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BACKGROUND OF THE INVENTION 
     The present invention relates to apparatus and a method for obtaining a sample, such as a core sample, from a subterranean formation, such as those found in an oil or gas reservoir. 
     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, difficulties arise as the coring equipment is recovered to the surface. As the coring equipment is retrieved from the subterranean formation, the ambient pressure of the environment reduces and gases within the core sample expand and expel fluids, such as oil, water or a mixture of these fluids, from the sample. If the expelled fluid cannot be recovered, this reduces the authenticity of the sample and the accuracy of the data that can be gathered from it. 
     BRIEF SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided apparatus for recovering a sample from a subterranean formation comprising a receptacle for receiving a sample and at least two seal assemblies disposed on an inner surface of the receptacle. 
     Typically, the sample is a core sample. 
     Typically, each seal assembly is arranged to allow passage of a portion of the core sample therethrough during the sampling process, but can retain fluids within the receptacle. 
     According to a second aspect of the present invention there is provided a method for recovering a sample from a subterranean formation or the like, comprising the steps of:
         (a) providing a receptacle having an inner surface and disposing at least two seal assemblies on the inner surface of the receptacle;   (b) running the receptacle into a subterranean formation;   (c) accommodating a sample from the subterranean formation in the receptacle such that at least a portion of the sample is disposed between the seal assemblies; and   (d) recovering the receptacle with the sample disposed therein.       

     Preferably, the at least two seal assemblies are arranged to isolate portions of the receptacle, such that the seal assemblies create a fluid-tight seal when the sample is disposed in the receptacle in use. The seal assemblies can comprise any type of seal able to withstand the temperatures and pressures associated with the environment in which it is used. Elastomeric seals are useful in this regard. The seals can be lip-type seals. The seals can be manufactured from rubber or plastics material or the like, and some useful embodiments are formed from Viton™. 
     The seal assemblies can comprise at least one seal that can extend radially inwardly from the inner surface of the receptacle, so that when the sample is disposed therein, the seals seal off an annulus between the sample and the inner surface of the receptacle. One advantage of this arrangement is that during recovery of the sample, the seals form the main part of the receptacle in contact with the core sample, thereby minimising friction between the receptacle and the sample and reducing the risk of damage to the sample as it is being collected. 
     The apparatus can also comprise at least one fluid chamber arranged to receive fluids expelled from the sample. Typically, a change in hydrostatic pressure occurs in the sample during transit from the subterranean formation (with a high ambient hydrostatic pressure) to the surface (with a relatively lower atmospheric pressure) and this causes fluids to be expelled from the core sample during recovery. Each fluid chamber can be arranged to receive and retain the fluid expelled from the sample. Preferably, the at least one fluid chamber is provided between adjacent seal assemblies such that the fluid is retained within the chamber sealed between two seal assemblies. Each pair of seal assemblies can define an annular fluid chamber therebetween when the core sample is disposed within the receptacle. Each fluid chamber may be defined by the annular space between adjacent seal assemblies, the inner surface of the receptacle and the exterior of the core sample when disposed therein. 
     The receptacle can comprise an inner barrel, and an outer barrel spaced relative to and coaxial with the inner barrel, thereby creating a reservoir between the inner barrel and the outer barrel. Preferably, the seal assemblies are provided on the inner surface of the inner barrel. Preferably, the reservoir is in selective fluid communication with the throughbore of the inner barrel where the sample is retained. Preferably, the reservoir between the inner barrel and the outer barrel is also sealed at each end, in the region of the seal assemblies provided on the inner surface of the inner barrel. Thus, any fluid expelled from the core sample can be captured between adjacent seal assemblies in the fluid chamber and transferred to the reservoir by virtue of the fluid communication therebetween. In this way, fluid expelled from the core sample can be effectively retained between the seal assemblies in one or both of the fluid chamber and the reservoir. 
     The receptacle can be provided in at least two separable portions for ease of access to the sample after recovery. The at least two separable portions of the receptacle can be complementary to form a cylinder. The cylindrical embodiment of the receptacle has a cylindrical axis defined by the long axis extending through the bore of the cylinder. The at least two portions can be separable along a line extending between the two ends of the portions, typically substantially parallel to the cylindrical axis, so that the at least two portions can be separable laterally from one another. Typically the portions are in the form of half shells. Provision of at least the inner barrel of the receptacle in separable portions is advantageous since the core sample does not then have to be withdrawn axially from the receptacle for analysis, which generates friction and could result in the core sample being damaged. Rather, the core can be accessed and exposed by lifting one of the portions away from the core sample, without direct manipulation of the sample. 
     A plurality of pairs of seal assemblies can be spaced along the length of the inner surface of the receptacle. Each pair of seal assemblies can be provided with fluid chambers therebetween, such that fluids can be recovered from and associated with discrete segments of core sample from which they were expelled during transit. This enables the quantity of fluids, such as oil and water, to be measured from the sample and any variation in the quantity or composition of fluids contained within each segment can be determined over the length of the sample. The greater the number of seal assemblies and sealed fluid chambers over a certain length of sample, the greater the resolution of the collected data on the variation in composition of the fluids contained within the sample. Therefore, the number of sealed chambers, and the axial spacing between them can be varied to adjust the resolution required. 
     The seals can be provided with at least one fluid pocket, configured to change shape, as the volume of fluid therein alters in response to a pressure differential. The at least one fluid pocket can be filled with fluid at atmospheric pressure and arranged to at least partially collapse as the volume of fluid in the pocket decreases under the high pressures experienced in subterranean formations. The seals can be provided with at least one air pocket at atmospheric pressure. As the receptacle is transported to the subterranean formation of interest, an air pocket in the seals at least partially collapses under the higher subterranean pressures, thereby reducing the amount of friction between the seals and the core sample during entry of the sample into the receptacle. 
     The at least one fluid pocket can be in selective fluid communication with an ambient pressure to which the apparatus is exposed. An activation means can be provided, and optionally the activation means is operable to selectively alter the pressure differential across the at least one fluid pocket. Optionally, the activation means can be operable to selectively expose the at least one fluid pocket to the ambient pressure to which the apparatus is exposed i.e. the at least one fluid pocket is capable of fluid communication with an ambient pressure to which the apparatus is exposed on operation of the activation means. 
     At least one of the outer barrel and the inner barrel can be arranged in relation to the seal assemblies to move between a first configuration in which the fluid pocket is not exposed to an ambient pressure and a second configuration in which the fluid pocket is exposed to the ambient pressure, wherein the activation means is optionally operable to cause relative movement of the inner and outer barrel between the first and second configurations. Preferably, the seals are resilient. Before running the apparatus to the subterranean formation, the seals can be resiliently biased radially inwardly in the throughbore of the inner barrel with the fluid pocket of the seals optionally at or near atmospheric pressure. As the apparatus is moved towards the subterranean formation, the pressure can increase and the pressure differential across the seals can cause the fluid pocket to collapse thereby altering the configuration of the seals. Once the sample has been collected, the activation means can cause relative movement of the inner barrel and outer barrel to bring the fluid pocket into contact with the ambient pressure. At this point, no pressure differential exists across the fluid pocket. Therefore, the configuration of the seals can alter under its own resilience to occupy the original shape, biased radially inwardly to seal against the sample. 
     A releasable plug member engagable with the seal assemblies can be provided, such that when the plug member is engaged with the seal assemblies there is no fluid communication between the at least one fluid pocket and the ambient environment and wherein releasing the plug member allows fluid communication between the ambient environment and the fluid pocket. The activation means can be provided to selectively release the plug member. The plug member can comprise at least one hollow shear screw coupled to a band. The activation means can comprise a diverting member capable of diverting a fluid flow e.g. mud flow to act on and cause movement of the band to thereby shear the at least one shear screw. 
     Alternatively, as the receptacle is withdrawn from the formation to the surface, the environmental pressure decreases until the air pockets regain their original shape at atmospheric pressure. Thus the seal is improved between the seals and the core sample as the core barrel assembly is recovered from the subterranean formation and the environmental pressure decreases. In the case where the receptacle is cylindrical and the seals are annular, they can be provided with an annular air pocket. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       Embodiments of the invention will now be described with reference to and as shown in the following drawings, in which: 
         FIG. 1  is a sectional perspective view of a core barrel assembly having a core sample disposed therein; 
         FIG. 2  is a perspective view of one half of a liner module of the core barrel assembly shown in  FIG. 1 ; 
         FIG. 3  is a detailed sectional perspective view of a portion of the core barrel assembly of  FIG. 1 ; 
         FIG. 4  is an exploded view of the liner module shown in  FIG. 2 ; 
         FIG. 5  is a perspective view of one half of a coupling; 
         FIG. 6  is a sectional view of a closed port in a coupling ring; 
         FIG. 7  is a sectional view of an open port in the coupling ring of  FIG. 6 ; 
         FIG. 8  is a sectional view of a lip seal including an air pocket; 
         FIG. 9  is a sectional view of the lip seal of  FIG. 8  with the air pocket partially collapsed; 
         FIG. 10  is a perspective view of one half of two liner modules provided with an alternative seal assembly and prior to transport into a subterranean formation; 
         FIG. 11  is a perspective view of the liner modules of  FIG. 10 , with the seals represented in the downhole configuration; 
         FIG. 12  is a perspective view of the liner modules of  FIG. 11  with a sample disposed therein; 
         FIG. 13  is a perspective view of the liner modules of  FIG. 12  showing relative movement of an inner and outer liner; 
         FIG. 14  is a perspective view of the liner modules of  FIG. 13 , with the seals in communication with an ambient pressure; and 
         FIG. 15  is a perspective view of one half of a liner module provided with an alternative seal assembly; 
         FIG. 16  is a perspective view of one half of a core barrel assembly; 
         FIG. 17  is a perspective view of the core barrel assembly of  FIG. 16  showing a diverted mud flow; 
         FIG. 18  is a perspective view of one half of the liner module of  FIG. 15  located within the core barrel assembly; 
         FIG. 19  is a perspective view of the liner module within the core barrel assembly of  FIG. 18  showing a sheared outer band; and 
         FIG. 20  is a perspective view of the liner module and core barrel assembly of  FIG. 19 , showing the seals in their original configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a core barrel assembly indicated generally at  10  and having a core sample  12  disposed therein. The core barrel assembly  10  comprises an inner assembly  14  and an outer assembly  18  sharing a common cylindrical axis  20 . The outer assembly  18  houses the inner assembly  14 . 
     The outer assembly  18  comprises a tubular outer casing  28  with a core head  26  comprising a plurality of cutters  22  provided at a lower end  24  of the outer casing  28 . The cutters  22  are provided to engage a geological formation (not shown) to cut a core sample  12  which may then be recovered in the inner assembly  14 . The outer casing  28  is typically made of steel. 
     The inner assembly  14  comprises a barrel  30 , which houses a series of liner modules  32 ,  132 . The barrel  30  is removably accommodated within the outer casing  28 . 
     Each liner module  32  is provided in two portions which engage along their long edge parallel to the cylindrical axis  20  of the core barrel assembly  10 . One portion forming half of the liner module  32  is shown in greater detail in  FIG. 2 . Each portion of liner module  32  comprises an inner liner  34 , an outer liner  36  and a seal assembly  80  at each end. 
     The inner liner  34  has a throughbore  35  which can accommodate the core sample  12 . The outer liner  36  is coaxial with and spaced around the inner liner  34  to create an annular fluid reservoir  40  therebetween. The inner liner  34  and outer liner  36  are typically manufactured from aluminium. 
     The inner liner  34  and the outer liner  36  are connected at each end by the seal assembly  80 . Each seal assembly  80  includes a coupling ring  43 ,  44  and a lip seal  41 ,  42 . The lip seals  41 ,  42  are typically manufactured from Viton™, although it will be appreciated by a person skilled in the art that any elastomeric seal suitable for the application can be used. 
     As shown in  FIG. 1 , the coupling ring  44  is provided at the lower end of the liner module  32  and the coupling ring  43  is provided at the upper end. Each coupling ring  43 ,  44  has an annular step  44 S shown in detail in  FIG. 3 . The annular step  44 S radially spaces the inner liner  34  from the outer liner  36 , and its radial dimensions define the radial width of the annular reservoir  40 . Each coupling ring  43 ,  44  is also provided with a recessed portion  44 R on its inner surface, which houses the lip seal  41 ,  42 . The lower coupling ring  44  carries the lower lip seal  42  and the upper coupling ring  43  carries the upper lip seal  41 . The lip seals  41 ,  42  are both upwardly facing, so as to present very little frictional resistance on entry of the core sample into the bore  35 . In the present embodiment, the distance between the lip seals  41 ,  42  is one metre, but this distance can be altered to modify the resolution of the apparatus. 
     Each liner module  32  is attached to an adjacent liner module  132  by means of a coupling band  54 . Several liner modules  32 ,  132  etc. are attached in series and housed within the barrel  30  to form the inner assembly  14 . 
     The coupling band  54  is shown in more detail in  FIG. 5 . The coupling band  54  has a generally T-shaped half-shell construction that has grooves to engage and retain the lower coupling ring  144  from one liner module  132  and the upper coupling ring  43  from the adjacent liner module  32 . The coupling band  54  forms a rigid connection between the two coupling rings  43 ,  144 . 
     The upper coupling ring  43  is provided with two ports (not shown) which are used to recover liquid sealed in the annular reservoir  40 . These ports remain closed during insertion and recovery of the core barrel assembly  10  and are only opened in the laboratory to allow fluids to be recovered from the annular reservoir  40 . 
     The lower coupling ring  44 ,  144  is provided with four ports  70 . Two of these ports are plugged and remain closed during use of the core barrel assembly  10 , until the fluids contained within each liner module  32 ,  132  need to be accessed in the laboratory. The remaining two ports  70  are provided to selectively allow the reservoir  40  to be in fluid communication with an annulus between outer liner  36  and the barrel  30  when the core sample  12  is accommodated in the inner assembly  14 . These ports  70  are opened and closed when subject to pressure of a predetermined value. 
       FIGS. 6 and 7  show the coupling ring  44 , housing a valve  60  provided adjacent the port  70 . The coupling ring  44  is provided with threads  69  which engage corresponding threads (not shown) on the outer liner  36  to connect and seal the coupling ring  44  and the outer liner  36 . 
     Each valve  60  comprises a chamber  62  and a piston  64  sealed in the chamber  62  by an O-ring  66 . The chamber  62  contains the piston  64  and the remainder of the chamber  62  is filled with fluid such as air. When the core barrel assembly  10  is at atmospheric pressure the volume of fluid in the chamber  62  is high, causing the piston  64  to abut a valve seat  68  and close the port  70 . 
     Before use, the inner assembly  14 , comprising the required number of liner modules  32 ,  132  etc. joined by coupling bands  54 , is inserted into the outer assembly  18  to form the core barrel assembly  10 . The core barrel assembly  10  is lowered on a drill string to a location from which the core sample  12  is to be obtained. The pressure of the environment gradually increases as the core barrel assembly  10  is transported to the subterranean formation. The increased pressure causes the air in the chamber  62  of valve  60  to compress. At a predetermined level, for example, in the present embodiment when the hydrostatic pressure is greater than 2 bars, the air in the chamber  62  will be compressed to such an extent that the piston  64  moves away from the valve seat  68  to open a fluid channel between each port  70  and the fluid reservoir  40 . 
     In order to obtain a core sample the cutters  22  are rotated and the core barrel assembly  10  is drilled into the geological formation. The core sample is collected in the inner assembly  14  as the cutters  22  drill into the formation. Frictional forces on the core sample  12  are reduced on entry into the inner assembly  14  by spacing the inner surface  31  of the inner assembly  14  away from the sample by means of the annular fluid chamber, and ensuring that the main areas of contact between the core sample  12  and the inner assembly  14  are the seals  41 ,  42 . Thus, the contact surface area between the inner assembly  14  and the core sample  12  is minimised to restrict the friction therebetween in order to reduce the risk of damaging the core sample  12  as it is being collected. Once the sample  12  is disposed within the throughbore  35  of the inner liner  34 , a spring catcher at the leading edge of the assembly  10  just above the cutters  22  is closed to cut the end of the sample and secure it within the core barrel assembly  10 . 
     As the core barrel assembly  10  is pulled out of the well by the drill string or the like, the ambient hydrostatic pressure decreases and fluid held within the core sample  12  expands and can be ejected from the sample  12 . This fluid is retained in the annular fluid chamber  38 , between the lip seals  41 ,  42 , the inner liner  34  and the core sample  12 . Some of the expelled fluid held in the annular fluid chamber  38  leaks into the reservoir  40 , where it is likewise retained for later recovery at surface. The expelled fluids can leak from the annular fluid chamber  38  to the reservoir  40  through the joint between the half shells of the inner liner  34  or through apertures (not shown) extending through the sidewall of the inner liner  34  and specially provided for the purpose. The lip seals  41 ,  42  prevent leakage from the area between the seals  41 , 42  into adjacent modules  132 . 
     In the present embodiment, oil is the fluid to be quantified and analysed and which is expelled from the core sample  12 . The expelled oil is immiscible with and less dense than the drilling fluids, mud and brine which were originally present within the inner assembly  14  as a result of the drilling process. Thus, on entry into the reservoir  40 , the expelled oil is collected towards the upper end of the reservoir  40 , thereby forcing some of the drilling fluid, brine and mud out of the liner modules  32 ,  132  through ports  70  and into the annulus  38 . 
     Alternatively, in an embodiment where the relative proportion of water is the expelled fluid of interest, ports  70  and accompanying valves  60  may instead be provided in the upper coupling ring  43  since the water has a greater density than the drilling fluids and brine originally present. This will ensure that the fluids expelled from the core sample  12  are retained within the modules  32 ,  132  at the lower end of the modules while the drilling fluids originally present are forced out of the ports  70  located in the upper coupling ring  43 . 
     The reduction in hydrostatic pressure as the core barrel assembly  10  is recovered to the surface causes the fluid in chamber  62  to expand until at a pressure approximately less than 2 bars, the piston  64  abuts the valve seat  68  so that the valve  60  closes off port  70  to prevent further fluid loss from the modules  32 ,  132 . 
     Once the core barrel assembly  10  has been recovered from the wellbore, the inner assembly  14  can be removed from the outer assembly  28  on the rig side. The inner assembly  14  with the core sample  12  contained therein can be cut into lengths of liner modules  32 ,  132 . A cut can be made in each coupling band  54  to split the first and second coupling rings  43 ,  144  and separate each liner module  32 ,  132 . Since each liner module  32 ,  132  is provided with a lip seal  41 ,  42 ,  142  at each end, the fluid ejected from the core sample  12  between the seals  41 ,  42 ,  142  remains contained within each respective module  32 ,  132 . 
     The liner modules  32  enclosing sections of core sample  12  are then transported to a laboratory for geological and geophysical data to be recovered therefrom. The ports (not shown) in the upper and lower coupling rings  43 ,  44  can be unplugged to allow solvent to be injected into each module  32  to flush out fluids in the fluid chamber  38  and the reservoir  40 . This process recovers fluids originally contained within pores in the core sample  12  and forced out due to the changes in hydrostatic pressure during recovery to surface. The quantities of the fluids present, such as oil and water can be measured. If required, the composition of these fluids can then be determined using standard laboratory techniques. When fluid quantity and composition data has been gathered from several modules, the information can be collated to form an indication of the variation of fluids present, as well as their composition, across the entire sample  12 . 
     One half of each liner module  32  can be lifted away to provide access and expose the core sample  12 . The arrangement of the liner modules  32 ,  132  into two halves allows easy access to the core and means that it is not necessary to draw the core sample  12  axially out of the inner barrel  30  which may have potentially harmful consequences as it could damage the core sample  12 . 
     The use of seals  41 ,  42  is advantageous as it splits the core sample  12  into segments between the seals  41 ,  42  allowing data to be recovered from a series of consecutive known depths and allowing accurate determination of the oil and water content and type originally contained within each segment of core sample  12  as this is retained within the fluid chamber  38  or the reservoir  40  between the seals  41 ,  42 . Thus, the core sample can be recovered with an accurate indication of fluids present within the sample  12  as a whole. 
     The distance between the seals  41 ,  42  determines the resolution of the data regarding fluids from the core sample  12 . Accordingly, the resolution can be improved by decreasing the distance between the seals  41 ,  42 . More than one pair of seals can be provided per module  32  in order to increase the resolution. 
     The number of modules  32  which are positioned end to end within the inner assembly  14  is dependent on the length of each module  32  and the resolution required for each application. The modules  32  may be designed to be used within standard core barrel lengths. Alternatively, the application may dictate that a certain length of core sample  12  is required, along with a specific resolution and therefore the required number of modules  32  may be provided. 
     Although lip seals  41 ,  42 ,  142  are shown in the embodiment of  FIGS. 1-4 , it will be appreciated by a person skilled in the art that any suitable seal may be used. For example, core barrel assemblies  10  to be used downhole may have to withstand high pressures and therefore high temperature seals may be required. O-ring seals may be used. However, O-ring seals generally require a greater tolerance. A lip seal will be generally appreciated to provide a better fluid tight seal for this application than a standard O-ring seal. This may be important if the core sample  12  recovered by the cutters  22  has a variable diameter in places. 
       FIGS. 8 and 9  show a modified lip seal  92 . Lip seal  92  is annular and is provided with an annular air pocket  94 , although a number of discrete non-annular air pockets could instead be provided.  FIG. 8  shows the air pocket  94  at surface atmospheric pressure at which the air pocket  94  is substantially circular in cross-section. As the core barrel assembly  10  is transported downhole, the ambient hydrostatic pressure increases with the depth of the assembly  10 , and as a result of this increasing hydrostatic pressure, the air pocket  94  at least partially collapses as shown in the sectional view of  FIG. 9 . When the assembly arrives at the required depth to cut the sample  12 , the collapsing air pocket  94  changes the resting configuration of the seal to move the seal  92  radially inwards away from the sample  12  as it is being received within the assembly  10 . This reduces the frictional forces acting on the sample  12  during the sampling procedure, and reduces the risk that the sample will jam in the inner assembly  14  while it is being collected, thereby resulting in a more representative sample being collected. 
     After collection of the sample  12  and closure of the spring catcher, the upward movement of the assembly  10  through the well increases the ambient pressure acting on the assembly, and therefore expands the pocket  94 , gradually returning the pocket to its original shape and causing the seal  92  to move radially inwards once again to bear against the outer surface of the sample  12  and thereby improve the seal as the core barrel assembly  10  is removed from the wellbore. 
     An alternative seal arrangement and method of sealing around a core sample is described with reference to  FIGS. 10-14 . 
       FIG. 10  shows one half of two coupled liner modules  232 ,  332 . Each liner module  232 ,  332  is shown with the outer liner  36  surrounding and coaxial with the inner liner  34  as described for the previous embodiment. The inner liner  34  and the outer liner  36  are connected at each end by a seal assembly  280 ,  380  respectively. Each seal assembly  280 ,  380  includes a coupling ring  243 ,  344 . 
     A coupling band  154  joins adjacent coupling rings  243 ,  344  of the module  232 ,  332 . The coupling band  154  has a generally T-shaped half shelf construction and grooves to engage and retain the lower coupling ring  344  from the liner module  332  and the upper coupling ring  243  from the adjacent liner module  232 . The coupling band  154  thereby forms a rigid connection between the two coupling rings  243 ,  344 . 
     The coupling ring  243  is provided towards an upper end of the liner module  232  and the coupling ring  344  is provided towards the lower end of the liner module  332 . Each coupling ring  243 ,  344  has an annular step  243 S,  344 S at one end thereof to space the inner liner  34  relative to the outer liner  36  thereby defining the fluid reservoir  40 . The coupling rings  243 ,  344  also have an upper annular shoulder  243 U,  344 U and a lower annular shoulder  243 L,  344 L defining a centrally disposed recess  243 R,  344 R in which a respective annular seal cup  241 C,  342 C, each carrying a seal  241 ,  342  is accommodated. The seal cups  241 C,  342 C are attached to the inner liner  34 . Each annular seal  241 ,  342  is resilient to project radially inwardly into a throughbore  135 . The annular seals  241 ,  342  each have an annular air pocket  294 ,  394 . Each seal cup  241 C,  342 C carrying the seals  241 ,  342  and coupling ring  243 ,  344  are capable of relative movement that is limited by the upper shoulder  243 U,  344 U and the lower shoulder  243 L,  344 L of each coupling ring  243 ,  344 . 
     One or more radially disposed apertures (not shown) extending through a sidewall of the coupling ring  243 ,  344  are provided towards the lower shoulder  243 U,  344 U. The apertures are provided to ensure that the recesses  243 R,  344 R are in fluid communication with the exterior of the coupling ring  243 ,  344 . The seal cups  241 C,  342 C carrying the seals  241 ,  342  are also provided with one or more holes (not shown) extending through the side wall of the seal cup  241 C,  342 C enabling the fluid pockets  294 ,  394  to be in fluid communication with the recesses  243 R,  344 R. However, annular O-ring seals  85  are positioned on either side of the hole(s) extending through the sidewall of the seal cup  241 C,  342 C. The O-ring seals  85  ensure that the hole in the seal cup  241 C,  342 C is only in fluid communication with the aperture in the coupling ring  243 ,  344  when the seal cup  241 C,  342 C is moved into a position where the O-ring seals  85  are also positioned either side of the aperture(s) in the coupling rings  243 ,  344 . 
     Before use, several liner modules  232 ,  332 , etc. are attached in series and housed within the barrel  30  to form the inner assembly  14  of the core barrel assembly  10  as described for the previous embodiment. The air in the fluid pockets  294 ,  394  of the seals  241 ,  342  is at atmospheric pressure and the seals  241 ,  342  are resilient and project radially inwardly into the throughbore  135  of each liner module  294 ,  394 . Therefore, prior to insertion into the subterranean formation of interest, the seals protrude radially inwardly into the throughbore  135  of each liner module  232 ,  332  as shown in  FIG. 10 . The seal cups  241 C,  342 C housing the seals  241 ,  342  are shown in a first configuration in which they are positioned adjacent the upper shoulders  243 U,  344 U and the holes in the cups  241 C,  342 C are not in fluid communication with the apertures through the side wall of the coupling ring  243 ,  344 . Therefore, as the core barrel assembly  10  is run into the downhole formation of interest, the ambient pressure increases and the pressure differential between the ambient environment and the air pockets  294 ,  394  causes the air pockets  294 ,  394  to collapse as shown in  FIG. 11 . 
     A core sample  12  is obtained in a similar manner as previously described and the sample  12  is collected within the throughbore  135  of the core barrel assembly  10  as illustrated  FIG. 12 . At this stage, it is desirable to ensure that each portion of the core sample  12  between the seal assemblies  280 ,  380  of each liner module  232 ,  332  is isolated from the portion of core sample  12  in an adjacent part of the core barrel assembly  10  to preserve an accurate record of the core sample  12  and fluids contained therein at a particular depth. Accordingly, the outer liner  36  is pulled upwardly to move the outer liner  36 , the coupling rings  344 ,  243  and the coupling band  154  in relation to the seal cups  241 C,  342 C and the inner liner  34 . In this way, the recesses  243 R,  344 R are moved into a second configuration in relation to the seals  241 ,  342  such that the seal cups  241 C,  342 C abut the lower shoulder  243 L,  344 L as shown in  FIG. 13 . This action causes the aperture extending through the side wall of the coupling rings  243 ,  344  to move between the O-ring seals  85  and therefore enable fluid communication between the hole extending through the sidewall of the seal cups  241 C,  342 C and the aperture in the coupling rings  243 ,  344 . As a result, in this second configuration, the fluid pockets  294 ,  394  are brought into direct communication with the ambient pressure of the subterranean formation. Due to the equalising of pressures between the interior of the fluid pockets  294 ,  394  and the subterranean formation, as well as the resilience of the seals  241 ,  342 , the seals  241 ,  342  return to their original shape and extend radially inwardly, biased against the core sample. In this way, portions of the core sample  12  are isolated within each module  232 ,  332 , as shown in  FIG. 14 . The core barrel assembly  10  can then be retrieved from the subterranean formation with the seals  241 ,  342  biased against the sample  12  by their own resilience providing an effective sealing force against the core sample  12 . Collection of fluid in the reservoir  40  is enabled in a similar manner as previously discussed and the core sample  12  can be stored, transported and retrieved as described for the previous embodiment. 
     Another alternative seal arrangement is shown in and described with reference to  FIGS. 15 to 20 . A liner module  432  comprising the inner liner  34 , the outer liner  36  connected at each end by a seal assembly  480  is shown in  FIG. 15 . The inner liner  34  has a throughbore  435  which can accommodate the core sample  12 . The inner liner  34  is punctured with a plurality of openings  43  such that the reservoir  40  is in fluid communication with the throughbore  435 . 
     A lower ring  444  is provided at the lower end of the liner module  432  and an upper ring  443  is provided at the upper end. Each ring  443 ,  444  is provided with a recessed portion  443 R,  444 R on its inner surface. Each recessed portion  443 R,  444 R houses a seal  441 ,  442 . The lower ring  444  carries the lower seal  442  and the upper ring  443  carries the upper seal  441 . Each seal  441 ,  442  is resiliently biased radially inwardly into the throughbore  435  of the liner module  432 . The seals  441 ,  442  have an annular air pocket  494  at atmospheric pressure. An upper end of the liner module  432  is provided with threads  410  on a box connection and a lower end of the liner module has threads  411  on a pin connection. The threads  410 ,  411  are provided for engaging the liner module  432  with corresponding threads (not shown) of an adjacent liner module or another part of the inner assembly  14 . 
     As shown in the detailed view of  FIG. 15 , the upper ring  443  has an aperture  405  extending through the sidewall thereof. The aperture  405  is sealed using a hollow shear screw  401 . An outer band  400  surrounding the outer liner  36  is held in position by the shear screw  401 . 
       FIG. 16  shows an upper end of a core barrel assembly  10  having a conduit  600  therein. The conduit  600  has an upper passageway  630  and a lower passageway  610 . The passageways  630 ,  610  direct fluids into an annulus  638  created between the inner assembly  14  and the outer assembly  18  of the core barrel assembly  10 . An activation ring  700  is provided in the annulus  638 , located between the upper and lower passageways  630 ,  610 . The conduit  600  also has a portion of reduced inner diameter relative to the inner diameter of the remainder of the conduit to form a ball seat  605  located in a portion of the conduit  600  between the upper and the lower passageway  630 ,  610 . 
     Before use, each module  432  is assembled. The lower ring  444  is glued to the outer liner  36 . The inner liner  34  can then be correctly positioned relative to the outer liner  36  and spaced therefrom by the lower ring  444 . The upper ring  443  is then glued to the upper end of the outer liner  36  to create half a liner module  432  as shown in  FIG. 15 . A corresponding half of liner module  432  is similarly provided to create a full liner module  432 . A series of modules  432  are screwed to one another by means of the threads  410 ,  411  provided at the ends of each liner module  432  and inserted into the outer assembly  18  to form the core barrel assembly  10 . The core barrel assembly  10  is lowered on a drill string to a subterranean formation from which the core sample  12  is to be obtained. As described for the previous embodiment, the air pockets  494  within the seals  441 ,  442  collapse as the pressure differential increases and the assembly  10  is run towards the formation of interest. Drilling mud is circulated through the core barrel assembly  10  to lubricate the drill bit  22 . During operation of the drill bit  22  the mud flows through the conduit  600  and the lower passageway  610  in a direction indicated by arrows  615 . 
     Once the core sample  12  has been recovered in the core barrel assembly  10 , a ball  620  is dropped through the conduit  600 . The ball  620  has a diameter greater than the inner diameter of the conduit  600  in the region of the ball seat  605 . As a result, the ball  620  provides an obstruction to the mud flow in the conduit  600  and therefore the mud flow is forced through the upper passageway  630  in the direction shown by arrows  616  (shown in  FIG. 17 ). However, the annulus  638  is blocked by the activation ring  700 . As a result, the pressure increases behind the activation ring  700  until a point is reached when the pressure build-up forces the activation ring  700  to move through the annulus  638 . 
       FIG. 18  shows the activation ring  700  advancing through the annulus  638  towards the outer band  400 . Continued pressure applied by the mud flow behind the activation ring  700 , causes the activation ring  700  to contact the outer band  400 . At a predetermined force the hollow shear screw  401  shears as the outer band  400  is pushed through the annulus  638  by the activation ring  700  as shown in  FIG. 19 . The fact that the shear screw  401  is hollow means that once the shear screw  401  has sheared, the interior of the seal  441  is in fluid communication with the annulus  638  via the aperture  405 . The pressure of the seal will then equalise with the ambient pressure of the subterranean formation and the resilience of the seal  441  causes it to return to its original shape in the absence of a pressure differential across the pocket  494 . The mud flow can drive the activation ring  700  throughout the annulus  638  to cause the pockets  494  of all the upper seals  441  to return to their original shape biased against the core sample  12 . 
     However, the lower seals  442  are not in selective fluid communication with the ambient pressure and therefore the lower seals remain collapsed downhole. The lower seals  442  return to their original shape under their own resilience as the assembly  10  is recovered to surface and the pressure differential across the air pockets reduces. The sample  12  can then be recovered to surface and fluids obtained and collected from the sample  12  as previously described. 
     The above embodiment describes activation of the upper seal  441  in the subterranean formation. Since oil is generally immiscible with other downhole fluids and has a lower density relative to water and muds, the oil will float on the collected fluids. Thus, the above method and apparatus is useful for obtaining a sample where oil is the sampling fluid of interest, since the upper seal  441  of each module  432  is activated to seal off an upper end of the liner module  432 . However, if the water content of the sample is required to be analysed, the lower seal  442  can be provided with an aperture  405  plugged with a hollow shear screw  401  held in an outer band  400 . This arrangement allows activation of the lower seals  442  to seal each liner module  432  at the lower end. Alternatively, both seals  441 ,  442  can be provided with apertures  405 , thereby enabling both upper seals  441  and lower seals  442  to be activated downhole. 
     Modifications and improvements can be made without departing from the scope of the invention.

Summary:
The present invention relates to an apparatus and method for recovering a sample from a subterranean formation. The apparatus comprises a receptacle for receiving a sample and at least two seal assemblies disposed on an inner surface of the receptacle. The seal assemblies can be arranged to allow a portion of the sample therethrough during the sampling process and to retain fluids within the receptacle during recovery of the sample. The seal assemblies can comprise at least one seal. The at least one seal can be provided with at least one fluid pocket configured to change shape as the volume of fluid therein alters in response to a pressure differential. A plurality of pairs of seal assemblies can be spaced along the length of the inner surface of the receptacle.