Abstract:
A container for receiving and retaining a sample from a subterranean formation, wherein the container is arranged to be removably accommodated within a coring assembly. The container comprises a receptacle, formed from at least two receptacle portions and a connector for connecting each receptacle portion to the adjacent receptacle portion, such that the receptacle portions are separable on disconnection of the connector. The receptacle portions can be complementary to form a receptacle in the shape of a substantially hollow cylinder. A cylinder axis can be defined by the long axis extending through the cylinder. The receptacle portions can be connectable along a line parallel to the cylinder axis of the receptacle such that at least one of the receptacle portions is movable radially away from the sample on disconnection of the connector.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a container and a method of receiving, retaining and accessing a sample, such as a core sample from a subterranean formation.  
       DESCRIPTION OF BACKGROUND ART  
       [0002]     Extracting core samples from subterranean formations is an important aspect of the drilling process in the oil and gas industry. The samples provide geological and geophysical data enabling a reservoir model to be established. Core samples are typically retrieved using coring equipment, which is transported to a laboratory where tests can be conducted on the core sample. However, on occasion it is advantageous if a core sample can be inspected on-site after retrieval.  
         [0003]     Core samples are conventionally collected in aluminium tubes. In order to view the sample on site it would be necessary to withdraw the sample axially from the tube or to make a longitudinal cut along the tube. Both of these methods of sample extraction have the potential to damage the sample.  
       BRIEF SUMMARY OF THE INVENTION  
       [0004]     According to a first aspect of the invention, there is provided a container for receiving and retaining a sample from a subterranean formation, wherein the container is arranged to be removably accommodated within a coring assembly, the container comprising at least one receptacle, wherein the or each receptacle is arranged to receive and retain a sample and wherein the or each receptacle has at least two receptacle portions and a connecting means for connecting each receptacle portion to the adjacent receptacle portion, such that the receptacle portions are separable on disengagement of the connecting means.  
         [0005]     According to a second aspect of the invention, there is provided a method of receiving, retaining and accessing a sample from a subterranean formation, comprising the steps of:  
         [0006]     a. forming a receptacle by providing at least two receptacle portions and connecting each receptacle portion to the adjacent receptacle portion using a connecting means;  
         [0007]     b. accommodating the receptacle within a coring assembly;  
         [0008]     c. receiving and retaining a sample within the receptacle;  
         [0009]     d. removing the receptacle from the coring assembly; and  
         [0010]     e. accessing the sample by disengaging the connecting means and removing one or more of the receptacle portions.  
         [0011]     According to a third aspect of the invention, there is provided an apparatus for receiving, retaining and accessing a sample from a subterranean formation, wherein the apparatus comprises a container arranged to be removably accommodated within a coring assembly, the container comprising at least one receptacle, wherein the or each receptacle is arranged to receive and retain a sample and wherein the or each receptacle has at least two receptacle portions and a connecting means for connecting each receptacle portion to the adjacent receptacle portion, and wherein the apparatus further comprises a tool for disengaging the connecting means to separate the receptacle portions.  
         [0012]     Removal of one or more of the receptacle portions provides easy access to the sample after recovery and the connecting means allow the receptacle portions to be separated with minimal or no damage to the sample. Provision of the receptacle portions is advantageous since the sample does not then have to be withdrawn axially from the receptacle for analysis, which generates friction and could result in the sample being damaged. Rather, the sample can be accessed and exposed by disengaging the connecting means to enable one or more of the portions to be lifted away from the sample without direct manipulation of the sample.  
         [0013]     The method can include providing a tool and accessing the sample by disengaging the connecting means using the tool.  
         [0014]     Each receptacle portion can have two long edges and two short end edges. The long edges of each receptacle portion can be arranged to connect with the long edge of the adjacent receptacle portion.  
         [0015]     The tool of the third aspect of the invention is usable with the container of the first aspect of the invention to disengage the connecting means and separate at least one of the receptacle portions. The tool can be provided to force the connecting means to disengage.  
         [0016]     The tool can comprise a bar having a pointed or bevelled end for insertion between the receptacle portions. Movement of the bar, following insertion of the end between the receptacle portions, can act to disengage the connecting means and force at least one of the receptacle portions away from the other receptacle portion(s).  
         [0017]     The end of the bar can be inserted between the two long edges of the receptacle portions. An outer portion of the or each long edge of the or each receptacle portion can be chamfered to facilitate access of the tool to the join between the long edges.  
         [0018]     The or each receptacle can be substantially cylindrical. Preferably, the receptacle portions and the connecting means are complementary to form a receptacle in the shape of a substantially hollow cylinder. According to the embodiment where the receptacle is substantially cylindrical, a cylinder axis can be defined by the long axis extending through the cylinder. The receptacle portions can be connected along a line parallel to a cylinder axis of the receptacle.  
         [0019]     The two or more receptacle portions can be separable along the line extending between the two ends of the portions, typically substantially parallel to the cylindrical axis, so that the two or more receptacle portions can be separable laterally from one another. Preferably at least one of the two or more receptacle portions are movable radially away from the sample on disengagement of the connecting means.  
         [0020]     Typically, each receptacle comprises two receptacle portions and the receptacle portions are in the form of half-shells.  
         [0021]     The connecting means are typically arranged to maintain the long edges of each receptacle portion in contact with one another when the container is receiving a sample.  
         [0022]     The connecting means can be integral with the or each receptacle portion. The connecting means can comprise moulded long edges of the receptacle portions.  
         [0023]     According to one embodiment, the connecting means can comprise a shaped recess disposed on at least a part of the long edge of a receptacle portion and a shaped protrusion disposed along a corresponding part of the long edge of an adjacent receptacle portion wherein the shaped protrusion can mate with the shaped recess. Each receptacle portion can have a protrusion disposed along one long edge and a recess disposed along the other long edge. The protrusion can be formed with a head having a width greater than an opening of the recess. Both the recess and the protrusion can be shaped to have a neck and a wider diameter head portion in section.  
         [0024]     Alternatively, the connecting means can comprise a separate shaped insert and each receptacle portion can be provided with recesses disposed along the long edges for receiving the shaped insert. The long edges of the receptacle portions can be formed with recesses shaped to securely receive the inserts. The recesses can have an opening that widens to an enlarged portion. The insert can have a head portion that is oversized relative to the width of the opening. The inserts can be substantially dumb-bell shaped.  
         [0025]     According to an alternative embodiment of the invention, the connecting means can comprise long edges of the receptacle portions having a centrally disposed recess such that the long edges of adjacent receptacle portions can be aligned to form one or more apertures between adjacent receptacle portions. The apertures can extend along the connection between the receptacle portions. The aperture can be filled with fluid. The fluid is typically air. The aperture can be sealed to restrict fluid communication between the aperture and the ambient environment. A length of sealing material can be provided parallel to and adjacent each side of the aperture. Typically, a change in hydrostatic pressure occurs during transit from the subterranean formation (with a high ambient hydrostatic pressure) to the surface (with a relatively lower atmospheric pressure) and thus the fluid trapped in the aperture can cause a pressure differential to exist between the recess and the ambient environment thereby urging the portions into sealing engagement.  
         [0026]     The above-described embodiments of the connecting means have the advantage that each receptacle portion can be manufactured from the same pattern and therefore a universal mould can be used. Shaping each long edge of the receptacle is simple to achieve by adding a shape to the mould through which the receptacle portions are extruded during manufacture. Thus the cost of manufacture of the receptacle portions is maintained at a low level. The receptacle portions can be manufactured from aluminium.  
         [0027]     The connecting means can comprise a weakened region. The weakened region can include an area of reduced wall thickness. Preferably, the region of reduced wall thickness is spaced away from an inner surface of the receptacle portions.  
         [0028]     The connecting means can comprise at least one binding member arranged to apply a radial compressive force to the receptacle portions. Each binding member can comprise a sleeve arranged to circumscribe the circumference of the receptacle portions. The sleeve can be of a length less than the length of the receptacle portions. The sleeve can be formed from a polymer such as a heat-shrinkable polymer or any other heat shrinkable fabric. According to this embodiment, the sleeve can be heated to cause shrinkage and apply a radial compressive force to the receptacle portions. Disengagement of the connecting means can be achieved by cutting along the binding member to relieve the compressive force applied by the binding member to the receptacle portions.  
         [0029]     The binding member can be used in conjunction with any other connecting means where suitable.  
         [0030]     Alternatively, the tool can comprise a cutting means for making a cut through the weakened region and/or the binding member of the or each receptacle portion.  
         [0031]     The sample can be a core sample.  
         [0032]     The or each receptacle can be disposable. According to some embodiments, use of the tool to disengage the connecting means is likely to damage the receptacle and thus render the receptacle unsuitable for reuse. The or each receptacle can be reconfigured prior to reuse. Alternatively, the or each receptacle can be recycled and reformed.  
         [0033]     The container is preferable sealed to prevent fluid ingress and egress. The container can comprise seal means to provide a fluid tight seal across the container. Each long edge of the receptacle can be provided with a line seal. The or each short edge can also be provided with seals therealong. Alternatively, or additionally, an inner surface of the or each receptacle towards each end can be provided with an annular seal means. The annular seal means can include O-rings, lip-type seals and seals containing a fluid pocket to cause selective dilation of the seal in response to a pressure differential. Preferably the ends of the container are also sealed. The seal means can be elastomeric.  
         [0034]     The container can comprise a plurality of receptacles and wherein the short end edge of each receptacle is arranged to be coupled to the short end edge of the adjacent receptacle by a joining member.  
         [0035]     The joining member can be arranged to engage adjacent receptacles to couple the receptacles to one another.  
         [0036]     An outer surface of each receptacle can comprise a recess and the joining member can be provided with at least two keyed parts, wherein each keyed part is arranged to engage the respective receptacle.  
         [0037]     A securing means can be provided for securing the joining member in position for engaging with adjacent receptacles.  
         [0038]     The securing means can comprise two securing members arranged to abut the joining member on either side thereof and retain the joining member in its position. The securing members can be provided with corresponding threads.  
         [0039]     According to another embodiment, the joining member can comprise a threaded connector and the receptacle can be provided with a partially threaded outer surface towards each end for engaging with the connector.  
         [0040]     Alternatively, the receptacle can have threaded end regions. A first end region having a reduced diameter relative to the remainder of the receptacle can have threads on an outer surface and a second end region can have threads on an inner surface such that the first end of one receptacle can be received within and threadedly coupled to the second end of an adjacent receptacle. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]     Embodiments of the invention will now be described with reference to and as shown in the following drawings, in which: — 
         [0042]      FIG. 1  is a sectional view of a receptacle within a core barrel;  
         [0043]      FIG. 1   a  is a sectional view of detail A;  
         [0044]      FIG. 2  is a sectional view of an alternative receptacle in a core barrel;  
         [0045]      FIG. 2   a  is a sectional view of detail B;  
         [0046]      FIG. 3  is a sectional view of another receptacle within a core barrel;  
         [0047]      FIG. 3   a  is a sectional view of detail C;  
         [0048]      FIG. 4  is a sectional view of another receptacle within a core barrel;  
         [0049]      FIG. 4   a  is a sectional view of detail D;  
         [0050]      FIG. 5  is a sectional view of another receptacle within a core barrel;  
         [0051]      FIG. 5   a  is a sectional view of detail E;  
         [0052]      FIG. 6  is a sectional view of another receptacle within a core barrel;  
         [0053]      FIG. 6   a  is a sectional view of detail F;  
         [0054]      FIG. 7   a  is an end view of the receptacle of  FIG. 2 ;  
         [0055]      FIG. 7   b  is a side view of the receptacle of  FIG. 7   a;    
         [0056]      FIG. 8  is an exploded perspective view of two receptacles similar to that of  FIG. 7   b  arranged end to end with a joining and securing assembly therebetween;  
         [0057]      FIG. 9  is a sectional view of the assembled container of  FIG. 8 ;  
         [0058]      FIG. 9   a  is a part-sectional, part-side view of the section A-A of the container of  FIG. 9 .  
         [0059]      FIG. 9   b  is a view of detail B from  FIG. 9   a;    
         [0060]      FIG. 10   a  is an end view of another receptacle;  
         [0061]      FIG. 10   b  is a side view of the receptacle of  FIG. 10   a ; and  
         [0062]      FIG. 11  is an exploded perspective view of two receptacles similar to that of  FIG. 10   a  arranged end to end with a joining and securing assembly therebetween. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0063]      FIG. 1  is a sectional view of a receptacle shown generally at  26 . The receptacle  26  is constructed from two receptacle portions  20 ,  21  that are semi-cylindrical and hollow in shape. Each receptacle portion  20 ,  21  has two long linear edges and two semicircular end edges. The long edges of the portion  20  are arranged to contact the long edges of the portion  21  to form a hollow cylinder joined by a connecting means along a line parallel to an axis of the cylinder. The join between the two portions  20 ,  21  is preferably provided with a line seal (not shown) to prevent ingress of muds in the receptacle  26 .  
         [0064]     The receptacle  26  of  FIG. 1  is shown housed within and co-axial with a core barrel  10  from a core barrel assembly (not shown). The receptacle  26  is centralised within the barrel  10  by a hexagonal centraliser  12 . Similarly, each receptacle described and shown with reference to  FIGS. 2-6  is centralised within the core barrel  10  by the centraliser  12 .  
         [0065]     According to this embodiment, the connecting means comprise mating portions integrally formed along the long edges of the receptacle portions  20 ,  21 . A centrally disposed recess  22  extends along one of the linear long edges of each portion  20 ,  21 . A centrally disposed protrusion  24  extends along the other linear long edge of each portion  20 ,  21 . The centrally disposed recess  22  has an opening  22   o  and a narrow portion  22   n  leading away from the opening  220  to an enlarged portion  22   h , wherein the enlarged portion  22   h  has a greater maximum width than the narrow portion  22   n . Similarly, the centrally disposed protrusion  24  has a neck  24   n  and an enlarged head  24   h . The detail A of  FIG. 1   a  shows the protrusion  24  disposed on the long edge of the portion  20  and the recess  22  disposed on the long edge of the portion  21 . The dimensions of the enlarged head  24   h  of the protrusion  24  are selected such that it can be forced through the opening  220  and the narrower portion  22   n  that must part slightly to allow passage of the head  24   h  therethrough. The enlarged head  24   h  can then be retained within the enlarged portion  22   h  of the recess  22 .  
         [0066]      FIG. 2  shows a receptacle  36  comprising two receptacle portions  30 ,  31  that are hollow and semi-cylindrical in shape. Each portion  30 ,  31  has two long linear edges provided with seals and two circular end edges. The long edges of the portion  30  are arranged to contact the long edges of the portion  31  to form a hollow cylinder and join along a line parallel to an axis of the cylinder. Each long edge of the portions  30 ,  31  has a recess  32  with a narrow opening  320  leading to an enlarged portion  32   h.    
         [0067]     An insert  34  has a central neck portion  34   n  and two wider diameter end portions  34   h . The end portions  34   h  of the insert  34  can be forced through the narrower opening  320  of the recess  32  to nest within the enlarged part  32   h  of the recess  32  to thereby retain the portions  30 ,  31  into engagement to form the receptacle  36 .  
         [0068]      FIG. 3  shows a receptacle  46  constructed from two hollow semi-cylindrical portions  40 ,  41  each having two long linear edges and two semi-circular end edges. The portions  40 ,  41  are generally hollow and semi-cylindrical in shape and arranged to engage one another along adjacent long edges as previously described in connection with the first and second embodiments. The long edges of the portions  40 ,  41  have centrally disposed semi-cylindrical recesses  42  and one long edge of each portion  40 ,  41  has lengths of seal  44  arranged parallel and on both sides of the recess  42 . Thus, when the portions  40 ,  41  are positioned to form a receptacle  46 , the long edges of the portions  40 ,  41  engage and are arranged so that the corresponding recesses  42  form a cylindrical air pocket  48  that is sealed on either side by the seals  44 .  
         [0069]     The air pockets  48  will also need to be sealed at each end. Lengths of air pockets  48  can be laid end to end by joining a plurality of receptacles  46  end to end as described hereinafter. However, the outermost regions of the air pockets are required to be sealed. This can be achieved by plugging the outermost ends with sealing material. The seals  44  and sealing material preferably isolate the air pocket  48  and prevent fluid communication between the interior of the air pocket  48  and the ambient environment. The seals  44  and sealing material can be any type of seal able to withstand the temperatures and pressures associated with the downhole environment in which they are used. Elastomeric seals are useful in this regard. The seal means can be manufactured from rubber or plastics material or the like and some useful embodiments can be formed from Viton™.  
         [0070]      FIG. 4  shows a receptacle made from two semi-cylindrical hollow portions  50 ,  51  having two long linear edges provided with seals and two end edges. The portions  50 ,  51  are generally hollow and semi-cylindrical in shape as previously described in connection with the foregoing embodiments. The portions  50 ,  51  join along their long edges parallel to an axis of the cylinder. One long edge of each portion  50 ,  51  is provided with a protruding barb  54  having a neck  54   n  leading to a head  54   h  with a pointed end  54   p  and a secondary point  54   b . The other long edge has a recess  52  with a narrow opening  520  that is slightly wider then the neck  54   n  of the protruding barb  54 . The recess  52  is shaped corresponding to the form of the barb  54 . The narrow opening  520  of the recess  52  is sufficiently deformable to allow the head  54   h  of the barb  54  to be forced therethrough. Thereafter, the barb  54  is retained within the recess  52  to secure the portions  50 ,  51  to one another and form a cylindrical hollow receptacle  56 .  
         [0071]      FIG. 5  shows a receptacle  66  having two semi-cylindrical hollow portions  60 ,  61  that are integrally formed with a waisted bridging portion  64  therebetween. The waisted bridging portion  64  has a reduced wall thickness compared with the wall thickness of the portions  60 ,  61 . The bridging portion  64  is recessed away from an inner surface of the portions  60 ,  61  as shown in detail E, so that the inner diameter of the bridging portion  64  is wider then the inner diameter of the portions  60 ,  61 .  
         [0072]      FIG. 6  shows a receptacle  76  comprising two semi-cylindrical hollow portions  70 ,  71 , each portion having two long edges provided with seals and two end edges. The long edges of each portion  70 ,  71  are arranged to align and engage one another to form a hollow cylindrical receptacle  76 . An outer part of the portions  70 ,  71  in the region of the long edge is provided with an L-shaped recess  72  facing towards the long edge. The L-shaped recess  72  creates a shoulder  73 . A length of spring clip  74  having inwardly protruding ends  75  is removably accommodated within the L-shaped recess  72  and retained therein by the shoulder  73 , as shown in detail F.  
         [0073]     According to another embodiment, the connecting means comprise a heat shrinkable sleeve formed from any suitable polymer such as a polyolefin, PVDF (polyvinylidene difluoride), PTFE (polytetrafluoroethylene) and FEP (fluorinated ethylene propylene). The sleeve is selected to be of a length slightly less than that of the end to end length of the receptacle portions. The shrink ratio can be varied depending on the required amount of compressive force. The sleeve is fed over the sealed receptacle portions and heated such that the sleeve shrinks around the exterior of the receptacle portions to apply a radial compressive force thereto. The sleeve can also be used in addition to the various connecting means described with reference to FIGS.  1  to  6   a.    
         [0074]      FIG. 7   a  is an end view of the portions  30 ,  31  of  FIG. 2  prior to assembly.  FIG. 7   b  shows each portion  30 ,  31  having an end region  38  with a recessed circumferential band  37 . The portions  30 ,  31  can be connected using the insert  34  such that a recessed annular band  37  is formed at each end region  38 .  
         [0075]     The exploded view of  FIG. 8  shows another receptacle  136  arranged to be joined end to end with the receptacle  36 . The receptacle  136  is similar to the receptacle  36  and like parts of the receptacle  136  have been allotted like reference numerals with a prefix “1”.  
         [0076]     The receptacles  36  and  136  are positioned with the end regions  38 ,  138  immediately adjacent one another. A joining member  88  comprises two hollow semi-cylindrical parts  80 ,  81  having two joining edges and two arcuate end edges. Each joining edge is arranged to abut the joining edge of the adjacent part  80 ,  81  such that the parts  80 ,  81  are complimentary to form an annular band. Each part  80 ,  81  also has two parallel tracks  83  (shown in  FIG. 9   b ) along an inner surface proximate each arcuate end edge. The tracks  83  are shaped to engage the recessed bands  37 ,  137  provided in each end region  38 ,  138  respectively.  
         [0077]     A first and second threaded securing member  82 ,  84  respectively are also provided to secure the joining member  88  in position. The inner diameter of the securing members  82 ,  84  is slightly larger than the outer diameter of the portions  30 ,  31  to allow the securing members  82 ,  84  to be positioned thereover. The first threaded securing member  82  has a stepped outer surface  82   s  and a screw thread  82   t . An inner surface of the first securing member  82  has an end portion formed with a depression  82   d  that corresponds with the length of the joining member  88  as shown in  FIG. 9   b . The second securing member  84  has a step  84   s  on its inner surface to allow the end of the first securing member  82  to shoulder out on the step  84   s . The second securing member  84  also has a threaded portion  84   t  on an inner surface thereof to engage with the threads  82   t  of the first securing member  82 .  
         [0078]     Before use within a core barrel assembly, the container is assembled. The portions  30 ,  31  are connected by forcing the insert  34  into the recesses  32  along the long edges of the portions  30 ,  31  to form the receptacle  36 . The or each additional receptacle  136  is also assembled in the same way. The first securing member  82  can then be slid over the end region  38  of the receptacle  36 . Similarly, the second securing member  84  is slid over the end region  138  of the receptacle  136 .  
         [0079]     The joining member  88  engages the receptacles  36 ,  136  and is arranged such that the joining edges of each part  80 ,  81  are positioned perpendicular to the long edges along which the receptacle portions  30 ,  31  are connected. This arrangement avoids an area of the container having a weak link. The tracks  83  of the parts  80 ,  81  engage with the recessed bands  37 ,  137  thereby joining the receptacles  36 ,  136 . The first securing member  82  can then be moved such that the depression  82   d  abuts the joining member  88  that protrudes slightly relative to the outer diameter of the portions  30 ,  31 . The second securing member  84  is screwed along the first securing member  82  such that the threads  84   t  engage with the threads  82   t  until the step  84   s  abuts the opposing side of the joining member  88 . This has the effect of securing the joining member  88  in position so that the assembled receptacles  36 ,  136  are in secured engagement. Additional receptacles can be added using similar joining members  88  and securing members  82 ,  84  to form a container.  
         [0080]     Prior to insertion in a coring assembly (not shown), the container comprising a plurality of receptacles  36 ,  136 , etc. securely fastened to one another and sealed along its length is assembled in the manner described above. The container is then located within the core barrel  10  and centralised therein using hexagonal centralisers  12 . A leading end of the coring assembly (not shown) has a plurality of cutters provided to engage a geological formation and cut a core sample therefrom. The cutters are actuated and a core sample is collected within the container. During collection, if the core sample is entering the container at a slightly offset angle, there may be a tendency for the core sample to catch on an inner surface of the receptacles. However, radial separation of the portions  30 ,  31  is resisted by the enlarged end portions  34   h  of the insert  34  retained within the recesses  32 . Once the sample has been collected within the container a spring catcher (not shown) is actuated and the sample is sealed within the receptacle so that it is isolated from downhole drilling muds. The coring assembly can then be pulled out of the hole to retrieve the sample.  
         [0081]     Once the coring assembly is retrieved to surface, the container can be removed therefrom. Typically, the container and the core sample within is divided into lengths corresponding to the length of each receptacle  36 ,  136  using a cutting tool. If on-site inspection of the core sample is required a tool such as a crow bar has its flattened end inserted into the join between the receptacle portions  30 ,  31 . The crow bar can then be moved such that it acts as a lever to apply a force to separate the receptacle portions  30 ,  31  by urging the enlarged end  34   h  through the narrow opening  32   o  such that the inserts  34  are urged out of engagement of the recesses  32  allowing at least one of the portions  30 ,  31  to be lifted radially away from the core sample. In order to facilitate the separation of the receptacle portions  30 ,  31 , the leading outer edges of the portions  30 ,  31  can be chamfered to provide a purchase for the tool in use. The act of separation may have damaged the or each portion  30 ,  31 , which is thus treated as disposable and may be recycled or reconfigured for reuse.  
         [0082]     The outer surface of each of the receptacles  26 ,  46 ,  56 ,  66 ,  76  shown in  FIGS. 1, 1   a  and  3 - 6   a  can similarly be provided with recessed bands  37  and secured to like receptacles using joining members  88  and securing members  82 ,  84 .  
         [0083]     A similar procedure for collection, retrieval and inspection of the core sample can be followed for the receptacle  26  shown in  FIG. 1  and the receptacle  56  is shown in  FIG. 4 .  
         [0084]     The receptacle  46  shown in  FIG. 3  is assembled to form part of a container assembly in a similar manner as described with reference to FIGS.  8  to  9   b . As the receptacle  46  is assembled prior to insertion downhole, the air pocket  48  is at ambient atmospheric pressure. However, since the receptacles  46  making up the container assembly are transported downhole, the pressure of the environment gradually increases towards the subterranean formation. The pressure differential increases since the air pocket  48  is sealed from the ambient environment downhole by the seals  44 . This urges the portions  40 ,  41  into contact with one another. Thus, during collection of the sample separation of the receptacles  46  is resisted by the pressure differential across the air pocket  48  acting to maintain the portions  40 ,  41  in engagement. Withdrawal of the coring assembly from the downhole environment reduces the pressure differential across the air pocket  48  until the coring assembly and the receptacle  46  is once again subject to atmospheric pressure. In the absence of a pressure differential the two portions  40 ,  41  are easily parted on the surface and one or more of the portions  40 ,  41  can simple be lifted away to provide access to the core sample on-site.  
         [0085]     The receptacle  66  shown in  FIG. 5  is integrally formed and has a waisted bridging portion  64 . Several such receptacles can be assembled end to end to form a container. Once a core sample has been retrieved to surface following collection from the subterranean formation, a cutting tool (not shown) can be used to cut along the length of the waisted bridging portion  64  of the receptacle  66 . Spacing the waisted portion  64  away from the inner surface of the receptacle  66  by the depth of the recess  62  significantly reduces the risk that the core sample will be damaged during the cutting operation. Furthermore, a smaller cutting force is required to divide the waisted section  64  having a smaller wall thickness than the wall thickness of the portions  60 ,  61 .  
         [0086]     The portions  70 ,  71  of the receptacle  76  shown in  FIG. 6  are retained by a spring clip  74  having retaining ends  75  that abut shoulders  73  of the L-shaped recess  72 . The clips  74  are deformable and can be removed following retrieval of the coring assembly to surface, thus providing access to the core sample.  
         [0087]     Each embodiment of the connecting means described with reference to FIGS.  1  to  6  enables the core sample to be accessed by lifting one or more of the receptacle portions therefrom. Thus, axial withdrawal of the sample from the container is not necessary.  
         [0088]     An alternative joining and securing means is shown in  FIGS. 10   a  to  11 .  FIGS. 10   a  shows a receptacle having receptacle portions  230 ,  231  and a shaped insert  234  similar to those described with reference to  FIG. 7   b . The receptacle portions  230 ,  231  have two end regions  238 ,  239 . The end region  238  has threads  237  provided on an outer surface and the end region  239  has threads  237  provided on an inner surface.  
         [0089]      FIG. 11  shows a similar receptacle with like features labelled with the prefix “3”, rather than “2”. Before use, the inserts  234 ,  334  are used to couple the receptacle portions  230 ,  231 ,  330 ,  331  in the manner previously described. A joining and securing member  188  is provided with internal threads adapted to engage with the threads  237 ,  337  at the end regions of the receptacle portions  230 ,  231 ,  330 ,  331 .  
         [0090]     This method of joining receptacle portions end-to-end can be used in preference to that described with reference to  FIGS. 7   a  to  9   b  and can also be used with any of the described connecting means.  
         [0091]     Modifications and improvements can be made without departing from the scope of the invention.