Abstract:
A wellbore formation sample acquisition and analysis instrument includes an annular drill bit configured to couple to one end of a drill string. The bit defines a passageway extending from a cutting face thereof to an exterior surface at a longitudinally spaced apart position from the cutting face. The instrument includes at least one sensor configured to measure a selected parameter of a sample of subsurface formation urged into the passageway by action of the cutting face against subsurface formations. Samples of the subsurface formations are ejected from the exterior surface end of the passageway by the samples entering the cutting face end thereof.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates generally to the field of wellbore drilling and formation evaluation. More particularly, the invention relates to devices for extracting samples of subsurface formations during drilling of a wellbore and analyzing such samples with respect to various physical parameters during wellbore drilling. 
         [0003]    2. Background Art 
         [0004]    Wellbore drilling through subsurface Earth formations is performed, for among other purposes, to provide a hydraulic path from subsurface reservoirs to the Earth&#39;s surface. During the drilling of such wellbores various instruments are inserted into the wellbore, either during drilling or shortly thereafter, that make measurements of various petrophysical properties of the subsurface formations. Such measurements may include, for example, electrical conductivity, acoustic compressional velocity and shear velocity, neutron slowing down length and related parameters, natural gamma radiation, density, and longitudinal and transverse nuclear magnetic resonance relaxation properties. 
         [0005]    The foregoing measurements may be used to estimate the amount of hydrocarbons in place in various subsurface reservoirs, and to estimate the amount of and rate at which hydrocarbons may be produced from such reservoirs. It is known in the art to take samples of subsurface formations for the purpose of making more direct measurements of certain physical properties of the formations, for example, porosity, permeability, and capillary pressure behavior. Such properties are related to the structure of the void spaces of the various formations and are not readily susceptible to determination by the indirect measurements described above without actual formation samples to establish relationships between the foregoing properties and the previously described petrophysical measurements. 
         [0006]    One technique for obtaining samples of the subsurface formations is called “coring.” Coring is typically performed using a specialized drill bit, that has an annular drilling surface rather than one that occupies the full cross section of the forward or cutting face of the bit. The annular bit leaves a centrally disposed cylinder of rock formation as it drills the wellbore. In a coring system, the cylinder of rock formation is moved, as drilling progresses, into a non-rotating barrel or sleeve inside a drill string used to rotate the drill bit. Once the barrel is full of core sample, it is typically retrieved from the wellbore. Various core barrels have been devised that may be retrieved without removing the entire wellbore drilling assembly or “string” from the wellbore. Such retrievable barrels can substantially reduce the time needed to obtain core samples, because replacement of the core barrel with an empty one may be performed, for example, by lowering and retrieving an electrical cable or slickline inside the drill string to retrieve the full core barrel and replace it with an empty one so that coring can continue. One such cording system is described, for example, in U.S. Pat. No. 7,124,841 issued to Wada, et al. 
         [0007]    As mentioned above, it is known in the art to make petrophysical measurements during the drilling of a wellbore. Instruments used for this purpose are known in the art as “logging while drilling (LWD) instruments. It is known in the art to perform coring concurrently with making LWD measurements. A system and method for performing such functions are described, for example, in U.S. Pat. No. 7,168,508 issued to Goldberg, et al. An advantage purportedly offered by the device shown in the Goldberg, et al., patent is to assure that the depth of rock formation samples obtained by coring is accurately correlated to the depth at which the various LWD measurements are made. It is also possible using such system to select core depths, and to avoid changing drill strings to include core bits where an ordinary “full cross section” bit had been used during LWD operations when the desired core depth is reached. 
         [0008]    It is also known in the art to make measurements on the core samples themselves during the drilling thereof. U.S. Pat. No. 5,984,023 issued to Sharma, et al., describes a core drilling system in which the core sample is moved past one or more sensors in order to make petrophysical measurements of the core sample while it is being drilling. The measurements made by the sensor(s) may be stored in a data storage device in the instrument while it is in the wellbore, and/or some of the measurements may be transmitted to the Earth&#39;s surface using a form of telemetry in which pressure of drilling fluid (“drilling mud”) in the wellbore is modulated, such telemetry being known in the art as “mud pulse telemetry.” Making measurements of petrophysical properties on core samples shortly after they have been drilled and while still at wellbore environmental conditions may provide the advantages of more precise measurements relating to the pore structure and native fluid content of the subsurface formations. 
         [0009]    In all of the foregoing coring methods, it is necessary to remove the core barrel after it is filled with core sample. However the core barrel is removed and replaced, e.g., whether by wireline or by removing the drill string from the wellbore, it is necessary to interrupt the drilling process to retrieve and/or replace the core barrel. Such interruption can be time consuming and therefore costly, and particularly in the case of wireline core barrel retrieval, can risk having the drill string become stuck in the wellbore. 
         [0010]    There exists a need for a formation sampling and formation sample analysis method and device that does not require interruption of drilling. 
       SUMMARY OF THE INVENTION 
       [0011]    A wellbore formation sample acquisition and analysis instrument according to one aspect of the invention includes an annular drill bit configured to couple to one end of a drill string. The bit defines a passageway extending from a cutting face thereof to an exterior surface at a longitudinally spaced apart position from the cutting face. The instrument includes at least one sensor configured to measure a selected parameter of a sample of subsurface formation urged into the passageway by action of the cutting face against subsurface formations. Samples of the subsurface formations are ejected from the exterior surface end of the passageway by the samples entering the cutting face end thereof. 
         [0012]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  shows an example drilling system with which the invention may be used. 
           [0014]      FIG. 2  shows an example sample taking and analysis unit. 
           [0015]      FIG. 2A  shows another example sample taking analysis unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    An example wellbore drilling system is shown in  FIG. 1  and includes an example of a formation sample acquisition and analysis device according to the invention. A drilling rig  24  or similar lifting device suspends a conduit called a “drill string  20 ” within a wellbore  18  being drilled through subsurface Earth formations  11 . The drill string  20  may be assembled by threadedly coupling together end to end a number of segments (“joints”)  22  of drill pipe. The drill string  20  may include a formation sample-taking drill bit  12  at its lower end. Particular features of the drill bit  12  will be further explained with reference to  FIG. 2 . When the drill bit  12  is axially urged into the formations  11  at the bottom of the wellbore  18  by the applying some of the weight of the drill string  20 , and when it is rotated by equipment (e.g., top drive  26 ) on the drilling rig  24 , such urging and rotation causes the bit  12  to axially extend (“deepen”) the wellbore  18  by drilling the formations  11 . As will be explained with reference to  FIG. 2 , such drilling may enable acquiring a sample of the formations  11  as a result of such drilling. The lower end of the drill string  20  may include, at a selected position above and proximate to the drill bit  12 , a sample analysis unit  10 . The sample analysis unit  10  may include one or more sensors ( FIG. 2 ) for measuring selected properties of a formation sample ( FIG. 2 ) passed therethrough by the action of the drill bit  12 . The one or more sensors ( FIG. 2 ) in the sample analysis unit  10  may be coupled to a telemetry transmitter or transceiver ( FIG. 2 ) to communicate the measurements to the Earth&#39;s surface along an electrical and/or optical conductor (not shown) in the drill string  20 . Proximate its lower end, the drill string  20  may also include an MWD instrument  14  and an LWD instrument  16  of types well known in the art. 
         [0017]    During drilling of the wellbore  18 , a pump  32  lifts drilling fluid (“mud”)  30  from a tank  28  or pit and discharges the mud  30  under pressure through a standpipe  34  and flexible conduit  35  or hose, through the top drive  26  and into an interior passage (not shown separately in  FIG. 1 ) inside the drill string  20 . The mud  30  exits the drill string  20  through courses or nozzles ( FIG. 2 ) in the drill bit  12 , where it then cools and lubricates the drill bit  12  and lifts drill cuttings generated by the drill bit  12  to the Earth&#39;s surface. Some examples of MWD instrument  14  or LWD instrument  16  may include a telemetry transmitter (not shown separately) that modulates the flow of the mud  30  through the drill string  20 . Such modulation may cause pressure variations in the mud  30  that may be detected at the Earth&#39;s surface by a pressure transducer  36  coupled at a selected position between the outlet of the pump  32  and the top drive  26 . Signals from the transducer  36 , which may be electrical and/or optical signals, for example, may be conducted to a recording unit  38  for decoding and interpretation using techniques well known in the art. The decoded signals typically correspond to measurements made by one or more of the sensors (not shown) in the MWD instrument  14  and/or the LWD  16  instrument, and may, in some examples, include measurements made by the analysis unit  10 . In the present example, such mud pressure modulation telemetry may be used in conjunction with, or as backup for an electromagnetic telemetry system including wired drill pipe. 
         [0018]    An electromagnetic transmitter (not shown separately) may be included in the either or both the sample analysis unit  10  and LWD instrument  16 , and may generate signals that are communicated along electrical conductors in the wired drill pipe. One type of “wired” drill pipe, as mentioned above in the Background section herein, is described in U.S. Patent Application Publication No. 2006/0225926 filed by Madhavan, et al., and assigned to the assignee of the present invention. A wireless transceiver sub  37 A may be disposed in the uppermost part of the drill string  20 , typically directly coupled to the top drive  26 . The wireless transceiver  37 A may include communication devices to wirelessly transmit data between the drill string  20  and the recording unit  38 , using a second wireless transceiver  37 B associated with the recording unit. In another example, a drilling rig may include a wired surface communications device between wired drill pipe and the recording unit  38 . 
         [0019]    It will be appreciated by those skilled in the art that the top drive  26  may be substituted in other examples by a swivel, kelly, kelly bushing and rotary table (none shown in  FIG. 1 ) for rotating the drill string  20  while providing a pressure sealed passage through the drill string  20  for the mud  30 . Accordingly, the invention is not limited in scope to use with top drive drilling systems, but may be used with any type of rotary drilling system 
         [0020]    An example drill bit and sample analysis unit combination is shown in cut away view in  FIG. 2 . The drill bit  12  may be a fixed cutter bit, in which cutting elements  12 B each of which includes a polycrystalline carbide compact (PDC) cutter bonded to a cutting structure to form the cutting element  12 B. Each cutting element  12 B may then be affixed to a bit body  12 A. The bit body  12 A may be made from matrix material including tungsten carbide and a binder alloy according to materials and processes well known in the art, or can be made from steel or other high strength metal. The bit body  12 A includes a sample receiving passageway  12 D located substantially coaxially with the center line or rotational center (not shown) of the bit  12 . As explained with reference to  FIG. 1 , as the bit  12  cuts through the formations ( 11  in  FIG. 1 ), a cylindrical “plug” or sample of the formation remains undrilled and is urged into the passageway  12 D by the action of the bit  1  against the lowermost face of the formations ( 11  in  FIG. 1 ). The bit body  12 A may include courses  12 F for movement of the drilling mud ( 30  in  FIG. 1 ) therethrough outward into the wellbore through jets or nozzles  12 C as is well known in the art. 
         [0021]    The sample analysis unit  10  may in some examples, such as shown in  FIG. 2 , be disposed in a separate housing  10 A that threadedly couples at a lower end  10 D thereof to mating thread  12 E in the bit body  12 A. The housing  10 A may include a corresponding threaded coupling  10 C at the other longitudinal end for connection to the drill string ( 20  in  FIG. 1 ). In the present example, the sample analysis unit  10  can be configured to operate with wired drill pipe of the kind explained above with reference to  FIG. 1 , and can include a communication device  42  such as a toroidal transformer disposed in a groove  10 E in a thread shoulder on the upper threaded coupling  10 C. An example of such communication device, as stated above, is described in U.S. Patent Application Publication No. 2006/0225926 filed by Madhavan, et al., and assigned to the assignee of the present invention. In another example, the sample analysis unit  10  may be formed integral with the drill bit  12 , instead of using a separate sub, as shown in  FIG. 2A . 
         [0022]    The passageway  12 D in the bit  12  is coupled at the end opposite the cutting face of the bit to one end of a corresponding passageway  10 F in the housing  10 A. In the present example, the passageway  10 F is disposed at the bit end substantially coaxial with the passageway  12 D in the bit body  12 A to form a continuous passageway for receiving samples of the formations as the wellbore is drilled. The passageway  10 F in the housing  10 A may gradually turn and form an exit  40  at its other end on the side of the housing  10 A. When disposed in a wellbore, the exit  40  will be in the annular space between the drill string and the wall of the wellbore. Thus configured, as formation samples are urged into the passageway  12 D in the bit body  12 A and then into passageway in the housing  10 A, the samples ultimately are discharged at the exit  40 . The samples discharged from the exit  40  are moved into the annular space in the wellbore between the exterior of the drill string ( 20  in  FIG. 1 ) and the wall of the wellbore ( 18  in  FIG. 1 ) where they may, through action of the drilling mud and motion of the drill string, be crushed, and the crushed particles lifted to the surface by the action of the drilling mud. 
         [0023]    In the present example, the passageway  10 F in the housing  10 A may gradually expand in internal diameter from the bit end to the exit  40 , to reduce the possibility that samples of the formation could become stuck in the orifice. Such sticking would reduce the effectiveness of the drill bit  12  in extracting samples of the formation for analysis. 
         [0024]    Analysis of the samples may be performed in the sample analysis unit  10  by one or more sensors  48 ,  44 ,  46  disposed inside the housing  10 A proximate the orifice  10 F. Such sensor(s) are configured to measure one or more selected properties of the rock samples disposed proximate the sensor(s). Examples of suitable types of sensors are described in U.S. Pat. No. 5,984,023 issued to Sharma, et al., and incorporated herein by reference. Measurements made by the various sensors  44 ,  46 ,  48  may be transferred to a telemetry transceiver  50 . The signals may then be transferred to the communication device  42  for transmission to the Earth&#39;s surface as explained with reference to  FIG. 1 . Alternatively, or in addition thereto, the signals may be transferred to a device (not shown in  FIG. 2 ) for communication to the Earth&#39;s surface using mud pressure modulation telemetry of any type known in the art. 
         [0025]    Non-limiting examples of the types of sensors that may be used include: electrical resistivity sensors, both of the galvanic and electromagnetic induction type; acoustic velocity sensors, both compressional and shear; capacitance sensors; density sensors; neutron porosity and/or capture cross-section sensors; natural gamma radiation and/or neutron activation gamma radiation sensors; nuclear magnetic relaxometry and/or spectroscopy sensors; pressure sensors; and sensors for determining the quality of the core sample. In other examples, the sensors may include various types of imaging devices, including optical, acoustic electrical and/or x-ray tomographic devices. In examples wherein the telemetry transceiver  50  transmits signals over wired drill pipe, it may be possible to analyze images from one or more of the foregoing types of sensors as the formation sample is being created by the bit  12  essentially in real time during the drilling of the wellbore. Such analysis may assist the wellbore operator in deciding future activities with respect to drilling and/or completing the wellbore. 
         [0026]    It will be readily appreciated by those skilled in the art that during drilling of the wellbore ( 18  in  FIG. 1 ), the shape of the wellbore and the resulting actual rotational motion of the drill bit ( 12  in  FIG. 1 ) will depend to some extent on the type of formation being drilled. For certain types of formations not usually associated with hydrocarbon bearing reservoirs, e.g., “shale”, it may be unnecessary or undesirable to extract samples through the drill bit, but rather to drill such formations as rapidly as possible. In such circumstances, the drill string ( 20  in  FIG. 1 ) may be operated using parameters that result in erratic (other than uniaxial) rotation. Such rotation may in fact preclude efficient creation of rock samples and their movement through the orifice ( 10 F in  FIG. 1 ). In one example of a method according to the invention, when the sensors on the MWD instrument ( 16  in  FIG. 1 ) are indicative of a subsurface formation in which samples are highly desired, the drilling rig operator may adjust the operating parameters (axial force on the bit and rotation rate) so as to stabilize the rotation along the bit axis and increase the probability of obtaining well defined formation samples. 
         [0027]    A possible advantage of using a separate housing and bit body as shown in  FIG. 2  for a sample taking and analysis device is that the bit may be readily replaced when it becomes worn, without the need to remove the active components for making measurements of the sample that are disposed in the housing  10 A. It should be clearly understood that it is also possible to include all the components shown disposed in the housing  10 A in a unitary bit body having suitable spaces therein for the illustrated components. Thus, for purposes of defining the scope of the invention, the passageway may be considered as extending through a single housing or bit body, or through a combination bit body and separate housing as shown herein. 
         [0028]    A wellbore formation sample acquisition and analysis device as explained herein may improve the quality of evaluation of subsurface reservoirs, while reducing the time needed to analyze physical samples of formation. 
         [0029]    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.