipment associated with the gun train  60  includes a bottom sub  70 , a top sub  72 , and an accessories package  74  that may carry equipment such as a casing collar locator, formation sampling tools, casing evaluation tools, etc. 
     The guns  62   a - b  and connector  68  are constructed such that a portion of the energy released by the exploding charges of the gun  62   a  is used to directly or indirectly initiate the firing of gun  62   b . The connector  68  can be a tubular member, a wire, a cable or other suitable device for physically interconnecting the guns  62   a - b  and can include a signal transmission medium, such as an incompressible fluid or electrical cable, adapted to convey signals across the connector  68 . 
     In a direct initiation, the tubular connector  68  directs an energy wave from the gun  62   a  to the gun  62   b . For example, the tubular connector  68  can be filled with a fluid F. When the energy released by gun  62   a  impacts the fluid F in the tubular connector  68 , the subsequent pressure change moves the fluid. This pressurized fluid movement acts similar to hydraulic fluid in a hydraulic line. This pressurized fluid movement is transferred downward through the tubular connector  68  to a pressure activated firing head device  66   b  for the gun  62   b . Thus, the pressure change caused by the detonation of the first gun  62   a  acts as an activation signal that activates the firing head  66   b  that in turn detonates the perforating gun  62   b . The detonation of the gun  62   b  can be used to initiate the firing of additional guns (not shown). That is, the detonation and generation of pressure changes can be repeated. The number of times it is repeated is only dependent on the number of zones or intervals to be perforated. The pressure change can be a pressure increase, a pressure decrease, or a pressure pulse (i.e., a transient increase or decrease). Other suitable signal transmission mediums include conductive cables for conveying electrical signals or fiber optic signals and rigid members for conveying acoustic signals. 
     Referring now to  FIG. 3 , the energy released by the gun  62   a  can also be used to indirectly initiate a firing sequence for gun  62   b . In  FIG. 3 , an activator  80  is used to initiate the firing sequence for gun  62   b  while the energy released by the gun  62   a  is used to actuate the activator  80 . The activator  80  can be actuated explosively, mechanically, electrically, chemically or other suitable method. For example, the energy release may include a high detonation component that detonates material in the activator  80 , a pressure component that moves mechanical devices in the activator  80 , or a vibration component that jars or disintegrates structural elements in the activator  80 . 
     When actuated, the activator  80  transmits an activation signal, such as a pressure change, electrical signal, or projectile, to the firing head  66   b  of the gun  62   b . The type of activation signal will depend on the configuration of the firing head  66   b , i.e., whether it has pressure sensitive sensors, a mechanically actuated pin, electrically actuated contact, etc. 
     Referring now to  FIGS. 3 and 4A , there is shown an activator  82  for activating a mechanically actuated firing head. The activator  82  include a projectile  84  such as a metal bar that is retained by a retaining device  86  such as slips, frangible elements, combustible elements or other suitable device. The energy released by the gun  62   a  causes the retaining device  86  to release the projectile  84 , which then travels downward via the tubular connector  68  and strikes the firing head  66   b  of the gun  62   b.    
     Referring now to  FIGS. 3 and 4B , there is shown an activator  88  for actuating a pressure sensitive firing head. The activator  88  includes a pressure generator or chamber  90  on the bottom of a gun  62   a . The tubular member  68  is attached to the gun  62   a  and includes a fluid F. The chamber  90  includes an energetic material  92  such as detonating cord, a black powder charge, or propellant material that produce a rapid pressure increase in the chamber  90  when ignited. The chamber  90  can also include chemicals that react to produce a pressure increase in the chamber  90 . At the bottom of the chamber  90  is a sealing member  94 . The sealing member  86  acts as a barrier between the chamber  90  and the tubular  68 . The sealing member  86  may be formed of a frangible material such as glass or ceramic, a flapper valve, a metal o-ring seal, a blow out plug, etc. During use, the pressure increase in the chamber  90  fractures or otherwise breaks the sealing member  94  and acts upon the fluid F in the tubular member  68 . In a manner described previously, the pressure change is transferred via the tubular member  68  to the firing head  66   b.    
     In yet other embodiments, the activator  80  can include an electrical generator (not shown) that produces an electrical signal that is conveyed via suitable wires (not shown) in the tubular connector  68  to an electrically actuated firing head  66   b . In yet another embodiment, the activator  80  can manipulate a mechanical linkage connected to a suitable firing head  66   b.    
     Referring now to  FIG. 5 , there is shown an exemplary perforating gun system  100  made in accordance with one embodiment of the present invention. The gun system  100  includes a plurality of guns  110   a - c  that are connected by tubular connectors  112   a - b . The guns  110   a - c  each have an associated firing head  114   a - c , respectively. The firing head  114   a  is a primary firing device that is actuated by a surface signal such as a pressure increase, a bar, an electrical signal, etc. Firing heads  114   b  and  114   c  are actuated by the firing of guns  110   a  and  110   b , respectively and/or by activator  118   a  and  118   b , respectively. The gun system  100  is connected to a suitable conveyance device such as tubing or coiled tubing  120 . For simplicity, reference is made only to gun  110   a , activator  118   a , tubular connector  112   a , and firing head  114   b  for further discussion with the understanding that the discussion applies to other similarly labeled elements. 
     Referring now to  FIGS. 2 ,  4 B and  5 , the activator  118   a  includes an energetic material  92  that is explosively coupled to the charges  64   a  or the detonator cord (not shown) of the gun  110   a . That is, the charges  64   a  and/or detonator cord (not shown) of the guns  110   a  and the energetic material are arranged such that detonation of the charges  64   a  or the detonator cord (not shown) causes a high order detonation of the energetic material  92 . Upon detonation, the energetic material  92  causes a rapid pressure increase within the activator  118   a . This pressure increase is transmitted to the firing head  114   b  in a manner described below. 
     The tubular connector  112   a  provides a hydraulic connection between the activator  118   a  and the firing head  114   b  that transmits the pressure change from the activator  118   a  to the firing head  114   b . The tubular connector  112   a  includes a bore  122  filled with a fluid F. The tubular connector  112   a  can be a substantially sealed unit that is filled at the surface with the fluid such as oil. 
     In another embodiment, the tubular connector  112   a  is configured to fill selectively itself with wellbore fluids WF using a flow control unit  124 . The flow control unit  124  is adapted to (i) allow wellbore fluids WF to fill the tubular connector  112   a  to form the hydraulic connection, (ii) seal the tubular connector  112   a  such that the fluid F in the tubular connector  112   a  is at least temporarily isolated from the wellbore fluids WF, and (iii) drain the fluid F from the bore  122  before the gun system is extracted from the wellbore  38 . The flow control unit  124  can include a fill valve  126  and a vent valve  128  which may be one-way check valves, flapper valves, orifices, adjustable ports and other suitable flow restriction devices. The fill valve  124  allows wellbore fluids WF from the wellbore to enter the bore  122  while a weep hole (not shown) allows the air in the bore  122  to escape during filling. The vent valve  128  drains the fluid F into the wellbore  38 . In arrangements, the vent valve  128  can be configured to selectively vent fluids F in the bore  122  into the wellbore  38 . This selective venting or drain can occur immediately after a pressure increase, after the firing head  114   b  is actuated, upon hydrostatic pressure of the fluid F in the bore  122  or the wellbore fluid WF reaching a preset value, or some other predetermined condition. Moreover, the release of fluids F from the bore  122  can be gradual or rapid. The fluid F may be at high-pressure after being subjected to the pressure increase caused by the gun  110   a  and/or activator  112   a . Thus, it will be appreciated that allowing the fluid F to drain from the bore  122  before the gun system is extracted from the wellbore  38  can facilitate the safety and ease of handling the gun system at the surface. Moreover, the fill valve  126  and vent valve  128  flow rates are configured to ensure that pressure in the bore  122  remains below the burst pressure of the tubular connector  112   a . While the fill valve  126  and vent valve  128  are described as separate devices, a single device may also be used. Also, the isolation between the fluid F and the wellbore WF need not be complete. A certain amount of leakage from the bore  112  may be acceptable in many circumstances, i.e., substantial isolation may be adequate. 
     The firing heads  114   a - c  can fire their respective guns  110   a - c , respectively, using similar or different activation mechanisms. In one embodiment, all the firing heads  114   a - c  have pressure sensitive sensors that initiate a firing sequence upon detection of a predetermined pressure change in a surrounding fluid. For example, the firing head  114   a  is positioned to detect pressure changes in the wellbore fluid WF and the firing heads  114   b - c  are positioned to detect pressure changes in the fluid F in the adjacent tubular connector  112   a - b , respectively. In another embodiment, the firing head  114   a  is activated by an electrical signal transmitted from the surface or a bar dropped from the surface while the firing heads  114   b - c  have pressure sensitive sensors positioned to detect pressure changes inside the fluid F in the adjacent tubular connector  112   a - b , respectively. In yet another embodiment, the firing head  114   a  is activated by an electrical signal transmitted from the surface or a bar dropped from the surface, the firing head  114   b  is activated by a bar released from the activator  118   a , and the firing head  114   c  has pressure sensitive sensors. It should be appreciated that the activation mechanisms of the firing heads  114   a - c  can be individually selected to address the needs of a given application or wellbore condition. Further, the firing heads  114   a - c  can include time delays to provide control over the sequential firing of the guns  110   a - c.    
     Because the fluid F is isolated from the wellbore fluids WF, pressure changes in the wellbore fluids WF will not be transmitted to the firing heads  114   b - c . Thus, a pressure increase in wellbore fluid WF can be used to activate the firing head  114   a  without also firing the firing heads  114   b - c  because the firing heads  114   b - c  detect pressure of the fluid F in the tubular connectors  114   a - b.    
     Referring now to  FIGS. 1 and 5 , during use, the gun system  100  is assembled at the surface and conveyed into the wellbore via a coiled tubing  50 . As the gun system  100  descends into the wellbore  38 , the flow control devices  124  allow wellbore fluids WF to fill the tubular connectors  112   a - b  and seal off or close the tubular connectors  112   a - b  once filling is complete. At this point, hydraulic communication via a closed conduit is established between the firing head  114   b  and activator  118   a  and/or gun  110   a  and between the firing head  114   c  and activator  118   b  and/or gun  10   b.    
     After the gun system  100  is positioned adjacent the zones to be perforated, a firing signal is transmitted from the surface to the gun system  100 . This firing signal can be caused by increasing the pressure of the fluid in the wellbore via suitable pumps (not shown). This pressure increase will activate the firing head  114   a  but not the firing heads  114   b - c , which are isolated from the pressure of the fluid in the wellbore. Upon receiving the firing signal, the firing head  114   a  initiates a high order detonation that fires the perforating gun  110   a . This high order detonation also actuates the activator  118   a , which is explosively coupled to the perforating gun  110   a , by detonating the energetic material in the activator  118   a . The pressure increase produced by detonating energetic material in the activator  118   a  travels in the form of a pressure wave or pulse in the fluid F in the tubular connector  112   a  from the activator  118   a  to the firing head  114   b . Upon sensing the pressure increase, the firing head  114   b  initiates a firing sequence to fire gun  110   b . These steps are repeated for any remaining guns. 
     During the firing of the perforating gun system  100 , the controller  54  can include a monitoring device for measuring and/or recording parameters of interest relating to the firing sequence. The listening device can be an acoustical tool coupled to the coiled tubing  50 , a pressure sensor in communication with the wellbore fluid, or other suitable device. As the gun system  100  fires, each gun  110   a - c , releases energy such as acoustical waves or pressure waves. By measuring and these waves or pulses, an operator can determine the number of guns  110   a - c  that have fired. It should be appreciated that because embodiments of the present invention provide for sequential firing, the order of the firing of the guns  110   a - c  is already preset. It should also be appreciated that the activators  118   a - b , firing heads  114   a - b , and/or tubular connector  112   a - b  can be configured to provide a predetermined amount of time delay between sequential firing to facilitate detection of the individual firing events. Thus, for example, if three distinct firings are measured, then personnel at the surface can be reasonably assured that all guns  110   a - c  have fired. If only two distinct firings are measured, then personnel at the surface are given an indication that a gun may not have fired. 
     The teachings of the present invention can also be applied to gun systems that do not use the firing of a perforating gun to initiate subsequent gun firings. Referring now to  FIG. 6 , there is shown a wellbore  150  having a vertical section  152  and a horizontal section  154 . A perforating gun  156  is positioned in a horizontal section  154 . The gun  156  includes an activator  80  and tubular connector  68  of a configuration previously described. Advantageously, the activator  80  is positioned in the vertical section  152 . Thus, a “drop bar” activated firing head may be used to fire the gun  156 . Alternatively, as discussed previously, the activator  80  can be actuated explosively, electrically, chemically or by any other suitable method. It should be appreciated that such an arrangement provides for flexible and remote downhole firing of the perforating gun  156 . 
     The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention. For example, while a “top down” firing sequence has been described, suitable embodiments can also employ a “bottom up” firing sequence. Moreover, the activator can be used to supplement the energy release of a perforating gun to initiate the firing sequence rather than act as the primary or sole device for initiating the firing sequence. It is intended that the following claims be interpreted to embrace all such modifications and changes.