CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of the filing date of U.S. Provisional Patent Application No. 62/008,821 , filed June 6, 2014, and U.S.

Provisional Patent Application No. 62/023014, filed July 10, 2014, both of which are incorporated herein by reference in its entirety.

FIELD

[0002] This invention relates to a core lifter case for receiving a core lifter, and more particularly, to a core lifter case that eliminates the need for a snap ring.

BACKGROUND

[0003] In conventional drilling systems, and as shown in Figure 1 , a drill string includes an outer tube 7, a reaming shell 9 securely attached to the outer tube, and a drill bit 13 securely attached to the reaming shell. The drill string also includes an inner tube 15 coupled to a head assembly (not shown), and the inner tube and the head assembly (together, the inner tube assembly) are seated within the outer tube 7. The inner tube assembly typically has an adjustable length, and a gap is provided between the inner tube assembly and the drill bit 13 to permit control of fluid flow and pressure at the formation being drilled. The drill string also includes an inner tube stabilizer 1 1 , a core lifter case 17 secured to an end of the inner tube 15, a core lifter 19, and a snap ring 21 that is used to hold the core lifter inside the core lifter case. In operation, the core lifter grips a core sample to facilitate retrieval of the sample. Typically, a groove is defined proximate a reduced-diameter end of the core lifter case to receive the snap ring, thereby weakening the body of the core lifter case. Conventional snap rings can only be inserted or removed through a larger-diameter end of the core lifter case that is opposed from the reduced-diameter end. This complicates and extends the time required for removal and replacement of used core lifters.

[0004] Thus, there is a need in the pertinent art for core lifter cases that can function without a snap ring, have a stronger body, and permit insertion or removal of a core lifter through the reduced-diameter end of the core lifter case. SUMMARY

[0005] Described herein, in one aspect, is a core lifter case for receiving a core lifter. The core lifter can be configured to receive a portion of a core sample and have a plurality of circumferentially spaced ribs defined by an outer surface of the core lifter. The core lifter can comprise an elongate body having a longitudinal axis, a first end portion, an opposed second end portion, and an inner surface defining a central bore. The first and second end portions can define respective openings in communication with the central bore. The inner surface of the first end portion can define a plurality of circumferentially spaced slots. Each slot of the plurality of slots can be configured to receive a corresponding rib defined by the outer surface of the core lifter.

[0006] In another aspect, a core lifter system for permitting lifting of a core sample is described. The core lifter system can comprise a core lifter case having a longitudinal axis, a first end portion, an opposed second end portion, and an inner surface defining a central bore. The first and second end portions can define respective openings in communication with the central bore. The inner surface of the first end portion can define a plurality of circumferentially spaced slots. The core lifter system can further comprise a core lifter having an inner surface and an outer surface. The outer surface of the core lifter can define a plurality of circumferentially spaced ribs. Each slot of the plurality of slots of the core lifter case can be configured to receive a corresponding rib defined by the outer surface of the core lifter.

[0007] In an additional aspect, a method of collecting a core sample within a formation is described. The method can comprise inserting a core lifter within a core lifter case through an opening of a first end portion of the core lifter case. The inner surface of the first end portion of the core lifter case can define a plurality of circumferentially spaced slots. An outer surface of the core lifter can define a plurality of circumferentially spaced ribs. Each slot of the plurality of slots of the core lifter case can receive a corresponding rib defined by the outer surface of the core lifter. The method can further comprise engaging a portion of the core sample with the core lifter.

[0008] Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

DETAILED DESCRIPTION OF THE FIGURES

[0009] These and other features of the preferred embodiments of the invention will become more apparent in the detailed description in which reference is made to the appended drawings wherein:

[0010] Figure 1 is a cross-sectional view of a portion of a drill string as is known in the art. As shown, the drill string includes an outer tube, a reaming shell, a drill bit, an inner tube, a core lifter case, a core lifter, and a stop ring for securing the core lifter within the core lifter case.

[001 1] Figure 2 is a cross-sectional view of an exemplary core lifter system as disclosed herein. As shown, the core lifter case can be integrally formed with the inner tube.

[0012] Figure 3 is a cross-sectional view of another exemplary core lifter system as disclosed herein. As shown, the core lifter case can be configured for

complementary engagement with the inner tube.

[0013] Figures 4A and 4B are isometric views of an exemplary core lifter case as disclosed herein. Figure 4A is a cross-sectional perspective view of the core lifter case, while Figure 4B is an end perspective view of the core lifter case.

[0014] Figure 5 is an isometric perspective view of an exemplary core lifter as disclosed herein.

DETAILED DESCRIPTION

[0015] The present invention can be understood more readily by reference to the following detailed description, examples, drawings, and claims, and their previous and following description. However, before the present devices, systems, and/or methods are disclosed and described, it is to be understood that this invention is not limited to the specific devices, systems, and/or methods disclosed unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0016] The following description of the invention is provided as an enabling teaching of the invention in its best, currently known embodiment. To this end, those skilled in the relevant art will recognize and appreciate that many changes can be made to the various aspects of the invention described herein, while still obtaining the beneficial results of the present invention. It will also be apparent that some of the desired benefits of the present invention can be obtained by selecting some of the features of the present invention without utilizing other features. Accordingly, those who work in the art will recognize that many modifications and adaptations to the present invention are possible and can even be desirable in certain

circumstances and are a part of the present invention. Thus, the following

description is provided as illustrative of the principles of the present invention and not in limitation thereof.

[0017] As used throughout, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a slot" can include two or more such slots unless the context indicates otherwise.

[0018] Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0019] As used herein, the terms "optional" or "optionally" mean that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

[0020] The word "or" as used herein means any one member of a particular list and also includes any combination of members of that list.

[0021] Described herein with reference to Figures 2-4B is a core lifter case 10 for receiving a core lifter 40. With reference to Figures 2-3, also described is a core lifter system 100 that comprises a core lifter case 10 and a core lifter 40 as disclosed herein. In operation, the core lifter 40 can be configured to receive a portion of a core sample. As shown in Figure 5 and further disclosed herein, the core lifter 40 can have an inner surface 42, an outer surface 44, and a plurality of circumferentially spaced ribs 46 defined by the outer surface of the core lifter. It is contemplated that the core lifter case 10 and core lifter system 100 disclosed herein can permit recovery of a core sample without the use of a snap ring as is typically required in conventional drilling systems. It is further contemplated that, compared to

conventional drilling systems, the core lifter case 10 and the core lifter system 100 disclosed herein can permit easier insertion of a core lifter into the core lifter case. It is still further contemplated that the core lifter case 10 and core lifter system 100 disclosed herein can be stronger than conventional core lifter cases and associated systems, which require a thin-wall portion proximate a snap ring groove. Thus, in operation, it is contemplated that the core lifter case and associated systems and methods disclosed herein can save drill operators time and money by improving the process for insertion and removal of the core lifter, improving product life (by, among other things, reducing crack formation), and reducing the need for component inventory.

[0022] In one aspect, the core lifter case 10 can comprise an elongate body 12 having a longitudinal axis 14, a first end portion 16, an opposed second end portion 20, and an inner surface 24 defining a central bore 26. In this aspect, the first and second end portions 16, 20 can define respective openings 18, 22 in communication with the central bore 26. In an additional aspect, as shown in Figures 2-4B, the inner surface 24 of the first end portion 16 of the elongate body 12 can define a plurality of circumferentially spaced slots 28. Optionally, in this aspect, each slot 28 of the plurality of slots can be configured to receive at least a portion of a corresponding rib 46 defined by the outer surface of the core lifter. In exemplary aspects, and in contrast to conventional core lifter cases, the inner surface 24 of the elongate body 12 does not comprise a groove configured to receive a snap ring. In a further aspect, the elongate body 12 can be configured to receive the core lifter 40 through the opening 18 of the first end portion 16. [0023] In exemplary aspects, the slots 28 of the core lifter case 10 can comprise a plurality of flutes. In these aspects, it is contemplated that the flutes can be machined using conventional methods.

[0024] In another aspect, the inner surface 24 of the core lifter case 10 can define a shoulder 30 that projects radially inwardly relative to the longitudinal axis 14 of the elongate body 12 of the core lifter case. In this aspect, as the core lifter 40 is inserted within the core lifter case 10 through the opening 18 of the first end portion 16 of the core lifter case, it is contemplated that the shoulder 30 can be configured to engage an end portion of the core lifter to restrict further axial movement of the core lifter. Optionally, in exemplary aspects, the shoulder 30 can extend circumferentially about the inner surface 24 of the core lifter case 10. In further exemplary aspects, the shoulder 30 can be axially spaced from the slots 28 relative to the longitudinal axis 14 of the elongate body 12 such that, following engagement between the core lifter 40 and the shoulder 30, the core lifter 40 is positioned substantially between the slots 28 and the shoulder 30 relative to the longitudinal axis 14. However, it is contemplated that the core lifter 40 can at least partially overlap, or be at least partially engaged with, the slots 28 when the core lifter engages the shoulder 30.

[0025] In still another aspect, each slot 28 of the plurality of slots of the elongate body 12 of the core lifter case 10 can have a variable circumferential width.

Optionally, in this aspect, and as shown in Figure 4A, it is contemplated that the circumferential width of each slot 28 of the plurality of slots of the elongate body 12 can decrease in a first direction 50. Optionally, the first direction 50 can correspond to movement away from the opening 18 of the first end portion 16 relative to the longitudinal axis 14 of the elongate body.

[0026] In a further aspect, the second end portion 20 of the elongate body 12 of the core lifter case 10 can be configured for engagement with an inner tube 60 of a drilling system as is known in the art. Optionally, in this aspect, at least a portion of the inner surface 24 of the second end portion 20 can be threaded. With reference to Figure 3, it is contemplated that the threaded portion of the inner surface 24 of the second end portion 20 can be configured for complementary engagement with a corresponding threaded portion of the inner tube 60. [0027] In various aspects, the core lifter case 10 can be provided as part of a core lifter system 100 for permitting lifting of a core sample. In these aspects, the core lifter system 100 can further comprise a core lifter 40 as disclosed herein. In one aspect, the core lifter 40 can have a longitudinal axis 48. As described above, each slot 28 of the plurality of slots of the core lifter case 10 can be configured to receive a corresponding rib 46 defined by the outer surface 44 of the core lifter 40. In exemplary aspects, the core lifter system 100 does not comprise a snap ring.

[0028] In another aspect, as shown in Figure 5, the core lifter 40 can define a longitudinal slit 45 that extends substantially parallel to the longitudinal axis 48 of the core lifter along the entire axial length of the core lifter. In this aspect, the longitudinal slit 45 can permit radial compression of the core lifter 40. In use, it is contemplated that, upon alignment between a rib 46 of the core lifter 40 and a corresponding slot 28 of the core lifter case, the core lifter can be selectively radially compressed to permit insertion of the core lifter into the core lifter case, as well as removal of the core lifter from the core lifter case. Following radial compression of the core lifter 40, the core lifter can be configured for radial expansion to return to its original configuration; that is, it is contemplated that the core lifter can be self- expanding.

[0029] In exemplary aspects, each rib 46 of the plurality of ribs of the core lifter 40 can have a variable circumferential width. In these aspects, and with reference to Figures 2 and 3, when the core lifter 40 is positioned in an insertion orientation in which the longitudinal axis 48 of the core lifter is substantially axially aligned with the longitudinal axis 14 of the core lifter case 10, the circumferential width of each rib 46 can increase in the first direction 50.

[0030] In exemplary aspects, the core lifter can be formed using conventional lathe-turning methods. Alternatively, in other exemplary aspects, the core lifter can be formed using a stamping process as is known in the art. Exemplary methods for forming a core lifter using a stamping process are disclosed in U.S. Patent

Application Publication No. 201 1 /0100718, which is incorporated by reference herein in its entirety.

[0031] In further aspects, the core lifter system (part of an inner tube assembly as is known in the art) can further comprise an inner tube 60 as is known in the art. In addition to the core lifter system, the inner tube assembly can further comprise a head assembly as is known in the art.

[0032] Optionally, in exemplary aspects, and as shown in Figure 2, it is contemplated that the core lifter case 10 and the inner tube 60 can be integrally formed and be of unitary construction. In these aspects, it is contemplated that the inner tube 60 can have a wall with a variable thickness. It is further contemplated that the thickness of the inner tube 60 can have a portion of increased thickness positioned proximate the core lifter case 10. It is still further contemplated that the portion of increased thickness can permit stable integration of the core lifter case 10 with the inner tube 60 while reducing the likelihood of crack formation. In contrast, conventional inner tubes have a thin and generally uniform thickness from end to end.

[0033] With the inner tube assembly locked to the outer tube, the drill bit, a core barrel assembly, drill rods and/or other portions of a drill string can be rotated and/or pushed into a formation to allow a core sample to be collected within one or more receptacles of the inner tube assembly, including, for example, the inner tube 60, the core lifter case 10, or the core lifter 40. After the core sample is collected, the inner tube assembly can be unlocked from the outer tube. The inner tube assembly can then be retrieved, for instance using a wireline retrieval system, while the drill bit, the outer tube, one or more of the drill rods and/or other portions of the drill string remain within the borehole. The core sample can be removed from the retrieved inner tube assembly, and after the core sample is removed, the inner tube assembly can be sent back and locked to the outer tube.

[0034] With the inner tube assembly (comprising the core lifter system) once again locked to the outer tube, the drill bit, the core barrel assembly, the drill rods and/or other portions of the drill string can be rotated and/or pushed further into the formation o allow another core sample to be collected within the one or more receptacles of the inner tube assembly. It is contemplated that the inner tube assembly can be repeatedly retrieved and sent back in this manner to obtain several core samples, while the drill bit, the outer tube, one or more of the drill rods and/or other portions of the drill string remain within the borehole. This can advantageously reduce the time necessary to obtain core samples because the drill string need not be tripped out of the borehole for each core sample. [0035] As further disclosed herein, with the core lifter 40 positioned within the core lifter case 10 and the drill bit, the core barrel assembly, the drill rods and/or other portions of the drill string being rotated and/or pushed into the formation, the inner tube assembly can collect a core sample. For example, one or more portions of a core sample can enter the core lifter case 10, pass through the core lifter 40, exit the core lifter case, and enter the inner tube 60.

[0036] During this process, the core sample can urge the core lifter 40

longitudinally within the core lifter case 10. For example, the core sample can urge the core lifter 40 longitudinally towards a trailing portion of the core lifter case 10 (and away from the opening 18 of the first end portion 16) until the core lifter contacts and/or abuts shoulder 30.

[0037] With the core lifter 40 contacting and/or abutting the shoulder 30, portions of the core sample can pass through the core lifter 40, which can cause the core lifter to resiliently deform and/or expand. As portions of the core sample pass through the core lifter 40, friction between the core lifter and the core sample can cause the core lifter to continue to contact and/or abut the shoulder 30. After the core sample is collected within the inner tube assembly, the inner tube assembly can be unlocked from the outer tube, and the inner tube assembly can be retrieved by a retrieval system. A trailing portion of the head assembly of the inner tube assembly can be connected to the retrieval system using conventional methods.

[0038] To facilitate core sample retrieval, a portion of the drill string can be pulled, lifted and/or withdrawn out of the borehole. This can cause one or more portions of the core sample to pass back through the core lifter 40 and/or exit the leading portion of the core lifter case 10. Friction between these portions of the core sample and the core lifter 40 can cause the core lifter and the core lifter case 10 to move relative to each other, which can cause the core lifter to grip the core sample. This gripping of the core sample and/or the pulling of the drill string can break the core sample off from the formation. It will be appreciated, however, that the core sample can be broken off from the formation using any other suitable means. After the core sample is broken off from the formation, the inner tube assembly and the core sample can then be retrieved by the retrieval system as discussed above, while the drill bit, the outer tube, one or more of the drill rods and/or other portions of the drill string remain within the borehole. [0039] When the portion of the drill string is pulled, lifted and/or withdrawn out of the borehole, an interior portion of the core lifter case 10 can compress the core lifter 40, which can contact, grip and/or break off the core sample. For example, as shown in Figure 4A, at least a portion of the inner surface 24 of the core lifter case 10 can be inwardly tapered (i.e., have a decreasing inner diameter) moving toward the first end portion 16, thereby providing compression of the core lifter 40 as the core lifter moves longitudinally within the core lifter case (e.g., during pulling, lifting, and/or withdrawal of the drill string). Optionally, in exemplary aspects, it is contemplated that the tapered portion 32 of the inner surface 24 of the core lifter case 10 can be positioned between the shoulder 30 and the opening 18 of the first end portion 16 relative to the longitudinal axis 14 of the core lifter case. Optionally, in further exemplary aspects, the tapered portion 32 of the inner surface 24 of the core lifter case 10 can be oriented at a taper angle relative to the longitudinal axis 14 of the core lifter case. In these aspects, the taper angle can range from about 1 degree to about 10 degrees, and more preferably, from about 2 degrees to about 4 degrees. As shown in Figures 4A-4B, in exemplary aspects, the longitudinally- oriented slots 28 of the core lifter case 10 can intersect the tapered portion 32 of the inner surface 24 to thereby produce slots having a variable circumferential width as further described herein. In these aspects, it is contemplated that each rib 46 of the core lifter 40 can be configured for receipt within at least a portion of a corresponding longitudinally-oriented, variable-width slot 28. It is further contemplated that the tapered portion 32 of the inner surface 24 and the longitudinally-oriented, variable- width slots 28, can be shaped to wedge and/or drive the core lifter 40 during core breaking actions. For example, and as further described herein, it is contemplated that each rib 46 of the core lifter 40 can have a variable-width profile that is complementary to a variable-width profile of a corresponding slot 28 of the core lifter case 10 such that the core lifter case wedges and/or drives the core lifter during core breaking actions. Optionally, it is contemplated that at least a portion of the longitudinally-oriented slots 28 can be tapered such each slot has a variable inner diameter). For example, in some exemplary aspects, it is contemplated that at least a portion of each slot 28 can be inwardly tapered such that the slot has a decreasing inner diameter moving toward the opening 18 of the first end portion 16.

Alternatively, in other exemplary aspects, it is contemplated that at least a portion of each slot 28 can be tapered such that the slot has an increasing inner diameter moving toward the opening 18 of the first end portion.

[0040] In exemplary aspects, the ribs 46 of the core lifter 40 can define respective contact surfaces that are configured for contact with the inner surface 24 of the core lifter case 10. As the contact surfaces of the ribs 46 of the core lifter 40 contact the inner surface 24 of the core lifter case, the core lifter can be radially compressed, which can, in turn, cause one or more portions of the inner surface 42 of the core lifter 40 to contact, grip and/or break off the core sample. For instance, as shown in Figure 5, the inner surface 42 of the core lifter 40 can comprise a plurality of inner projections 43 that define a gripping surface configured to contact, grip and/or break off the core sample. In exemplary aspects, the outer surface 44 of the core lifter 40 can comprise a plurality of outer recesses 49, with each respective recess 49 being positioned between circumferentially spaced ribs 46. Similarly, it is contemplated that the inner surface 42 of the core lifter 40 can comprise a plurality of inner recesses 47, with each respective inner recess being positioned between circumferentially spaced projections 43. If desired, the ribs 46, projections 43, and the associated recesses 47, 49 of the inner and outer surfaces 42, 44 can be longitudinally-oriented, can have a variable width, can be tapered to provide a variable thickness, and/or can extend along at least 50 percent, 60 percent, 70 percent, 80 percent, 90 percent and/or more of the length of the core lifter 40. It will be appreciated, however, that the ribs 46, projections 43, and the associated recesses 47, 49 of the inner and outer surfaces 42, 44 can have other suitable sizes, shapes and/or configurations.

[0041] It is contemplated that the recesses 49 defined in the outer surface 44 of the core lifter 40 can advantageously reduce the friction between the core lifter case 10 and the core lifter. This can advantageously reduce the amount of force used to pull, lift and/or withdraw the portion of the drill string, which can longitudinally move the core lifter 40. In addition, this can reduce wear and tear on the core lifter 40, thus extending the lifespan of the core lifter. In some embodiments, the contact surfaces defined by the ribs 46 of the core lifter 40 can comprise 90 percent, 80 percent, 70 percent, 60 percent, 50 percent, 40 percent and/or less of the surface area of the outer surface 44 of the core lifter. [0042] It is further contemplated that the recesses 47 defined in the inner surface 42 of the core lifter 40 can advantageously reduce the friction between the core sample and the core lifter. This can reduce wear and tear on the core lifter 40, thus extending the lifespan of the core lifter. In some aspects, the gripping surfaces defined by the projections 43 of the core lifter 40 can comprise 90 percent, 80 percent, 70 percent, 60 percent, 50 percent, 40 percent and/or less of the surface area of the inner surface 42 of the core lifter.

[0043] Desirably, the ribs 46, projections 43, and recesses 47, 49 of the core lifter 40 can facilitate resilient compression and/or expansion of the core lifter. For example, the ribs 46, projections 43, and recesses 47, 49 of the core lifter 40 can facilitate compression of the core lifter 40 when the core lifter case 10 contacts and/or exerts a force against the core lifter. Also, for example, the ribs 46, projections 43, and recesses 47, 49 of the core lifter 40 can facilitate resilient expansion of the core lifter when portions of the core sample are passing through the core lifter during collection of the core sample. This can be particularly advantageous for collecting an irregularly shaped or unconsolidated core sample. It is

contemplated that the plurality of ribs can comprise any number of ribs, provided the ribs provide suitable gripping surface area and flexibility for conforming to the core sample.

[0044] It is contemplated that the core lifter case 10, the core lifter 40, and the inner tube 60 can comprise conventional materials as are known in the art. In exemplary aspects, the core lifter case 10 and the inner tube 60 can comprise alloy steel. In these aspects, it is contemplated that alloy steel can permit post-forming, thru-wall quench and temper hardening of the core lifter case 10 and/or inner tube to thereby increase the wear resistance and strength of the core lifter case and inner tube. Optionally, when the core lifter case 10 and inner tube 60 are integrally formed, it is contemplated that the post-forming, thru-wall quench, and/or temper hardening can be performed along substantially the entire length of the integrated core lifter case and inner tube. Alternatively, when the core lifter case 10 and inner tube 60 are integrally formed, it is contemplated that the post-forming, thru-wall quench, and/or temper hardening can be selectively performed using induction heating at the thick end of the inner tube 60 proximate the core lifter case 10. When the core lifter case 10 and inner tube 60 are integrally formed, the alloy steel preferably has sufficient ductility to endure conventional inner tube making processes and conventional variable wall cold drawing processes, prior to machining of internal features within the integrated core lifter case and inner tube. In some aspects, consistent with conventional methods, quench and/or temper hardening can be applied to the core lifter case 10. Optionally, in these aspects, it is contemplated that the core lifter case 10 can be made from 4130 alloy steel and hardened to a medium hardness ranging from about 40 HRC to about 46 HRC, thereby increasing wear resistance while retaining sufficient toughness. In exemplary aspects, at least a portion of the core lifter case 10, the core lifter 40, and/or the inner tube 60 can be coated with anti-abrasion or wear-resistant coatings or treatments, such as, for example and without limitation, a metal and micro-diamond composite coating bonded in an immersive electro-chemical process. In other exemplary aspects, it is contemplated that case hardening heat treatments as are known in the art can be applied to at least a portion of the core lifter case 10, the core lifter 40, and/or the inner tube 60. In exemplary aspects, at least a portion of an inner surface of the inner tube 60 can be coated with chrome plating. In further exemplary aspects, when the core lifter case 10 and the inner tube 60 are integrally formed, at least a portion of the inner surface 24 of the core lifter case and at least a portion of an inner surface of the inner tube can be coated with chrome plating.

[0045] In operation, the core lifter 10 and core lifter system 100 can be used in a method of collecting a core sample within a formation. In one aspect, the method can comprise inserting a core lifter 40 within a core lifter case 10 through the opening 18 of the first end portion 16 of the core lifter case, wherein each slot 28 of the plurality of slots of the core lifter case receives a corresponding rib 46 defined by the outer surface of the core lifter. In another aspect, the method can comprise engaging a portion of the core sample with the core lifter. Optionally, in a further aspect, the method does not comprise using a snap ring to secure the core lifter within the core lifter case.

[0046] In exemplary aspects, the method can further comprise aligning the plurality of ribs of the core lifter with corresponding slots of the core lifter case. In these aspects, the method can further comprise selectively radially compressing the core lifter and axially advancing the core lifter relative to the longitudinal axis of the core lifter case to either insert the core lifter into the core lifter case or remove the core lifter from the core lifter case.

[0047] It is contemplated that the profile shape of the slots (e.g., flutes) of the core lifter case does not have to match the profile shape of the ribs of the core lifter. In some optional aspects, as shown in Figures 2-3, only corner portions of the ribs of the core lifter will mate against the inside surface of the slots (e.g., flutes). However, it is contemplated that the slots (e.g., flutes) of the core lifter case can optionally be machined to more closely match the profile of the ribs of the core lifter.

Exemplary Aspects

[0048] In various exemplary aspects, disclosed herein is a core lifter case for receiving a core lifter, the core lifter being configured to receive a portion of a core sample and having a plurality of circumferentially spaced ribs defined by an outer surface of the core lifter, the core lifter case comprising: an elongate body having a longitudinal axis, a first end portion, an opposed second end portion, and an inner surface defining a central bore, the first and second end portions defining respective openings in communication with the central bore, wherein the inner surface of the first end portion defines a plurality of circumferentially spaced slots, each slot of the plurality of slots being configured to receive at least a portion of a corresponding rib defined by the outer surface of the core lifter.

[0049] In another exemplary aspect, the inner surface defines a shoulder that projects radially inwardly relative to the longitudinal axis of the elongate body, wherein the shoulder is configured to engage an end portion of the core lifter to restrict axial movement of the core lifter.

[0050] In another exemplary aspect, the inner surface of the elongate body does not comprise a groove configured to receive a snap ring.

[0051] In another exemplary aspect, the elongate body is configured to receive the core lifter through the opening of the first end portion.

[0052] In another exemplary aspect, each slot of the plurality of slots of the elongate body has a variable circumferential width. In another exemplary aspect, the circumferential width of each slot of the plurality of slots of the elongate body decreases moving away from the opening of the first end portion relative to the longitudinal axis of the elongate body. In another exemplary aspect, at least a portion of the inner surface of the core lifter case is inwardly tapered moving toward the opening of the first end portion, wherein the plurality of slots intersect the tapered portion of the inner surface.

[0053] In another exemplary aspect, the second end portion of the elongate body is configured for engagement with an inner tube assembly of a drilling system. In another exemplary aspect, at least a portion of the inner surface of the second end portion is threaded.

[0054] In various exemplary aspects, disclosed herein is a core lifter system for permitting lifting of a core sample, the core lifter system comprising: a core lifter case having a longitudinal axis, a first end portion, an opposed second end portion, and an inner surface defining a central bore, the first and second end portions defining respective openings in communication with the central bore, wherein the inner surface of the first end portion defines a plurality of circumferentially spaced slots; and a core lifter having an inner surface and an outer surface, the outer surface defining a plurality of circumferentially spaced ribs, wherein each slot of the plurality of slots of the core lifter case is configured to receive at least a portion of a corresponding rib defined by the outer surface of the core lifter.

[0055] In another exemplary aspect, the inner surface of the core lifter case defines a shoulder that projects radially inwardly relative to the longitudinal axis of the core lifter case, wherein the core lifter has an end portion, and wherein the shoulder of the core lifter case is configured to engage the end portion of the core lifter to restrict axial movement of the core lifter.

[0056] In another exemplary aspect, the core lifter system does not comprise a snap ring.

[0057] In another exemplary aspect, the inner surface of the core lifter case does not comprise a groove configured to receive a snap ring.

[0058] In another exemplary aspect, the core lifter case is configured to receive the core lifter through the opening of the first end portion of the core lifter case.

[0059] In another exemplary aspect, each slot of the plurality of slots of the core lifter case has a variable circumferential width. In another exemplary aspect, the circumferential width of each slot of the plurality of slots of the core lifter case decreases in a first direction, wherein the first direction corresponds to movement away from the opening of the first end portion relative to the longitudinal axis of the core lifter case. In another exemplary aspect, at least a portion of the inner surface of the core lifter case is inwardly tapered moving toward the opening of the first end portion of the core lifter case, wherein the plurality of slots of the core lifter case intersect the tapered portion of the inner surface of the core lifter case. In another exemplary aspect, each rib of the plurality of ribs of the core lifter has a variable circumferential width. In another exemplary aspect, the core lifter has a longitudinal axis, wherein when the core lifter is positioned in an insertion orientation in which the longitudinal axis of the core lifter is substantially axially aligned with the longitudinal axis of the core lifter case, the circumferential width of each rib increases in the first direction.

[0060] In another exemplary aspect, the second end portion of the core lifter case is configured for engagement with an inner tube assembly of a drilling system. In another exemplary aspect, at least a portion of the inner surface of the second end portion of the core lifter case is threaded.

[0061] In another exemplary aspect, the core lifter system further comprises an inner tube, wherein the core lifter case and the inner tube are integrally formed.

[0062] In various exemplary aspects, disclosed herein is a method of collecting a core sample within a formation, comprising: inserting a core lifter within a core lifter case through an opening of a first end portion of the core lifter case, an inner surface of the first end portion of the core lifter case defining a plurality of circumferentially spaced slots, an outer surface of the core lifter defining a plurality of circumferentially spaced ribs, wherein each slot of the plurality of slots of the core lifter case receives at least a portion of a corresponding rib defined by the outer surface of the core lifter; and engaging a portion of the core sample with the core lifter.

[0063] In another exemplary aspect, the core lifter case has a second end portion that is axially opposed from the first end portion, wherein the second end portion is configured for engagement with an inner tube assembly of a drilling system.

[0064] In another exemplary aspect, the method does not comprise using a snap ring to secure the core lifter within the core lifter case. [0065] In another exemplary aspect, at least a portion of the inner surface of the core lifter case is inwardly tapered moving toward the opening of the first end portion of the core lifter case, wherein the plurality of slots of the core lifter case intersect the tapered portion of the inner surface of the core lifter case, and wherein the tapered portion of the inner surface of the core lifter case applies a wedging force to the core lifter to thereby engage a portion of the core sample.

[0066] Although several embodiments of the invention have been disclosed in the foregoing specification, it is understood by those skilled in the art that many modifications and other embodiments of the invention will come to mind to which the invention pertains, having the benefit of the teaching presented in the foregoing description and associated drawings. It is thus understood that the invention is not limited to the specific embodiments disclosed hereinabove, and that many modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although specific terms are employed herein, as well as in the claims which follow, they are used only in a generic and descriptive sense, and not for the purposes of limiting the described invention, nor the claims which follow.