Patent Abstract:
An apparatus and method is given for evaluating a well fluid sub-sample at the well surface as the sample is transported to the well surface from a downhole wellbore location. The invention collects a formation fluid sample under pressure. The fluid sample is further pressurized with a traveling piston powered by the hydrostatic wellbore pressure. The pressurized formation fluid sample is contained under high pressure within a fixed volume chamber for retrieval to the well surface. Multiple collection tanks can be lowered into the wellbore during the same run to sample different zones with minimal rig time. A pair of valves in series along the supply/discharge conduit respective to each tank accommodates extraction of a field sample to verify the sample integrity while still on location. The tanks can be emptied at the well surface with an evacuation pressure so that the fluid sample pressure is maintained above a selected pressure at all times or transported to an analytical laboratory.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the art of earth boring and the collection of formation fluid samples from a wellbore. More particularly, the invention relates to methods and apparatus for collecting a deep well formation sample and preserving the in situ constituency of the sample upon surface retrieval. Once the sample is retrieved, this invention describes methods and apparatus for isolating and extracting a sub-sample for a field determination of the quality of the primary sample without altering the primary sample composition. 
     2. Description of Related Art 
     Earth formation fluids in a hydrocarbon producing well typically comprise a mixture of oil, gas, and water. The pressure, temperature and volume of formation fluids control the phase relation of these constituents. In a subsurface formation, high well fluid pressures often contain gas within the oil above the bubble point pressure. When the pressure is reduced, as by raising an in situ captured sample of the formation fluid to the surface, the dissolved gaseous compounds separate from the liquid phase sample. The accurate measure of pressure, temperature, and formation fluid composition from a particular well affects the commercial interest in producing fluids available from the well. The data also provides information regarding procedures for maximizing the completion and production of the respective hydrocarbon reservoir. 
     Certain techniques analyze the well fluids downhole in the wellbore. U.S. Pat. No. 5,361,839 to Griffith et al. (1993) disclosed a transducer for generating an output representative of fluid sample characteristics downhole in a wellbore. U.S. Pat. No. 5,329,811 to Schultz et al. (1994) disclosed an apparatus and method for assessing pressure and volume data for a downhole well fluid sample. 
     Other techniques capture a well fluid sample for retrieval to the surface. U.S. Pat. No. 4,583,595 to Czenichow et al. (1986) disclosed a piston actuated mechanism for capturing a well fluid sample. U.S. Pat. No. 4,721,157 to Berzin (1988) disclosed a shifting valve sleeve for capturing a well fluid sample in a chamber. U.S. Pat. No. 4,766,955 to Petermann (1988) disclosed a piston engaged with a control valve for capturing a well fluid sample, and U.S. Pat. No. 4,903,765 to Zunkel (1990) disclosed a time delayed well fluid sampler. U.S. Pat. No. 5,009,100 to Gruber et al. (1991) disclosed a wireline sampler for collecting a well fluid sample from a selected wellbore depth, U.S. Pat. No. 5,240,072 to Schultz et al. (1993) disclosed a multiple sample annulus pressure responsive sampler for permitting well fluid sample collection at different time and depth intervals, and U.S. Pat. No. 5,322,120 to Be et al. (1994) disclosed an electrically actuated hydraulic system for collecting well fluid samples deep in a wellbore. 
     Downhole temperatures in a deep wellbore often exceed 300 degrees F. When a hot formation fluid sample is retrieved to the surface at 70 degrees F., for example, the resulting drop in temperature causes the formation fluid sample to contract. If the volume of the sample is unchanged, such contraction substantially reduces the sample pressure. A pressure drop changes the in situ formation fluid parameters thereby inducing phase separation between liquids and dissolved gases within the formation fluid sample, for example. As another example, dramatic pressure changes in a formation sample may precipitate dissolved solids such as waxes and asphaltines. These types of phase separation represents significant and irreversible changes in the formation fluid characteristics, and reduces the ability to evaluate the actual properties of the formation fluid. 
     To overcome this limitation, various techniques have been developed to maintain pressure of the formation fluid sample. U.S. Pat. No. 5,337,822 to Massie et al. (1994) teaches the concept of pressurizing a formation fluid sample with a hydraulically driven piston powered by a high pressure gas. Similarly, U.S. Pat. No. 5,662,166 to Shammai (1997) teaches the use of a pressurized gas to charge the formation fluid sample. U.S. Pat. Nos. 5,303,775 (1994) and U.S. Pat. No. 5,377,755 (1995) to Michaels et al. disclose a bi-directional, positive displacement pump for increasing the formation fluid sample pressure above the bubble point so that subsequent cooling does not reduce the fluid pressure below the bubble point. 
     More recently, U.S. patent application Ser. No. 09/648,410 by Paul A. Reinhardt, filed Aug. 25, 2000, has disclosed a multiple tank sample extraction system in which each sample tank in a magazine carrier has a two stage piston chamber by which the in situ wellbore pressure of a deep well fluid within a sample retrieval chamber is amplified to overcome the contraction consequences of removing a sample of deepwell fluid to the earth surface. At the interface of the apparatus where each of several independently removable tanks is severed from a common charging magazine, a small quantity of high pressure formation fluid is isolated in a sample transfer conduit between a magazine distribution valve and a tank closure valve. Although both valves are closed when an individual tank is removed from its respective magazine alcove, this small quantity of fluid is vented to the atmosphere as a preparatory step to severance of the tank from the magazine for individual transport and sample testing. 
     Although the quantity of this atmospherically vented fluid is small, it is important to observe the nature and quality of the vented fluid as a qualitative clue to the fluid within the main body of the sample chamber. Notwithstanding extreme care in downhole sampling procedures, it is still possible for the wireline magazine to return with contaminated samples in one or more tanks. Such contamination may take the form, for example, of water seepage from other strata, mud cake deposited against the borehole wall or wellbore drilling fluid. Filtrate from oil based drilling mud is especially a problem. 
     Samples must be representative of fluid in the formation and consequently must be substantially free of contaminates from drilling operations. In particular, samples need to contain less than a few percent of filtrate from an oil base mud for that sample to be representative of the formation fluid. Usually, 10% contamination in a sample is too much for a reliable pressure/volume/temperature analysis. Acquisition of a formation fluid sample this pure and greater is difficult to obtain. Moreover, it is essential to know the relative contamination in a sample to a reasonable degree of certainty at the time the sample is extracted. The physical and intellectual effort committed to extracting a deepwell sample is of such magnitude that repetition of the effort is to be avoided if possible. Consequently, it is desirable to obtain a small sub-sample of the recovered fluids to determine whether or not the contamination level is sufficiently low to warrant laboratory analysis. It is imperative that this sub-sample be extracted without altering the physical properties of the primary sample reserved for a more expansive laboratory analysis. 
     It is an object of the present invention, therefore, to controllably secure a portion of the transfer conduit fluid for the purpose of field analysis. Also an object of the present invention is provision of means to evaluate the nature of a fluid sample confined within a high pressure tank chamber without risking the integrity of the sample composition. 
     SUMMARY OF THE INVENTION 
     These and other objects of the present invention as will become apparent from the following description of the preferred embodiments are accomplished by a deep well sampling system that is capable of isolating the last portion of sample fluid that is collected into a sample chamber. The sampling system extracts formation fluid directly from the desired formation through a probe that is pressed into the borehole sidewall. This formation fluid is pumped by a downhole equipment pump dedicated to the wellbore equipment along a pump discharge conduit and through a distribution valve or valves. The distribution valve is controlled to direct the flow of pumped fluid drawn from the borehole sidewall into a selected tank or into the wellbore. In a preferred embodiment, each of the tanks may be selectively separated from the magazine for reduced transport weight and handling bulk. 
     From the distribution valve, the pumped fluid flow is directed along respective supply/discharge conduits having at least two valves between the distribution valve and a respective sample receiving chamber. Significantly, the two valves are positioned along a respective supply/discharge conduit so that the conduit volume between the two valves is greater than the conduit volume between the distribution valve and the outermost of the two valves. Additionally, the conduit volume between the two valves should be about 1% to about 1.5% of the sample chamber volume or more. 
     A representative embodiment of the invention includes sample tanks having a compound piston within a tank housing interior. The compound piston defines the fluid sample chamber wherein the piston is moveable within the housing interior to selectively change the fluid sample chamber volume. The compound piston comprises an outer sleeve and an inner sleeve. The inner sleeve is moveable relative to the outer sleeve and both are moveable relative to the housing. However, movement of the inner sleeve relative to the outer sleeve is unidirectional. Both sleeves are displaced toward the lower head end by filling the sample collection chamber with formation fluid. A piston face portion of the outer sleeve includes a fluid transfer conduit that is flow controlled by a normally closed valve. The valve is opened by physical engagement with the lower head end of the tank housing. The lower head end of the housing includes a conduit that may be opened directly to the wellbore fluid via a valve in the magazine body that is controlled from the surface. Consequently, when the outer sleeve piston valve is opened by engagement with the lower housing head, wellbore fluid at wellbore pressure is admitted through the outer sleeve piston into an inner chamber. Wellbore pressure in the inner chamber displaces the inner sleeve relative to the outer sleeve whereby the solid structure of the inner sleeve cylinder edge is forced into the high pressure liquid sample chamber. Since the high pressure liquid sample chamber is a completely filled liquid volume, the inner sleeve cylinder edge penetrates the sample chamber only by compression of the liquid. 
     When the magazine and all tanks are returned to the surface, each tank is separated from the magazine for either shipment to an analysis laboratory or for immediate sample analysis. Because the fluid samples always contain some percentage of filtrate (contamination), it is important to assess the level of contamination without altering the sample volume within the sample chamber and before incurring the expense of laboratory analysis. Often, contamination of less than 10% is acceptable. Under certain conditions, however, a sample may have over 30% contamination and that is usually unacceptable. 
     For separation of a tank from the magazine, the outer conduit valve is closed. Supply/discharge conduit fluid between the distribution valve in the tank magazine and the outer conduit valve is vented through the wellbore fluid valve in the magazine. Various methods may be employed to investigate or retrieve the sub-sample for sample quality or contamination level. For example, a sight glass or optical port may be employed in the sub-sample conduit to visually or optically determine the sample quality. Other methods may include transfer of the sample into a controlled environment for analysis. 
     When the tank is free of the magazine, a low pressure receiver tank may be secured to the supply/discharge conduit nipple that serves as the connective interface between the tank and the magazine. With the tank supply/discharge conduit valve most proximate of the high pressure tank chamber closed, the outer valve is opened to release the formation fluid trapped between the two conduit valves into the low pressure receiver where it may be field examined. From such field examination, it may be determined whether the sample is excessively contaminated by wellbore water, oil, mud cake, drilling fluid or oil filtrate from oil based drilling mud. 
     After the field sample is extracted, the outer conduit valve is again closed and the tank disposed for completion of the laboratory analysis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which: 
     FIG. 1 is a schematic earth section illustrating the invention operating environment; 
     FIG. 2 is a schematic of the invention in operative assembly with cooperatively supporting tools; 
     FIG. 3 is a schematic of a representative formation fluid extraction and delivery system; 
     FIG. 4 is an isometric view of a sampling tank magazine; 
     FIG. 5 is an isometric view of an isolated sampling tank; 
     FIG. 6 is an axial section view of a pressure amplification sampling tank; 
     FIG. 7 is a schematic of the present invention; 
     FIG. 8 is a sectioned detail of the invention; 
     FIG. 9 is a sectioned detail of the invention in partial combination with the magazine control valves. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 schematically represents a cross-section of earth  10  along the length of a wellbore penetration  11 . Usually, the wellbore will be at least partially filled with a mixture of liquids including water, water and oil mixtures, drilling fluid, and formation fluids that are indigenous to the earth formations penetrated by the wellbore. Hereinafter, such fluid mixtures are referred to as “wellbore fluids”. The term “formation fluid” hereinafter refers to a specific formation fluid exclusive of any substantial mixture or contamination by fluids not naturally present in the specific formation. Although it is a theoretical world objective to obtain samples of formation fluid free of wellbore fluid, the actual world reality is that most formation fluid samples will be contaminated to some degree. Hence, one objective of the present invention is to evaluate that level of contamination. 
     Suspended within the wellbore  11  at the bottom end of a wireline  12  is a formation fluid sampling tool  20 . The wireline  12  is often carried over a pulley  13  supported by a derrick  14 . Wireline deployment and retrieval is performed by a powered winch carried by a service truck  15 , for example. 
     Pursuant to the present invention, a preferred embodiment of a sampling tool  20  is schematically illustrated by FIG.  2 . Preferably, such sampling tools are a serial assembly of several tool segments that are joined end-to-end by the threaded sleeves of mutual compression unions  23 . An assembly of tool segments appropriate for the present invention may include a hydraulic power unit  21  and a formation fluid extractor  22 . Below the extractor  22 , a large displacement volume motor/pump unit  24  is provided for line purging. Below the large volume pump is a similar motor/pump unit  25  having a smaller displacement volume that is quantitatively monitored as described more expansively with respect to FIG.  3 . Ordinarily, one or more tank magazine sections  26  are assembled below the small volume pump. Each magazine section  26  may have one, two, three or more fluid sample tanks  30 . 
     The formation fluid extractor  22  comprises an extensible suction probe  27  that is opposed by borewall pistons  28 . Both, the suction probe  27  and the opposing pistons  28  are hydraulically extensible to firmly engage the suction probe with the wellbore walls. Construction and operational details of the fluid extraction tool  22  are more expansively described by U.S. Pat. No. 5,303,775, the specification of which is incorporated herewith by reference. 
     Operation of the tool may, for example, be powered by electricity delivered from the service truck  15  along the wireline  12  to the hydraulic power supply unit  21 . Other tool powering systems may include a drill string tool support having a mud driven downhole generator and using the mud column for data transmission. 
     With respect to FIG. 3, the constituency of the hydraulic power supply unit  21  comprises an A.C. or D.C. motor  32  coupled to drive a positive displacement, hydraulic power pump  34 . The hydraulic power pump energizes a closed loop hydraulic circuit  36 . The hydraulic circuit is controlled, by solenoid actuated valves  47 , for example, to drive the motor section  42  of an integrated, positive displacement, pump/motor unit  25 . The pump portion  44  of the pump/motor unit  25  is monitored by means such as a rod position sensor  46 , for example, to report the pump displacement volume at any position of the rod. Formation fluid drawn through the suction probe  27 , is directed by a solenoid controlled valve  48  to alternate chambers of the pump  44  and to a remotely controlled tank distributor  49 . By this route, sample volumes of selected formation fluid are extracted directly from respective in situ formations and delivered to designated sample chambers among the several sample tank tools  30 . 
     As sub-steps in the formation fluid extraction procedure of the present invention, the large volume motor/pump unit  24  is employed to purge the formation fluid flow lines between the suction probe  27  and the small volume pump  25 . Otherwise, the motor/pump unit  24  may be substantially the same as motor/pump unit  25  except for the preference that the pump of unit  24  have a greater displacement volume capacity per stroke. 
     A representative magazine section  26  is illustrated by FIG. 4 to include a fluted cylinder  50 . Preferably, the cylinder  50  is fabricated to accommodate three to six tanks  30 . Each tank  30  is operatively loaded into a respective alcove  52  with a bayonet-stab fit. Two or more cylinders  50  are joined by an internally threaded sleeve  23  that is axially secured to the opposite end of a second cylinder. The sleeve  23  is turned upon the external threads of a mating joint boss  53  to draw the boss into a compression sealed juncture therebetween whereby the fluid flow conduits  54  drilled into the end of each boss  53  are continuously sealed across the joint. 
     FIGS. 5 and 6 illustrate each tank  30  as comprising a cylindrical pressure housing  60  that is delineated at opposite ends by cylinder headwalls  63  and  64 . The bottom-end headwall  63  comprises a valve sub-assembly having a socket boss and a fluid conduit nipple  66  projecting axially therefrom. A conduit  68  within the nipple  66  is selectively connected by a respective conduit not shown to the tank distributor valve  49  and, ultimately, to the suction probe  27  of the formation fluid extractor  22 . With respect to FIG. 9, a remotely controlled purge valve  102  within the body of the magazine  30  selectively connects the nipple conduit  68  with the wellbore fluid environment, or, alternatively, connects the conduit  70  in the top-end headwall  64  to the wellbore fluid environment. 
     As shown by FIGS. 8 and 9, within the valve sub-assembly  63  is a supply/discharge flow path extension  74  from the nipple conduit  68  to an outer valve  75 . The supply/discharge flow path continues serially from the outer valve  75  with an intermediate conduit  78  to an inner valve  76 . From the inner valve  76 , the supply/discharge conduit continues with an inner conduit  104  into the primary sample chamber  95 . Both valves  75  and  76  are capable of complete flow blockage of the supply/discharge conduit. Accordingly, the conduit  68  connects to the outer valve  75  on the downstream side of the valve seat. Intermediate conduit  78  connects to the outer valve  75  on the upstream side of the valve seat and on the downstream side of the inner valve  76  seat. Inner conduit  104  connects to the inner valve  76  upstream of the valve seat. The valves  75  and  76  are positioned so that the volume  78  between the inner and the outer valve is greater than the volume between the distribution valve  49  and the outer valve  75  in the tank. Additionally, the conduit intermediate volume is preferably about 1% to about 1.5% of the sample chamber volume. The magnitude of the sub-sample volume is a very important element of the sample in situ qualities as well as the size of the sample to make an adequate conclusion. Representatively, the volume of sample chamber  95  may be in the order of 400 to 1000 CC. 
     Although the operating nature of valves  75  and  76  is preferably manual, it should be understood that many types of remotely actuated valves may also be used for this purpose. In particular, valves  75  and  76  may be electrically powered solenoid valves or fluid driven motor valves. 
     Referring again to the axial half-section of FIG. 6, the pressure housing top-end headwall comprises a sub  64  having a wellbore fluid inlet conduit  70  that connects the interior bore  80  of the pressure housing  60  with a threaded tubing nipple socket  72 . The conduit  70  is a fluid flow path between the interior bore  80  and the in situ wellbore environment that is remotely controlled by the magazine purge valve  102 . 
     Within the interior bore  80  of the pressure housing  60  is a traveling trap sub-assembly  82  that comprises the coaxial assembly of an inner traveling/locking sleeve  86  within an outer traveling sleeve  84  extending from a piston wall  85 . Unitized with the outer traveling sleeve  84  by a retaining bolt through the piston wall  85 , is a locking piston rod  90 . A fluid channel  92  along the length of the rod  90  openly communicates the inner face of a floating piston  94  with the open well bore conduit  70 . The floating piston  94  is axially confined within the inner bore of the inner traveling/locking sleeve  86  by a retaining ring. A mixing ball  99  is placed within the sample (formation fluid) receiving chamber  95  that is geometrically defined as that variable volume within the interior bore  80  of pressure housing  60  between the valve sub-assembly and the end area of the traveling trap sub-assembly  82 . 
     A body lock ring  100  having internal and external barb rings selectively connects the rod  90  to the inner traveling/locking sleeve  86 . The selective connection of the barbed lock ring  100  permits the sleeve  86  to move coaxially along the rod  90  from the piston  84  but prohibits any reversal of that movement. 
     Another construction detail of the inner traveling/locking sleeve  86  is the sealed partition  122  between the opposite ends of the sleeve  86 . The chamber  124  created between the partition  122  and the piston head  106  of the rod  90  is sealed with the atmospheric pressure present in the chamber at the time of assembly. 
     The body lock ring  100  between the locking piston rod  90  and the inner bore wall of the inner traveling/locking sleeve  86  above the partition  122  does not provide a fluid pressure barrier. Consequently, the chamber  126  between the partition  122  and the body lock ring  100  functions at the same fluid pressure as the wellbore fluid flood chamber  120  when the flood valve  110  is opened. 
     Still with respect to FIG. 6, the base of the floating piston wall  84  includes a flood valve  110  having a pintle  112  biased by a spring against a seal seat. The pintle  112  includes a stem that projects beyond the end plane of the piston wall  85 . When the end plane of the piston wall  85  is pressed against the inner face of the top sub  64 , the pintle  112  is displaced from engagement with the seal seat to admit wellbore fluid into the flood chamber  120 . The flood chamber  120  is geometrically defined as the variable volume bounded by the annular space between the outer perimeter of the rod  90  and the inner bore  85  of the outer traveling sleeve  84 . 
     Operational 
     Sanitation of the sample tank chambers, conduits and other vessels to remove the presence of all contaminating substances coming into contact with a formation sample cannot be overemphasized. Typically, all internal components should be cleaned with a solvent such as toluene to remove hydrocarbon residue. Preparation of the sample tanks  30  prior to downhole deployment includes the opening of the valves  74  and  75 . Under the power and control of instrumentation carried by the service truck  15 , the sampling tool is located downhole at the desired sample acquisition location. When located, the hydraulic power unit  21  is engaged by remote control from the service truck  15 . Hydraulic power from the unit  21  is directed to the formation fluid extractor unit  22  for borewall engagement of the formation fluid suction probe  27  and the borewall piston feet  28 . Once engaged, the suction probe  27  provides an isolated, direct fluid flow channel for extracting formation fluid. Such formation fluid flow into the suction probe  27  is first induced by the suction of large volume pump  24 , which is driven by the hydraulic power unit  21 . Initially, however, a small volume is drawn for a pressure test to confirm that probe  27  is engaged with the borehole wall. With the purge valve  102  set to direct the formation fluid flow from the large volume pump into the wellbore, the large volume pump  24  is operated for a predetermined period of time to flush contaminated wellbore fluids from the sample distribution conduits with a flow of formation fluid drawn through suction probe  27 . When the predetermined line flushing interval has concluded, hydraulic power may be switched from the large volume pump  24  to the small volume piston pump  25  and the purge valve  102  is switched to connect the conduit  70  in the top-end headwall with the wellbore. Referring to FIG. 3, formation fluid drawn from the suction probe  27  by the pump  25  is shuttled by a conduit control system such as is represented by 4-way valve  48  into successively opposite chambers  44 . Simultaneously, the valve  48  directs discharge from the chambers  44  to a valve manifold  49 , which may be a series of valve sets  102  and  49  as shown by FIG. 9, for example, which further directs the formation fluid onto the desired sample tank  30 . 
     Formation fluid enters the tank  30  through the nipple conduit  68  and is routed along the flow paths  74 ,  78  and  104  into the sample receiving chamber  95 . Pressure of the pumped formation fluid in the receiving chamber  95  displaces both, the outer traveling sleeve  84  and the inner traveling/locking sleeve  86 , against the standing wellbore pressure in the interior bore  80  of pressure housing  60 . When the sample receiving chamber  95  is full, the base plane of the outer traveling sleeve piston wall  85  will engage the inside face of the top sub  64 . Thereby, the stem of valve pintle  112  is axially displaced to open the flood valve  110 . Internal conduits within the outer traveling sleeve  84  direct wellbore fluid from the seat of valve  110  into the flood chamber  120 . The wellbore pressure in the flood chamber  120  bears against the inner traveling/locking sleeve  86  over the cross-sectional area of the flood chamber  120  annulus. 
     Opposing the flood chamber force on the traveling/locking sleeve  86  are two pressure sources. One source is the formation fluid pressure in the sample chamber  95  bearing on the annular end section of the traveling/locking sleeve  86  as was provided by the small volume pump unit  25 . The other pressure opposing the flood chamber pressure is the closed atmosphere chamber  124  acting on the area of the annular partition  122 . Initially, the force balance on the traveling/locking sleeve  86  favors the flood chamber side to press the annular end of the sleeve  86  into the sample chamber  95 . Since the liquid formation fluid is substantially incompressible, intrusion of the solid structure of the sleeve  86  annulus into the sample chamber volume exponentially increases the pressure in the sample chamber until a final force equilibrium is achieved. Nevertheless, at the pressures of this environment, measurable liquid compression may be achieved. 
     This axial movement of the inner traveling/locking sleeve  86  relative to the outer sleeve  84  also translates to the piston rod  90 , which is secured to the outer sleeve  84  via the retaining bolt through piston wall  85 . Consequently, the sleeve  86  partition  122  is displaced toward the piston head  106  to compress the gaseous atmosphere of chamber  124  thereby adding to the equilibrium forces. 
     Due to the internal and external barb rings respective to the body lock ring  100 , movement of the piston  90  relative to the inner traveling sleeve  86  is rectified to maintain this volumetric invasion of the structure  86  into the sample chamber volume. 
     By compressing the volume of the formation fluid sample, the fluid sample pressure is greatly above the wellbore pressure but lower than the safe working pressure of the chamber. Although this greatly increased in situ pressure declines when the confined formation sample is removed from the wellbore, the operative components may be designed so at surface selected overpressures when and where the collected formation sample is removed from the well, the sample pressure does not decline below the bubble point of dissolved gas. Movement of the inner traveling/locking sleeve  86  further compresses the collected formation fluid sample above the boost capability of the pump  25 . Such compression continues until the desired boost ratio is accomplished. 
     For example, a down hole fluid sample can have a hydrostatic wellbore pressure of 10,000 psi. The typical compressibility for such a fluid is 5×10 −6  so that a volume decrease of only eight percent would raise the fluid sample pressure by 16,000 psi to 26,000 psi, for a boost ratio of 2.6 to 1.0. When the magazine section  26  and the collected formation fluid sample is raised to the surface of wellbore  11 , the formation fluid sample temperature will cool, thereby returning the formation fluid sample pressure toward the original pressure of 10,000 psi. If the downhole fluid temperature is 270° F. and the wellbore  11  surface temperature is 70° F., the resulting 200° F. drop in temperature will lower the fluid sample pressure by approximately 15,300 psi in a fixed volume, thereby resulting in a surface fluid sample pressure of approximately 10,700 psi. 
     To hold the volume of fluid sample chamber  95  constant as the magazine  26  is removed from the wellbore  11 , inner traveling/locking sleeve  86  is fixed relative to outer traveling sleeve  84  during retrieval of the magazine  26 . The invention accomplishes the fixed relationship by means of the body lock ring  100 . This mechanism permits additional boost to be added to the formation fluid sample pressure within the sample chamber  95  as a proportionality of the in situ wellbore pressure. For example, the magazine section  26  may subsequently be lowered to additional depths within a wellbore  11  where the hydrostatic pressure is greater than a prior sample extraction. The hydrostatic wellbore pressure increase is transmitted through flood valve  112  into flood chamber  120  to further move the inner traveling/locking sleeve  86  and to further compress the formation fluid sample within the sample chamber  95  to a greater pressure. Such pressure boost can be accomplished quickly and magazine  26  removed to the surface of wellbore  11  before a significant amount of heat from the additional wellbore depth is transferred to the previously collected formation fluid sample. 
     At the surface of wellbore  11 , the outer valve  75  of the two valves  75  and  76  is closed to trap the formation fluid sample within the chamber  95 . While still connected with the magazine  26 , and the inner valve  76  open, the purge valve  102  is switched to vent the nipple conduit  68  outside of the outer valve  75 . The tank  30  may thereafter be safely removed from its respective alcove  52  in the magazine  26 . 
     With the tank  30  isolated from the magazine  26 , and the inner valve  76  open, the tank  30  is heated and agitated to restore homogeneity to the fluid in conduits  104  and  78  with the fluid in sample chamber  95 . Thereafter, the valve  76  is closed and a receiving tank, not shown, may be connected to the nipple  66 . By closing the inner valve  76 , the enclosed spacial volume is reduced by the intrusion of the valve pintle element. Such spacial volume reduction increases the pressure of the sub-sample in the conduit  78 . The receiver tank includes a compensation piston to accommodate the volume change and maintain the in situ sample qualities. The outer valve  75  is then opened to discharge wellbore fluid trapped in the conduit  78  between the valves  75  and  76 . This small volume fluid sample captured in the receiving tank, may provide operators with an indication of the contamination level of the fluid actually trapped in the sample chamber  95 . Mud filtrate, wellbore water, mud cake, drilling fluid and other contaminants are readily discerned from this fluid sample. If contamination is excessive, it is known immediately, while all sampling equipment is on the well site, that another sample acquisition procedure may be undertaken. 
     Although the invention has been described in terms of certain preferred embodiments, it will become apparent to those of ordinary skill in the art that modifications and improvements can be made to the inventive concepts herein without departing form the scope of the invention. The embodiments shown herein are merely illustrative of the inventive concepts and should not be interpreted as limiting the scope of the invention.

Technology Classification (CPC): 4