US20050133267A1 - [coring tool with retention device] - Google Patents

Abstract

In some embodiments, the invention relates to a sidewall coring tool that includes a tool body, a hollow coring shaft extendable from the tool body, and a formation cutter disposed at a distal end of the hollow coring shaft. The coring tool includes a retention member segmented into a plurality of petals and disposed proximate a distal end of the internal shaft. An internal sleeve may be disposed inside the hollow coring shaft.

Description

BACKGROUND OF INVENTION
• Wells are generally drilled into the ground to recover natural deposits of oil and gas, as well as other desirable materials, that are trapped in geological formations in the Earth's crust. A well is drilled into the ground and directed to the targeted geological location from a drilling rig at the Earth's surface.
• Once a formation of interest is reached, drillers often investigate the formation and its contents by taking samples of the formation rock and analyzing the rock samples. Typically, a sample is cored from the formation using a hollow coring bit, and the sample obtained using this method is generally referred to as a “core sample.” Once the core sample has been transported to the surface, it may be analyzed to assess, among other things, the reservoir storage capacity (porosity) and the flow potential (permeability) of the material that makes up the formation; the chemical and mineral composition of the fluids and mineral deposits contained in the pores of the formation; and the irreducible water content of the formation material. The information obtained from analysis of a sample is used to design and implement well completion and production facilities.
• “Conventional coring,” or axial coring, involves taking a core sample from the bottom of the well. Typically, this is done after the drill string has been removed, or “tripped,” from the wellbore, and a rotary coring bit with a hollow interior for receiving the core sample is lowered into the well on the end of a drill string. Some drill bits include a coring bit near the center of the drill bit, and a core sample may be taken without having to trip the drill string. A core sample obtained in conventional coring is taken along the path of the wellbore; that is, the core is taken along the axis of the borehole from the rock below the drill bit.
• A typical axial core is 4-6 inches (˜10-15 cm) in diameter and can be over 100 feet (˜30 m) long. The rotary motion is typically generated at the surface, and the coring bit is driven into the formation by the weight of the drill string that extends back to the surface. The core sample is broken away from the formation by simply pulling upward on the coring bit that contains the sample.
• By contrast, in “sidewall coring,” a core sample is taken from the side wall of a drilled borehole. Sidewall coring is typically performed after the drill string has been removed from the borehole. A wireline coring tool that includes a coring bit is lowered into the borehole, and a small core sample is taken from the sidewall of the borehole.
• In sidewall coring, the drill string cannot be used to rotate the coring bit, nor can it provide the weight required to drive the bit into the formation. Instead, the coring tool must generate both the rotary motion of the coring bit and the axial force necessary to drive the coring bit into the formation.
• In sidewall coring, the available space is limited by the diameter of the borehole. There must be enough space to withdraw and store a sample. Because of this, a typical sidewall core sample is about 1 inch (˜2.5 cm) in diameter and less than about 2 inches long (˜5 cm). The small size of the sample does not permit enough frictional forces between the coring bit and the core sample for the core sample to be removed by simply withdrawing the coring bit. Instead, the coring bit is typically tilted to cause the core sample to fracture and break away from the formation.
• An additional problem that may be encountered is that because of the short length of a side wall core sample, it may be difficult to retain the core sample in the coring bit. Thus, a coring bit may also include mechanisms to retain a core sample in the coring bit even after the sample has been fractured or broken from the formation.
• Sidewall coring is beneficial in wells where the exact depth of the target zone is not well known. Well logging tools, including coring tools, can be lowered into the borehole to evaluate the formations through which the borehole passes. Multiple core samples may be taken at different depths in the borehole so that information may be gained about formations at different depths.
• FIG. 1 shows an example of an existingsidewall coring tool101 that is suspended in aborehole113 by awireline107, as disclosed in U.S. Pat. No. 6,412,575, which is assigned to the assignee of the present invention. A sample may be taken using acoring bit103 that is extended from thecoring tool101 into theformation105. Thecoring tool101 may be braced in the borehole by one ormore support arms111. An example of a commercially available coring tool is further described in U.S. Pat. Nos. 4,714,119 and 5,667,025, both assigned to the assignee of the present invention.
• FIG. 2 shows a perspective view of an existingcoring device201 taking acore sample207 from aformation203. Acoring bit205 is connected to thecoring device201, which may include a motor to extend thebit205 and impart rotary motion to thecoring bit205. Thecoring bit205 extends into theformation203, and acore sample207 is captured in the interior of thecoring bit205. It is noted that thecoring device201 would typically be disposed in a coring tool (e.g.,101 inFIG. 1) for use downhole. Thecoring bit205 would extend from thedevice201 and tool (e.g.,101 inFIG. 1) and into theformation203.
• Rotary coring tools typically use a hollow cylindrical coring bit with a formation cutter at a distal end of the coring bit. The coring bit is rotated and forced against the wall of the bore hole. As the coring bit penetrates the formation, the hollow interior of the bit receives the core sample. A rotary coring bit is extended from the tool using a shaft of mechanical linkage. The shaft is typically connected to a motor that imparts rotary motion to the coring bit and forces the bit against the formation wall. Rotary coring tools are generally braced against the opposite wall of the bore hole by a support arm. The cutting edge of the rotary coring bit is usually embedded with tungsten carbide, diamonds, or other hard materials for cutting into the formation.
• FIG. 3 shows an example of a conventionalrotary coring bit301 that may be used with a sidewall coring tool, such as thecoring tool101 ofFIG. 1. A similar coring bit is disclosed in U.S. Pat. No. 6,371,221, which is assigned to the assignee of the present invention. Thecoring bit301 includes ashaft303 that has ahollow interior305. Aformation cutting element307 for drilling is located at one end of theshaft303. As thecoring bit301 penetrates a formation (not shown) and a sample core (not shown) may be received in thehollow interior305 of thebit301. After a sample is received in thehollow interior305, the core sample typically is broken from the formation by displacing or tilting the drill system. Thecoring bit301 is then removed from the formation, with the core sample retained in thehollow interior305 of thecoring bit301. Other known formation cutting elements for a rotary coring bit may be used. Examples of such formation cutting elements are described in copending U.S. patent application Ser. No. 09/832,606, assigned to the assignee of the present invention.
• While existing coring tools are useful, there is still a need for a coring tool that will more effectively ensure a good core sample can be retrieved for analysis.
SUMMARY OF INVENTION
• In one or more embodiments, the invention relates to a sidewall coring tool that includes a tool body, a hollow coring shaft extendable from the tool body, a formation cutter disposed at a distal end of the hollow coring shaft, and a retention member segmented into a plurality of petals and disposed in the hollow coring shaft. In some embodiments, the plurality of petals comprises three petals.
• In some embodiments, the invention relates to a method for taking a core sample that includes extending a coring bit into a formation, receiving the core sample in an internal sleeve having a retention member segmented into a plurality of petals proximate a distal end of the internal sleeve, and withdrawing the coring bit from the formation.
• In some other embodiments, the invention related to a sidewall coring tool that includes a tool body, a hollow coring shaft extendable from the tool body, a formation cutter disposed at a distal end of the hollow coring shaft, an internal sleeve disposed inside the hollow coring shaft, and at least one retention mechanism selected the group consisting of a piston and a check valve, wherein the piston is disposed in the internal sleeve and moveable with respect to the internal sleeve, and the check valve is disposed in the internal sleeve.
• In some embodiments, the intention relates to a method for taking a core sample that includes extending a coring bit into a formation, receiving the core sample in an internal sleeve having a piston disposed therein such that the piston is moveable with respect to the internal sleeve, and withdrawing the coring bit from the formation.
• In some embodiments, the invention relates to a sidewall coring tool that includes a tool body, a hollow coring shaft extendable from the tool body, a formation cutter disposed at a distal end of the hollow coring shaft, and an internal sleeve disposed inside the hollow coring shaft. The internal sleeve may include a bladder configured to apply radial pressure to a core sample when the bladder is selectively filled with a fluid.
• In some embodiments, the invention relates to a sidewall coring tool that includes a tool body, a hollow coring shaft extendable from the tool body, a formation cutter disposed at a distal end of the hollow coring shaft, and an elastic retention member disposed proximate a distal end of coring tool and having an aperture at its center.
• Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
• FIG. 1 is a cross-section of a wellbore with a prior art coring tool suspended in the wellbore.
• FIG. 2 is a perspective view of a prior art coring device.
• FIG. 3 is a perspective view of a prior art rotary coring bit.
• FIG. 4A is a cross section of a coring bit in accordance with one embodiment of the invention.
• FIG. 4B is a cross section of a coring bit in accordance with one embodiment of the invention.
• FIG. 4C is a cross section of a coring bit in accordance with one embodiment of the invention.
• FIG. 5A is a cross section of a coring bit with a retention device in accordance with one embodiment of the invention.
• FIG. 5B is a cross section of a coring bit with a retention device in accordance with one embodiment of the invention.
• FIG. 6A is a top view of a coring bit retention member in accordance with one embodiment of the invention.
• FIG. 6B is a top view of a coring bit retention member in accordance with one embodiment of the invention.
• FIG. 6C is a top view of a coring bit retention member in accordance with one embodiment of the invention.
• FIG. 6D is a top view of a coring bit retention member in accordance with one embodiment of the invention.
• FIG. 7A is a cross section of a coring bit retention member in accordance with one embodiment of the invention.
• FIG. 7B is a cross section of a coring bit retention member in accordance with one embodiment of the invention.
• FIG. 7C is a cross section of a coring bit retention member in accordance with one embodiment of the invention.
• FIG. 7D is a cross section of a coring bit retention member in accordance with one embodiment of the invention.
• FIG. 7E is a cross section of a coring bit retention member and internal sleeve in accordance with one embodiment of the invention.
• FIG. 8A is a cross section of a coring bit with a piston in accordance with one embodiment of the invention.
• FIG. 8B is a cross section of a coring bit with a piston in accordance with one embodiment of the invention.
• FIG. 9 is a cross section of a coring bit with a cushion in accordance with one embodiment of the invention.
• FIG. 10 is a cross section of a coring bit with a sample retention device in accordance with one embodiment of the invention.
DETAILED DESCRIPTION
• In some embodiments, the invention relates to a coring bit with a retention member that retains a core sample in a coring bit. In other embodiments, the invention includes a piston or cushion that enables a core sample to be received and retained in a coring tool. In other embodiments, the invention relates to methods for retaining a core sample in a coring tool. The invention will now be described with reference to the attached drawings.
• FIG. 4A is a cross section of acoring bit401 with aretention member411 in accordance with one embodiment of the invention.FIG. 4A shows only thecoring bit401, but those having skill in the art will understand that thecoring bit401 forms part of a coring tool (not shown) that is used to take core samples from a formation. By way of example, the coring bit may form part of a coring tool, such as thecoring tool101 inFIG. 1.
• Thecoring bit401 inFIG. 4A includes ahollow shaft403 with aformation cutter405 disposed at a distal end of theshaft403. Theformation cutter405, or formation cutter, is formed of a material for drilling into theformation402. Theformation cutter405 may be formed of a strong material that is coated with a super hard material, such as polycrystalline diamond or tungsten carbide. In other embodiments, theformation cutter405 may include other devices for cutting through soft formation, such as brushes. The term “distal end” is used to describe the end of thecoring bit401 that first contacts the formation. The distal end is the end of theshaft403 that is the farthest from the center of the coring tool (not shown) while a sample is being taken. It is the first part of thecoring bit401 to penetrate a formation.
• As shown inFIG. 4A, acoring bit401 may include aninternal sleeve407 that is disposed inside thehollow shaft403. Theinternal sleeve407 is for receiving a core sample (not shown inFIG. 4A) as it enters thecoring bit401. In some embodiments, theinternal sleeve407 is a “non-rotating” internal sleeve. A non-rotating internal sleeve is an internal sleeve that is free to rotate independent of thehollow shaft403. Thus, as the coring tool penetrates aformation402, friction between the internal sleeve and the core sample (e.g.,410 inFIGS. 4B and 4C) prevents the internal sleeve from rotating with respect to theformation402. In some other embodiments, a mechanical stop, such as a key (not shown) may prevent the rotation of the internal sleeve. This reduces the erosion of the core sample by eliminating friction between the core sample and the internal sleeve during the sampling process. Examples of coring sleeves are disclosed in copending U.S. patent application Ser. No. 10/248,475, assigned to the assignee of the present invention.
• Aretention member411 is disposed at the distal end of theinternal sleeve407. Theretention member411, as will be seen, enables a core sample to enter thecoring bit401 and theinternal sleeve407, and it also retains thecore sample410 in theinternal sleeve407 once thecore sample410 has been received in thecoring bit401.
• FIG. 4B shows a cross section of acoring bit401 in the process of receiving acore sample410. As theformation cutter405 penetrates theformation402, acore sample410 enters thecoring bit401. As thecore sample410 enters theinternal sleeve407, it pushes thepetals411a,411bof theretention member411 out of the way so that thecore sample410 may enter thecoring bit401. As thepetals411a,411bmove, they apply a radially inward force to thecore sample410 that serves to guide thecore sample410 and hold it in place.
• FIG. 4C shows a cross section of acoring bit401 that has received acore sample410 in theinternal sleeve407 disposed inside thehollow shaft403 of thecoring bit401. Thecore sample410 is retained in thecoring bit401 by thepetals411a,411bof the retention member (411 inFIG. 4A) in at least two ways. First, thepetals411a,411bpress inward on thecore sample410 to stabilize it and hold it in place. Second, when thecoring bit401 retracts from theformation402, thepetals411a,411bwill tend to close and grip thecore sample410. In hard rock, the additional friction between thecore sample410 and thepetals411a,411bwill act as a wedge gripper that retains thecore sample410 in thecoring bit401.
• In soft rock, thepetals411a,411bmay completely close and trap thecore sample410 in thecoring bit401. This may be advantageous because of the tendency of unconsolidated or soft formations to fall out of the coring bit. Instead of losing ¾ inch (˜1.9 cm) to 1 inch (˜2.5 cm) of the core sample of an unconsolidated formation, thepetals411a,411bmay close to retain thecore sample410 in thecoring bit401. Theonly core sample410 that is lost is that part of the core sample that extends past the petals511a,511b.In some embodiments, the petals are about ¼ inch (˜0.6 cm) in length, and about ¼ inch of the core sample is lost in the closing of the petals. This assists in capturing and retaining core samples of a soft formation that can simply fall out of the coring bit when the sample is taken using a conventional coring bit.
• Theretention member411 shown inFIGS. 4A, 4B, and4C is preferably made of rubber, although it can be made of any material that is flexible and still has a memory. A material with a memory will “remember” its original position such that it will tend to move back to its original position whenever it is displaced. In some embodiments, material remains in the elastic deformation regime even when completely displaced by the core sample. Thus, when the petals of a retention member are pushed radially outward by a core sample, the petals are flexible enough to give way so that the core sample can easily enter the coring bit, but they also tend to push radially inward toward their original position. This tendency to move back to the original position is what creates the radial pressure against the core sample that will guide it into the coring bit and retain it there while the coring bit is being withdrawn from the formation.
• In some embodiments, a retention member may not be attached at a distal end of an internal sleeve. For example,FIG. 5A shows acoring bit501 with aninternal sleeve507 disposed inside ahollow coring shaft503. Aformation cutter505 is disposed at the distal end of thehollow coring shaft503. Theretention member511 is located near the mid-point along the axial length of theinternal sleeve507. In this position, aretention member511 provides guidance so that a core sample (not shown) will be maintained near the axial center of theinternal sleeve507, while still offering the ability to retain the core sample in thecoring bit501 when the bit is withdrawn from the formation (not shown). For example, in a hard formation, theretention member511 may act as a wedge gripper that retains the core sample (not shown) in thecoring bit501.
• FIG. 5B shows another embodiment of a coring bit with aretention member521 in accordance with the invention. Thecoring bit521 includes ahollow coring shaft523 with aformation cutter525 at its distal end. Aretention member531 is held in the center opening of the formation cutter by aring533 in the formation cutter. In this position, theretention member531 may enable a core sample (not shown) to enter thecoring bit521, and it may also retain the core sample in thecoring bit521 once the sample is received.
• It is noted that a coring bit in accordance with the invention may have various combinations of the described features. For example, may include a retention member located as shown inFIG. 5A, but without an internal sleeve. In another example, a coring bit may include a ring (e.g.,ring533 inFIG. 5B) that is not disposed proximate the distal end of the coring bit. Those having ordinary skill in the art will be able to devise other embodiments of an coring bit that do not depart from the scope of the invention.
• FIG. 6A shows an end view of aretention member601 in accordance with one embodiment of the invention. Theretention member601 has threepetals602a,602b,602cthat are cut from the center of theretention member601 out to anouter petal circumference605. In some embodiments, thepetal circumference605 is substantially the same size as the inner diameter of the formation cutter (e.g.,505 inFIGS. 5A, 5B, and5C). This enables the core sample to fit snugly through the retention member. In other embodiments, thepetal circumference605 may be larger than the inner diameter of the formation cutter (e.g.,505 inFIGS. 5A, 5B, and5C).
• Thepetals602a,602b,602cshown inFIG. 6A are located adjacent to one another. That is, the edges of one petal,602afor example, are adjacent to edges on the other petals,602b,602c, for example.
• In some embodiments, aretention member601 includes cuts orperforations607. Thecuts607 provide additional flexibility for thepetals602a,602b,602cwhen theretention member601 is constructed of a stiff material or when there are only a small number of petals making each petal stiff.
• FIG. 6B shows an embodiment of aretention member621 withpetals622a,622b,622cthat are not adjacent to each other. In this embodiment, thepetals622a,622b,622care separated from each other going back to thepetal circumference625.
• FIG. 6C shows another embodiment of aretention member631 in accordance with the invention. Thepetals637,638,639 overlap with each other. For example,petal637 hasedge637athat overlapsedge639bofpetal639. Theother edge637bofpetal637 is overlapped byedge638aofpetal638. Similarly,petal639 hasedge639athat overlapsedge638bofpetal638.
• FIG. 6D shows another embodiment of a retention member641 in accordance with the invention. The retention member includes anaperture646 at its center. Theaperture646 is created because the retention member641 extended inwardly only to anaperture circumference647. A core sample (not shown) may push its way through theaperture646 by displacing the retention member641. The elasticity of the retention member641 will cause the retention member641 to exert an inward force on the core sample when it is received.
• FIG. 6D also shows some other optional features of a retention member. For example, a retention member641 with anaperture646 may not have any petals. A core sample may simply displace a solid retention member. In other embodiments, such as the one shown inFIG. 6D, the retention member641 may include one ormore petals642a,642b,642c.Thepetals642a,642b,642cmay be individual petals, or thepetals642a,642b,642cmay be perforated with perforations643 extending between theaperture circumference647 to the petal circumference645. When a core sample (not shown) is taken, the core sample will break the perforations643, and the core sample may be received in the coring bit (not shown).
• In fact, it is noted that the many of the above disclosed embodiments of a retention member may use radial perforations to segment the retention member into petals.
• This would enable the retention member to serve as a cover that will prevent contaminants from entering the coring bit before a sample is taken and the perforations are broken.
• It is noted that radial perforations are distinguished from circumferential perforations that may be used to increase the flexibility of the retention member.
• FIGS. 7A-7E show various embodiments of a retention member for use with a coring bit in accordance with the invention.FIG. 7A shows aretention member711 withpetals711a,711bthat are tapered inwardly. Thepetals711a,711bhave a petal circumference that is substantially the same as the inner diameter of theformation cutter705. A core sample will snugly pass through thepetals711a,711bof theretention member711.
• FIG. 7B shows another embodiment of aretention member721 where thepetals721a,721bare tapered outwardly.
• In this embodiment, when thepetals721a,721bare displaced by a core sample (not shown), the pressure applied by thepetals721a,721bwill be slightly greater because they are displaced farther from their original position.
• FIG. 7C shows another embodiment of aretention member731 in accordance with the invention. Thepetals731a,731bof theretention member731 are rounded and extruding into theinternal sleeve707. When a core sample (not shown)is received in theinternal sleeve707, thepetals731a,731bwill be displaced inwardly.
• FIG. 7D shows another embodiment of aretention member741 in accordance with the invention. Thepetals741a,741bof theretention member741 are rounded and extruding outwardly from theinternal sleeve707. When a core sample (not shown) is received in theinternal sleeve707, thepetals741a,741bwill be displaced inwardly.
• FIG. 7E shows an embodiment of aretention member751 that is similar to that shown inFIG. 7B. InFIG. 7E, theinternal sleeve757 has anotch753 that provides space for thepetals751a,751bin their displaced position. The inner diameter D2 of theinternal sleeve757 in thenotch753 is larger than the nominal diameter D1755 of theinternal sleeve757. In the embodiment shown, the nominal diameter D1755 of theinternal sleeve757 is substantially the same as the inner diameter of theformation cutter705. As a core sample (not shown) passes into theinternal sleeve757, thepetals751a,751bof theretention member751 will be displaced into thenotch753. Thepetals751a,751b,when displaced into thenotch753, have substantially the same inner diameter as the nominal diameter D1755 of theinternal sleeve757. This enables the core sample701 to fit snuggly at all points along the axis of theinternal sleeve757, while still gaining the advantages of a retention member in accordance with embodiments of the invention.
• The embodiment of aninternal sleeve757 that is shown inFIG. 7E may be used with various embodiments of a retention member. For example, aninternal sleeve757 with anotch753 may be used with any of the embodiments of a retention member shown inFIGS. 7A-7E.
• A retention member in accordance with any of the embodiments of the invention may be designed specifically for a single use, or it may be designed to capture and retain multiple cores. For example, some coring bits are designed so that the core samples are stored in the internal sleeve. That is, the internal sleeve is moved from inside the coring bit into a storage area. In other embodiments, only the core sample is moved into a storage device, and the internal sleeve is used to capture another sample.
• As will be understood by those having ordinary skill in the art,FIGS. 7A-7E show a cross section of particular embodiments of a coring bit and a retention member in accordance with the invention. As such, the figures show only two petals in each embodiment. This is simply a function of a cross section, and it is not intended to limit the invention. A retention member in accordance with the invention may have any number of petals. Optionally, the retention member may be uniform, solid, tapered, or have one or more apertures therethrough. Other configurations may be envisioned. The retention member may be adapted to tear and/or stretch as the core sample advances into the sleeve. Portions of the retention member that are stretched or torn may apply force to the core sample to grip the core sample. The retention member is preferably elastic so that it may retract to substantially its original configuration and close behind the core sample thereby restricting portions of the core sample from exiting the coring sleeve.
• FIG. 8A shows a cross section of acoring bit800 with aninternal sleeve807 having apiston802 in accordance with the invention. Thepiston802 is axially moveable with respect to theinternal sleeve807. Thepiston802 is initially positioned proximate the distal end of theinternal sleeve807. When a core sample is being collected from theformation810, the core sample will displace thepiston802 with respect to theinternal sleeve807. Thepiston802 may also includeseals812 or bearings to enable easier movement of thepiston802 within theinternal sleeve807.
• In the embodiment shown, theinternal sleeve807 has a diameter that is substantially the same as the inner diameter of theformation cutter805. In order to fit with theinternal sleeve807, thepiston802 has a diameter that is substantially the same as the inner diameter of theinternal sleeve807 so that the piston seals812 are able to form a seal between theinternal sleeve807 and thepiston802.
• FIG. 8B shows a cross section of thecoring bit800 with acore sample801 received inside thecoring bit800. Thecore sample801 has displaced thepiston802 to a position proximate the proximal end of theinternal sleeve807. Thepiston802 moves as thecore sample801 is received in thecoring bit800. Thus, thepiston802 provides support for thecore sample801. This may be advantageous in unconsolidated formations, where the formation core sample would fall apart as it came into the coring bit. Thepiston802 may prevent the formation from falling apart.
• Additionally, when thecoring bit800 is withdrawn from theformation810, thepiston802 helps to hold the core sample in theinternal sleeve807. In some embodiments, thechamber815 behind thepiston802 includes a check valve or other means (not shown) to allow air or fluid to be pushed out of thechamber815, but that will not allow the return flow. Thus, a vacuum behind thepiston802 will prevent thepiston802 from moving on the outward direction.
• In some embodiments, thechamber815 behind the piston is completely vented. Nonetheless, thecore sample801 may not be able to move out of theinternal sleeve807 without also moving thepiston802. This may be caused by a vacuum created between thepiston802 and thecore sample801. The friction between thepiston802 and theinternal sleeve807 will create additional resistance to the movement of thecore sample801, which will help retain thecore sample801 in thecoring bit800.
• Further, in addition to asimple piston802, theinternal sleeve807 may also include a ratchet device or a locking device. Such a device would prevent the piston from moving in the outward direction.
• FIG. 9 shows a cross section of acoring bit900 that includes a cushion for receiving and retaining thecore sample901 in thebit900. A hollowouter shaft903 penetrates aformation910 using aformation cutter905 disposed at the distal end of theshaft903. Acore sample901 is received in aninternal sleeve917 that is disposed inside thehollow shaft903.
• The cavity (shown at918) in theinternal sleeve917 behind thecore sample901 is filled with a fluid, such as water. The proximal end of theinternal sleeve917 includes avalve921 for selectively permitting fluid to pass between thesleeve917 and the rest of the tool. Thevalve921 may be, for example, a check valve that enables the fluid to exit thecavity918 as acore sample901 moves into theinternal sleeve917. When thecoring bit900 is withdrawn from the formation, thevalve921 may be used to prevent the reverse flow of fluid into thecavity918, and a vacuum is created behind thecore sample901 that retains thecore sample901 in thecoring bit900.
• In at least one embodiment, thecheck valve921 inFIG. 9 may be combined with thecoring bit800 inFIGS. 8A and 8B. In such an embodiment, the piston (802 inFIGS. 8A and 8B) would force the fluid through the check valve (921 inFIG. 9). The check valve (921 inFIG. 9) would prevent the return flow of fluid and the vacuum behind the piston (802 inFIGS. 8A and 8B) and, thereby, retain the piston core sample in place.
• FIG. 10 shows a cross section of acoring bit1001 in accordance with another embodiment of the invention. Ahollow shaft1003 has aformation cutter1005 at a distal end of theshaft1003. Abladder1007 is used as an internal sleeve in thecoring bit1001 inFIG. 10. Thebladder1007, when deflated, provides enough space to accept a core sample. Thebladder1007 may then be selectively inflated by filling it with fluid. The fluid may be stored hydraulic fluid, or it may be drilling mud that is pumped into the bladder. The type of fluid used is not intended to limit the invention.
• When thebladder1007 is filled, it will compress inwardly and exert a radial pressure on a core sample (not shown).
• The pressure will apply an overburden to the core sample that will both stabilize and retain the core sample.
• Embodiments of the invention may present one or more of the following advantages. A coring bit with a retention member or other retention device in accordance with the invention will retain the core sample in the coring bit while the coring bit is being withdrawn from the formation. This will prevent the core sample from being damaged or lost during this process.
• Advantageously, a coring bit may include a retention member that will close completely when capturing a sample in soft or unconsolidated formation. When the retention member closes, the core sample will be completely enclosed in the coring bit and protected against further damage and loss.
• Advantageously, a coring bit that includes a non-rotating internal sleeve will not degrade the core sample through friction between the core sample and the internal sleeve and the retention member. The internal sleeve and the retention member will not rotate with respect to the formation and the core sample as it is being captured.
• Advantageously, embodiments of the invention that include a piston in the internal sleeve provide additional guidance for a core sample as it is being received. The piston is displaced by the core sample, and once the sample is fully received, the piston creates a vacuum or void behind the core sample that retains the core sample in the internal sleeve as the coring bit is withdrawn from the formation.
• Advantageously, embodiments of the invention that include a cushion provide steady guidance for the core sample as it enters the coring bit. Once received in the coring bit, the core sample is retained by a vacuum or void behind the core sample.
• 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.

Claims (34)

1. A sidewall coring tool, comprising:

a tool body;

a hollow coring shaft extendable from the tool body;

a formation cutter disposed at a distal end of the hollow coring shaft; and

a retention member defining one of a plurality of petals, an aperture and combinations thereof, the retention member disposed in the hollow coring shaft.

2. The sidewall coring tool ofclaim 1, further comprising an internal sleeve disposed inside the hollow coring shaft, and wherein the retention member is connected to the internal sleeve.

3. The sidewall coring tool ofclaim 2, wherein the retention member is disposed proximate a distal end of the internal sleeve.

4. The sidewall coring tool ofclaim 2, wherein the internal sleeve comprises a non-rotating sleeve.

5. The sidewall coring tool ofclaim 2, wherein the internal sleeve comprises a radial notch such that the petals of the retention member can be positioned radially outward into the notch.

6. The sidewall coring tool ofclaim 5, wherein the retention member has a petal circumference that is substantially the same as an inner diameter of the internal sleeve.

7. The sidewall coring tool ofclaim 2, further comprising a piston disposed inside the internal sleeve and axially moveable with respect to the internal sleeve.

8. The sidewall coring tool ofclaim 2, further comprising a check valve disposed in the internal sleeve.

9. The sidewall coring tool ofclaim 8, wherein the check valve is disposed in a proximal end of the internal sleeve.

10. The sidewall coring tool ofclaim 9, wherein the check valve enables a fluid to flow out of the internal sleeve.

11. The sidewall coring tool ofclaim 1, wherein an inner diameter of the internal sleeve is substantially the same as an inner diameter of the formation cutter.

12. The sidewall coring tool ofclaim 1, wherein an inner diameter of the internal sleeve is larger than an inner diameter of the formation cutter.

13. The sidewall coring tool ofclaim 1, wherein the internal sleeve comprises a bladder configured to apply radial pressure to a core sample when the bladder is selectively filled with a fluid.

14. The sidewall coring tool ofclaim 1, wherein the plurality of petals comprises 3 petals.

15. The sidewall coring tool ofclaim 1, wherein the plurality of petals overlap.

16. The sidewall coring tool ofclaim 1, wherein the plurality of petals are separated by gaps.

17. The sidewall coring tool ofclaim 1, wherein the retention member comprises perforations.

18. The sidewall coring tool ofclaim 17, wherein the perforations are circumferential perforations disposed outside a petal circumference.

19. The sidewall coring tool ofclaim 17, wherein the perforations are radial perforations disposed at least partially inside a petal circumference.

20. The sidewall coring tool ofclaim 1, wherein the plurality of petals are adjacent.

21. The sidewall coring tool ofclaim 1, wherein the retention member is constructed of rubber.

22. The sidewall coring tool ofclaim 1, wherein the retention member is rounded and extrudes towards a distal end of hollow coring shaft.

23. The sidewall coring tool ofclaim 1, wherein the retention member is rounded and extrudes towards a proximal end of the hollow coring shaft.

24. A method for taking a core sample, comprising:

extending a coring bit into a formation, the coring bit having a retention member segmented into a plurality of petals;

receiving the core sample in the coring bit; and

retaining the core sample in the coring bit with the retention member while withdrawing the coring bit from the formation.

25. The method ofclaim 24, further comprising selectively filling a bladder with a fluid to apply a radial pressure to the core sample.

26. The method ofclaim 24, wherein the retention member is connected to an internal sleeve disposed in the coring bit and the core sample is received in the internal sleeve.

27. A sidewall coring tool, comprising:

a tool body;

a hollow coring shaft extendable from the tool body;

a formation cutter disposed at a distal end of the hollow coring shaft;

an internal sleeve disposed inside the hollow coring shaft; and

at least one retention mechanism selected from the group consisting of a piston and a check valve, wherein the piston is disposed in the internal sleeve and moveable with respect to the internal sleeve, and the check valve is disposed in the internal sleeve.

28. The sidewall coring tool ofclaim 27, wherein the at least one retention mechanism is the piston.

29. The sidewall coring tool ofclaim 28, further comprising a seal disposed between the piston and the internal sleeve.

30. The sidewall coring tool ofclaim 28, wherein an inner diameter of the internal sleeve is substantially the same as an inner diameter of the formation cutter.

31. The sidewall coring tool ofclaim 28, further comprising a check valve operatively connected to the internal sleeve.

32. The sidewall coring tool ofclaim 27, further comprising a retention member segmented into petals disposed proximate an opening at a distal end of the internal sleeve.

33. A method for taking a core sample, comprising:

extending a coring bit into a formation;

receiving the core sample in an internal sleeve having a piston disposed therein such that the piston is moveable with respect to the internal sleeve; and

withdrawing the coring bit from the formation.

34. The method ofclaim 33, further comprising selectively filling a bladder with a fluid to apply a radial pressure to the core sample.

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