Patent Publication Number: US-6655458-B2

Title: Formation testing instrument having extensible housing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to the field of wellbore testing and sample taking instruments. More particularly, the invention relates to designs for such instruments which reduce a possibility of the instrument and/or conveyance device becoming stuck in a wellbore. 
     2. Background Art 
     When drilling a wellbore through earth formations for the purpose of producing hydrocarbons, frequently the wellbore operator requires information concerning formation and wellbore parameters, such as fluid pressure and fluid content of the various formations penetrated by the wellbore. Such pressure and fluid content information is used for, among other purposes, determining a depth at which to set casing, determining which formations are likely to be commercially productive of hydrocarbons or whether to set casing at all. 
     Various instruments are known in the art for taking formation fluid pressure measurements and/or formation fluid samples. Many of these instruments are designed to be conveyed at one end of an armored electrical cable (“wireline” conveyed). Other types of instruments may be conveyed by coiled tubing, drill pipe or similar conveyances. These instruments typically include an elongated instrument housing adapted to traverse the wellbore. The instrument housing includes therein a probe adapted to be extended from the housing and placed in externally sealed engagement with the wall of the wellbore at the position of a formation to be tested. Various flowlines, pressure transducers and sample chambers are disposed in the instrument housing and are adapted to cause fluid to be withdrawn from the selected formation while pressure and fluid composition properties are measured. In some cases a sample of the formation fluid will be directed to a storage tank for ultimate removal from the wellbore and subsequent analysis at the earth&#39;s surface. Examples of such formation pressure measuring and sample testing instruments are described in U.S. Pat. No. 6,058,773 issued to Zimmerman et al. and U.S. Pat. No. 4,936,139 issued to Zimmerman et al. 
     One particular concern associated with substantially all formation pressure measuring and sampling instruments such as the ones described in the above references is that the instrument must be stopped in the wellbore in order to take a sample and/or make a pressure measurement. Stopping the instrument in the wellbore substantially increases the risk of the instrument and/or means of conveyance becoming stuck in the wellbore. Mechanisms for becoming stuck include debris settling out of the drilling fluid and lodging between the instrument and the wellbore wall, differential pressure between the drilling fluid in the wellbore and the formation being tested, and the conveyance becoming “keyseated” in the wall of the wellbore. So called “tractor” devices have been developed to prevent wellbore tools from sticking in the wellbore. Examples of such tractor devices include U.S. Pat. No. 5,954,131 issued to Sallwasser on Sep. 21, 1999 and U.S. Pat. No. 6,179,055 issued to Sallwasser et al. on Jan. 30, 2001, the entire contents of both are hereby incorporated by reference. These tractor devices convey a tool along a wellbore using a cam system to lock against the borehole wall. 
     What is needed is a device for enabling continued motion of the conveyance and a substantial portion of the instrument while the tool conducts wellbore operations, such as deploying a probe to make a formation pressure measurement and/or fluid test. One such device is described for example in U.S. Pat. No. 4,600,059 issued to Eggleston et al. The device disclosed in this reference includes a telescoping section coupled between a wireline conveyed fluid testing instrument and the armored electrical cable. When the testing instrument is deployed to test a particular earth formation, and is thus stationary, the armored electrical cable may be kept in continuous motion by repeated extension and retraction of the telescoping section. This is known in the art as “yo-yoing” the cable. Yo-yoing the cable requires the cable operator to pay very close attention to a winch control system to avoid too much upward and/or downward motion of the cable for operating the telescoping section. It is desirable to have a telescoping section for a wellbore test instrument which does not require cable yo-yoing. 
     It is desirable to have a wellbore instrument, such as a formation fluid pressure and/or sampling instrument, which enables substantially continuous motion of a well logging conveyance in order to prevent sticking and reduce the duration of wellbore operations. This combination of a wellbore instrument in a continuous motion enables economically combining wellbore options, such as a combined pressure/fluid sample test instrument with other types of well logging instruments that make measurements while moving along the wellbore. Typically, such “moving measurements” have not been combined with formation pressure and sampling instruments to operate simultaneously because the former are adapted to make measurements while moving along the wellbore, and the latter, as previously explained, must be stopped. Examples of the former include, without limitation, acoustic devices, resistivity devices and nuclear porosity and lithology measuring devices. 
     SUMMARY OF INVENTION 
     One aspect of the invention is a well logging instrument which includes a lower housing having therein a formation testing system adapted to be operated in an axially fixed position in a wellbore. The instrument also includes an upper housing adapted to be operatively coupled to a well logging conveyance. The instrument includes an axial extension mechanism operatively coupled between the lower housing and the upper housing. The extension mechanism is adapted to controllably extend and retract to lengthen and shorten the instrument, respectively. 
     A method for testing an earth formation according to another aspect of the invention includes moving a logging instrument axially along a wellbore by operating a logging conveyance coupled to an upper end of the instrument. A testing system adapted to test the earth formation at a fixed axial position along the wellbore is deployed, while continuing to move the conveyance along the wellbore. A length of the logging instrument between the conveyance and the testing system is increased by operating an axial extension mechanism disposed between the conveyance and the testing system, while continuing to move the conveyance along the wellbore. The earth formation is tested, the testing system is retracted; and the axial extension mechanism is then retracted. In one embodiment, tension between the instrument and the conveyance is measured, and the axial extension mechanism is extended at a rate adapted to maintain the tension substantially constant. 
     Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 shows an example embodiment of a formation testing instrument according to one aspect of the invention. 
     FIG. 2 shows another embodiment of an axial extension mechanism according to one aspect of the invention. 
     FIG. 3 shown another embodiment of an axial extension mechanism according to one aspect of the invention. 
     FIGS. 4-8 show a well logging/pressure testing operation according to another aspect of the invention. 
     FIGS. 9-13 show a well logging/pressure testing operation according to another aspect of the invention. 
     FIGS. 14-19 show a well logging/pressure testing operation according to another aspect of the invention. 
     FIG. 20 shows an example embodiment of a cable tension measuring device used in another aspect of the invention. 
    
    
     DETAILED DESCRIPTION 
     An embodiment of a formation testing instrument is shown schematically in FIG.  1 . The instrument  10  in this embodiment is adapted to make formation pressure measurements and/or take fluid samples from an earth formation. Formation fluid pressure measuring/sample taking devices are a principal example, but only one example, of a type of formation testing system which is adapted to perform its testing function while in an axially fixed position within a wellbore. 
     The instrument  10  includes an upper housing  28  adapted to couple at its upper end to an instrument conveyance, which in this example is an armored electrical cable (not shown). Connection to the cable (not shown) can be either directly, or through other intervening well logging instruments (not shown in FIG. 1 for clarity). The upper housing  28  is adapted to slidingly, sealingly engage a lower housing  26 . 
     The lower housing  26  in this embodiment includes therein the various components of a testing and sampling system  12 . The system  12  includes a probe  14  which is adapted to be extended laterally from the lower housing  26  by hydraulic cylinders  16  or the like, and may include a back up pad system  20  located circumferentially opposite the probe  14  about the lower housing  26 . The back up pad system  20  can be of any type well known in the art adapted to provide the probe  14  with adequate ability to be sealingly forced against the wall of a wellbore (not shown) in which the instrument  10  is disposed, particularly when the wellbore has a large diameter as compared with the diameter of the instrument  10 . The back up pad section  20  can be extended and retracted using hydraulic cylinders  18  or the like. 
     The probe  14  is in selective hydraulic communication with a pressure testing cylinder  22  having therein a pressure transducer (not shown separately) which makes measurements of the fluid pressure of the selected earth formations adjacent to the wellbore. The pressure testing cylinder  22  may be operatively controlled by a controller/telemetry unit  24 , which operates the pressure testing cylinder  22  and records, formats and/or transmits measurements made by the transducer (not shown) so fluid that pressure of the selected earth formations can be determined. Systems including the system  12 , pressure test cylinder  22  and transducer therein, controller/telemetry unit  24  and the back up pad system  20  may be any one or more of a number of types well known in the art, such as disclosed, for example, in U.S. Pat. No. 6,058,773 issued to Zimmerman et al. and U.S. Pat. No. 4,936,139 issued to Zimmerman et al. The type and structure of the system  12 , pressure test cylinder  22 , controller/telemetry unit  24  and the back up pad system  20  are only provided to help explain the invention, and are not in any way intended to limit the scope of the invention. 
     The system  12  of FIG. 1 is depicted as a formation fluid pressure measuring/sample taking system with a probe and hydraulic cylinders. However, the system may be substituted with any downhole instrument capable of performing operations in the apparatus  10 . Example of such downhole instruments include devices, such as a rotary or percussion “core” sampling device, perforation tools, rock testing and sampling tools as well as others instruments usable with downhole tools. 
     As previously explained, the upper housing  28  and the lower housing  26  are adapted to slidingly, preferably sealingly, engage each other. An axial position of the upper housing  28  with respect to the lower housing  26  is controlled, in various embodiments of the invention, by an axial extension mechanism  38 . One end of the axial extension mechanism  38  is fixedly coupled to a selected position along the lower housing  26 , such as at lower bulkhead  38 A. The other end of the axial extension mechanism  38  is fixedly coupled to a selected position along the upper housing  28 , such as at upper bulkhead  38 B. 
     The embodiment of the axial extension mechanism  38  shown in FIG. 1 may include an electric motor  30  the rotary output of which turns an extension screw, or ball screw  32 . The ball screw  32  engages a ball nut  34  fixed to the lower bulkhead  38 A or other element coupled to the lower housing  26 . The motor  30  in this embodiment is controlled by a motor controller  36 , functionality of which will be further explained. To summarize, the motor  30  may be turned to rotate the ball screw  32  to cause the lower housing  26  to slide outward from the upper housing  28  (or as may be described inversely, the upper housing  28  slides outwardly from the lower housing  26 ). The outward relative sliding lengthens the instrument  10 . The motor  30  may also be turned in the opposite direction to ultimately cause the housings  26 ,  28  to slide together with respect to each other, to shorten the instrument  10 . 
     As will be appreciated by those skilled in the art, when the pressure testing system  12  is engaged with the wall of a wellbore (not shown) to make a pressure test of an earth formation, its axial position in the wellbore (not shown) is fixed. By causing the motor  30  to operate to lengthen the instrument  10 , the cable (not shown) and any intervening logging instruments (not shown) may continue to move along the wellbore (not shown). After a pressure measurement is made, and the pressure measuring system  12  is retracted, the motor  30  may be operated to cause the instrument  10  to shorten, still while moving the cable and any intervening logging instruments. 
     Another possible embodiment of the axial extension mechanism  38  is shown in FIG.  2 . In this embodiment, the axial extension mechanism includes an hydraulic cylinder  40  coupled at one end to bulkhead  38 B in the upper housing  28 , and an hydraulic piston  41  coupled at one end to bulkhead  38 A in the lower housing  26 . The piston  41 /cylinder  40  combination may be any conventional type adapted to extend and retract the piston  41  from the cylinder  40  upon application of suitable hydraulic pressure. The piston  41 /cylinder  40  combination should be operatively coupled to a suitably controlled hydraulic pressure source (not shown) to extend and retract the piston  41  from the cylinder  40  to lengthen and shorten the instrument  10  as explained with respect to the previous embodiment of the axial extension mechanism  38 . 
     Another possible embodiment of the axial extension mechanism  38  is shown in FIG.  3 . This embodiment is a linear electric actuator including a primary winding  43  mechanically coupled to the lower housing  26  and a secondary winding  42  mechanically coupled to the upper housing  28 . 
     For any embodiment of the axial extension mechanism, such as the ones described above, it is understood that the positions of the various elements of any embodiment of the mechanism  38  described above within either of the upper housing  28  and lower housing  26  are only to illustrate the general principle of an instrument made according to this aspect of the invention. Accordingly, the relative positions of the various components of the axial extension mechanism shown herein are not meant to limit the invention. For example, the motor  30  and balls crew  32  of FIG. 1 could as easily and effectively be located in an coupled to the lower housing  26 . It is also understood that having the lower housing  26  be adapted to slide within the upper housing  28  as shown in FIGS. 1,  2  and  3  is also meant only to illustrate the principle. The upper housing  28  could as easily be adapted to slide within the lower housing  26  while performing as intended within the scope of the invention. 
     A method of performing wellbore operations according to the invention is illustrated in FIGS. 4 through 8. Specifically, FIGS. 4 through 8 show a method of taking pressure measurements and/or fluid samples. FIGS. 4 through 8 also show how the overall length of the instrument  10  extends and retracts over time. 
     In FIG. 4, an instrument  10  according to the invention is coupled to a well logging cable  50 . The instrument  10  has an upper housing  28  coupled to the cable  50  through an intervening logging instrument  51  adapted to make one or more types of petrophysical measurements while the intervening instrument  51  is moved along the wellbore  52 . The instrument  10  also has a lower housing  26  coupled to the upper housing  28  as previously described. Other embodiments of a method according to the invention may exclude the intervening logging instrument  51 . FIG. 4 shows the instrument  10  at initial time to with the axial extension mechanism fully retracted. The test system  12  is deployed in an earth formation which is intended to be tested, and the various components of the test system  12  which are adapted to contact the wellbore  52  are placed in contact therewith. 
     FIG. 5 shows the tool as it has advanced up the wellbore at a time t 1 . The logging cable  50  continues to be withdrawn from the wellbore  52 , in some embodiments, at substantially the same rate as prior to deployment of the test system  12 . As the cable  50  continues to be withdrawn, the axial extension mechanism  38  is operated to enable the upper housing ( 28  in FIG. 1) to continue to move at the same rate as the cable  50 . The lower housing ( 26  in FIG. 1) remains axially fixed within the wellbore  52 . 
     FIG. 6 show the tool at time t 3 . The lower housing  26  of the instrument  10  is stopped with the system  12  deployed to perform wellbore operations. Upper housing  28  continues to advance uphole thereby increasing the overall instrument  10  length as shown in FIG. 6 as the pressure test system  12  is operated to make at least one fluid pressure test from the surrounding earth formation. 
     FIG. 7 shows the instrument  10  at time t 4 . In FIG. 7, the pressure test is completed, and the pressure test system is retracted to enable resumed upward motion of the lower housing  26  having the pressure test system  12  therein. The lower housing  26  of the instrument  10  is released from the wellbore and begins to retract into the upper housing and the overall length of the tool  10  begins to decrease. The lower housing is retracted by operating the axial extension mechanism  38  to shorten the instrument length as discussed previously. 
     FIG. 8 shows the instrument  10  at time t 4 . In FIG. 8, the lower housing  26  is fully retracted and the overall instrument length is returned to its original, retracted length at t 1 . The tool may then be moved into another position within the wellbore to take additional tests, or be withdrawn from the borehole. 
     Referring now to FIG. 9, the instrument  10  is shown in combination with an extender  100 . The extender  100  has an upper portion  28   a  coupled to the lower housing  26  of instrument  10 , and a lower portion  26   a.  The upper portion  28   a  and the lower portion  26   a  having an axial extension mechanism  38   a  adapted to axially extend and retract upper portion  28   a  and lower portion  26   a  as previously described with respect to axial extension mechanism  38  of FIGS. 1 through 3. The lower portion  26   a  of the extender  100  may optionally be provided with additional instruments to perform tests. 
     A method of performing wellbore operations using the instruments  10  with the extender  100  is illustrated in FIGS. 9 through 13. FIGS. 9 through 13 show the instrument  10  advance up the wellbore as previously described with respect to FIGS. 4 through 8. At time t 0 , the instrument  10  is in the fully retracted position and the extender  100  is in the fully extended position. As shown in FIG.  10  and at time t 1 , the upper housing  28  of the instrument  10  and the lower portion  26   a  of the extender  100  have begun to move uphole. At time t 2  of FIG. 11, the instrument  10  is in the fully extended position, and the extender  100  is in the fully retracted position. FIG. 12 shows the instrument  10  at time t 3  with the sampling probe  14  having completed its test. The instrument  10  begins to retract while the extender  100  begins to extend. At time t 4  shown in FIG. 13, the instrument  10  has fully retracted and the extender  100  has fully extended. The cycle may then begin again at another position in the wellbore. 
     FIGS. 9 through 13 depict the instrument  10  extending while the extender  100  retracts and the extender  100  extending as the instrument  10  retracts. This depiction of the instrument  10  operating at alternate intervals with the extender is one example of an operation with multiple extension mechanisms. The instrument and extender may be timed to operate simultaneously, out of sync, or at any desired interval. 
     Another embodiment of the present invention is depicted in FIG.  14 . The instrument  200  is provided with a slotted housing  130  having an upper end  140  and a lower end  150 . An axial mechanism  180  having an upper portion  32   a  and a lower portion  32   b  is disposed within the housing. A mechanical stop  160  is disposed between the upper portion  32   a  and the lower portion  32   b.    
     An axially movable testing systems  12   a  is positioned on upper portion  32   a,  and an axially movable testing system  12   b  is positioned on lower portion  32   b.  Each testing system is provided with a probe  14  and opposing back up pad section  18  extendable through slots (not shown) in the housing  130 . The testing systems  12   a  and  12   b  are axially movable along their respective portion of the axial mechanism  180 . 
     A method of performing wellbore operations using the instrument  200  in accordance with the invention is illustrated in FIGS. 14 through 19. The instrument  200  is shown progressing uphole in the wellbore  52  from time t 0  of FIG. 15 to time t 5  of FIG.  20 . As shown in FIGS. 14 through 16 at times t 0  through t 2 , the testing system  12   a  extends through the slot (not shown) in the housing and engages the wellbore  52  to perform a testing function. Testing system  12   a  advances toward mechanical stop  160  along the upper portion  32   a  of the axial mechanism  180 , and the testing system  12   b  advances toward mechanical stop  160  along the lower portion  32   b  of the axial mechanism  180 . 
     Referring now to FIG. 17 at time t 3 , testing system  12   a  retracts back into the housing, and testing system  12   b  extends through the slotted housing to perform a test. As the instrument  200  continues uphole as shown in FIG. 18 at time t 4 , instrument  12   b  advances towards the lower end  150  of the instrument, and testing system  12   a  advances toward the upper end  140  of the instrument  200 . As shown in FIGS. 14 through 19, testing systems  12   a  and  12   b  test at alternate intervals, but could be timed at alternate, simultaneous or random intervals to perform a variety of tests. 
     It is understood that reference to a well logging cable as explained with respect to FIGS. 4-19 are merely examples of a well logging conveyance which may be used in various embodiments of an instrument and method according to the invention. Coiled tubing and drill pipe logging conveyances may also be used in other embodiments. 
     Another aspect of the invention can be better understood by referring to FIG.  20 . FIG. 20 shows a typical cable head  53  which is used to make electrical and mechanical connection between the logging cable  50  and the instrument ( 10  in FIGS.  4 - 9 ). This embodiment of the cable head  53  includes therein a sensor  54  having an output related to the amount of tension between the logging cable  50  and the cable head  53 . As will be appreciated by those skilled in the art, the instrument upper housing ( 28  in FIG. 1) synchronously moves with the cable even when the lower housing ( 26  in FIG. 1) is axially fixed in the wellbore, as explained with respect to FIGS. 4-9. If the cable motion matches the rate at which the axial extension mechanism ( 38  in FIGS. 4-9) increases the instrument length, the tension between the cable head  53  and the cable should remain substantially constant. In this embodiment of the invention, the sensor  54  is operatively coupled to the motor controller ( 36  in FIG.  1 ), and the controller is adapted so that the rate of extension of the axial extension mechanism  38  may be substantially matched to the rate of motion of the logging cable  50 . If the cable  50  moves faster than the extension mechanism  38  lengthens, it would be expected that the tension indicated by the sensor  54  will increase, and vice versa. 
     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.