FIELD OF INVENTION

[0001 ] The present invention relates to a ring replacement system for a core lifter assembly used in core drilling.

[0002] More particularly, the present invention relates to a ring replacement system for a core lifter assembly enabling the replacement of a core lifter ring in a core lifter assembly. The replacement may involve either or both of: inserting the core lifter ring into a core lifter case; and removing a core lifter ring from a core lifter case.

BACKGROUND ART

[0003] A core lifter assembly is attached to a downhole end of a core barrel which in turn is carried by a core drill. When the core drill is in operation it cuts a core sample of the ground which passes through the core lifter assembly and into the core barrel. In order to retrieve the core sample once drilling has ceased the core drill is lifted from the toe of the hole. During this process the core lifter assembly grips the core so that the lifting force on the drill is transferred onto the core, breaking it from the ground. When the core barrel is retrieved either via use of a wireline, or by withdrawal of the entire core drill, the core sample is held in the core barrel by the core lifter assembly.

[0004] The core lifter assembly comprises two main components namely a core lifter case that encloses a core lifter ring, both being roughly in the form of hollow cylinders with the core lifter ring being concentrically surrounded by the core lifter case. An outer circumferential surface of the core lifter ring and an inner circumferential surface of the core lifter case are formed with complimentary tapered surfaces that taper radially inwardly towards the downhole end of the core lifter assembly. The core lifter ring is able to slide axially within and relative to the core lifter case.

[0005] The core lifter ring is not a full or complete ring but is commonly a split ring having a longitudinal slot through its side wall forming opposed first and second edges of the ring. The ring is made of a resilient material, such as spring steel, which biases the ring toward a maximum (expanded) outer diameter and a corresponding maximum width of the slot, which is achieved when the core lifter ring is in an uphole position relative to the case. Conversely, the ring becomes compressed and narrows the slot as it is moved towards a downhole position relative to the case. The minimum (compressed) outer diameter of the ring is achieved when the edges of the slot abut against each other to close the slot.

[0006] In use, when an associated core drill is drilling a core sample and the core sample is entering the core barrel, the core lifter ring is biased by the core towards its uphole position. During a core breaking operation the core drill, and accordingly its attached core lifter case, is lifted in an uphole direction. However the ring is retarded by friction against the core with the effect that the core lifter case slides uphole relative to the ring. Due to the tapered surfaces of the case and ring, the ring becomes compressed about an outer circumferential surface of the core sample.

[0007] The open downhole end of the core lifter case has internal diameter that is smaller than the compressed outer diameter of the ring so that the core lifter ring is retained at the downhole end of the case. In order to retain the core lifter ring at an uphole end of the core lifter case, a shoulder or similar feature is needed in the uphole end of the core lifter case, commonly called a stop ring. By moving the shoulder axially away from the uphole end, the shoulder also prevents the core lifter ring from sliding too far axially in an uphole direction within the core lifter case. To provide effective functionality, the shoulder has an inner diameter that is also smaller than the compressed outer diameter of the core lifter ring. Such a shoulder has usually been formed by either providing an integral shoulder within the case or by providing a removable circlip type of component internally within the case. The integral shoulder is often preferred by drill rig operators because removable stop rings can be problematic, e.g. they may slide out of place axially, rotate radially and jam or dislodge from the core lifter case altogether. When this sort of thing happens during a drilling operation the core may become stuck causing a blockage or the core lifter my not function causing the core to be left in the borehole.

[0008] However, the disadvantage of a fixed shoulder is that it is more difficult to remove the core lifter ring from the core lifter case for servicing. This is due to the compressed outer diameter of the core lifter ring being larger than both the internal diameter of the open downhole end of the core lifer case and also larger than the internal diameter of the shoulder. Thus, in order for the core lifter ring to be removed, the core lifter ring must be physically manipulated to radially bend the first edge of the ring inwardly relative to the opposed second edge so that the first edge can slide past the second edge inside the ring, thereby to allow the outer diameter of the ring to be reduced more than the compressed outer diameter. This allows the outer diameter of the core lifter ring to be reduced enough so that it can fit out through the internal opening of the fixed shoulder.

[0009] The physical manipulation is cumbersome. Normally an operator will use a screwdriver, or similar thin pointed implement to bend the edge of the core lifter ring radially inwards. They then have to simultaneously compress the ring circumferentially and axially press the core lifter ring to remove it from the core lifter case. This may require considerable force due to the resiliency of the core lifter ring. The operator may attempt to press the core lifter ring out by hand or, if that does not succeed, they may resort to using a hammer, punch or other instrument to force it out.

[0010] Using a pointed implement and applying hand force simultaneously can present a significant safety risk. This risk is increased if the core lifter case is not secured in a vice or other clamping device, but is held by hand. Also, the pointed implement commonly results in damage to the core lifter components, which is problematic as it may cause the core lifter assembly to malfunction. Further, the inability to easily remove the core lifter ring from the core lifter case causes time delays and frustration to the operators.

[001 1 ] Throughout this specification and claims the term "downhole end" is intended to denote a toe end of a bore hole while the expression "uphole end" is intended to denote a collar end. Accordingly the downhole end of a hole may be vertically above an uphole end where for example a hole is drilled upwardly or with at least a vertical upward inclination.

[0012] The above described background art is not intended to limit the application of the ring replacement system for a core lifter assembly as disclosed herein.

SUMMARY OF THE INVENTION

[0013] In one aspect there is disclosed a ring replacement system for a core lifter assembly for use in inserting a core lifter ring into a core lifter case or for removal thereof, the core lifter ring having a ring wall with an axial slot extending through the ring wall to define opposed first and second edges, the ring replacement system comprising:

a body defining a passage configured to receive the core lifter case;

a distorting member arranged to extend into the core lifter case when received in the body; and a plunger being adapted to move the core lifter ring relative to the core lifter case and to bring the core lifter ring into contact with the distorting member to distort the core lifter ring in manner to reduce an outer diameter of the core lifter ring to enable the plunger to move the core lifter ring into or out of the core lifter case.

[0014] In one embodiment edge relative to the first edge so that the second edge is simultaneously deflected radially inwardly and circumferentially in a direction towards the first edge enabling the second edge to move past the first edge.

[0015] In one embodiment the passage comprises a first part and a second part, the first part having a first internal diameter and the second part having a concentrically larger second internal diameter.

[0016] In one embodiment the first internal diameter is substantially similar to an outer diameter of the core lifter ring when the core lifter ring is in an unloaded state.

[0017] In one embodiment the second internal diameter is substantially similar to an outer diameter of the core lifter case.

[0018] In one embodiment the distorting member comprises a ramp along which the second edge can progressively ride to cause the reduction in the outer diameter of the core lifter ring.

[0019] In one embodiment the distorting member is supported by the body in a cantilever having a movable free end and an opposed fixed heel supported by the body.

[0020] In one embodiment, the distorting member has a flattened or tapered point at its free end.

[0021 ] In one embodiment, the point is flattened or tapered in a plane being concentric with or substantially parallel to an internal surface of the passage.

[0022] In one embodiment the distorting member is configured whereby, when an up- hole end of the core lifter case is inserted into the passage, the distorting member extends through the up-hole end of the core lifter case and towards an internal shoulder provided within the core lifter case. [0023] In one embodiment, the distorting member has a length sufficient to traverse the internal shoulder.

[0024] In one embodiment, the body comprises a sidewall and the distorting member extends though the sidewall to be manipulate from outside the sidewall.

[0025] In one embodiment, the plunger comprises an axial recess, wherein the recess is adapted to at least partially receive the distorting member in use.

[0026] In one embodiment, the body comprises an intermediate tapered surface between the first part and the second part wherein the intermediate tapered surface progressively decreases in inner diameter in a direction from the first part to the second part.

[0027] In one embodiment the plunger comprises an engagement mechanism configured to engage an up hole end of a core lifter ring when the core lifter case is received in the passage and the plunger is inserted through the passage into the core lifter case.

[0028] In one embodiment the engagement mechanism comprises one or more levers pivotally connected to the plunger wherein each of the one or more levers is provided with a hook for engaging the up-hole end of the core lifter ring.

[0029] In one embodiment, each of the one or more levers is provided with an insertion shoulder arranged to engage the downhole end of a core lifter ring to enable insertion of a core lifter ring into the core lifter case.

[0030] In one embodiment of the ring replacement system comprises one or more insertion levers pivotally connected to the plunger, each of the one or more insertion levers being provided with an insertion shoulder arranged to engage the downhole end of a core lifter ring to enable insertion of a core lifter ring into the core lifter case.

[0031 ] In one embodiment, the insertion shoulders are spaced from the hook by a distance enabling the core lifter ring to be disposed between the insertion shoulder and the hooks.

[0032] In one embodiment the levers are biased in a manner to disengage from an otherwise engaged core lifter ring. [0033] In one embodiment the levers are biased in a manner to self-engage the core lifter ring.

[0034] In a second aspect there is disclosed a ring replacement system for a core lifter assembly for use in inserting a core lifter ring into a core lifter case or for removal thereof, the core lifter ring having a ring wall with an axial slot extending through the ring wall to define opposed first and second edges, the ring replacement system comprising:

a body defining a passage configured to receive the core lifter case and an associated distorting member capable of extending into the passage to lie between the core lifter ring and the core lifter case when the core lifter case is received in the body to facilitate distortion of the core lifter ring in manner to reduce an outer diameter of the core lifter ring enabling core lifter ring to be moved into or out of the core lifter case.

[0035] In a third aspect there is disclosed a ring replacement system for a core lifter assembly for use in inserting a core lifter ring into a core lifter case or for removal thereof, the core lifter ring having a ring wall with an axial slot extending through the ring wall to define opposed first and second edges, the ring replacement system comprising:

a distorting member capable of being located between a core lifter case and a core lifter ring; and

a plunger configured to enable travel into and out of the core lifter case and arranged to contact the core lifter ring and move the core lifter ring against the distorting member to distort the core lifter ring in a manner to reduce an outer diameter of the core lifter ring to enable the core lifter ring to pass out of the core lifter case for removal or into the core lifter case for installation.

[0036] In one embodiment when the method is used for installation of a core lifter ring into a core lifter case the method comprises: inserting a core lifter ring into a ring-less core lifter case by locating the core lifter ring adjacent to or partially in an end of the core lifter case and then using the plunger to push the core lifter ring against the distorting member and fully into the core lifter case.

[0037] In one embodiment when the method is used for removal of core lifter ring from a core lifter case, the method comprises: inserting the plunger into the core lifter case;

engaging the plunger with an up-hole end of the core lifter ring and pulling the plunger out of the core lifter case wherein the core lifter ring abuts and rides along the distorting member and reduces in outer diameter to facilitate passage out of the core lifter case. [0038] In one embodiment the method comprises inserting the core lifter case into a passage of a body from one end and wherein the plunger is inserted into the core lifter case through the passage from an opposite end of the body.

[0039] In a fourth aspect there is disclosed a method of replacing a core lifter ring in a core lifter case, the core lifter ring having a ring wall with an axial slot extending through the ring wall to define opposed first and second edges, the method comprising: locating a distorting member between an inner surface of the core lifter case and an outer surface of the core lifter ring; and

inserting a plunger through an end of the core lifter case to contact the core lifter ring and subsequently moving the plunger to move the core lifter ring against the distorting member to distort the core lifter ring in a manner to reduce an outer diameter of the core lifter ring to enable the core lifter ring to pass out of or into the core lifter case.

[0040] In one embodiment the method comprises inserting the downhole end of the core lifter case into the passage.

[0041 ] In one embodiment inserting the core lifter case comprises inserting a core lifter case without a core lifter ring into the passage; and the method further comprises inserting a core lifter ring into the core lifter case by placing the core lifter ring into the passage from an end opposite the core lifter case and then using the plunger to push the core lifter ring against the distorting member and into the core lifter case.

[0042] In one embodiment inserting the core lifter case comprises inserting a core lifter case provided with a core lifter ring into the passage; and the method further comprises: inserting the plunger into the passage from an end opposite the core lifter case; engaging the plunger with an upper-hole end of the core lifter ring and pulling the plunger out of the end wherein the core lifter ring abuts the distorting member and reduces in outer diameter to facilitate passage out of the core lifter case.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Notwithstanding any other forms which may fall within the scope of the system and method as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: Figure 1 is a perspective view of a ring replacement system for a core lifter assembly according to a first embodiment of the invention, showing a body arranged to receive a plunger;

Figure 2 is a side view of the ring replacement system seen along arrow II in Figure 1 , showing the plunger located adjacent to the body;

Figure 3 is an exploded perspective view of the ring replacement system being aligned for use to insert a core lifter ring into a core lifter case;

Figure 4 is a sectional side view of an initial step during use of the ring replacement system for insertion of the core lifter ring into the core lifter case;

Figure 5 is a sectional side view of an intermediate step during use of the ring replacement system for insertion of the core lifter ring into the core lifter case;

Figure 6 is a partial perspective view of the intermediate step showing deflection of the core lifter ring;

Figure 7 is a sectional side view of a final step during use of the ring replacement system for insertion of the core lifter ring into the core lifter case;

Figure 8 is a sectional side view of an intermediate step during use of the ring replacement system for removal of the core lifter ring from the core lifter case;

Figure 9 is a sectional side view of a final step during use of the ring replacement system for removal of the core lifter ring from the core lifter case;

Figure 10 is a sectional side view of a ring replacement system for a core lifter assembly according to a second embodiment of the invention.

Figure 1 1 is a schematic representation of a second embodiment of the ring replacement system in an initial stage of inserting a core lifter ring into a core lifter case;

Figure 12 is a representation of the second embodiment shown in Figure 1 1 in an intermediate stage of insertion of the core lifter ring into the core lifter case; Figure 13 is a representation of the second embodiment shown in Figure 1 1 in a final stage of insertion in which the core lifter ring is wholly located within the core lifter case;

Figure 14 is a representation of the second embodiment of the ring replacement system in an initial stage of use when removing the core lifter ring from the core lifter case;

Figure 15 is a representation of the ring replacement system shown in Figure 14 in an intermediate stage of removal of the core lifter ring from the core lifter case;

Figure 16 shows the ring replacement system in a further stage of removal to that shown in Figure 15 in which the core lifter ring is fully withdrawn from the core lifter case;

Figure 17 is a schematic representation of the second embodiment of the ring replacement system when removing the core lifter ring from the core lifter case and at this stage marginally prior to the core lifter ring leaving the core lifter case;

Figure 18 is an enlarged view of detail A of Figure 17;

Figure 19 is a schematic representation of a third embodiment of the ring replacement system;

Figure 20 is an enlarged view of detail B of Figure 19;

Figure 21 is a schematic representation of a fourth embodiment of the ring replacement system; and

Figure 22 is an enlarged view of detail B of Figure 21 .

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0044] Referring to Figures 1 and 2 of the drawings, there is shown a first embodiment of a ring replacement system 100 for a core lifter assembly in accordance with the invention. The ring replacement system 100 comprises a hollow cylindrical body 102 being arranged to slidingly receive a plunger 104.

[0045] The body 102 has an annular sidewall 106 defining a passage 108 being open at both a first end 1 10 and a second end 1 12 of the body 102. An internal annular step 1 14 is provided in the sidewall 106 within the passage 108 so that the passage 108 has a first internal diameter extending from the step 1 14 to the first end 1 10 and a concentrically enlarged second internal diameter extending from the step 1 14 to the second end 1 12. The step 1 14 operatively divides the body 102 into a ring part 1 16 and a case part 1 18, wherein during use the ring part 116 is adapted to receive a core lifter ring and the case part 1 18 is adapted to receive a core lifter case, as will be further described in due course.

[0046] A distortion member in the form of an elongated pin 120 is arranged to extend into the passage 108 in substantial axial alignment with the body 102. In this embodiment the distortion member/pin 120 is carried by the body and in particular is cantilevered having a heel 122 that is secured to the body 102 within the ring part 1 16 and from which the pin 120 extends into the case part 1 18 so that it traverses the step 1 14. The heel 122 forms a ramp leading from the sidewall 106 onto the pin 120. The pin 120 terminates before exiting the second end 1 12 and has a flattened point 124. The point 124 is flatted in a plane that is substantially parallel to or concentric with the sidewall 106. In the exemplary embodiment, the heel 122 is shown extending through a slot 126 in the sidewall 106 and being wrapped externally annularly around the sidewall 106 to secure it to the body 102. However, in other embodiments the heel 122 can be secured to the body 102 in any other suitable manner, such as being embedded into the sidewall 16 or being integrally formed with the body 102.

[0047] A depression 128 is formed externally in the sidewall 106 at the slot 126 so that the heel 122 extends though the depression 128. The pin 120 is made of a resilient material. In the exemplary embodiment the pin 120 is made of metal, such as spring steel, so that it is substantially rigid but has at least a slight resilience allowing it to be manipulated from outside the body 102, for example by manually pressing the heel 122 into the depression 128 so that the radial space between the point 124 and an internal surface 130 of the

sidewall 106 can be enlarged. When the pressing force is released, the point 124 returns to its original position lying closer to the internal surface 130.

[0048] The plunger 104 is in the form of a solid cylindrical shaft 132 having a base 134 at one end of the shaft 132 and a handle 136 provided at an opposed end thereof. A recess 138 is axially provided in the shaft 132 and extends from the base 134 towards the handle 136. The recess 138 is adapted to receive the pin 120 when the shaft 132 is inserted into the passage 108. The shaft 132 has a diameter being smaller than the internal diameter of the passage 108 within the ring part 1 16. As will be explained later, the diameter of the shaft 132 must be large enough so that the base 134 is able to circumferentially abut against an end of a core lifter ring but small enough so that the shaft 132 can pass through a core lifter case.

[0049] The plunger 104 has at least one abutting formation to stop the shaft 132 and prevent it from penetrating too deeply into the passage 108 during use and thereby preventing damage to the pin 120 or injury to an operator. The exemplary embodiment of the plunger 104 displays two types of abutting formations that may be utilised, but only one is needed in practice. The first abutting formation is in the form of an annular collar 140 surrounding the shaft 132, wherein the collar 140 is spaced apart from the base 134 by a distance being substantially equivalent to a height of the body 102. Thus in use, the shaft 132 is only able to slide through the passage 108 to the extent until the collar 140 abuts against the sidewall 106. The second abutting formation is in the form of an elongated buttress 142 extending axially from the base 134 of the shaft 132, wherein the buttress 142 is adapted to contact a working surface supporting the body 102 to prevent further movement of the shaft 42 through the passage 108.

[0050] In use the ring replacement system 100 is adapted to either insert a core lifter ring 200 into a core lifter case 300 or to remove the core lifter ring 200 from the core lifer case 300. Hereinafter the core lifter ring 200 will be referred to as "ring 200" whereas the core lifter case will be referred to as "case 300". The use will first be described with reference to Figures 3 to 7, which show the steps during insertion of the ring 200 into the case 300. Thereafter the use will be described with reference to Figures 8 and 9, which show the steps during removal of the ring 200 from the case 300.

[0051 ] The ring 200 is in the form of a split ring having an annular ring wall 202 in which there is an axially extending slot 204. Accordingly the ring wall has a first edge 206 and a second edge 208 bordering the slot 204. The ring wall 202 is made from a resilient material such as but not limited to spring steel. As a consequence the ring 200 can be

circumferentially compressed and expanded, thereby to reduce or enlarge a width of the slot 204. The edges 206, 208 can also be radially deflected to a slight extent to move them closer to or further away from a centre of the ring 200. However the ring 200 is configured so that in an unloaded state it assumes an expanded outer diameter. The ring wall 202 has a tapered outer surface 210 that reduces from a large diameter end 212 to a small diameter end 214. Thereby the ring wall 202 is in the shape of a wedge. [0052] The case 300 is in the form of a hollow cylinder and has an uphole end 302 and a downhole end 304. The uphole end 302 is provided with an internal screw thread 306 to enable coupling to an inner core barrel. Downhole of the thread 306 there is provided an internal shoulder 308 and downhole of the shoulder 308 there is provided a tapered surface portion 310 leading to the downhole end 304. The surface portion 310 has a taper substantially complimentary to the taper of the outer surface 210. In use, when the ring 200 is located inside the case 300, the tapers of the surface portion 310 and the outer surface 210 cooperate with each other to circumferentially compress the ring 200 as the ring 200 slides axially relative to the case 300 from the shoulder 308 towards the downhole end 304, thereby reducing the width of the slot 204. At some stage along such axial sliding the slot 204 will close and the first edge 206 will abut the second edge 208, at which stage the ring 200 has what is referred to as its compressed outer diameter. This prevents further compression of the ring 200 and also prevents further movement of the ring 200 towards the downhole end 304, thereby preventing the ring 200 from exiting the case 300 through the downhole end 304. In use, when removing a core in a drilling operation, the ring will clamp against the core before the slot 204 becomes fully closed.

[0053] When the ring 200 slides axially towards the uphole end 302, the shoulder 308 acts as a stop to prevent the ring 200 exiting the uphole end 302. The shoulder 308 has an internal diameter being smaller than both the expanded outer diameter and the compressed outer diameter of the ring 200.

[0054] As shown in Figures 3 to 7, in use in order to insert the ring 200 into the case 300, in an initial step shown in Figures 3 and 4 the case 300 is inserted into the body 102 by sliding its uphole end 302 into the passage 108 in the case part 1 18. The case part 1 18 has an internal diameter that is substantially similar to the outer diameter of the case 300 so that the case 300 fits snugly within the passage 108 and cannot wobble therein. The case 300 is inserted into the passage 108 until it abuts against the step 1 14. While inserting the case 300, the point 124 of the pin 120 is pushed further radially into the passage 108, by pressing the heel 122 into the depression 128, so that the case 300 is directed to be located between the pin 120 and the sidewall 106. The pin 120 has a length sufficient that the point 124 extends over the shoulder 308 (as can be clearly seen in Figure 4). However, it should be understood that in other embodiments the pin 120 can have a shorter length so that it merely abuts against the shoulder 308. [0055] The ring 200 is inserted into the body 102 by sliding it into the passage 108 in the ring part 1 16. The ring part 1 16 has an internal diameter that is substantially similar to orjust slightly smaller than the expanded outer diameter of the ring 200 so that the ring 200 can be easily pressed therein by hand and fits snugly within the passage 108 so that it does not wobble therein. The ring 200 is rotated within the ring part 1 16 so that one of its

edges 206, 208 is axially aligned to be closely in line with the pin 120. In Figures 3 to 7, it can be seen that the second edge 208 is aligned with the pin 120.

[0056] The plunger 104 is subsequently used to press the ring 200 further into the passage 108. In an intermediate step shown in Figures 5 and 6, as the second edge 208 contacts against the pin 120, it rides up the ramp formed by the heel 122 and is resiliently helically deflected to be bent radially inwards into the passage 108 so that the second edge 208 is located radially inwards from the first edge 206. The deflection simultaneously circumferentially compresses the ring wall 202 so that the second edge 208 moves circumferentially towards and past the first edge 206, thereby causing the ring 200 to be circumferentially compressed to such an extent that the ring 200 has a reduced outer diameter being smaller than its compressed outer diameter, and whereby the reduced outer diameter is also smaller than the internal diameter of the shoulder 308. The appearance of the deflected ring 200 can be more clearly seen in Figure 6.

[0057] Further pressing by the plunger 104 causes the deflected ring 200 to move beyond the shoulder 308 until it rides off the point 124 of the pin 120. At such final stage, shown in Figure 7, the second edge 208 springs back to revert to its original non-deflected position or until the outer surface 210 contacts and conforms to the corresponding taper of the surface portion 310. Lastly, the case 300 is removed from the body 102 for use as a core lifter assembly in normal manner.

[0058] During the intermediate step, as the first edge 206 is not deflected it remains aligned with the shoulder 308 and can come into contact with the shoulder 308 while the ring 200 is pressed through the passage 108. Although this contact may cause a hindrance to the movement of the ring 200, the hindrance is overcome by pressing the plunger 104 with sufficient force and/or by rotationally wiggling the plunger 104 within the passage 108. Due to the resiliency of the ring 200, this causes the second edge 208 to move slightly beyond the shoulder 308 whereafter the end of the ring wall 202 rides circumferentially along the shoulder 308 and is successively deflected radially inwardly until the first edge 206 is also able to move beyond the shoulder 308. [0059] As shown in Figures 8 and 9, in use in order to remove the ring 200 from the case 300, the body 102 is inverted and the case 300 is inserted into the body 102 by sliding its downhole end 304 into the passage 108 in the case part 1 18. The case 300 is inserted into the passage 108 until it abuts against the step 1 14. While inserting the case 300, the ring 200 is rotated within the case 300 so that one of its edges 206, 208 is axially aligned with the pin 120. In Figure 8, it can be seen that the second edge 208 is again aligned with the pin 120. Simultaneously, the point 124 of the pin 120 is directed to enter between the ring wall 202 and the case 300. This is assisted by the flatness of the point 124 enabling it to slide into and initially deflect the second edge 208 radially inwardly.

[0060] The plunger 104 is subsequently inserted through the uphole end 302 and used to press the ring 200 towards the downhole end 304. This causes the second edge 208 to ride up the point 124 onto the pin 120 and be resiliently helically deflected radially into the passage 108 so that the second edge 208 is located radially inwards from the first edge 206. The deflection simultaneously circumferentially compresses the ring wall 202 so that the second edge 208 moves circumferentially towards and past the first edge 206. The circumferential compression is further effected by the respective tapers of the outer surface 210 and the surface portion 310, thereby causing the ring 200 to be circumferentially compressed to such an extent that the ring 200 has a reduced outer diameter being smaller than its compressed outer diameter, and whereby the reduced outer diameter is also smaller than the internal diameter of the downhole end 304. The appearance of the deflected ring 200 will be largely similar to that shown in Figure 6 during the insertion step.

[0061 ] Further pressing by the plunger 104 causes the deflected ring 200 to move through the downhole end 304 until it rides off the heel 122 of the pin 120 and is located in the ring part 1 16 of the passage 108. Lastly, the case 300 and ring 200 can be separately removed from the body 102 for inspection, lubrication, repair or for insertion of a new ring 200 into the case 300.

[0062] It should be borne in mind that when inserting the plunger 104 into the passage 108 to press on the ring 200, the plunger is rotated to align the recess 138 with the pin 120 so that the pin 120 is received in the recess 138 during use. [0063] In the exemplary embodiment shown in Figures 3 to 9, the inner diameter of the passage 108 in the ring part 1 16 is substantially the same as the inner diameter of the uphole end 302 of the case 300.

[0064] In a second embodiment shown in Figure 10, the ring replacement system 100 can include a sleeve 150 insertable into the uphole end 302 of the case 300 to lead from the ring part 1 16 to the shoulder 308. The sleeve 150 is tapered so that it has an internal diameter at its entry adjacent the ring part 1 16 being substantially the same as the inner diameter of the ring part 1 16 and has an internal diameter at its exit adjacent the shoulder 308 being substantially the same as the inner diameter of the shoulder 308. The sleeve 150 is adapted to be inserted between the pin 120 and the case 300. Thereby in use, as the second edge 208 quickly rides up and along the pin 120, the first edge 206 subsequently slowly rides up along the taper of the sleeve 150. Thereby both edges 206, 208 are deflected radially inwardly to avoid the first edge 206 being hindered by contacting against the shoulder 308. The sleeve 150 may optionally be removably attached to the body 102 within the case part 1 18.

[0065] Although not shown in the drawings, the body 102 can be provided with an alignment system to ensure that either or both the plunger recess 138 and the ring 200, namely either the first or second edge 206, 208, are correctly aligned with the pin 120 during use. Such an alignment system can include a ridge, protrusion, pin or grub screw extending radially into the passage 108 and being adapted to be received into the slot 204. A corresponding groove will then need to be provided in the shaft 132 for receiving such a ridge, protrusion, pin or grub screw.

[0066] The above-described first and second embodiments of the ring replacement system 100 are arranged to facilitate replacement of the ring 200 by insertion of the plunger 104 through an up-hole end 302 of the case 300. This of course requires the case 300 to be unscrewed from an associated inner core barrel. Further embodiments of the ring replacement system will now be described which enable replacement of the ring 200 by inserting the plunger 104 through the downhole end 304 of the case 300 thereby avoiding the need to unscrew the case 300 from the inner core barrel.

[0067] Figures 1 1 -18 depict a second embodiment of the ring replacement system 100D which facilitates replacement of a ring 200 via the downhole end 304 of the case 300. In describing this embodiment of the system 100D all features which have the same or similar structure and/or function as those in the first embodiment of the system 100 will be denoted with the same reference numbers. The system 100D comprises a body 102 and the plunger 104. The body 102 differs from that of the first embodiment by the inclusion of an intermediate tapered surface160 in the central passage 108. The tapered surface 160 reduces the diameter in a direction from the ring part 1 16 to the case part 1 18. A smallest diameter end 162 of the tapered surface 160 terminates concurrently with the step 1 14. Moreover the smallest of diameter end 162 is arranged to have a diameter substantially the same as the inner diameter of the downhole end 304 of the case 300. This is shown most clearly in Figure 17.

[0068] When the system 100D is used to insert a ring 200 into the case 300 the case 300 is inserted into the case part 1 18 in an orientation so that the downhole end 304 abuts the shoulder 1 14. This is the inverse orientation to that shown for example in Figure 4. During this insertion process the pin 120 is pushed inwardly through the recess 128 so that the pin 120 is inside of the case 300 as shown in Figures 1 1 -16.

[0069] The ring 200 is inserted into the ring part 1 16 in an orientation so that its largest diameter end 212 is closest to the case portion 1 18. This is also the reverse orientation to that shown in Figure 4. The ring 200 when inserted into the ring part 1 16 is orientated so that one of its edges 206, 208 is axially aligned to be closely in line with the pin 120.

[0070] The plunger 104 is now inserted into the ring part 1 16 and pushed in an inward direction so that the base 134 abuts the small diameter end 214 of the ring 200. In the same manner as described above in relation to the first embodiment the second edge 208 contacts the pin 120, rides up the ramp formed by the heel 122 and is resiliently helically deflected to be bent radially inwards into the passage 108 so that the second edge 208 is located radially inwards from the first edge 206. The deflection simultaneously circumferentially compresses the ring wall 202 so that the second edge 208 moves circumferentially towards and past the first edge 206, thereby reducing the outer diameter of the ring 200. This reduction in outer diameter is further assisted by abutment with the tapered surface 160. The combined effect of the tapered surface 106 and the pin 120 is to reduce the outer diameter of the ring 200 to be less than the inner diameter of the downhole end 304 of the case 300. Therefore continued pushing of the plunger 104 in a direction toward the case 300 results in the ring 200 passing through the downhole end 304 and into the core lifter case 300 as shown progressively in Figures 12 and 13. The plunger 104 can now be withdrawn from the body and the core lifter assembly is now ready for use. [0071 ] With particular reference to Figures 14-18 in order to facilitate the withdrawal of a ring 200 from the downhole end at 304 of the case 300 the plunger 104 is provided with, in this embodiment, a ring engagement mechanism which is configured to engage the large diameter end 212 (i.e. the up hole end) of the ring 200 when located within the core lifter case 300. The ring engagement mechanism is in the form of one or more (but in the presently depicted embodiment two) levers 170 that are pivotally connected to the shaft 132 about respective points 172. When two or more levers are used it is preferable for the levers to be evenly spaced about the plunger 104. When one lever is used it is preferable but not essential that the one lever extends adjacent to the recess 138.

[0072] Each lever 170 is also provided at one end with a button 174 that protrudes from the handle 136, and a hook 176 at an opposite end. A biasing device, which in this embodiment is in the form of a spring 178, biases the levers 170 away from each other on the side of the pivot pins 172 opposite the hooks 176. The biasing device is arranged to pivot the hooks 176 toward each other. Moreover the plunger 104 is arranged so that in the absence of an externally applied force acting on the levers 170, the hooks 176 are biased to fit within a diameter less than the inner diameter of, and therefore do not engage, the up hole end 212. Accordingly, the biasing device 178 biases the levers 170 to a disengaged position in which the hooks 176, if they were in engagement with the core lifter ring 200, would pivot inwardly and disengage from the core lifter ring 200. Alternatively, the levers could be arranged so that the biasing device 178 biases the levers 170 to an engaged position and an external force on the levers 170 disengages the hooks 176 from the core lifter ring 200.

[0073] In order to remove the ring 200 from the case 300 the case 300 is inserted over and pushed onto the downhole end 304 of the body 102 so that the downhole end at 304 locate against the step 1 14. The up-hole end 302 of the case 300 is outside of the body 102. This orientation of the case 300 and body 102 is the same as in the first embodiment shown in Figure 8. As in the first embodiment while inserting the case 300, the ring 200 is rotated within the case 300 so that one of its edges 206, 208 is axially aligned with the pin 120. Simultaneously, the point 124 of the pin 120 is directed to enter between the ring wall 202 and the case 300. This is assisted by the taper of the point 124 enabling it to slide into and initially deflect the second edge 208 radially inwardly.

[0074] The plunger 104 is now inserted into the body 102 from the ring part 1 16 so that the plunger enters the case 300 from its downhole end 304 rather than the up hole end 302 is in the first embodiment. The spring 178 is biasing the ends of the levers 170 provided with the hooks 176 in a radial inward direction enabling the hooks 176 to pass through the ring 200. The plunger 104 is inserted to a depth so that the hooks 176 can hook onto the up-hole end 212 of the ring 200. This juxtaposition can be arranged by dimensioning the plunger 104 and buttress 142 so when the end of the buttress 142 is coplanar with the up hole end at 302 of the case 300 the hooks 176 are past the up-hole end 212 of the ring 200.

[0075] The user can now push inwardly on the buttons 174 against the bias of the spring 178 and pivoting the levers 170 outwardly so that the hooks 176 can engage the up-hole end 212. Simultaneously the plunger 104 is pulled outwardly away from the case 300 are shown progressively in Figures 14-16, and in enlarged view in Figures 17 and 18. While this is happening one of the edges 206, 208 rides up the pin 120 causing that edge to helically deflect radially inward of the other edge thereby reducing the overall diameter of the ring 200. The diameter is reduced to the extent that the ring carried by the hooks 176 can now pass through the downhole end 304 of the case 300 as shown in Figure 16. If a user maintains pressure on the buttons 174 and now fully extracts the plunger 104 the ring 200 will be carried out of the body 102 on the plunger 104. Release of pressure on the buttons 174 will allow the spring 178 to pivot the hooks 176 radially inward toward each other releasing the ring 200. Alternately the user can release pressure on the buttons 174 when the ring 200 has been called wholly into the ring part 1 16. The body 102 can now be pulled off the case 300 and inverted so that the ring 200 falls out of the body 102.

[0076] In a variation of the embodiment of the system 100D which is denoted as system 100Da shown in Figures 19 and 20 each the levers 170 can be provided with an additional insertion shoulder 180 located between the hook 176 and the pivot pin 172. The insertion shoulder 180 is used to engage the downhole end 214 of the ring 200 during the installation process instead of the base 134 of the plunger 104 as in the earlier described embodiments. In this embodiment the distance between the shoulder 180 and the hook 176 can be arranged to be marginally greater than the axial length of ring 200. Other than the shoulder 180 being used to engage the ring 200 during the insertion process the operation of the system 100Da is otherwise the same as described above in relation to the systeml OOD.

[0077] Figures 21 and 22 show yet another embodiment of the systeml OODb which differs from the system 10ODa by the provision of a second set of levers 182 which are generally coextensive with the levers 170 and pivotally connected to the shaft 132 by the common pivot pin 172. Each of the levers 182 is now provided with the shoulder 180. The levers 182 are provided with buttons 184 which can be pressed inwardly to pivot the shoulders 180 radially outward away from each other to engage the downhole end 214 of the ring 200 during the insertion process.

[0078] Whilst a number of specific system and method embodiment have been described, it should be appreciated that the method and system may be embodied in many other forms. For example in the described embodiments the distorting member/pin 120 shown as being attached to the body 102. However the distorting member may be associated with the system 100 in other ways. For example the distorting member may be a separate component of the system in the same way as the body 102 and the plunger 104 and simply inserted between the core lifter ring 200 and the core lifter case 300 during the installation or removal process. Alternately, the distorting member may be carried or otherwise supported by the plunger 104. In yet another embodiment the system 100 may comprise only the plunger 102 and the distorting member/pin 120. In such an embodiment when inserting or removing a core lifter ring 200 the core lifter case 300 may be either: (a) held stationary for example by a vice, particularly if the core lifter assembly has been removed from an inner core tube; (b) held attached to inner core barrel which is particularly suitable when the ring is installed or removed from the downhole end of the core lifter case; or (c) placed freely on a bench or other support surface in which case a user may attempt to rely on their own strength and dexterity to facilitate relative movement between the plunger and the core lifter case to install or remove the core lifter ring.

[0079] In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" and variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the system and method as disclosed herein.