Patent Publication Number: US-7902469-B2

Title: Perforation gun pressure-actuated electrical switches and methods of use

Description:
BACKGROUND 
     The present application relates to pressure actuated electrical switches. More particularly, methods and devices are provided for arming successive explosive charges upon actuation of a switch by pressure waves from previous detonations. 
     In oil and gas exploration and production operations, well bores are drilled into the ground to gain access to subsurface hydrocarbon-bearing formations or reservoirs. Well bores are typically lined with steel tubing, known as casing or liner, to provide the wellbore with a stable, permanent barrier. This casing is often secured to the wellbore by cement that is pumped into the annulus between the outside diameter of the casing and the inside diameter of the wellbore wall. 
     While the casing stabilizes the wellbore wall, it also seals the fluids within the earth strata. Thus, the casing must be opened or perforated to allow the inflow of hydrocarbons into the casing for extraction. To selectively open the casing to such fluid flow, the casing is often penetrated in the region of a fluid production zone by shaped or oriented charge explosives, which when detonated, penetrate the casing creating perforations through which fluid in the formation may flow. The tubular tool section that carries these explosives is often referred to as a “perforation gun” or more simply as a “gun.” 
     Often, it is desired to perforate a casing at multiple locations to access hydrocarbons residing in multiple subterranean zones. To accomplish these perforations in the casing, charged explosives are typically used to penetrate the casing. The charged explosives are usually delivered by way of a tubular gun, typically referred to as a perforation gun. 
     Inadvertent activation of such explosives pose a potential hazard to personnel. Additionally, inadvertent firing of an perforation gun or self-detonation thereof while the gun is being positioned or retrieved can damage the wellbore, such as perforating the casing at an undesired depth. Moreover, explosives that fail to fire or for some reason are not fired must be retrieved from the wellbore in its unfired condition, creating a potential hazard to both personnel and the wellbore, not to mention the resulting lost operation time. Further complicating operation of these perforation guns is the requirement of creating multiple perforations at multiple depths. Plus, each perforation may require activation of a different number or set of explosives. 
     Accordingly, a variety of switching mechanisms have been designed to control activation of multiple explosives. U.S. Pat. No. 4,457,383 describes one example of a conventional switching unit. In devices of this type, a plurality of blasting cap-perforating element assemblages are spaced apart along the length of a perforation gun. The assemblage that is furthest downhole is typically armed, while the other successive assemblages are disarmed. When the armed assemblage is fired, the next adjacent assemblage closest to the discharged assemblage is armed through the use of a mechanically operated switch. 
     Thus, conventional switching units have been described that arm a subsequent charge upon a first charge being fired while, at the same time, disconnecting the firing mechanism from the first charge. This result is accomplished because the hot wire side of the firing circuit includes a switch for each initiator-perforating element assemblage which completes a bypass circuit to the next upper assemblage while disarming its associated assemblage. Upon firing the lowermost assemblage, the switch of the next upper assemblage is manipulated to arm its associated blasting cap. Firing of charges carried by the perforation gun may in this fashion proceed from the bottom of the gun toward the top of the perforation gun. 
     Generally, conventional switches of this type involve a “bullet” that is thrust axially in the switching mechanism by the explosive force of a preceding charge. The axial movement of the bullet is intended to disconnect the arming of the previously activated charge and at the same time, or immediately thereafter, engage the arming mechanism of a subsequent explosive charge. The disadvantages of such conventional switches are numerous, including malfunctions involving the bullet failing to move the desired axial distance or being propelled farther than its desired distance. Where the bullet is insufficiently propelled the desired axial distance, the bullet will not properly engage the arming mechanism of the subsequent explosive charge and thus fail to engage the subsequent explosive charge for activation. Additionally, the bullet, by failing to be propelled the desired axial distance will also fail to disconnect with the previously activated explosive charge. Where the bullet is propelled past its intended destination, on the other hand, it may fail to adequately engage the subsequent arming mechanism. 
     Additionally, because of the design limitations of conventional switching units, such switching units only effectively operate within a narrow range of temperatures and pressures. Therefore, such conventional switches frequently fail to operate outside of the narrow range of conditions for which they are designed. Moreover, fluid contamination in portions of the perforation gun may contaminate the arming mechanisms or switching units so as to prevent the proper operation thereof. For example, fluid within the above described prior art switch often has the effect of inhibiting the pressure mechanism used to propel the “bullet.” Without sufficient force to propel the bullet, the mechanism will fail as described above. 
     Therefore, improved pressure actuated electrical switching devices are needed to address one or more disadvantages of the prior art. 
     SUMMARY 
     The present invention generally relates to devices and methods for coupling sections of electronic enclosures together through the use of a clamping belt. 
     An example of one embodiment of a switch for controlling detonations in a perforation gun comprises a housing; a pressure port extending into the housing; a piston disposed in the housing, the piston having a portion of its surface area exposed to the pressure port wherein the piston is configured to slide from a first position to a second position in the housing upon pressure being applied to the piston from the pressure port; a first electrical contact disposed at least partially in the housing such that the first electrical contact is in electrical contact with the piston when the piston is in the first position and when the piston is in the second position; a second electrical contact disposed at least partially in the housing such that the second electrical contact is in electrical contact with the piston when the piston is in the first position and not in electrical contact with the piston when the piston is in the second position; a third electrical contact disposed at least partially in the housing such that the third electrical contact is in electrical contact with the piston when the piston is in the second position and not in electrical contact with the piston when the piston is in the first position; wherein the piston is electrically conductive so as to allow current to flow from the first electrical contact to the second electrical contact or from the first electrical contact to the third electrical contact; and wherein the first electrical contact, the second electrical contact, and the third electrical contact are electrically conductive. 
     An example of one embodiment of an electrical switch actuated by pressure comprises a housing having a first end and a second end; a piston disposed in the housing slidable from a first position to a second position, the piston having a first end and a second end; a pressure port extending into the housing from the second end of the housing wherein the pressure port is at least partially exposed to the second end of the piston so as to cause the piston to slide from the first position to the second position upon an application of pressure to the second end of the piston; a first pin disposed at least partially in the housing such that the first pin is in electrical contact with the first end of the piston when the piston is in the first position and when the piston is in the second position; a second pin disposed at least partially in the housing such that the second pin is in electrical contact with the second end of the piston when the piston is in the first position and not in electrical contact with the piston when the piston is in the second position; a third pin disposed at least partially in the housing such that the third pin is in electrical contact with the first end of the piston when the piston is in the second position and not in electrical contact with the piston when the piston is in the first position; wherein the piston is electrically conductive so as to allow current to flow from the first pin to the second pin or from the first pin to the third pin; and wherein the first pin, the second pin, and the third pin are electrically conductive. 
     An example of one embodiment of a method for arming a charge upon detection of a pressure wave comprises providing a pressure switch comprising a housing, a pressure port extending into the housing, a piston disposed in the housing wherein the piston has a portion of its surface area exposed to the pressure port wherein the piston is configured to slide from a first position to a second position in the housing upon pressure being applied to the piston from the pressure port, a first electrical contact disposed at least partially in the housing such that the first electrical contact is in electrical contact with the piston when the piston is in the first position and when the piston is in the second position, a second electrical contact disposed at least partially in the housing such that the second electrical contact is in electrical contact with the piston when the piston is in the first position and not in electrical contact with the piston when the piston is in the second position, a third electrical contact disposed at least partially in the housing such that the third electrical contact is in electrical contact with the piston when the piston is in the second position and not in electrical contact with the piston when the piston is in the first position wherein the piston is electrically conductive so as to allow current to flow from the first electrical contact to the second electrical contact or from the first electrical contact to the third electrical contact, and wherein the first electrical contact, the second electrical contact, and the third electrical contact are electrically conductive; detonating an explosive charge to generate a pressure wave; directing said pressure wave through said pressure port; and utilizing the directed pressure wave to slide the piston from the first position to the second position so as to disengage electrical contact between the first electrical contact and the second electrical contact and to engage electrical contact between the first electrical contact and the third electrical contact. 
     An example of one embodiment of a switch for controlling detonations in a perforation gun comprises a housing; a first non-conductive insert in which a piston cylinder is formed, said cylinder having a first end and a second end; a piston slidingly disposed in said piston cylinder and movable from a first position adjacent the first end to a second position adjacent the second end; a second non-conductive insert in which a pressure port is defined, said first and second inserts disposed in the housing so that the pressure port is in fluid communication with the piston cylinder; a first electrical contact adjacent the piston cylinder; a second electrical contact adjacent the first end of the piston cylinder; a third electrical contact adjacent the second end of the piston cylinder; wherein the piston is electrically conductive so as to allow current to flow from the first contact to the second contact or from the first contact to the third contact. 
     An example of one embodiment of a perforating gun comprises a first blasting cap; a second blasting cap; and a switch disposed between said blasting caps, said switch comprising a switch housing; a first non-conductive insert in which a piston cylinder is formed, said cylinder having a first end and a second end; a piston slidingly disposed in said piston cylinder and movable from a first position adjacent the first end to a second position adjacent the second end; a second non-conductive insert in which a pressure port is defined, said first and second inserts disposed in the housing so that the pressure port is in fluid communication with the piston cylinder; a first electrical contact in electrical contact with the piston; a second electrical contact adjacent the first end of the piston cylinder; a third electrical contact adjacent the second end of the piston cylinder; and wherein the piston is electrically conductive so as to allow current to flow from the first contact to the second contact or from the first contact to the third contact. 
     The features and advantages of the present invention will be apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying figures, wherein: 
         FIG. 1  illustrates a cross-sectional view of an electrical switch actuated by a pressure wave in accordance with one embodiment of the present invention. 
         FIG. 2  illustrates a spring-loaded electrical contact. 
         FIG. 3  illustrates a cross-sectional view of another embodiment of an electrical switch. 
         FIG. 4A  illustrates a cross-sectional view of an electrical switch having a piston shown in a first position. 
         FIG. 4B  illustrates a cross-sectional view of an electrical switch having a piston shown in a second position. 
     
    
    
     While the present invention is susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present application relates to pressure actuated electrical switches. More particularly, methods and devices are provided for arming successive explosive charges upon actuation of a switch by pressure waves from previous detonations. 
     Methods and devices of the present invention allow for the selected activation of a plurality of explosive charges of a perforation gun at desired depths. As one example of a pressure switch device of the present invention, a first set explosive charges may be armed while a second set of charges remain unarmed. Detonation of the first set of charges have the effect of arming the second set of charges and simultaneously disarming the first set of charges. Any multiple of charges may be used in this fashion where subsequent charges are armed by the previous detonation of other charges. 
     In certain embodiments, pressure switches of the present invention comprise a housing having a pressure port therein, a plurality of electrical contacts (e.g. pins), and a slidable piston. An electrically-conductive piston in the housing slides from a first position to a second position. A pressure port in the housing allows a pressure wave from a first detonation to induce axial displacement of the piston from a first position to a second position. 
     As will be explained further below, the movement of the piston electrically disengages the piston from one arming mechanism and electrically engages the piston with a subsequent arming mechanism. 
     Advantages of certain embodiments include, but are not limited to, a more reliable switching mechanism, operability over a larger range of conditions including a larger range of pressures and temperatures, and a decreased susceptibility to failures due to fluid leakages in the perforation gun. Fluid leakages can cause a number of problems including corrosion from corrosive fluids. Conductive fluids such as water may cause short circuit failures of switching mechanisms. 
     Although the pressure switches discussed herein are discussed in the context of their usefulness in perforation guns, it is explicitly recognized that the electrical pressure switches herein are adaptable to any application that would benefit from the use of a pressure actuated electrical switch. 
     To facilitate a better understanding of the present invention, the following examples of certain embodiments are given. In no way should the following examples be read to limit, or define, the scope of the invention. 
       FIG. 1  illustrates a cross-sectional view of an electrical switch actuated by a pressure wave in accordance with one embodiment of the present invention. 
     Pressure-actuated electrical switch  100  comprises housing  160 , pressure port  140 , first pin  110 , second pin  120 , third pin  130 , and piston  150 . Piston  150  is adapted to slide in piston cylinder  151  from first position A to second position B. Preferably, piston cylinder  151  is formed in a non-conducting block or insert  152  carried within housing  160 . Piston  150  may be any shape suitable for displaying within piston cylinder  151 , including, but not limited to cylindrical shaped. 
     As shown, first pin  110  and third pin  30  may also be mounted in insert  152 . Moreover, insert  152  is characterized by a shoulder  154  which abuts corresponding shoulder  156  formed by housing  160 . Pressure port  140  is likewise formed in a non-conducting block or insert  142 . Second pin  120  may also be mounted in insert  142 . Insert  142  is disposed in housing  160  so as to abut insert  152 , permitting fluid communication between pressure port  140  and piston cylinder  151 . 
     As can be seen in  FIG. 1 , when piston  150  is in first position A, piston  150  is in electrically engaged with first pin  110  and second pin  120 , while third pin  130  is electrically disengaged with piston  50 . Also, pressure switch  100  is further configured such that first pin  110  remains in electrical engagement with piston  150  regardless of whether piston  150  is in first position A or second position B. 
     Upon sufficient pressure imposed through pressure port  40 , piston  150  is motivated to move from first position A to second position B. Upon piston  150  moving from first position A to second position B, piston  150  is electrically disengaged from second pin  120  also resulting in electrical disengagement between second pin  120  and first pin  110 . Additionally, this movement of piston  150  from first position A to second position B also electrically engages third pin  130  with piston  150 , which also electrically engages first pin  110  with third pin  130 . 
     Since shoulder  154  abuts shoulder  156 , insert  152  will remain secured in housing  160  under application of pressure from pressure port  140 . 
     Such operation of switch  100  is particularly useful in the context of controlling activation of multiple-staged explosive charges. In such an application, first pin  110  is electrically connected to an arming power source  105  via hot wire  111 , second pin  120  is electrically engaged with first explosive charge  170  via wiring  121 , and third pin  130  is electrically engaged with a second explosive charge  180  via wiring  131 . In this way, a pressure wave from a detonation of first explosive charge  170  acting through pressure port  140  motivates piston  150  to move from first position A to second position B. This movement from first position A to second position B electrically disengages the first explosive charge from the power source  105  (by electrically disengaging piston  50  from second pin  20 ) while simultaneously electrically engaging the power source  105  to second explosive charge  180  via third pin  30 . 
     It is explicitly recognized that the pressure wave may act directly upon piston  150  through pressure port  140  or alternatively, may act indirectly upon piston  150  by acting upon a fluid which then acts directly on piston  150 . 
     Although the above described pins could take the form of any various types of electrical contacts, in the preferred embodiment, electrical pins  110 ,  120 ,  130  are spring-loaded pins carried in a cylinder, sometimes referred to as Pogo® pins. An example of a spring-loaded electrical contact is illustrated in  FIG. 2 . Electrical contact  200  comprises slender cylinder  215 , which houses at least partially, electrically-conductive pin contact  217 . Pin contact  217  is mechanically biased by spring  213  and is in electrical communication with wiring  211 . 
     Returning to  FIG. 1 , first pin  110  and third pin  130  are disposed in a non-conducting block parallel to one another. However, first pin  110  is preferably slightly offset from third pin  130  so that the spring-loaded pin of first pin  110  is urged against piston  150  when piston  150  is in its first position. As piston  150  moves to second position B under pressure applied to the piston surface adjacent pressure port  140 , the spring-loaded pin of first pin  110  is compressed. Those skilled in the art will appreciate that because first pin  10  is spring-loaded, it will compress while maintaining electrical contact with piston  150 . Likewise, pins  120  and  130  are also spring-loaded so that the spring within the pins urges pins  120  and  130  into contact with piston  150  when piston  150  is in its first or second position, respectively. 
     In another embodiment, the pins or electrical contacts may simply be an electrically conductive plate fastened so as to extend into the piston cylinder. Such plate may even be bent, such as in the shape of a “v” to form a simple spring which compresses against the surface of the piston. 
     While the foregoing spring-loaded pins are the most desirable configuration for the invention, pins  120  and  130  could be replaced with fixed contacts extending into the cylinder in which the piston is mounted. Similarly, hot wire  111  could be hard wired to the piston  150 , such as on the non-pressure piston surface. In yet another embodiment, hot wire  11  is disposed to extend from the side of the piston cylinder and electrically engage the side of piston  150 , regardless of whether piston  150  is in its first position or second position. An electrical contact may be mounted in the wall of the piston cylinder for this purpose. 
     Optional diode  192  provides an additional limitation on the arming of the second explosive charge in that only a current of the correct polarity will be communicated through wiring  131 . 
     Various o-ring grooves  144  may be disposed to carry o-rings  146  to permit sealing of various components described herein in a manner known in the art. 
     The foregoing pressure switch  100  may be incorporated into a perforating gun and disposed between consecutive explosive charges  170  and  180 , which in certain embodiments may be blasting cap-perforating element assemblages. 
       FIG. 3  illustrates a cross-sectional view of another embodiment of an electrical switch. Pressure-actuated electrical switch  300  is similar to pressure-actuated electrical switch  100 , except that secondary piston  381  is disposed in pressure port  340 . 
     Optional secondary piston  381  may be any object suitable for displacement through pressure port  340 , including, but not limited to, a non-conducting piston, a seal ball, shaft, or combination thereof. Gel  382  or any flowable material may optionally be disposed in pressure port  340  between secondary piston  381  and piston  350 . Gel  382  may be any non-conducting or dielectric gel including, but not limited to a silicone grease. 
     As before, a pressure wave from a preceding explosion is communicated through pressure port  340 . Here, secondary piston  381  is displaced along the length of pressure port  340  and causes piston  350  to displace from first position A to second position B. Where  382  is present, secondary piston  381  transmit force through gel  382  to motivate piston  350  to displace from first position A to second position B. 
     The use of secondary piston  381  and/or gel  382  is advantageous to reduce the likelihood of a fluid leak into switch  300  by acting as a barrier to fluid entering pressure port  340 . 
     In certain embodiments, secondary piston  381  will form an interference fit with pressure port  340 . O-rings may further be disposed in pressure port  340  to form an improved seal of pressure port  340  against the undesirable entry of fluid. Gel  382  may be positively or negatively pressurized between secondary piston  381  and piston  350  in certain embodiments. Gaskets or other seals may be used to retain gel  382  within pressure port  340 . 
       FIGS. 4A and 4B  illustrate a cross-sectional view of an electrical switch having a piston shown in a first position and a second position.  FIG. 4A  shows piston  450  in first position A whereas  FIG. 4B  shows piston  450  in second position B. 
     Similar to the embodiments heretofore described, electrical contact  420  is in electrical communication with piston  450  when piston  450  is in first position A but not in second position B. Electrical contact  410  is in electrical communication with piston  450  regardless of the position of piston  450 . Finally, electrical contact  430  is in electrical communication with piston  450  only when piston  450  is displaced to second position B. 
     In this way, piston  450  provides electrical communication between electrical contacts  410  and  420  when piston  450  is in first position A and between electrical contacts  410  and  430  when piston  450  is in second position B. 
     Inset  432  allows a configuration in which electrical contact  420  does not contact piston  450  when piston  450  is in first position A. Inset  432  may be any suitable geometric modification to piston  450  including, but not limited to, a notch, an indentation, or an aperture capable of ensuring that electrical contact  420  is not in contact with piston  450  when piston  450  is in first position A. 
     It is explicitly recognized that any of the features of the disclosed embodiment may be combined with one or more of the features of any other embodiment described herein. 
     Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.