Patent Publication Number: US-6216779-B1

Title: Downhole tool actuator

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of tools run downhole in a borehole. More particularly, the invention relates to an improved actuator for operating the tool at a selected location within the borehole. The invention is particularly useful in narrow slimholes and in wells having multiple lateral lines. 
     Tools are run in boreholes to perform various functions and to identify certain data relevant to subsurface geologic formations and entrained hydrocarbons. For example, logging tools are run in borehole to determine the orientation, structure and composition of the borehole and subsurface geologic formations, and to identify the presence of hydrocarbons within the geologic formations. To prevent such tools from becoming stuck within a borehole, such tools are typically run “slick” with a lubricating fluid such as a drilling mud. However, lubricating fluid reduces log quality by interfering with the detection signals generated and received by the downhole tools. 
     Logging tools are typically centered within a borehole with articulated arms which extend outwardly to engage the borehole wall. The arms are stored in a collapsed position as the tool is lowered into the borehole and are moved outwardly from the housing by electric motors or hydraulic mechanisms. The downhole motor operates a gearbox, mechanical drive jackscrew, and actuation shoulder to open the engagement arms. The motor is powered through a cable extending to the wellbore surface. The jackscrew is engaged with cam pivots for moving the arms outwardly from the housing. A thrust bearing prevents axial movement of the motor relative to the housing, and high pressure dynamic seals prevent fluid intrusion into the housing. Such dynamic seals are subject to failure, and the resulting fluid intrusion can damage motors and electrical connections, and can pack off internal spaces with fluid solids. 
     Advanced drilling techniques and new completion procedures have increased the complexity of downhole boreholes. Multilateral and horizontal completions shorten the turning radius in deviated wellbores and in the transition between connecting borehole sections. Such boreholes require compact tools which are manueverable through tight borehole turns and intersections. To navigate narrow boreholes, new tool designs must be smaller than conventional systems. However, the systems must be smaller without reducing the data acquisition and processing capabilities of the tool. Improved downhole tools should be able to carry increased instrumentation capabilities and to carry high resolution equipment. 
     Materials such as shape memory alloy (“SMA”) provide actuators for different applications, however SMAs are not conventionally used downhole in boreholes because of operating temperature limitations. SMAs comprise special alloys having the ability to transform from a relatively hard, austenitic phase at high temperature to a relatively flexible, martensitic phase at a lower temperature. SMAs comprise highly thermally sensitive elements which can be heated directly or indirectly to deform the SMA, and can be produced with one-way or two-way memory. An electrical current can resistively heat the SMA to a phase activation threshold temperature by the application of a small electric current through contact leads. Alloy materials providing SMA characteristics include titanium/nickel, copper/zinc/aluminum, and copper/aluminum/nickel compositions. 
     An SMA in a wire form has two states separated only by temperature. When cool, the SMA is in the martensitic state where the wire is relatively soft and easily deformable. When warmed above the activation temperature, the SMA wire is transformed into the austenitic state wherein the wire is stronger, stiffer and shorter than in the martensitic state. In the martensitic state, an SMA wire is deformed under a relatively low load. When heated above the activation temperature, the SMA wire remembers the original shape and tends to return to such shape. As the SMA wire is heated and contracts, internal stresses opposing the original deformation are created so that the SMA wire can perform work. SMA actuators can use SMA wire in tension as a straight wire or in torsion as a helical wire coil. 
     The SMA phase transition occurs at a temperature known as the activation temperature. For a titanium/nickel (TiNi) composition, activation temperatures in a range between plus one hundred degrees and minus one hundred degrees C have been demonstrated. In the lower temperature martensitic phase, the SMA is relatively soft and has a Young&#39;s modulus of 3000 Mpa. After the SMA is heated above the activation temperature, the phase transition to a relatively hard austenite phase has a Young&#39;s modulus of 6,900 Mpa. If the SMA is not overly deformed or strained, the SMA will return to the original, memorized shape. If the SMA is then cooled, the SMA mechanically deforms to the original martensitic phase. In an SMA formed as a coil spring, heating of the SMA shortens the spring, and cooling the SMA permits the SMA to return to the longer original configuration. 
     During the manufacture of an SMA, the SMA material is annealed at high temperature to define the structure in the parent, austenitic phase. For TiNi, the annealing temperature can be 510 degrees C. for one hour. Upon cooling, the SMA will automatically deflect away from the programmed shape to the configuration assumed by the SMA in the martensitic phase. The SMA can then be alternately heated or cooled with conductive or internal resistance heating techniques to convert the SMA between the austenitic and martensitic phase structures. 
     As the SMA is heated and cooled, the SMA structurally contracts up to 5% in typical cyclic applications. Contractions up to 16% have been demonstrated, however the number of useful cycles are limited. Deflection of the SMA between the austenitic and martensitic phases can be harnessed with mechanical linkages to perform work. Although 5% contraction provides a relatively small range of motion, the recovery force can provide forces in excess of 35 to 60 tons per square inch for linear contractions. The rate of mechanical deformation depends of the rate of heating and cooling. In conventional applications, the SMA can be mechanically returned by a restoring force to the configuration of the martensitic shape. This use of a restoring force impacts the geometry and size of mechanisms proposed for a particular use. 
     SMA materials can be formed into different shapes and configurations by physically constraining the element as the element is heated to the annealing temperature. SMA alloys are available in wire, sheet and tube forms and can be designed to function at different activation temperatures. Large SMAs require relatively high electric current to provide the necessary heating, and correspondingly large electrical conductors to provide high electric current. Efforts have been made to combine SMA elements with different mechanical devices to accomplish the desired work. 
     SMAs are used in medical devices, seals, eyeglasses, couplings, springs, actuators, and switches. Typically, SMA devices have a single SMA member deformable by heating and have a bias spring for returning the SMA to the original position when cooled. Other actuators termed “differential type actuators” are connected in series so that heating of one SMA deforms the other, and heating of the other SMA works against the first SMA. 
     U.S. Pat. No. 4,556,934 to Lemme et al. (1985) disclosed a shape memory actuator having an end fitting thickness forty percent of the original thickness. The end thickness was reduced so that less current through the end section was required to raise the end temperature above the activation temperature, and the end was cold rolled to strengthen such end against failure. 
     In U.S. Pat. No. 4,899,543 to Romanelli et al. (1990), a pretensioned shape memory actuator provided a clamping device for compressing an object. The actuator comprised a two-way shape memory alloy pre-tensioned to a selected position, and then partially compressed to an intermediate position. The actuator shortened when heated, and then returned to the intermediate clamping position when cooled. The shape memory actuator was formed as a clamping ring or as a coiled spring to accomplish the selected clamping motion. 
     U.S. Pat. No. 5,127,228 to Swenson (1992) described a shape memory actuator having two concentric tubular shape memory alloy members operated with separate heaters. The torsioned members were engaged at one end so that actuation of one element performed work on the other element, thereby providing a torque density higher than that provided by electromechanical, pneumatic or hydraulic actuators. 
     U.S. Pat. Nos. 4,979,672 (1990) and 5,071,064 (1991) to AbuJudom et al. disclosed two shape memory alloy elements in the form of a coil spring for operating a damper plate. An electrically conductive rotational connector connected each shape memory element to a control unit and to a stationary member. Each shape memory element was incrementally heated to move a damper plate into intermediate, open and closed positions. U.S. Pat. No. 5,176,544 to AbuJudom et al. (1993) disclosed an actuator having two shape memory elements to control the position of a damper plate. The shape memory elements were shaped as coil springs. One shape memory element moved the damper to an open position, and another shape memory element moved the damper to a closed position. 
     U.S. Pat. No. 5,445,077 to Dupuy et al. (1995) disclosed a SMA for providing a lock to prevent accidental discharge of a munition. Environmental heating around the munition activated the SMA to operate a munition lock. 
     U.S. Pat. No. 5,405,337 to Maynard (1995) disclosed a flexible film having SMA actuator elements positioned around a flexible base element. A flexible polyimide film provided the foundation for the SMA actuator elements. Switches were attached with each SMA actuator element, and a microprocessor controller selectively operated the switches and SMA actuator elements to guide the deformation of the base element. U.S. Pat. No. 5,556,370 to Maynard (1996) disclosed an actuator formed with a negative coefficient of expansion material for manipulating a joint. SMA actuators were coiled around a joint to provide three dimensional movement of the joint. 
     SMAs are limited due to certain operating characteristics. The operable speed of SMAs is limited by the cooling rate of the elements. After the heat source is removed by disconnecting the electrical current or by removing the heat source, the SMA cools through convection or conduction. Bias spring actuators do not inherently have two stable positions, and the work output for SMAs per unit volume significantly decreases if the SMAs are used in a bending application. Internally heated SMAs are limited to relatively small cross sections because the current requirements increase with larger cross sectional area. SMAs are limited by the range of deflection, the deflection of the SMA in a single direction, power requirements, the environmental operating temperatures, and the time required for operation of the SMA. 
     Conventional downhole tools are limited by the motor size necessary to operate the tools, and the borehole dimensions and configuration. Accordingly, a need exists for improved downhole tools operable within narrow boreholes. Such tools should be compact, inexpensive, reliable, and should be retractable when not in use. 
     SUMMARY OF THE INVENTION 
     The invention provides an apparatus for orienting a downhole tool relative to a borehole, and for allowing tool components to conform to the borehole dimensions. The invention comprises a phase change material engaged with the tool in an initial position which is activatable to move into an operating position relative to the tool. An actuator activates the phase change material to orient the tool relative to the borehole. 
     In other embodiments of the invention, a housing is engaged with the phase change material, and a member is engaged with said housing and with the phase change material for selective movement relative to said housing between an initial position and an operating position. The actuator activates said phase change material to move said member. The phase change material can comprise a shape memory alloy capable of returning to the initial position when the actuator is deactivated, and a return means can move the phase change material to or from the initial position. The invention can be combined with a logging tool or other downhole device to orient the tool within a borehole. In different applications, the invention can center the tool or can urge the tool against one side of the borehole wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a tool in an initial position for entry into a borehole. 
     FIG. 2 illustrates the tool after an arm has been extended. 
     FIG. 3 shows more detail regarding the cooperation between a phase change material and the extendible arm. 
     FIG. 4 illustrates the position of a locking dog and locking slot. 
     FIG. 5 illustrates the locking dog as it exits the locking slot. 
     FIG. 6 illustrates the relationship of the locking dog when the arms are in the operating position. 
     FIG. 7 illustrates the reentry of the locking dog into the locking slot when the phase change material is activated to the maximum change in length. 
     FIG. 8 shows the retention of the locking dog within the locking slot. 
     FIG. 9 illustrates the operation of the phase change material shoulder to operate the cam associated with an extendible arm. 
     FIG. 10 illustrates a cross sectional view of the phase change material and through tubing bus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention provides an apparatus for actuating downhole tools with a phase change material such as a shape memory alloy. The invention is particularly suited for downhole tools in slender boreholes such as slimholes, in highly deviated wells, and in the connections between multilateral wells. 
     Referring to FIG. 1, downhole tool  10  is positioned within borehole  12 . Tool  10  can be lowered into borehole with a cable or tubing element identified as slickline l 4 . One or more extendible arms  16  are pivotably attached to tool housing  18  and are run into borehole  12  in an initial position having a minimal cross section. This configuration reduces tool sticking as tool  10  is run into borehole  12 , particularly in areas where borehole  12  has a tight turning radius or where multiple boreholes are joined. 
     FIG. 2 illustrates the invention after tool  10  has been actuated to extend arms  16 . Phase change material member such as a shape memory alloy tube (“SMA”)  20  is attached to shoulder  60  within housing  18  and is selectively heated with internal heater  22 . Heater  22  can comprise an electrical circuit which passes electric current through SMA  20  and heats SMA  20  with resistance heating. Alternatively, heater  22  can comprise a free standing heating element for heating SMA  20  through conduction, convection, radiation, or a combination of these techniques. Insulation jacket  24  is positioned on the outside of SMA  20  to reduce thermal losses and to more carefully control the temperature of SMA  20 . SMA  20  is attached to load transfer sleeve  26  so that shrinkage of SMA  20  moves sleeve  26  axially within housing  18 . Compression coil spring  28  is positioned between extension  40  and shoulder  60  so that spring  28  can return SMA  20  to the initial position as described below. The extension ( 40 ) is a single circular plate with a centrally located hole such that the inner diameter of the plate hole matches the inner diameter of the part of sleeve ( 26 ) that extends under cam ( 32 ). The outer portion of the extension plate ( 40 ) is suitably notched to fit into axial notches in the housing ( 18 ) and to slide axially when SMA ( 20 ) is heated or cooled. 
     Referring to FIG. 3, sleeve  26  has shoulder  30  in contact with cam  32 . Cam  32  is rotatable about pivot  34  and is connected to linkage  36 . Linkage  36  is pivotably attached to arm  16  and can comprise an element of arm  16 . Leaf spring  38  is attached to housing  18  and to linkage  36  for urging linkage  36  radially outwardly from housing  18 . Sleeve  26  further has extension  40  having locking dog  42  on an outer radial surface of extension  40 . Locking dog  42  is initially retained within locking slot  44  when arm  16  is retained in an initial locked position, and is released from locking slot  44  when arm  16  is extended as shown in FIG.  3 . 
     FIGS. 4-8 illustrate details of one inventive embodiment which selectively engages and disengages arm  16 . As tool  10  is run into borehole  12 , locking dog  42  is initially retained within locking slot  44  as shown in FIG.  4 . When SMA  20  is activated by heating or another actuation technique SMA  20  contacts and sleeve  26  moves axially to compress coil spring  28  and to move locking dog  42  through locking slot  44  until locking dog  42  exits locking slot  44  through detent  46  as shown in FIG.  5 . At this point, leaf spring  38  acts against linkage  36  to move linkage  36  and arm  16  radially outward from housing  18 . Coil spring  28  is compressed during this movement and is unable to overcome the foreshortening force provided by SMA  20 . Potentiometer  48  detects the deployment of arm  16  and is engaged with heater  22  to deactivate heater  22  at such point. As heater  22  is deactivated and SMA  20  cools down, SMA  20  lengthens to the initial, elongated position and sleeve  26  is pushed toward such position by coil spring  28 . Operation of tool  10 , such as logging or other operations, can continue as arm  16  orients tool  10 . As shown in FIG. 6, locking dog  42  cannot reenter locking slot  44  during such operating position because detent  46  blocks such reentry. 
     At the selected time when tool  10  has surveyed the desired length of borehole  12 , arm  16  is collapsed from the operating position to the initial position. This collapse can be accomplished in different ways. For the embodiment of the invention illustrated, arm  16  is collapsed by operating heater  22  to activate SMA  20 . SMA  20  is activated to the full transition amount, which shortens SMA  20  and translates sleeve  26  to collapse arms  16  toward housing  18 . Locking dog  42  snaps through detent  50  to enter locking slot  44  as shown in FIG. 7, and potentiometer  48  detects such position and generates a signal to deactivate heater  22 . SMA  20  again cools and elongates, is returned with coil spring  28 , and unloads shoulder  30  from contact with cam  32 . Locking dog  42  moves past detent  52  and is returned to the initial position within locking slot  44  as shown in FIG.  8 . 
     The extension of linkage  36  and arm  16  can be controlled by the movement of shoulder  30  against cam  32 . FIG. 9 illustrates the full transition heating of SMA  20  wherein shoulder  30  engages cam  32  to close arm  16  and to force locking dog  42  into locking slot  44 . Alternatively, SMA  20  and sleeve  26  can continue to be moved axially until shoulder  30  releases contact with cam  32 , thereby allowing arm  16  and linkage  36  to engage the wall of borehole  12  and to float between such contact and the spring force furnished by leaf spring  38 . 
     Through-bus tube  54  extends through an interior space within sleeve  26  as shown in FIGS. 9 and 10 to permit the insertion of wire (not shown) through tool  10 . Tube  54  permits other tools to be run above and below tool  10  to provide for a unique combination of different tools. Tube  54  can be fixed relative to tool  10  to eliminate the need for dynamic seals, and static seals  56  at both ends of tube  54  prevent the intrusion of fluids. Notably, all of the working elements of tool  10  can be sealed with static seals instead of the dynamic seals found in conventional tools. The elimination of dynamic seals significantly improves tool reliability by avoiding failures associated with dynamic seals. Tube  54  can be stationary to sleeve  26  as sleeve  26  moves axially relative to tool housing  18 . 
     As used herein, the term “phase change material” means any material or structure capable of initiating movement in a member. Such materials include and are not limited by SMAs, piezoelectrics, magnetostrictive, and Terfenol-D (a registered mark of Extrema Company) materials. Phase change materials such as SMAs are activated with different techniques which can include heat, chemical processes, or mechanical movements. Phase change materials other than SMAs may accomplish less deflection and handle lower loads than SMAs, however the capabilities and characteristics of such materials are being extended. As used herein, the terms “activate” and “activatable” encompass different features which can include motion or a reaction such as heat, chemical processes, or mechanical movements. The term “orient” as used herein means to locate or place in a particular location or relationship, or to become adjusted or aligned. 
     The invention uses a phase change material such as an SMA to orient a housing relative to borehole  12 . Although a preferred embodiment of the invention uses an SMA as the phase change material, other compositions and materials can be used to accomplish the functional result of actuating a downhole tool. The invention can orient or position downhole tool  10  within borehole  12 , or can move one component of tool  10  relative to another component of tool  10 . Alternatively, the invention can also accomplish the function of conforming tool  10  to borehole  12 . Other features of the invention can increase the capacity and operating rate of the phase change material. For example, magnetic switches can be incorporated with an SMA to decrease the cycle time of the SMA, and the phase change material can be operated in a waveform type of operation to iteratively cycle the deformation and work performing characteristics of the phase change material. 
     A change of state in SMAs also changes the geometry and stress/strain relationships of the material or alloy. Such changes can cause relative motion of tool components and can actuate the tool to perform a selected task. The SMA are made of the same alloy so that they have essentially the same hysteresis and phase characteristics. The properties of the shape memory alloy will relate to the activation temperature, to the hysteresis between phases, and to the initial and final temperatures. 
     Because the phase transition temperature of a SMA is constant, the resistance of each SMA is directly related to the displacement. For an SMA tube having a unit length of ten, a 4% shortening would leave a final length of 9.6 units. One SMA having a 4000 pounds of force capability incorporates a central cartridge heater inside a frame having six aluminum spokes. A total of  170  wire are wound on each of the spokes, and such SMA is capable of shortening at least 140 thousandths of an inch from a total SMA length of 3.5 inches. 
     Operation of tool can proceed through the selected section of borehole  12 . In one embodiment of the invention, a plurality of arms  16  freely float against borehole  12 . If tool is pushed against one side of borehole  12 , arms  16  will not snap into locking slots  44  because locking dogs  42  have been moved to a position where arms  16  rest against locking slots  44  but are unable to snap into locking slots  44 . Arms  16  can center tool within borehole  12 , or one or more arms  16  can urge tool  10  against one side of borehole  12 . Alternatively, one or more arms  16  can orient tool in any selected direction relative to borehole  12 . 
     Tool  10  is not “parasitic” because overtravel is not required for operation of the moving components. In typical linear locking devices, such as in a ballpoint pen, overtravel of the device is necessary to establish the locked position. The operation of the phase change material in the invention can reach the operating position without overextending or moving past the operating position. The absence of overtravel in the present invention reduces the overall length required for the operable mechanisms. 
     The invention replaces motorized devices, thereby reducing the actuation lengths and weights by over fifty percent. This capability provided by the invention permits operation of the invention in slimholes and highly deviated wells previously inaccessible to conventional tools. By reducing the length requirements for each tool, more tools can be run within a single tool string. The ability to reliably extend and retract standoffs permits the tools to be run within the borehole in a closed position, and opened only within the region of investigation. 
     The invention requires fewer components and significantly simplifies the manufacture and operation of downhole tools. The elimination of downhole electric motors provides a unique capability to the actuation of tools downhole. Such conventional systems contaminate signals in the wireline and instrument bus associated with the equipment. By eliminating downhole motors, brushes, rotors and other moving parts which generate acoustic and electric noise, the invention provides a “quieter” actuating mechanism. Because downhole instrument packages such as telemetry systems are highly sensitive to undesirable noise, interruptions to data gathering operations are reduced, certain noise filter systems can be eliminated, and the overall quality of data is enhanced. Dynamic seals are eliminated, thereby eliminating a significant maintenance requirement. These unique features of the invention significantly enhance the quality of data gathering operations The invention permits the actuating means to return to the original, unpowered position and facilitates subsequent operation of the tool through the work cycle. 
     In addition to the logging tool described herein, the invention is applicable to retractable standoffs in acoustic and other tools, and can center a tool or provide a lesser radial displacement away from the borehole wall. The invention reduces the possibility of binding within a borehole, therefore reducing the need to run the tool slick. This feature of the invention significantly improves the quality of borehole data by eliminating the need for lubricating fluid as the tool is run in the borehole. Additionally, the invention reduces the need for expensive dynamic seals susceptible to failure, and facilitates the placement of through-bus communication wires through the device. 
     Although the invention has been described in terms of certain preferred embodiments, it will be apparent to those of ordinary skill in the art that modifications and improvements can be made to the inventive concepts herein without departing from the scope of the invention. The embodiments shown herein are merely illustrative of the inventive concepts and should not be interpreted as limiting the scope of the invention.