Coring tools and related methods

An example coring tool includes a cylindrical body having a leading edge to contact a substance and a cavity defined at least in part by an inner surface of the cylindrical body. The inner surface is to engage and retain a sample from the substance with a plurality of raised features. The raised features are shaped so that at least one of the raised features or an exterior surface of a sample in the cavity deforms to increase a force required to remove the sample from the cavity.

BACKGROUND OF THE DISCLOSURE

Wellbores or boreholes may be drilled to, for example, locate and produce hydrocarbons. During a well development operation, it may be desirable to evaluate and/or measure properties of encountered formations, formation fluids and/or formation gasses. Some formation evaluations may include extracting a core sample (e.g., a rock sample) from sidewall of a wellbore. Core samples may be extracted using a coring tool coupled to a downhole tool that is lowered into the wellbore and positioned adjacent a formation. A hollow coring shaft or bit of the coring tool may be extended from the downhole tool and urged against the formation to penetrate the formation. A formation or core sample fills the hollow portion or cavity of the coring shaft and the coring shaft is removed from the formation retaining the sample within the cavity. The formation or core sample may then be removed from the coring shaft for further evaluation at, for example, a laboratory.

DETAILED DESCRIPTION

The example apparatus and methods described herein relate to coring tools and coring bits or shafts that may be used to collect samples (e.g., rock samples, tar sand samples, etc.) from subterranean formations adjacent a borehole or a wellbore. The example coring shafts described herein may be used in conjunction with sidewall coring apparatus and methods. The example coring shafts generally include a cylindrical body having a leading edge to contact and penetrate a subterranean formation to be sampled. The cylindrical body has a cavity defined at least in part by an inner surface of the cylindrical body. Additionally, the inner surface of the cylindrical body may include a plurality of raised features to engage and retain a sample from the formation. The raised features may be shaped so that the raised features deform and/or an exterior surface of the sample in the cavity deforms, thereby increasing an amount of force required to remove the sample from the cavity. In this manner, the raised features of the inner surface of the example coring shafts may become at least partially embedded in a sample captured within the cavity. As a result, the example coring shafts or bits described herein may provide a substantially greater amount of sample retention force compared to many known coring bits or shafts.

The example coring shafts described herein may use one or more types of raised features and/or surface treatments. For example, knurls or a knurled surface, a helical ridge, a spiraled ridge, threads, serrations and/or axial ridges may be used. Such raised features are shaped to provide portions or areas of relatively greater stress or force concentration against a formation or core sample and, thus, may be capable of causing the above-mentioned deformation(s). Additionally, different leading edge configurations may be used to implement the example coring shafts including, for example, bevels, lips, wedges and/or a diamond cutter to suit a particular application or applications.

In another aspect, the example coring shafts described herein may employ a circumferential groove or grooves on an exterior surface of the cylindrical body of the coring shaft to provide a relatively weakened portion or area on the coring shaft. In particular, the groove or grooves may result in at least a portion of a wall of the coring shaft having a reduced thickness sufficient to cause the cylindrical body to fracture and shear off in response to a predetermined load, torque, or force, thereby facilitating withdrawal of a coring tool from a sidewall of a borehole despite the coring shaft becoming stuck in the sidewall.

The example methods described herein may involve selecting a coring shaft type for use in sampling a formation based on a property of the formation. For example, in the case where the formation property relates to formation strength or formation lithology (e.g., tar sand), such a property or properties may be used to select a coring shaft having a relatively larger diameter or a relatively smaller diameter. The property of the formation may also result in selection of a coring shaft having a particular leading edge configuration such as, for example, a wedge or a diamond cutter configuration. The example methods may be employed with the example coring shaft or bits described herein or any other coring shafts or bits.

In another aspect, the example methods described herein may involve selecting an operational mode(s) for a coring tool based on a property or properties of a formation to be sampled. More specifically, the lithology of a formation may be used to select a punching or drilling operational mode for the coring tool and/or selecting whether each coring shaft of the coring tool is to collect one or multiple formation samples. Thus, the example methods noted above and described in more detail below can be used to enhance or optimize a coring operation through the selection of a particular coring shaft or bit configuration and/or a manner in which the coring tool is to be operated for use with a formation having particular properties.

FIG. 1Adepicts a coring tool10with which the example methods and coring shaft or bit apparatus described herein can be used. As shown, the coring tool10may be used in a drilled well to obtain core samples from a downhole or subterranean geologic formation. In operation, the coring tool10is lowered into a borehole11defined by a bore wall12, commonly referred to as the sidewall. The coring tool10is connected by one or more electrically conducting cables16to a surface unit17that includes a control panel18and a monitor19. The surface unit17is designed to provide electrical power to the coring tool10, to monitor the status of downhole coring and activities of other downhole equipment, and to control the activities of the coring tool10and other downhole equipment.

The coring tool10is generally contained within an elongate housing suitable for being lowered into and retrieved from the borehole12. The coring tool10may include an electronic sonde51, a mechanical sonde53, and a core magazine55. The mechanical sonde53contains a coring assembly including at least one motor44powered through the cables16, a coring bit or shaft24having a distal, open end26for cutting and receiving a core sample from a formation46, and a mechanical linkage (not shown) for deploying and retracting the coring shaft24relative to the coring tool10and for rotating the coring shaft24against the sidewall12.

FIG. 1Ashows the coring tool10in an active, cutting configuration. The coring tool10is positioned adjacent the formation46and urged firmly against the sidewall12by anchoring shoes28and30, which are extended from a side of the coring tool10opposing the coring shaft24. The distal, open end26of the coring shaft24may be rotated via the motor44against the formation46to cut a core sample from the formation46.

FIG. 1Bshows the general features of another type of coring tool1121with which the example methods and apparatus described herein can be used. This coring tool1121includes a plurality of coring shafts1123,1124,1125,1126, each of which may be used to collect and store a single formation sample.

WhileFIGS. 1A and 1Bshow coring tools deployed at the end of a wireline cable, a coring tool may be deployed in a well using any known or future-developed conveyance means, including drill pipe, coiled tubing, etc.

FIG. 2is a schematic view of an example mechanical sonde, such as the mechanical sonde53ofFIG. 1A. As shown inFIG. 2, the mechanical sonde53includes a coring assembly having the coring bit or shaft24and a housing42. To cut a core sample from the formation46with the coring shaft24, the mechanical sonde53uses a thrusting actuator to urge (e.g., punch, press, drive, etc.) the coring shaft24into the formation46and applies a weight-on-bit (WOB), which is a force that urges the coring shaft24into the formation46. The mechanical sonde53may include a rotating actuator to apply a torque to rotate the coring shaft24, thereby drilling the coring shaft24into the formation46.

For example, the WOB provided by the mechanical sonde53and applied to the coring shaft24may generated by an electric motor62and a control assembly61that includes a hydraulic pump63, a feedback flow control (“FFC”) valve64, and a kinematics piston65. The electric motor62supplies power to the hydraulic pump63. The flow of hydraulic fluid from the hydraulic pump63is regulated by the FFC valve64, and the pressure of hydraulic fluid drives the kinematics piston65to apply a WOB to the coring shaft24. The FFC valve64may regulate the flow of hydraulic fluid to the kinematics piston65based on the hydraulic pressure applied to a hydraulic coring motor44. Also, for example, to rotate the coring shaft24, torque may be provided by an electric motor66and a gear pump67. The electric motor66drives the gear pump67, which supplies flow of hydraulic fluid to the hydraulic coring motor44. The hydraulic coring motor44, in turn, imparts a torque to the coring shaft24that causes the coring shaft24to rotate.

FIG. 3shows a perspective view of an example coring apparatus, such as the apparatus including the coring shaft24, the housing42and the hydraulic motor44ofFIG. 1A and 2, when the coring apparatus is cutting or has cut into the formation46. A core sample48may be received into a hollow interior or cavity of the coring shaft24as cutting progresses.

FIGS. 4A and 4Bdepict a partial side view and an end view of a known coring shaft or bit. More specifically, the coring bit ofFIGS. 4A and 4Bis a surface set diamond bit. A more detailed description of such a coring bit can be found in U.S. Pat. No. 4,189,015, the disclosure of which is hereby incorporated by reference herein in its entirety. The known coring shaft or bit shown inFIGS. 4A and 4Btypically provides an internal cavity diameter of between about 1 and 1.5 inches, which may be substantially smaller than the examples described below in connection withFIGS. 5-7.

FIGS. 5A and 5Bshow a sectional view and an end view of an example coring bit or shaft500according to aspects of this disclosure. The example coring shaft500has a generally cylindrical body502having a leading edge504to contact and penetrate a formation (e.g., the formation46). The cylindrical body502includes a cavity506that is defined at least partially by an inner surface508of the cylindrical body502. The inner surface508is to engage and facilitate the retention of a core sample cut from a formation. For example, a substantial portion of the inner surface508may have a surface treatment such as a plurality of raised features510.

Turning briefly toFIGS. 8A,8B and8C, various types of surface treatments or example implementations of the raised features510are shown.FIG. 8Adepicts a knurled surface or knurls800,FIG. 8Bdepicts a spiraled ridge, a helical ridge or threads802, andFIG. 8Cdepicts axial ridges or serrations804. The axial ridges or serrations ofFIG. 8Cmay have an asymmetrical profile. In the case of the example ofFIG. 8B, the threads may have a pitch of twelve threads per inch and have a v-groove profile about 0.1 inch deep. The threads may span about 1.4 inches and may be left or right-handed. However, other pitches, dimensions and spans may be used without departing from the scope of the present disclosure.

Returning toFIG. 5A, the raised features510are shaped to increase a stress concentration or force at the points of contact between the raised features510and a sample within the cavity506. Such increased stress and/or force may deform an exterior surface of the sample and/or may deform the raised features, depending on the relative hardness of the sample and the material from which the raised features510are formed. In any event, such deformation may result in the raised features becoming at least partially embedded within the sample or at least creating a increased amount of mechanical interference contact between the sample and the inner surface508, thereby substantially increasing the force applied to remove the sample from the cavity506.

The leading edge504of the coring shaft500may be urged into a formation via a thrusting, punching or pressing operation using, for example, WOB provided by the electric motor62, the control assembly61, the hydraulic pump63, the FFC valve64, and the kinematics piston65as discussed above in connection withFIG. 2. In that case, the leading edge504may include a bevel, a lip or a wedge-shaped profile. In the example ofFIG. 5A, the leading edge has a taper angle512, which may, for example, be about ten degrees. However, the taper angle512may be selected to suit a particular application. The leading edge504may also be rotated or drilled into a formation. For example, the leading edge504may include a diamond cutter bit similar to that shown inFIGS. 4A and 4B.

The inner surface508, including the innermost surfaces or edges of any surface treatment thereon, may be tapered over at least a portion514. This taper may be about two degrees or any other taper angle to enable removal of the sample from the cavity506.

In contrast to many known coring shafts, the example coring shaft500may provide a relatively large formation sample. For example, the cavity506may have a diameter of approximately two inches and a length of approximately two inches. However, other diameters and lengths can be used without departing from the scope of this disclosure.

The cylindrical body502has a wall having reduced thickness portion516to cause the cylindrical body502to fracture or shear (at the portion516) in response to a predetermined load (e.g., torque, force, etc.). The portion516may be formed as a continuous circumferential groove as depicted inFIG. 5Aor may be an interrupted (i.e., discontinuous) groove, a plurality of holes or thinned sections, or any other configuration that serves to provide a relatively weaker portion of the cylindrical body502. In this manner, in the event that the cylindrical body502of the coring shaft500becomes stuck in a sidewall, the coring tool carrying the coring shaft500(e.g., the coring tool10ofFIG. 1A) can impart a sufficient load to shear off the cylindrical body502at the reduced thickness portion516, thereby enabling removal of the coring tool.

The example coring shaft500also includes an end518that enables the coring shaft500to be removably coupled to a thrusting actuator (see one example inFIG. 2) and optionally a rotating actuator (see one example inFIG. 2).

FIGS. 6 and 7are sectional views of alternative example coring shafts600and700that may be used with a coring tool such as the coring tool10ofFIG. 1A. The example coring shaft600ofFIG. 6has a leading edge configuration having a lip602and the example coring shaft700ofFIG. 7has a catcher ring type leading edge702. The lip602and the leading edge702shown inFIGS. 6 and 7, respectively, may be used to provide a space or gap between an outer surface of a drill shaft and the inner surface of a wellbore. Such a gap or space may be used to enable a drill motor to rotate about an axis perpendicular to the longitudinal axis of the wellbore (e.g., cock) at its end of travel to snap off the core.

The example coring shafts described herein may be used in conjunction with the example method900ofFIG. 9. Initially, a formation evaluation tool (e.g., the coring tool10or a downhole tool coupled to the coring tool10) is positioned in a borehole adjacent a subterranean formation (e.g., the formation46) (block902). One or more properties of the formation are then determined (block904). For example, a strength of the formation, a lithology of the formation (e.g., tar sand), and/or other properties may be determined at block904. A coring shaft type is then selected based on the one or more properties determined at block904(block906). For example, the example coring shafts ofFIGS. 5-7may be used to obtain samples from formations having an unconsolidated compressive strength that is less than 500 pounds per square inch and/or tar sand formations. The coring shaft selected at block906may also be selected based on whether the formation property (or properties) is defined within a value set. Such a value set may include particular target properties and/or formations that have been identified as being of particular interest for development.

Once the coring shaft type has been selected at block906, a coring shaft having the selected type is coupled to a coring tool (block908). The coring shaft coupled to the coring tool may be selected from a plurality of coring shafts stored in the coring tool or a portion of a downhole tool carrying the coring tool. The coring shafts may have different diameters and/or leading edges for use with different types of formations. For example, any or all of the coring shafts described here may be used. In cases where multiple coring shafts are kept at the surface, the formation evaluation tool may be withdrawn from the borehole and an appropriate one of the coring shafts (e.g., selected based on the property) may be attached to the coring tool, The coring tool may then be lowered into the borehole. Once the selected coring shaft has been coupled to the coring tool at block908, the coring tool may then obtain a sample (for transport back to the Earth's surface) from the formation using the selected coring shaft (block910).

The example coring shafts described herein may also be used in conjunction with the example method1000ofFIG. 1000. Initially, a formation evaluation tool (e.g., the coring tool10or a downhole tool coupled to the coring tool10) is positioned in a borehole adjacent a subterranean formation (e.g., the formation46) (block1002). One or more properties of the formation are then determined (block1004). A coring operational mode is then selected based on the one or more properties determined at block1004(block1006). For example, a punching or thrusting operational mode (i.e., where the coring shaft is pushed into the formation) may be selected where the one or more properties indicate a relatively soft formation. Any one of the example coring shafts ofFIGS. 5-7may, for example, be used in conjunction with a punching or thrusting operational mode. On the other hand, a drilling mode may be selected at block1006where the one or more properties indicate a relatively hard formation. In that case, the diamond cutter shaft/bit ofFIGS. 4A and 4Bmay be used. Still further, the operational mode selected at block1006may involve determining that one formation sample is to be collected with each or a particular coring shaft or, alternatively, determining that multiple samples are to be collected with each or a particular coring shaft. Once the operational mode has been selected at block1006, the coring tool may then obtain a sample (for transport back to the Earth's surface) from the formation using the selected operational mode (block1008).

While in the methods900and1000, the coring shafts are used to obtain samples from a subterranean formation adjacent a borehole, the example coring shafts described herein may also be used to acquire other types of samples, such as soil samples, ice samples, or samples of materials used in masonry.

The example ofFIG. 11shows a portion of a sectional view of a coring tool. An outer hollow coring shaft460is to extend through a wall of a wellbore penetrating a subterranean formation. A rotationally uncoupled internal sleeve464is disposed inside the outer hollow coring shaft460. U.S. Pat. No. 7,431,107, the entire disclosure of which is hereby incorporated by reference herein, describes a manner in which a sleeve may be rotationally uncoupled within a coring tool. An inner surface of the internal sleeve464includes any of the surface treatments or raised features described herein (e.g.,FIGS. 8A-8C).

The embodiment ofFIG. 12shows a portion of a sectional view of a coring tool. The coring tool comprises a plurality of core holders to retain samples from a subterranean formation penetrated by a borehole, for example as described in U.S. Patent Application Pub. No. 2009/0114447, the entire disclosure of which is hereby incorporated by reference herein. As shown, a hollow coring shaft300is to receive one of the plurality of core holders, such as core holder308. An inner surface of the core holder308includes any of the raised features described herein (e.g.,FIGS. 8A-8C).

In view of the foregoing description and the figures, it should be clear that the present disclosure introduces coring apparatus and methods to use the same. According to certain aspects of this disclosure, an example apparatus includes a coring tool to obtain a sample. The coring tool includes a cylindrical body having a leading edge to and a cavity defined at least in part by an inner surface of the cylindrical body. The inner surface is to engage and retain a sample with a plurality of raised features, and the raised features are shaped so that at least one of the raised features or an exterior surface of a sample in the cavity deforms to increase a force required to remove the sample from the cavity.

According to other aspects of this disclosure, a method involves disposing a coring tool in a borehole adjacent a subterranean formation to be sampled, determining a property of the formation, selecting a coring shaft type based on the property, coupling a coring shaft having the selected type to the coring tool, and obtaining a sample from the formation using the coupled coring shaft.

According to other aspects of this disclosure, a method involves disposing a coring tool in a borehole adjacent a subterranean formation to be sampled, determining a property of the formation, selecting a coring tool operational mode based on the property, and obtaining a sample from the formation using the coring tool operational mode