Abstract:
A sample tank for receiving and storing sampled connate fluid from a subterranean geological formation. The sample tank includes a piston coaxially disposed within the tank. The piston can be disposed close to the end of the tank where the sampled fluid is introduced into the tank and urged along the length of the tank as sampled fluid is added to the tank. The piston includes an agitator for mixing the fluid and keeping particulates suspended within the fluid. The agitator includes a magnetic member, and is rotated by applying a varying electromagnetic field to the member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application relates to U.S. provisional application 61/077,921 filed on Jul. 3, 2008, the entire specification of which being herein incorporated by reference. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates generally to the field of exploration and production of hydrocarbons from wellbores. More specifically, the present disclosure relates to an apparatus used for storing connate fluid sampled from within a subterranean geological formation. 
     2. Description of Related Art 
     The sampling of fluids contained in subsurface earth formations provides a method of testing formation zones of possible interest by recovering a sample of any formation fluids present for later analysis in a laboratory environment while causing a minimum of damage to the tested formations. The formation sample is essentially a point test of the possible productivity of subsurface earth formations. Additionally, a continuous record of the control and sequence of events during the test is made at the surface. From this record, valuable formation pressure and permeability data as well as data determinative of fluid compressibility, density and relative viscosity can be obtained for formation reservoir analysis. 
     Early formation fluid sampling instruments were not fully successful in commercial service because they were limited to a single test on each trip into the borehole. Later instruments were suitable for multiple testing; however, the success of these testers depended to some extent on the characteristics of the particular formations to be tested. For example, where earth formations were unconsolidated, a different sampling apparatus was required than in the case of consolidated formations. 
     Downhole multi-tester instruments have been developed with extensible sampling probes for engaging the borehole wall at the formation of interest for withdrawing fluid samples therefrom and measuring pressure. In downhole instruments of this nature it is typical to provide an internal draw-down piston which is reciprocated hydraulically or electrically to increase the internal volume of a fluid receiving chamber within the instrument after engaging the borehole wall. This action reduces the pressure at the instrument/formation interface causing fluid to flow from the formation into the fluid receiving chamber of the tool or sample tank. Heretofore, the pistons have accomplished suction activity only while moving in one direction. On the return stroke the piston simply discharges the formation fluid sample through the same opening through which it was drawn and thus provides no pumping activity. Additionally, such unidirectional piston pumping systems can only move the fluid being pumped in a single direction, resulting in a slowly operating sampling system. 
     As shown in  FIG. 1 , the sampling of subterranean formation fluid typically involves the insertion of a sampling tool  10  within a wellbore  5  that intersects the subterranean formation  6 . Generally the tool  10  is inserted on the end of a wireline  8  or other armored cable, but can also be disposed within the wellbore  5  on tubing (not shown). When wireline  8  is used, it is typically maintained on a spool from which the tool  10  is reeled within the wellbore  5 . When it is established that the tool  10  is adjacent to the region of the formation  6  where sampling is to occur, rotation of the spool is ceased thereby suspending the tool  10  at the proper depth within the wellbore  5 . Upon suspending the tool  10  at the predetermined downhole depth, an urging means  12  is extended from the tool  10  that pushes the tool  10  against the inner diameter of the wellbore  5  on the side of the tool  10  opposite to the urging means  12 . A probe  14  provided on the tool  10  opposite to the urging means  12  pierces the wellbore  5  inner diameter or wall extending a small distance into the formation  6 . The probe  14  includes a passage within its body allowing for fluid flow through its inner annulus. Within this annulus of the probe  14 , subterranean fluid can flow from the formation  6  to within the tool  10  for storage and subsequent analysis. 
     SUMMARY 
     The present disclosure involves a subterranean formation fluid sample storage tank that includes, a housing, a piston disposed within the housing, a fluid agitator assembly couplable with the piston, and a coil assembly in electromagnetic cooperation with the agitator assembly. Also disclosed herein is a method of storing fluid from a subterranean geological formation in a storage tank having a fluid agitation system. In an example, the method includes urging subterranean formation fluid from a subterranean formation into the storage tank, generating a phase changing electromagnetic field, and activating the fluid agitation system by applying the electromagnetic field to the fluid agitation system. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       Some of the features and benefits of the present disclosure having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  depicts in a side partial sectional view an example of a prior art sampling tool disposed within a wellbore. 
         FIG. 2  schematically represents in a side sectional view an embodiment of a pumping system with a sample tank in accordance with the present disclosure. 
         FIG. 2A  illustrates in perspective views alternate examples of agitators. 
         FIG. 3  is a side partial sectional view of an example of a portion of a sampling tool in a wellbore. 
     
    
    
     While the subject device and method will be described in connection with the preferred embodiments but not limited thereto. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the present disclosure as defined by the appended claims. 
     DETAILED DESCRIPTION 
     The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be through and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. 
     It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the improvements herein described are therefore to be limited only by the scope of the appended claims. 
     The present disclosure involves a novel sampling system useful for obtaining and collecting connate fluid resident within a subterranean geological formation. One embodiment of a sampling system  16  in accordance with the novel aspects disclosed herein is illustrated in partial cross sectional view in  FIG. 2 . Here, the sampling system  16  is comprised of a pumping device  18  in fluid communication with a tank  54 . The pumping device  18  comprises a pump  26  driven by a hydraulic system  22 , where the pumping device  18  draws connate fluid from the formation  16  and delivers it to the tank  54 . 
     More specifically, the hydraulic system  22  of the embodiment of  FIG. 2  drives the pumping device  18  by reciprocating a piston  36  housed within the pump  26 . The piston  36  comprises a rod  37  running coaxial within the pump housing  28  having an inner plunger  40  secured proximate to the mid-point of the rod  37 . The inner plunger  40  should be substantially coaxial with the rod  37  and have an outer diameter that extends outward into sealing contact with the inner diameter of the pump housing  28 . Disposed at the ends of the rod  37  are a first end plunger  38  and a second end plunger  42 . The plungers  38 ,  42  should also have outer diameters that extend outward into sealing contact with the inner circumference of the pump housing. In the embodiment shown in  FIG. 2 , the inner plunger  40  has a diameter greater than the diameter of both the first and second end plungers  38 ,  42 . However these diameters can be substantially the same or the inner plunger diameter can be less than the outer plunger diameters. 
     Reciprocation of the piston  36  of the embodiment shown is produced by selectively introducing pressurized hydraulic fluid on alternate sides of the inner plunger  40  thereby urging the inner plunger  40  back and forth inside a chamber  32  shown within the inside of the pump housing  28 . The pressurized hydraulic fluid is delivered to the pump  26  from the hydraulic fluid source  20  via the hydraulic circuit  22 . The hydraulic fluid source  20  can be a motor driven unit disposed downhole, or proximate the borehole entrance. Lines  23 ,  25  respectively connect the hydraulic fluid source  20  to the valves  24  and the valves  24  to the pump housing  28 . The fluid is selectively delivered to opposing sides of the inner plunger  40  by alternatingly opening/closing the automatic valves  24 . Reciprocating the piston  36  produces in and out movement of the outer plungers  38 ,  42  within their respective recesses  30 ,  34  correspondingly reducing pressure within the respective recess from which the plunger is retreating. 
     The pumping system  18  utilizes the low pressure within the recesses  30 ,  34  to induce connate fluid into the pump  26  from the formation  6 . As shown, a probe connector  15  is in fluid communication with a probe  17  that is selectively in communication with formation fluid. As discussed above, reciprocating the piston  26  within the housing  28  draws formation (or connate) fluid through the probe  17  and probe connector  15  to a connected inlet line  46 . A branch  45  depending from the inlet line  46  delivers formation fluid to chamber  30 ; inlet line  46  delivers formation fluid to chamber  34 . Check valves  50  in the branch  45  and inlet line  46  prevent backflow to the connector  15  while allowing flow to the chambers  30 ,  34 . 
     Subsequent piston  36  reciprocation backstrokes the outer plungers  38 ,  40  into a respective chamber  30 ,  34  and pushes formation fluid from the chamber  30 ,  34  into an outlet line  48 . As schematically illustrated, the outlet line  48  includes leads connecting to the branch  45  and inlet line  46  downstream of the check valves  50 . Thus fluid being discharged from the chambers  30 ,  34  first reenters the branch  45  and inlet line  46  then flows to the outlet line  48 . The check valves  50  block backflow into these lines thus routing discharged flow from the pump  26  to the outlet line  48 . Optionally, the outlet line  48  could directly connect to the chambers  30 ,  34  instead of the branch  45  or inlet line  46 . Optional check valves  50  are shown in the outlet line  48  oriented to direct outlet flow through the outlet line  48  to a storage tank  54  coupled on the outlet line  48  terminal end. 
     The outlet line  48  includes a block valve  52  for selectively isolating the tank  54  from the pumping system  26 . This isolation may be desired for repairs and can also be utilized when removing the sampled connate fluid from within the tank  54 . In the embodiment of the tank  54  shown in  FIG. 2 , the tank  54  comprises an outer housing  55  with a substantially hollowed out middle section within thereby forming a plenum  57 . Disposed within the plenum  57  is a piston assembly  58  that includes a piston body  66 , a magnetic member  68  disposed within the piston body  66 . Also shown in the plenum  57  is an agitator  70  connected by a shaft  72  to the magnetic member  68 . The agitator  70  may be any suitable device configured to move or otherwise agitate fluid within the tank  54 . The agitator  70  may be configured to move axially, rotationally or a combination thereof within the tank  54 . 
     In one non-limiting embodiment, the agitator  70  includes a propeller-shaped end portion that may be rotated and or translated to agitate the fluid. Examples of agitator embodiments are provided in a perspective view in  FIG. 2A . The agitator  70 A includes rectangular vanes  701  projecting radially outward from a cylindrical hub  702 . Agitator  70 B, which is shown in a partial sectional view, includes a cylindrical body  704  through which fluid can pass. Vanes  703  are shown provided on the inner and outer surfaces of the body  704 . In another embodiment, agitator  70 C includes a disk-shaped member  705  having holes or openings  706  formed therethrough and projections  707  attached on the member  705  surface. The agitator  70  may be formed from a rigid material, from a pliable material to prevent fracture and/or permanent deformation if pressed against a tank end wall  59 , or the agitator  70  may be formed of a combination of materials. 
     The piston body  66  is moveable in the tank  54  along its longitudinal axis A L ; and can have outer dimensions substantially matching the plenum  57  inner dimensions. Optionally the piston body  66  may include one or more seals  65  for sealing between the piston body  66  and plenum  57 . In the embodiment shown, the magnetic member  68  is freely rotatable within the piston body  66 . An opening  67  shown formed through the piston body  66  is substantially coaxial to the tank  54  longitudinal axis A L . The shaft  72  is attached on one end of the magnetic member  68  and it extends outward from the magnetic member  68  through the opening  67  for attachment on its other end to the agitator  70 . 
     A coil assembly  60  shown circumscribing the tank  54  outer surface includes a coil housing  62  with coil leads  64  wound therein. In an example, a power source  63  is shown having leads  69 ,  71  connecting to the coil assembly  60 . The power source  63 , which can selectively energize the coil assembly  60 , can be provided downhole with the sampling system  16  or at the surface. The coil assembly  60  is selectively moveable along the tank  54  along a path substantially parallel with tank  54  longitudinal axis A L . Optionally, the coil housing  62  may be comprised of a ferrous material magnetically coupled to the magnetic member  68  that can couple the coil assembly  60  and piston assembly  58  so they move together along the tank&#39;s  54  length. Magnetic member  68  embodiments include a permanent magnet and an electromagnet. 
       FIG. 3  illustrates an example of operation where the sampling system  16  is deployed in a wellbore  5  within a carrier  19  and an urging means  21  pushes the carrier  19  so the probe  17  pierces the formation  6 . Fluid, represented by arrows, is then drawn into the probe  17  by activating the pump system  18  and is pumped to the tank  54 . During, or prior to deployment in the wellbore  5 , the piston assembly  58  may be positioned adjacent the tank end wall  59 . Fluid pumped to the tank  54  is deposited in the plenum  57  where it accumulates between piston body  66  and end wall  59  forcing the piston assembly  58  towards the opposite end wall  61 . As noted above, magnetically coupling the magnetic member  68  and coil assembly  60  causes the coil assembly  60  to “track” the piston assembly  58  as it moves within the tank  54 . Since fluid addition in the tank  54  affects piston assembly  58  position, coil assembly  60  position can be an indicator of fluid volume in the tank  54 . 
     Another novel aspect of the present disclosure is externally driving the agitator  70 . In one embodiment of use, the power source  63  selectively provides electrical energy in the form of power, voltage, and/or current to the coil assembly  60  via lead(s)  69 ,  71 . The electrical energy energizes the coil leads  64  to create an electromagnetic field around and in the tank  54 , including the magnetic member  68 . The electromagnetic field rotates the magnetic member  68 , attached shaft  72 , and agitator  70 . Thus in one example of use, the driver for rotating the agitator  70  is an electromagnetic field. Other example drivers for the agitator  70  include the coil assembly  60  and the coil assembly  60  and power source  63 . The agitator  70  rotation agitates the connate fluid in the plenum  57  dispersing and suspending particulates in the fluid to prevent silting and particulate precipitation within the tank  54 . Optionally, agitator  70  operation circulates the fluid as illustrated by the arrows A. The agitator  70  can operate continuously or intermittently. 
     The term “carrier” as used herein means any device, device component, combination of devices, media and/or member that may be used to convey, house, support or otherwise facilitate the use of another device, device component, combination of devices, media and/or member. Exemplary non-limiting carriers include drill strings of the coiled tube type, of the jointed pipe type and any combination or portion thereof. Other carrier examples include casing pipes, wirelines, wireline sondes, slickline sondes, drop shots, downhole subs, bottom hole assemblies, drill string inserts, modules, internal housings and substrate portions thereof. 
     A “downhole fluid” as used herein includes any gas, liquid, flowable solid and other materials having a fluid property. A downhole fluid may be natural or man-made and may be transported downhole or may be recovered from a downhole location. Non-limiting examples of downhole fluids include downhole fluids can include drilling fluids, return fluids, formation fluids, production fluids containing one or more hydrocarbons, oils and solvents used in conjunction with downhole tools, water, brine and combinations thereof. 
     The system and method described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, the agitator  70  can be comprised of a flexible metal, such as stainless steel, as well as sturdy polymeric materials, such as high-density polyethylene. The magnetic member  68  and the agitator  70  could optionally be integrally formed with the piston body  66 . The shaft  72  can include magnetic material. In an example of forming a shaft  72  from magnetic material, the magnetic member  68  may not be necessary. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present disclosure and the scope of the appended claims.