BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates generally to electrical switch gear for use with electrically actuated wellbore tools. More specifically, the present invention relates to such electrical switches having thermal protection, wherein the switch completes an electrical circuit only under certain selected thermal conditions.

2. Background Information: Electrically actuated wellbore tools are conventional in the well-drilling art. Such electrically actuated wellbore tools include, among others, perforating guns and setting tools for setting other wellbore tools, such as packers and the like. The common denominator among these tools is that they are actuated by delivery of an electric signal through a wireline or other conductor to the wellbore tool.

In operation, the electrically actuated wellbore tool is assembled into a workstring including an electrical actuation signal source and means for conducting the signal to the wellbore tool. After assembly of the wellbore tool into the workstring, the tool and workstring are lowered or run into the wellbore. Inadvertent actuation of the wellbore tool, either on the surface or at an incorrect location within the wellbore can be fatal (in the case of explosive or pyrotechnic wellbore tools) or at least time-consuming and expensive to remedy.

U.S. Patent No. 3,327,792, June 27, 1967, to Boop, discloses a perforating gun including a plurality of shaped charges for perforating casing. Each shaped charge is actuated by an electrical signal. The shaped charges are wired such that detonation of a charge immediately below another charge closes an electrical switch and arms the charge immediately above the

previously detonated charge. However, at least one of the shaped charges must be fully electrically coupled to the actuation signal source at all times. Thus, the perforating gun disclosed is susceptible to inadvertent actuation, and its possibly disastrous consequences, at the surface or in an undesirable location within the wellbore.

A need exists, therefore, for a safety switch for use with electrically actuated wellbore tools that does not permit inadvertent actuation of the wellbore tool, either on the surface or at an undesirable location within the wellbore.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a thermal safety switch for use with an electrically actuated wellbore tool that permits communication of an electrical actuation signal to the wellbore tool only upon subjection of the wellbore tool to a selected thermal condition that is likely to be obtained only in a selected location within a wellbore.

This and other objects of the present invention are accomplished by providing an electrical safety switch for use with an electrically actuated wellbore tool, the switch having a first electrically conductive member and a second electrically conductive member. At least one biasing member, including a thermally responsive biasing member, is arranged to prevent electrical communication between the first and second electrically conductive members until a selected thermal condition is obtained.

According to one embodiment of the present invention, the thermally responsive biasing member is a coil spring formed of nickel-titanium memory metal alloy having a first spring constant until the selected thermal condition is obtained, and having a second spring constant, greater than the first spring constant, after the selected thermal condition is obtained. Preferably, the selected thermal condition is chosen to be unlikely to occur except at selected locations within a wellbore in which the electrically actuated wellbore tool is disposed. Preferably, the selected thermal condition is obtained at ambient temperatures not less than substantially 120° Fahrenheit.

Other objects, features, and advantages of the present invention will become apparent to those skilled in the art with reference to the drawings and detailed description, which follow.

DESCRIPTION OF THE DRAWINGS

Figure 1 is an elevation view, partially in section, of a workstring including an electrical safety switch according to the present invention and an electrically actuated wellbore tool.

Figure 2 is a partial longitudinal section view of an embodiment of the electrical safety switch according to the present invention, shown in a non-electrically conductive condition, prior to exposure of the safety switch to a selected thermal condition.

Figure 3 is a partial longitudinal section view of an embodiment of the electrical safety switch of the present invention shown, in an electrically conductive condition after exposure of the electrical safety switch to the selected thermal condition.

Figure 4 is a partial longitudinal section view of another embodiment of the electrical safety switch according to the present invention, shown in a non-electrically conductive condition, prior to exposure of the safety switch to the selected thermal condition.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the Figures and specifically to Figure 1, a workstring 1 is shown disposed in a wellbore 3. Wellbore 3 is illustrated as cased wellbore, however, the present invention has utility in open wellbores, production tubing, liners, and the like. Workstring 1 includes an electrically actuated wellbore tool assembly 5, 7, 9. Wellbore tool assembly includes a bridge plug 5, a setting tool 7, a firing head 9, and an electrical safety switch 11 according to the present invention. Bridge plug 5 is set into gripping and sealing engagement with wellbore 3 by actuation of setting tool 7. Setting tool 7 is illustrated as a Model E-4 wireline setting tool, sold by the Baker Service Tools division of Baker Hughes Incorporated, of Houston, Texas. Setting tool 7 is provided with firing head 9, which initiates a pyrotechnic chemical reaction in response to an electrical actuation signal generated by an electrical actuation signal source (not shown) , typically located at the surface and communicating with firing head 9 through workstring 1.

An electrical safety switch 11 according to the present invention is disposed intermediate workstring 1 and firing head 9 of electrically actuated setting tool 7. Those skilled in the art will appreciate that, while illustrated in use with a setting tool, electrical safety switch 11 according to the present invention has utility with any electrically actuated wellbore tool, including perforating guns and the like, in which it is desirable to prevent the inadvertent actuation of the electrically actuated wellbore tool at the surface or in undesirable locations within wellbore 3.

With reference now to Figures 2 and 3, which depict partial longitudinal section views of electrical safety switch 11 according to the present invention, the structure of the present invention will be described. Electrical safety switch 11 includes a housing 13 having a central bore 15 of varying diameter to define a plurality of shoulders within central bore

15. A plurality of insulating members 17, 19, 21 are disposed within central bore 15 of housing and are located therein by the aforementioned shoulders. The insulating members are formed of conventional electrically insulating material, such as polytetrafluoroethylene, and include a central insulator 17, a lower insulator 21, and an upper insulator 19. The insulator assembly 17, 19, 21 is secured within central bore 15 by a threaded plug 23 and mating engagement between shoulders on insulator members 17, 19, 21 and shoulders formed in central bore 15. Insulating members 17, 19, 21 serve to insulate other components of electrical safety switch 11 from electrically conductive contact with housing 13.

An electrically conductive member 25 is disposed within central insulator 17 in abutment with and extending through upper insulator 19. Conductor member 25 is formed of a conventional electrically conductive material, such as stainless steel or brass, and is in electrically conductive communication with an electrical actuating signal source (not shown) . A thermally responsive biasing member 27 is disposed within central insulating member 17 and abuts electrically conductive member 25 at one end thereof, and abuts an electrically conductive disk 29 at another end thereof.

Together, electrically conductive member 25, thermally responsive biasing member 27, and electrically conductive disk

29 form a first conductive member assembly.

According to a preferred embodiment of the present invention, thermally responsive biasing member 27 is a coil spring wound from wire formed of a nickel-titanium alloy commonly known as "shape-memory alloy," or "memory metal alloy." Such alloys are characterized by their ability to undergo a thermoelastic martensitic transformation, a crystalline phase change that occurs within a transition temperature range. These alloys may be worked, in an austenitic state wherein martensitic structure is not present, to one shape or configuration, cooled to below the transformation temperature range to produce the martensitic

structure at low temperature, and worked into another shape or configuration. Upon exposure of the memory metal article to a temperature above the transformation temperature range, the martensitic structure dissipates and the article returns to the shape or configuration given it in the austenitic state. During this transformation, the return of the article to the shape given it in the austenitic state occurs violently, in a high-stress transformation, which permits the article to perform work during the transformation. According to a preferred embodiment of the present invention, the memory metal alloy is TINEL alloy K, purchased in wire form from Raychem Corporation, and has a minimum transformation temperature of substantially not less than 120° Fahrenheit.

Accordingly, thermally responsive biasing member 27 can be formed in the austenitic state to have a selected austenitic-state condition spring constant. Thermally responsive biasing member 27 then may be cooled below the transformation temperature range to yield a biasing member 27 having a martensitic structure at room temperature. Biasing member 27 in the martensitic state will have a spring constant lesser in magnitude than the austenitic-state spring constant. Therefore, if thermally responsive biasing member is compressed a given distance, the resistive force exerted by thermally responsive biasing member will vary depending en its crystal structure, i.e., whether biasing member 27 is in a martensitic state, or is transformed to an austenitic state by exposure to elevated temperatures above the transformation temperature range. Preferably, thermally responsive member 27 is formed of a "two-way" memory metal that transforms back and forth between the austenitic and martensitic crystal structures repeatedly, dependent on the ambient temperature conditions. Thus, thermally responsive biasing member will have two spring constants: a relatively larger spring constant at ambient temperatures above the transformation temperature range, and a relatively smaller spring constant at ambient temperatures below the transformation temperature range.

An insulating ring 31 is disposed within central insulating member 17 and adjacent electrically conductive disk 29. Insulating ring 31 serves to temporarily insulate the first conductive member assembly 25, 27, 29 from the remainder of the components of electrical safety switch 11. A second biasing member 33, preferably a coil spring, is disposed within central insulator 17 and abuts insulating ring 31 at its upper end, and abuts an electrically conductive member 35 at its lower end. Second biasing member 33 cooperates with thermally responsive biasing member 27 in a force-additive relationship to maintain electrically conductive disk 29 spaced apart from, and out of electrically conductive communication with, second electrically conductive member 35.

Electrically conductive member 35 is formed of a conventional conductive material and includes an uppermost elongate portion. Another biasing member 37, preferably a coil spring formed of electrically conductive material, abuts a lower end of electrically conductive member 35 at its upper end, and abuts an upper end of an electrically conductive member 39 at its lower end. Biasing member 37 serves to maintain electrically conductive member 35 in a selected position within central insulator member 17 defined by a shoulder formed therein.

Still another electrically conductive member 39 is disposed within central insulator 17 and abuts second biasing member 37 at its upper end, and lower insulator 21 at its lower end. Electrically conductive member 39 is formed of a conventional electrically conductive material, and is in electrical communication at its lowermost end with a firing head (9 in Figure 1) or similar portion of an electrically actuated wellbore tool. Electrically conductive member 39 serves to communicate an electrical actuation signal from an electrical actuation signal source (not shown) to the electrically actuated wellbore tool for actuation thereof. Together, electrically conductive member 35, biasing member 37, and electrically conductive member 39 cooperate to form a

second electrical conductor assembly. The second electrical conductor is maintained within central insulating member 17, and therefore is electrically insulated from housing 13, by cooperation between a downwardly facing shoulder on electrically conductive member 39 and an upwardly facing shoulder lower on insulating member 21.

In a preferred embodiment of electrical safety switch 11 according to the present invention, a low-amperage-rating, Buss-type fuse 41 is secured to a terminal end of the elongate portion of electrically conductive member 35 and in abutment with electrically conductive disk 29. Fuse 41 serves to complete an electrical circuit through electrical safety switch 11 for testing purposes. Fuse 41 is selected to be of a sufficiently low amperage that it may be burned out or "blown" by application of a current of a magnitude insufficient to actuate the electrically actuate wellbore tool, preferably approximately 1/16 of an Ampere. Fuse 41 is also of sufficiently delicate mechanical construction to disintegrate easily and thus avoid interference with the movement of electrically conductive disk 29 relative to the elongate portion of electrically conductive member 35. Provision of electrical safety switch 11 according to the present invention with fuse 41 permits electrical testing of the components of electrical safety switch 11.

Figure 3 illustrates, in partial longitudinal section, electrical safety switch 11 according to the present invention in an electrically conductive condition, in which electrically conductive contact, and therefore electrical communication, is established between first conductor assembly 25, 27, 29 and second conductor assembly 33, 35, 37, 39. Such electrical communication is established by transformation of thermally responsive biasing member 27 from the martensitic state to the austenitic state, wherein the spring constant of thermally responsive biasing member 27 is enlarged. Such transformation of thermally responsive biasing member 27 occurs due to exposure of electrical safety switch 11 to ambient

temperatures in excess of the transformation temperature range of the memory metal alloy of thermally responsive biasing member 2 . As a result of the increased magnitude of the spring constant of thermally responsive biasing member 27, the biasing force of thermally responsive biasing member 27 overcomes that of biasing member 33, thereby moving electrically conductive disk 29 into electrically conductive contact with the elongate portion of electrically conductive member 35 to establish electrical communication between the electrical actuation signal source and the electrically actuated wellbore tool. Otherwise, the components of electrical safety switch 11 remain arranged substantially similarly as described with reference to Figure 2.

Figure 4 depicts, in partial longitudinal section, an alternative embodiment of an electrical safety switch 111 according to the present invention. Electrical safety switch 111 is illustrated in a normally open position in which electrically conductive contact, and therefore electrical communication between the electrical actuation signal source and the electrically actuated wellbore tool, is not permitted. Electrical safety switch 111 includes a housing 113, which is formed of insulating material, such as polytetrafluoroethylene, and includes a central bore 115 therethrough.

An electrically conductive member 125 is disposed within central bore 115 of housing 113. Electrically conductive member 125 is formed of conventional electrically conductive material, such as stainless steel or brass, and is in electrically conductive communication with an electrical actuating signal source (not shown) . A thermally responsive biasing member 127 is disposed within central bore 115 and abuts electrically conductive member 125 at one end thereof, and abuts an electrically conductive disk 129 at another end thereof. Together, electrically conductive member 125, thermally responsive biasing member 127, and electrically conductive disk 129 form a first conductive member assembly.

Thermally responsive biasing member 127 is formed substantially as described with reference to the embodiment shown in Figures 2 and 3.

An insulating ring 131 is disposed within central bore 115 and adjacent electrically conductive disk member 129. Insulating ring 131 serves to temporarily insulate the first conductive member assembly 125, 127, 129 from the remainder of the components of electrical safety switch 111. A second biasing member 133, preferably a coil spring, is disposed within central bore 115 and abuts insulating ring 131 at its upper end, and abuts an electrically conductive member 135 at its lower end. Second biasing member 133 cooperates with thermally responsive biasing member 127 in a force-additive relationship to maintain electrically conductive disk 129 spaced apart from, and out of electrically conductive communication with, second electrically conductive member 135. Second electrically conductive member 135 is formed of a conventional electrically conductive material, and is in electrical communication at its lowermost end with a firing head (9 in Figure 1) or similar portion of an electrically actuated wellbore tool. Second electrically conductive member 135 serves to communicate an electrical actuation signal from an electrical actuation signal source (not shown) to the electrically actuated wellbore tool for actuation thereof. Together, electrically conductive member 135 and biasing member 137 cooperate to form a second electrical conductor assembly.

In a preferred embodiment of electrical safety switch

111 according to the present invention, a low-amperage-rating,. Buss-type fuse 141 is disposed in a bore 143 in the terminal end of second electrically conductive member 135. A fuse biasing member 145 is also disposed in bore 143 below fuse 141, and serves to urge fuse 141 into electrically conductive contact with electrically conductive disk 129. Fuse 141 serves to complete an electrical circuit through electrical safety switch 111 for continuity testing purposes. Again, fuse 141 is

εelected to be of a sufficiently low amperage that it may be burned out or "blown" by application of a current of a magnitude insufficient to actuate the electrically actuated wellbore tool. Biasing member 145 permits fuse 141 to retract within bore 143 in second electrically conductive member 135. This, in turn, prevents fuse from interfering with the establishment of electrically conductive contact between electrically conductive disk 129 and second electrically conductive member 135 after thermally responsive biasing member 127 transforms from the martensitic to the austenitic state.

With reference now to Figures 1 - 4, the operation of electrical safety switch 11, 111 according to the present invention will be described. At the earth's surface, a workstring 1 is assembled including an electrically actuated wellbore tool 5, 7, 9. Also, included in workstring 1 is an electrical safety switch 11, 111 according to the present invention. As described herein, electrical safety switch 11, 111 includes a thermally responsive biasing member 27, 127 which is formed of memory metal alloy that possesses a martensitic crystal structure defining a first spring constant. The transformation temperature range of the particular memory metal alloy is selected to be of a magnitude considered not likely to be encountered at surface ambient temperature conditions, and is preferably substantially not less than 120° Fahrenheit. If electrical safety switch 11, 111 is provided with fuse 41, it may be advantageous to test switch 11, 111 for conductivity or continuity therethrough, both at the surface and at locations in the wellbore, without actuating wellbore tool 5.

At this point, electrical safety switch 11, 111 is in a normally open position in which electrical communication of a current in excess of fuse 41, 141 rating between the electrical actuation signal source (not shown) and the electrically actuated wellbore tool 5, 7, 9 is not permitted. Therefore, electrically actuated wellbore tool 5, 7, 9 is not susceptible to inadvertent actuation at the surface of the

earth. However, it is well known that ambient temperatures increase with depth in the earth's crust. These subterranean temperatures can reach large magnitudes, which substantially exceed 120° Fahrenheit. Thus, as workstring 1 is lowered into wellbore 3, ambient subterranean temperatures at some depth will exceed 120° Fahrenheit, precipitating the transformation of thermally responsive biasing member 27, 127 and placing firing head 9 of electrically actuated wellbore tool assembly 5, 7 in electrical communication with the electrical actuation signal source (not shown) for actuation of wellbore tool 5 responsive to the receipt of an electrical actuation signal.

When wellbore tool 5 is run into wellbore 3 to a selected depth or location therein, the electrical actuation signal may be supplied from the electrical actuation signal source, through electrical safety switch 11 and to firing head 9 of setting tool 7. After firing head 9 and setting tool 7 are actuated (or malfunction) , workstring 1 can be tripped-out of wellbore 3. Upon exposure of electrical safety switch 11, 111 to ambient temperatures less than 120 degrees Fahrenheit, thermally responsive biasing member 27, 127 transforms back to the martensitic state, and electrical communication between the electrical actuation signal source, firing head 9, and setting tool 7 is again interrupted, preventing potentially disastrous inadvertent actuation of wellbore tool 5.

The thermally responsive electrical safety switch according to the present invention has a number of advantages. The principal advantage is that the switch according to the present invention prevents an electrically actuated wellbore tool from being actuated inadvertently at the earth's surface or at locations in the wellbore where the ambient temperature conditions do not exceed the transformation temperature range of the material of the thermally responsive member of the safety switch. This advantage permits avoidance of the potentially disastrous consequences of inadvertent actuation of the wellbore tool. Another advantage of the present invention is that the safety switch is simple in construction and has

minimal number of moving parts, therefore providing an inherently reliable switch apparatus.

The present invention has been described with reference to a preferred embodiment thereof. Those skilled in the art will appreciate that the invention is thus not limited, but is susceptible to variation and modification without departing from the spirit and scope of the invention as defined by the following claims.