Patent Publication Number: US-11384615-B2

Title: Core retrieving tool

Description:
TECHNICAL FIELD 
     This is related to a retrieving tool for retrieving a core sample from an underground formation, and in particular, a retrieving tool that collects the fluids released by the core sample. 
     BACKGROUND 
     Samples of an underground formation are taken from a wellbore using a coring tool. U.S. Pat. No. 9,506,307 (Kinsella) entitled “High pressure coring assembly and method” discloses a coring tool used to obtain core samples from an underground formation. 
     SUMMARY 
     According to an aspect, there is provided a core retrieving tool for retrieving a core sample of an underground formation, the core retrieving tool comprising a coring assembly having a coring bit, a core barrel within the coring assembly, the core barrel defining a core-receiving chamber having a first end and a second end, and an expandable fluid chamber in fluid communication with the second end of the core-receiving chamber, and a valve that is moveable between an open position to receive the core sample and a closed position to seal the first end of the core-receiving chamber when the core sample is received within the core barrel, wherein, when the valve seals the first end of the core-receiving chamber, the expandable fluid chamber is expandable in response to a pressure differential between a pressure of the core-receiving chamber and a pressure outside the core barrel, and in a retrieval state, the expandable fluid chamber is in open fluid communication with the core-receiving chamber such that a pressure of the expandable fluid chamber is equalized with the pressure of the core-receiving chamber. 
     According to other aspects, one or more of the following features may be provided, alone or in combination: the expandable fluid chamber may be in open fluid communication with the core-receiving chamber when the valve is in the open position and in the closed position; the expandable fluid chamber may comprise a piston movable between a first position toward the core receiving chamber and a second position away from the core receiving chamber, wherein the piston moves in response to the pressure differential; expandable fluid chamber may comprise a first portion and a second portion separated from the first portion by the piston, such that, as the piston moves toward the second position, the second portion contracts to allow the first portion to expand and receive fluids from the core-receiving chamber; the second portion may be filled with hydraulic fluid; the retrieving may further comprise a pressure valve that is in fluid communication with the second portion, the pressure valve opening at a preset pressure to expel the hydraulic fluid from the second portion; the coring assembly may comprise an outer housing and an inner housing positioned between the outer housing and the core barrel, wherein the core barrel and the inner housing may define the core-receiving chamber, the inner housing may carry the valve and the core barrel may be moveable within the inner housing; and the core retrieving tool may further comprise a transfer valve in fluid communication with the expandable fluid chamber for selectively removing fluid from the expandable fluid chamber. 
     According to an aspect, there is provided a method of retrieving a core sample of an underground formation, the method comprising the steps of: 
     inserting a core retrieving tool in a wellbore, the core retrieving tool comprising a coring assembly comprising a coring bit, a core barrel within the coring assembly, the core barrel defining a core-receiving chamber having a first end and a second end, and an expandable fluid chamber in fluid communication with the second end of the core-receiving chamber, and a valve that selectively seals the first end of the core-receiving chamber; 
     drilling the core sample with the coring bit; 
     receiving the core sample into the core-receiving chamber; 
     closing the valve to seal the first end of the core-receiving chamber; and 
     withdrawing the core-retrieving tool from the wellbore and permitting the expandable fluid chamber to expand in response to a pressure differential between the core-receiving chamber and a pressure outside of the core barrel, the expandable fluid chamber being in open, fluid communication with the core-receiving chamber such that a pressure of the expandable fluid chamber is equalized with the pressure of the core-receiving chamber. 
     According to other aspects, one or more of the following features may be provided, alone or in combination: the expandable fluid chamber may be in open fluid communication with the core-receiving chamber before and after the valve is closed; permitting the expandable fluid chamber to expand may comprise moving a piston within the expandable fluid chamber from a first position toward the core receiving chamber towards a second position away from the core receiving chamber; the expandable fluid chamber may comprise a first portion and a second portion separated from the first portion by the piston; permitting the expandable chamber to expand may comprise contracting the second portion to allow the first portion to expand and receive fluids from the core-receiving chamber; the second portion may be filled with hydraulic fluid; the method may further comprise the steps of opening a pressure valve that is in fluid communication with the second portion upon reaching a preset pressure and expelling the hydraulic fluid from the second portion; the method may further comprise the step of transferring fluid collected in the core barrel to a surface storage container; the core retrieving tool may further comprise an inner housing between the outer housing and the core barrel, wherein the core barrel and inner housing may define the core-receiving chamber, the inner housing may carry the valve, and the core barrel may be moveable within the inner housing; and the method may further comprise the step of sealing the core sample within the inner housing and removing the inner housing from the outer housing 
     In other aspects, the features described above may be combined together in any reasonable combination as will be recognized by those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein: 
         FIG. 1  is a side elevation view in section of a core retrieving tool. 
         FIG. 2  is a side elevation view in section of a core sample entering the core retrieving tool. 
         FIG. 3  is a side elevation view in section of a core retrieving tool with an open valve. 
         FIG. 4  is a side elevation view in section of a core retrieving tool with a closed valve. 
         FIG. 5  is a side elevation view in section of a core-receiving chamber and expandable fluid chamber of a core retrieving tool with a piston in a first position. 
         FIG. 6  is a side elevation view in section of the core-receiving chamber of  FIG. 5  with the piston moving toward a second position. 
         FIG. 7  is a side elevation view in section of the expandable fluid chamber of a core retrieving tool with a piston moving in a second position. 
         FIG. 8  is an elevated side view in cross section of the expandable fluid chamber of a core retrieving tool connected to a surface storage vessel via a transfer valve. 
         FIG. 9  is an elevated side view in cross section of a core sample sealed within the inner housing of a core retrieving tool. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A core retrieving tool, generally identified by reference numeral  10 , will now be described with reference to  FIG. 1 through 9 . Core retrieving tool  10  is designed to be used for obtaining a core sample  100  from an underground formation through a wellbore (not shown). Core samples are obtained from underground formations to help analyse the hydrocarbon content, and will typically contain solids, liquid hydrocarbons, and gaseous hydrocarbons. Core retrieving tool  10  is designed to help obtain core samples from an underground formation by containing the various phases and components present in the core sample after it is drilled until tool is removed from the wellbore, which involves compensating for the change in pressure from the downhole environment and surface while avoiding a dangerous build-up of pressure. 
     Referring to  FIG. 1 , a non-limiting example of a core retrieving tool  10  is shown that includes a coring assembly  12  that may be mounted to a wireline or tubing string. Coring assembly  12  has a coring bit  14  at a downhole end  16  that is used to form a core sample  100  from the underground formation. Coring bit  14  may be designed and operated as known in the art to cause the core sample  100  to enter into coring assembly  12 . 
     As shown, coring assembly  12  has an inner housing  20  positioned within an outer housing  18 . Coring bit  14  is carried and driven by outer housing  18 , while inner housing  20  defines a core-receiving chamber  32  and an expandable fluid chamber  40 . Core-receiving chamber  32  has a first end  34  toward the downhole end  16  of coring assembly  12 , and a second end  36  that is open to expandable fluid chamber  40 . 
     Referring to  FIG. 2  through  FIG. 4 , core-receiving chamber  32  includes a core barrel  30  positioned within inner housing  20  that receives core sample  100  as core sample  100  enters through first end  34 . Core barrel  30  may be designed according to known principles to receive and secure core sample  100 . Once core sample  100  fully enters core-receiving chamber  32 , a valve  60  is used to seal core sample  100  within core-receiving chamber  32 . 
     Valve  60  is shown as a flapper valve, however valve  60  may have any suitable design that, in an open state as shown in  FIG. 3 , allows core sample  100  to enter core-receiving chamber  32 , and in a closed state as shown in  FIG. 4 , seals core-receiving chamber  32  at first end  34 . As a flapper valve design, valve  60  may be designed to improve its ability to seal when closed. For example, valve  60  may have a latch that, when engaged, holds valve  60  in the closed and sealed position, or valve  60  may be designed to use the pressure differential across the flapper to improve the sealing force. Other suitable valve designs may also be used. 
     In the depicted example, valve  60  is carried by inner housing  20  and core barrel  30  is movable in an axial direction relative to inner housing  20  and outer housing  18 . As is known in the art, core barrel  30  may be used to grip core sample  100 , which allows core sample  100  to be withdrawn into core-receiving chamber  32 , either by raising core barrel  30  or lowering outer and inner housings  18  and  20 . Core barrel  30  may be designed according to known processes to allow core sample  100  to be properly manipulated within coring assembly  12 . Typically, a core barrel will have a catcher element (not shown) that grips core sample  100  and breaks off core sample  100  from the formation from which it has been drilled. Once properly positioned within core-receiving chamber  32 , valve  60  is permitted to close and seal core-receiving chamber  32 . This may be done, for example, by releasing a catch that otherwise holds valve  60  open. Valve  60  may be biased to the closed position, such that, when released, it moves to the closed position. Alternatively, valve  60  may be designed to be pushed open as core sample  100  passes by valve  60 , which then closes after core sample  100  no longer holds valve  60  open. Those skilled in the art may provide different designs of valve  60 , including the manner in which the valve is opened and closed. In the depicted example, core-receiving chamber  32  is defined by core barrel  30  toward second end  36  and inner housing  20  with valve  60  toward first end  34 . As will be understood, the design of inner housing  20 , core barrel  30 , and valve  60  may vary as deemed appropriate by those skilled in the art, provided that the design permits a core sample to be drilled from a formation, and withdrawn into core-receiving chamber  32  sufficiently that it is able to be sealed within chamber  32 . As depicted, this is accomplished by permitting core barrel  30  to move relative to inner housing  20  and valve  60 , which closes once core sample  100  is withdrawn sufficiently into core-receiving chamber  32 . 
     Referring to  FIG. 5  and  FIG. 6 , expandable fluid chamber  40  is in fluid communication with core-receiving chamber  32 , and, once core-receiving chamber  32  is sealed by valve  60 , is designed to expand in response to a pressure differential between the pressure in core-receiving chamber  32  and an external pressure. This will typically be the downhole pressure that is applied to the other side of expandable fluid chamber  40 . Tool  10  may also be designed to expose expandable fluid chamber  40  to a different pressure, such as through the use of pressure valves, fluid lines to surface, etc. While this may provide benefits in certain circumstances, doing so would also increase the complexity of the tool. 
     As shown, expandable fluid chamber  40  is in open fluid communication with core-receiving chamber  32  at all times, i.e. in the core-drilling state, and the retrieval state after the core sample has been formed. However, at the very least, expandable fluid chamber  40  will be in open fluid communication with core-receiving chamber  32  when core sample  100  is sealed within core-receiving chamber  32  and core retrieving tool  10  is in a retrieval state. For example, withdrawing core barrel  30  or closing valve  60  may cause a separate valve or channel to open (not shown). With expandable fluid chamber  40  in open fluid communication with core-receiving chamber  32 , the pressure of expandable fluid chamber  40  is equalized with the pressure of core-receiving chamber  32 . With valve  60  closed to seal first end  34  of core-receiving chamber  32 , fluids  102  including gasses  102  released by core sample  100  will fill core-receiving chamber  32  and expandable fluid chamber  40 . As core retrieving tool is returned to surface, the pressure outside of core barrel  30  will be reduced, creating a pressure differential between the pressure in core-receiving chamber  32  and an external pressure. This pressure differential causes expandable fluid chamber  40  to expand, such that gasses  102  and other fluids that have been released or are permitted to be released by the change in pressure from core sample  100  will fill expandable fluid chamber  40  core-receiving chamber  32 . This process continues until expandable fluid chamber  40  reaches its largest permitted volume, or until the pressure differential is insufficient to further expand chamber  40 . 
     In the depicted example, expandable fluid chamber  40  is designed with a piston  42  within a chamber housing  44  where the piston is movable within chamber housing  44  between a first position toward core receiving chamber  32  and a second position away from core receiving chamber  32 , shown in  FIG. 5  and  FIG. 7 , respectively. As piston  42  moves from the first position toward the second position in response to the pressure differential, the volume of expandable fluid chamber  40  increases. Typically, piston  42  remains in the first position when core retrieving tool  10  is in the retrieval state and starts moving after valve  60  seals first end  34  of core-receiving chamber  32  and a pressure differential is applied. In some examples, piston  42  may be biased toward the first position by an initial force that is to be overcome by the pressure differential for expandable fluid chamber  40  to start expanding. This may be, for example, through the presence of a hydraulic fluid on the opposite side of piston  42  that is pushed out in order to allow piston  42  to expand. The hydraulic fluid may be any suitable fluid that allows the tool to operate. Examples may be oil-based or water-based, and may include oil, synthetics oils, vegetable oil, water, saline, or other suitable fluids. The type of fluid selected may be based on the preferences of the user, and the ability of a laboratory to differentiate between the captured fluids and the hydraulic fluids during testing. 
     As depicted, piston  42  separate chamber housing  44  into a first portion  48  and a second portion  50 , where first portion  48  is in fluid communication with core-receiving chamber  32 . As piston  42  moves from the first position to the second position, second portion  50  contracts to allow first portion  48  to expand and receive fluids from core-receiving chamber  32 . Second portion  50  may be filled with hydraulic fluid that is expelled through a pressure valve  46  in fluid communication with the hydraulic fluid chamber when second portion  50  contracts. Pressure valve  46  may be a check valve that opens once a preset pressure across valve  46  is reached, or it may be a flow restrictor that restricts the rate of flow, such as by appropriate selection of the orifice and/or the viscosity of the hydraulic fluid to provide a desired amount of resistance to movement. If a preset pressure is used, it may fully or partially determine the pressure differential at which expandable fluid chamber  32  expands. Restricting the flow rate through pressure valve  46  may be beneficial as depressurizing a core sample too quickly may damage the integrity of the sample. The hydraulic fluid within second portion  50  will typically be a non-compressible fluid such that the hydraulic fluid cooperates with pressure valve  46  to provide resistance to movement of piston  42 . Hydraulic fluid that is expelled through pressure valve  46  may be expelled to an alternate chamber within core retrieving tool  10  or it may be expelled into the wellbore. Other designs that provide an expandable fluid chamber, such as a telescopic chamber where piston  42  is the end of the chamber, may also be used, however having a chamber housing  44  with a fixed length simplifies the use and installation of tool  10 . 
     When piston  42  is in the second position, shown in  FIG. 7 , expandable fluid chamber  40  has reached its maximum and will not expand further. Core retrieving tool  10  may have an emergency relief valve  52  in fluid communication with the expandable fluid chamber that opens when the pressure reaches a predetermined release pressure. In this way, emergency relief valve  52  may be configured to prevent the pressure differential experienced by core-receiving chamber  32  and expandable fluid chamber  40  from reaching a dangerous level by venting fluid from expandable fluid chamber  40  in order to prevent failure of and/or damage to core retrieving tool  10 . 
     Referring to  FIG. 8 , once tool  10  has reached surface, a transfer valve  54  that is in fluid communication with expandable fluid chamber  40  may be used to remove fluid from expandable fluid chamber  40  and transfer them to a separate storage vessel  56 . This may be done by equalizing the pressure, by using a fluid pump or compressor to withdraw fluids from expandable fluid chamber  40 , or by pumping piston  42  back down to the first position, which will cause fluids to be expelled. Referring to  FIG. 8 , transfer valve  54  may be used to transfer gasses  102  or other fluids to a surface storage container  56 . As depicted, transfer valve  54  is connected to expandable fluid chamber  40  toward second end  36  of core-receiving chamber  32  and piston  42  moves from the second position toward the first position as gasses  102  are transferred to surface storage container  56 . Transfer valve  54  may be used to withdraw fluids for further sample, and to reduce the pressure within expandable fluid chamber  40  and core-receiving chamber  32  to atmospheric pressure, or to a non-dangerous pressure level. If the pressure is reduced to a pressure that is at or close to atmospheric pressure, core sample  100  may be removed more easily and safely than if a pressure differential remains, and the majority of downhole fluids released from core sample  100  may be captured. 
     Referring to  FIG. 9 , once fluids have been extracted to achieve a safe pressure level within tool  10 , core-receiving chamber  32  may be detached from tool  10  and expandable fluid chamber  40 , and closed by a plug  58  that seals second end  36  of core-receiving chamber  32 . Inner housing  20 , sealed by plug  58  and valve  60  and containing core sample  100 , may then be transported to a laboratory or other location for further testing and processing. Plug  58  may be installed at any convenient part of core-receiving chamber  32  or expandable fluid chamber  40  in order to properly seal core sample  100  and reduce to an acceptable the loss of any released fluids. Typically, storage container  56  (shown in  FIG. 8 ) that contains the withdrawn fluids will be sent along with the sealed core-receiving chamber  32  for further testing and processing. By providing the core sample as well some or all of the fluids that were released by the core during retrieval, a more accurate and detailed analysis may be provided of the downhole formation. 
     A method of retrieving core sample  100  using core retrieving tool  10  will now be described with reference to  FIG. 1  to  FIG. 9 . 
     Referring to  FIG. 1 , core retrieving tool  10  is assembled and inserted into a wellbore and lowered to an underground formation. Referring to  FIG. 2 , core sample  100  is drilled using coring bit  14  and core sample  100  is received into core-receiving chamber  32  through first end  34  of core-receiving chamber  32 . Once core sample  100  is formed, it may be gripped by core barrel  30  to break core sample  100  and withdraw core sample  100  into core-receiving chamber  32 , as shown in  FIG. 3 . After core sample  100  is in position, valve  60  is closed to seal the first end  34  of core-receiving chamber  32  as shown in  FIG. 4 . 
     Once core sample  100  is received within core-receiving chamber  32  and valve  60  is closed, core-retrieving tool  10  is removed from the wellbore back to surface. Referring to  FIG. 5-7 , as tool  10  is lifted through the wellbore, a pressure differential will develop between core-receiving chamber  32  and an external pressure, such as the wellbore pressure. This pressure differential will cause expandable fluid chamber  40 , which is in open fluid communication with core-receiving chamber  32 , to expand. As expandable fluid chamber  40  expands, the pressure is equalized between expandable fluid chamber  40  and core-receiving chamber  32 , and the pressure differential relative to the external pressure is reduced. This will permit core sample  100  to release some fluids, such as liquids, gasses, and liquids that vaporize under a reduced pressure, and enter expandable fluid chamber  40 . Typically, as expandable fluid chamber  40  is above core-receiving chamber  32 , the gasses will enter expandable fluid chamber  40  and any liquids that exit core sample  100  will remain in core-receiving chamber  32 . 
     Referring to  FIG. 8 , after core retrieving tool  10  reaches surface and has been withdrawn from the wellbore, the fluids  102  released by core sample  100  may be removed from expandable fluid chamber  40  and transferred to surface storage container  56 . Referring to  FIG. 9 , second end  36  of core receiving chamber  32  may be sealed by a plug  58  and inner housing  20 , still sealed at first end  34  by valve  60  and containing core sample  100 , may then be transported for further processing. 
     In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements. 
     The scope of the following claims should not be limited by the preferred embodiments set forth in the examples above and in the drawings, but should be given the broadest interpretation consistent with the description as a whole.