Abstract:
A borehole tool including a tool body having and an anchoring mechanism, the anchoring mechanism having a drive mechanism including a motor, drive shaft, and clutch; an anchor arm moveable between first and second positions relative to the tool body; a push rod connecting the anchor arm to the drive mechanism; and a spring acting to bias the arm into a first position relative to the tool body. The push rod extends through the clutch mechanism and is engaged by the spring to bias the arm into the first position, and is also driven by the drive mechanism through the clutch to move the arm between the first and second position. The push rod may be connected to the anchor arm by a link. Measurement devices may be used to determine the position of the anchor arm or the tool body.

Description:
This application is a continuation-in-part application of co-pending and commonly assigned U.S. patent application Ser. No. 09/508,586 file Mar. 14, 2000. 
    
    
     TECHNICAL FIELD 
     The present invention relates to borehole logging tools, and in particular to aspects of an actuating mechanism urging a borehole logging tool against the wall of a borehole. 
     BACKGROUND ART 
     Borehole logging tools are known for performing measurements in boreholes to evaluate surrounding underground formations and often contact between the tool and the borehole is necessary to perform the desired measurement. This contact can be provided by anchoring the tool to a borehole wall during a measurement operation through the use of an anchoring arm. It may be necessary to make measurements at a number of levels in a borehole so the anchoring arm must be released to allow the tool to be moved and the anchoring arm then re-engaged at the next level. The time taken for the anchor to release and to re-engage can be a significant factor in the time taken to make a measurement at each level. An anchor arm that can be anchored and released in a relatively short time is desirable. 
     For example, multi-shuttle seismic tools are known that comprise a number shuttles linked together by means of a cable and logged through a borehole while seismic signals are generated at the surface. At each measurement level, each shuttle is anchored to the wall of a borehole during a measurement operation by means of an anchoring arm. As the time required to anchor and release each shuttle increases, the cost of performing the measurement operation increases and the possibility of the tool becoming encumbered in the borehole increases. In Schlumberger&#39;s Combinable Seismic Imager tool (CSI) the anchoring arm of each shuttle extended under spring bias and a drive motor is used to provide the anchoring force or retraction. Aspects of the CSI are described in U.S. Pat. Nos. 4,563,757; 4,575,831; 4,987,969; and 5,200,581. In patents &#39;757 and &#39;831 relate to the anchoring mechanism and procedure. A schematic figure from the patents is shown in FIG.  1 . This prior art arrangement includes a motor  35 , an output reducer  36  with an electromagnetic brake  37  and an output shaft to a coupling device  39  comprising a clutch  50 , a mechanical logic  51  and torque limiter  54 . The mechanical logic  51  includes studs located in helical, V-shaped, cam slots that serve to bring the clutch into engagement on operation of the motor. Drive is transmitted to a push rod  34  connected to the anchoring arms  31 ,  32  by means of a ball screw  40  and nut  41 . The anchoring arms are urged away from the tool body  29  by a leaf spring  43  which is fixed to the tool body  29  and bears upon the arm  31 . When in the open position, a pad  30  at the end of the arms  31 ,  32  engages the borehole wall and causes the tool body  29  to be pushed against the opposite side of the borehole where it can be anchored for use. The motor  35  is used to provide the extra anchoring force to the arms  31 , 32  and to withdraw the arms when the tool is run in or pulled out of the borehole. When the tool is to be moved to a different level, the action of the clutch  50  allows the motor to be disengaged and the arms held only by the force of the leaf spring  43 . 
     An object of the present invention is a tool which has an anchoring arm which can be anchored and released in a relatively short time, and a further object is a tool which has a relatively compact anchoring arm. Another object is a borehole tool in which measurements relating to the anchoring mechanism or tool body position can be made. A further object is an anchoring mechanism that can operate after being loosed from an encumbered or jammed position. 
     DISCLOSURE OF INVENTION 
     The present invention provides a borehole tool comprising a tool body having an anchoring mechanism, the anchoring mechanism comprising a) a drive mechanism including a motor, a drive shaft and a clutch mechanism; b) an anchoring arm moveable between first and second positions relative to the tool body; and c) a push rod extending through the clutch mechanism connecting the anchoring arm to the drive mechanism; the push rod engaging a spring which acts to bias the arm into the first position, and driveably connecting the drive mechanism through the clutch such that the arm can be moved between the first and second positions. 
     In another embodiment, the present invention provides a borehole tool comprising a tool body having an anchoring mechanism comprising a) a drive mechanism including a motor, a drive shaft and a clutch; b) an anchoring arm moveable between first and second positions relative to the tool body; c) a push rod connecting the anchoring arm to the drive mechanism through a link; and d) a spring acting to bias the arm into a first position relative to the tool body; characterised in that the push rod extends through the clutch mechanism and is engaged by the spring to bias the arm into the first position, and is also driven by the drive mechanism through the clutch to move the arm between the first and second positions. 
     The present invention provides a borehole tool comprising a tool body having an anchoring mechanism comprising a) a drive mechanism including a motor, a drive shaft and a clutch; b) an anchoring arm moveable between first and second positions relative to the tool body; c) a push rod connecting the anchoring arm to the drive mechanism through a link; and d) a spring acting to bias the arm into a first position relative to the tool body; and e) at least one measurement device; characterised in that the push rod extends through the clutch mechanism and is engaged by the spring to bias the arm into the first position, and is also driven by the drive mechanism through the clutch to move the arm between the first and second positions. 
     In one embodiment, the present invention provides a link for connecting an anchoring arm to a borehole tool comprising at least one hole for affixing a fastener, an orifice for mounting a pivot, a cutout area, and a breakage area. 
     The invention is applicable to any type of borehole tool that requires the tool body to be urged against the borehole wall. The provision of the push rod extending through the clutch mechanism allows the overall length of the anchoring mechanism to be reduced over that provided by the prior art device. 
     A ball-bearing clutch can be used which comprises a collar having a number of balls that engage in grooves in the push rod to allow the drive mechanism to move the arm. A spring-loaded retaining ring can be provided to hold the balls in a driving position in the grooves when engaged by the collar. 
     The drive shaft is typically a drive screw and a nut is used to transmit the driving force to the push rod. Driving force can be applied either through the clutch or by bearing surfaces on the nut which engage directly extensions of the push rod. The two mechanisms can be used to provide reversible drive to the push rod. 
     The spring can be a coil spring that is located in the tool body around the drive mechanism. Other arrangements of springs or resilient biasing means can be used to urge the arm into the first position. 
     The anchor arm can be mounted on a pivot on the tool body with the first position being extending away from the tool body and the second position being along the tool body. Thus, the spring can be used to urge the arm away from the tool body and the motor used to provide further drive in this direction for anchoring force, or to provide a counteracting drive to withdraw the arm to the tool body. By reversing the drive to release the clutch, the arm can be held under spring force alone while the tool is moved in the borehole. The pivot can be placed in a link that connects the arm to the drive mechanism, the link having a propensity to fail in a predefined arrangement. 
     A measurement device can be used to indicate the position of the arm after movement. A measurement device attached to the push rod can be used to measure contact between the anchor arm and the borehole wall. A measurement device can be used to measure the contact force asserted on the borehole wall by the anchor arms. A measurement device can be used to detect forces that indicate the position of the anchor arm. A measurement device can be used to determine the orientation of the tool or borehole wall in a deviated wellbore. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 shows a schematic view of a prior art tool. 
     FIG. 2 shows a schematic view of a shuttle seismic logging tool incorporating the present invention. 
     FIGS. 3A and 3B show a detailed view of a part of the shuttle shown in FIG.  2  and use of measurement devices therein. 
     FIGS. 4A through 4D show the positions of the parts of the actuating mechanism of the shuttle of FIGS. 3A and 3B during various stages of deployment. 
     FIGS. 5A through 5D show detailed views of the link. 
    
    
     DETAILED DESCRIPTION 
     The present invention finds particular application in multi-shuttle seismic logging tools. Such tools are used in vertical seismic profile (VSP) surveys and comprise a number of identical or similar shuttles connected in end-to-end fashion by cable. A single shuttle is shown in FIG. 2 that comprises a tool body  100  and an anchoring mechanism  110  including an anchoring arm  120 . In use, a number of these shuttles, from 2 to 20, typically 4 to 8, are connected together and logged through the borehole  140 . 
     FIG. 3A shows a detailed view of the anchoring mechanism  110 . The mechanism includes a permanent magnet (or electromagnet) brake  212 , motor  214  and reducer arrangement  216  housed in the shuttle body  210 . The output drive from the reducer  216  connects through a joint  218  and bearing  220  to a ball screw  222 . The ball screw  222  drives a nut  224 . The end of the screw  222  projects into the hollow end of a push rod  226  and the end of the nut  224  engages the outer surface of the push rod  226  through a clutch mechanism  228  which is described in more detail below. The end of the push rod  226  is connected to a link  230  through which it drives the anchoring arm of the shuttle  120 . The inner end of the push rod  226  is formed into a base section  232  that fits inside the nut  224 . A compression spring  236  is located around the motor/ball screw mechanism inside the shuttle body and acts on the base section  232  so as to normally urge the push rod  226  and hence the arm, outwards. The extension of the push rod  226  under by the spring  236  is limited by the position of the nut  224  on the screw  222  such that operating the motor  214  to move the nut  224  causes the push rod  226  to move out due to the spring  236  or be pulled in by the action of the nut  224 . 
     The base section  232  can have extensions outside the nut  224  to provide a connection to a measurement device  234  for the position of the push rod  226 . This measurement device  234 , preferably a potentiometer or a linear variable differential transformer, can be used for a caliper measurement in the borehole by measuring the position of the push rod when it is fixed to the anchor arm. 
     FIG. 3B shows an alternative embodiment wherein measurement devices  235 , preferably strain gauges, can be used to measure compressive or tensile force response on the nut  224  to determine the contact force between the anchoring arm  120  and the borehole ( 140  in FIG.  2 ). In anchoring, measurement devices  235 , preferably strain gauges, can be used to determine the reaction force of the borehole on the anchoring arm. The reaction force is transferred through the anchoring arm  120  to the push rod  226  when the clutch  228  is engaged. Further when anchoring arm  120  is retracted, measurement device  235  can be used to measure response in anchor mechanism  110  which indicates the arm is fully retracted. 
     FIG. 2 shows an alternate embodiment wherein at least one measurement device  125 , preferably a relative bearing measurement device, can be used to measure relative orientation of the tool body in the borehole. One type of relative bearing measurement device includes a pin drum that is attached to the tool body. Gravity positions a pin in the drum and the relative bearing of the tool body is determined by reference to this pin. Measurement device  125  can be used to measure relative orientation of the tool body  100  in a deviated borehole. Measurement device  125  can be used further to measure relative orientation of a deviated borehole when tool body  100  is anchored against the borehole. Multiple measurement devices  125  can be used to determine the 3-D orientation of the tool body. 
     In FIG. 3, extension of the push rod  226  by the spring  236  is limited by either the arm contacting the borehole wall or by the base section  232  reaching the stops  238  positioned in the body (fully extended). Once the arm contacts the borehole wall, the nut  224  moves over the push rod  226  to activate the clutch  228  such that the screw  222  and nut  224  drives the push rod  226  directly and forces it against the borehole wall to anchor the tool or shuttle. 
     To release the arm, the motor is reversed and the screw  222  retracts the nut  224 , releasing the clutch  228 . The arm is then only held against the borehole wall by the spring  236  and so can move in or out as the tool or shuttle is moved to a different position in the well. It is not necessary to retract the arm completely. If it is desired to retract the arm completely, the reverse motor drive is continued and the nut  224  is retracted along the screw  222  until it contacts the base section  232  of the push rod  226  which it then pulls back against the action of the spring  236  to retract the push rod  226  and thus the anchor arm. When the arm is fully retracted, the motor stalls and this is detected to find the fully retracted/closed position of the arm. Measurement device  235  (in FIG. 3B) can be used to detect or confirm the fully retracted/closed position of the anchor arm  120 . 
     The clutch mechanism  228  (shown in more detail in FIG. 4A) is formed by the outer end of the nut  224  through which the push rod  226  projects and a collar  240  located in the tool body  210  around the push rod  226  by a spring  242 . The outer end of the nut has a number of seats  244  each having a ball bearing  246  located inside. A retaining ring  248  prevents the balls  246  from falling out of the seats  244 . A number of grooves  250  are formed in the outer surface of the push rod  226 . As the end of the nut moves over the push rod  226  after it has contacted the wall of the borehole, the balls  246  are free to move in and out of the grooves  250  without inhibiting movement of the nut  224 , until the outer end of the nut  224  contacts the collar  240  (FIG.  4 C). Once seats  244  reach grooves  250 , spring  242  biases collar  240  to drop ball  246 . At this point, once the balls  246  drop into groove  250 , the collar is allowed to move over the seats and prevent the balls  246  from moving out of the groove  250 . Further motion of the nut  224  is transmitted to the push rod  226  by the balls  246  engaged in the groove  250  to provide the anchoring force for the arm (FIG.  4 D). Reversing the motor drive retracts the nut  224  from the collar  240  so allowing the balls to move out of the groove  250  and permit the push rod to move back against the spring  236 . The motion of the nut required to activate the clutch between first contacting the collar  240  and driving or releasing the push rod  226  is small, for example in the order of 3 mm. Thus the time to lock and unlock the arm is small and has less impact on the time taken to move the shuttle between measurement locations. 
     In this arrangement, all of the drive mechanism and springs are located within the shuttle body with only simple mechanical linkages exposed. This is to be contrasted with the prior art mechanism which has the leaf spring outside the tool. Also, eliminating the clutch and engagement mechanism between the motor and the screw and implementing the clutch between the nut and the push rod in the manner described above allows a shorter overall length. 
     FIG. 5A shows link  230  in detail. Link  230  comprises hole  260  through which the link is connected by a fastener to the push rod ( 226  in FIG. 3A) and orifice  262  through which the link is connected by a pivot to the anchor arm ( 120  in FIG.  2 ). Pivots and fasteners may be pins, rivets, screws, bolts, or other means of connection. Cutout area  264  is proximity placed near orifice  262 , thereby forming a breakage area  266 . In the event the anchor arm cannot be retracted through typical methods of releasing the arm, the breakage area can be failed. This is done by using applying a force to the push rod connected to the link thereby stressing the link so that the breakage area can be failed by the resistance force applied by the anchor arm  120  to the link  230 . The force can be applied to the push rod by the drive mechanism or an outside force can be applied to the tool body. FIG. 5B shows link  230  after breakage area  266  has been failed wherein orifice  272  comprises cutout area  264  and hole  262 . FIGS. 5C and 5D shows some possible positions of pivot  274  attaching anchor arm  120  in orifice  272  after failure of breakage area  266 . The range of positions provides freedom of movement of pivot  274  controlled within orifice  272 . This freedom of movement can permit movement of the anchor arm sufficient to permit the arm to be retracted. The dimension of orifice  272  can be such that link  230  is operational even after the breakage area has failed and pivot is confined in orifice  272 . 
     In this arrangement, encumbered or jammed tools or shuttles can be unencumbered or released by failing the breakage area. Further this arrangement provides for operation and use of the tool and anchoring arm after such failure has occurred. 
     INDUSTRIAL APPLICABLITIY 
     The present invention finds application in the field of borehole logging tools, particularly seismic multi-shuttle logging tools which can be used to evaluate the formations surrounding boreholes such as are drilled for the extraction of hydrocarbons or geothermal energy.