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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in-part of co-pending application Ser. No. 11/951,946, filed Dec. 6, 2007, which is a continuation-in-part of application Ser. No. 11/702,810, filed Feb. 6, 2007 now U.S. Pat. No. 7,472,589 issued Jan. 6, 2009, which is a continuation-in-part of application Ser. No. 11/438,764, filed May 23, 2006 now U.S. Pat. No. 7,596,995 issued Oct. 6, 2009, which is a continuation-in-part of application Ser. No. 11/268,311, filed Nov. 7, 2005, now U.S. Pat. No. 7,197,923 issued Apr. 3, 2007. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    This invention relates, in general, to testing and evaluation of subterranean formation fluids and, in particular, to a wireline conveyed single phase fluid sampling apparatus for obtaining multiple fluid samples and maintaining the fluid samples above saturation pressure using a self-contained pressure source during retrieval from the wellbore. 
       BACKGROUND OF THE INVENTION 
       [0003]    Without limiting the scope of the present invention, its background is described with reference to testing hydrocarbon formations, as an example. 
         [0004]    It is well known in the subterranean well drilling and completion art to perform tests on formations intersected by a wellbore. Such tests are typically performed in order to determine geological or other physical properties of the formation and fluids contained therein. For example, parameters such as permeability, porosity, fluid resistivity, temperature, pressure and saturation pressure may be determined. These and other characteristics of the formation and fluid contained therein may be determined by performing tests on the formation before the well is completed. 
         [0005]    One type of testing procedure that is commonly performed is to obtain a fluid sample from the formation to, among other things, determine the composition of the formation fluids. In this procedure, it is important to obtain a sample of the formation fluid that is representative of the fluids as they exist in the formation. In a typical sampling procedure, a sample of the formation fluids may be obtained by lowering a sampling tool having a sampling chamber into the wellbore on a conveyance such as a wireline, slick line, coiled tubing, jointed tubing or the like. When the sampling tool reaches the desired depth, one or more ports are opened to allow collection of the formation fluids. The ports may be actuated in variety of ways such as by electrical, hydraulic or mechanical methods. Once the ports are opened, formation fluids travel through the ports and a sample of the formation fluids is collected within the sampling chamber of the sampling tool. After the sample has been collected, the sampling tool may be withdrawn from the wellbore so that the formation fluid sample may be analyzed. 
         [0006]    It has been found, however, that as the fluid sample is retrieved to the surface, the temperature of the fluid sample decreases causing shrinkage of the fluid sample and a reduction in the pressure of the fluid sample. These changes can cause the fluid sample to reach or drop below saturation pressure creating the possibility of asphaltene deposition and flashing of entrained gasses present in the fluid sample. Once such a process occurs, the resulting fluid sample is no longer representative of the fluids present in the formation. Therefore, a need has arisen for an apparatus and method for obtaining a fluid sample from a formation without degradation of the sample during retrieval of the sampling tool from the wellbore. A need has also arisen for such an apparatus and method that are capable of maintaining the integrity of the fluid sample during storage on the surface. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention disclosed herein provides a single phase fluid sampling apparatus and a method for obtaining fluid samples from a formation without the occurrence of phase change degradation of the fluid samples during the collection of the fluid samples or retrieval of the sampling apparatus from the wellbore. In addition, the sampling apparatus and method of the present invention are capable of maintaining the integrity of the fluid samples during storage on the surface. 
         [0008]    In one aspect, the present invention is directed to a method for obtaining a fluid sample in a subterranean well. The method includes running a fluid sampler on a wireline conveyance to a target location in the well, establishing a fluid communication path between an exterior of the fluid sampler and a sampling chamber of the fluid sampler by operating an actuator, obtaining a fluid sample in the sampling chamber of the fluid sampler and pressurizing the fluid sample using a self-contained pressure source of the fluid sampler that is in fluid communication with the sampling chamber. 
         [0009]    The method may also include receiving a predetermined input signal with a signal detector, activating a trigger to create a failure of a barrier with a control circuit to enable a fluid to flow from a first chamber to a second chamber in the actuator and shifting a piston from a first position to a second position in the actuator. In addition, the method may include obtaining a first portion of the fluid sample in a debris chamber, displacing a debris trap piston within the sampling chamber to receive a remainder of the fluid sample in the sampling chamber and determining the volume of the fluid sample based upon the position of the magnetic locator associated with the debris trap piston. The method may further include maintaining a differential pressure across a valving assembly disposed within the sampling chamber, actuating the valving assembly by contacting the valving assembly with a piston, piercing through at least a portion of a pressure disk associated with the valving assembly with a piercing assembly associated with the piston, equalizing the pressure across the valving assembly and pressurizing the fluid sample to a pressure greater than a saturation pressure of the fluid sample. 
         [0010]    In another aspect, the present invention is directed to a method for obtaining a plurality of fluid samples in a subterranean well. The method includes running a fluid sampler on a wireline conveyance to a target location in the well, establishing a fluid communication path between an exterior of the fluid sampler and a plurality of sampling chambers of the fluid sampler by operating an actuator, obtaining a fluid sample in each of the plurality of sampling chambers of the fluid sampler and pressurizing the fluid samples using a self-contained pressure source of the fluid sampler that is in fluid communication with the sampling chambers. 
         [0011]    The method may also include running the fluid sampler on a slickline conveyance to the target location in the well, running the fluid sampler on an electric line conveyance to the target location in the well, simultaneously obtaining the fluid samples in the plurality of sampling chambers, sequentially obtaining the fluid samples in the plurality of sampling chambers and simultaneously pressurizing the fluid samples in the plurality of sampling chambers. 
         [0012]    In a further aspect, the present invention is directed to an apparatus for obtaining a plurality of fluid samples in a subterranean well. The apparatus includes a wireline conveyance and a fluid sampler supported by and positioned with the wireline conveyance in the well. The fluid sampler includes an actuator operable to establish a fluid communication path between an exterior and an interior of the fluid sampler, a plurality of sampling chambers operable to receive fluid samples and a self-contained pressure source in fluid communication with the sampling chambers operable to pressurize the fluid samples obtained in the sampling chambers to a pressure above saturation pressure. 
         [0013]    In one embodiment, the wireline conveyance may be a slickline. In another embodiment, the wireline conveyance may be an electric line. In certain embodiments, the actuator may includes a signal detector, a control circuit and a trigger, wherein upon receipt of a predetermined input signal by the signal detector, the control circuit activates the trigger to create a failure in a barrier such that fluid flows from a first chamber to a second chamber in the actuator and a piston moves from a first position to a second position in the actuator. In some embodiments, each of the sampling chambers includes a debris trap piston that is operable to receive a first portion of the fluid sample in a debris chamber then displace within the sampling chamber. In these embodiments, a magnetic locator may be operably associated with the debris trap piston to provide a reference to determine the level of displacement of the debris trap piston. 
         [0014]    In one embodiment, each of the sampling chambers may includes a valving assembly having a pressure disk that is initially operable to maintain a differential pressure thereacross, wherein the valving assembly is actuated by longitudinally displacing a piston having a piercing assembly relative to the valving assembly such that at least a portion of the piercing assembly travels through the pressure disk, thereby allowing fluid flow therethrough. In other embodiments, the self-contained pressure source may include pressurized nitrogen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    For a more complete understanding of the present invention, including its features and advantages, reference is now made to the detailed description of the invention, taken in conjunction with the accompanying drawings in which like numerals identify like parts and in which: 
           [0016]      FIG. 1  is a schematic illustration of a fluid sampler system embodying principles of the present invention; 
           [0017]      FIG. 2  is a cross-sectional view of an embodiment of a sampler assembly of a fluid sampler embodying principles of the present invention; 
           [0018]      FIG. 3  is a cross-sectional view of an embodiment of a sampler assembly of a fluid sampler embodying principles of the present invention; 
           [0019]      FIG. 4  is a cross-sectional view of an embodiment of a sampler and pressure source assembly of a fluid sampler embodying principles of the present invention; 
           [0020]      FIG. 5A  is a cross-sectional view of an actuator assembly for controlling fluid communication into a fluid sampler embodying principles of the present invention in a run in configuration; 
           [0021]      FIG. 5B  is a cross-sectional view of an actuator assembly for controlling fluid communication into a fluid sampler embodying principles of the present invention in an actuated configuration; and 
           [0022]      FIGS. 6A-6F  are cross-sectional views of successive axial portions of an embodiment of a sampling chamber of a fluid sampler embodying principles of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the invention. 
         [0024]    Referring initially to  FIG. 1 , therein is representatively illustrated a fluid sampler system  10  and associated methods which embody principles of the present invention. A fluid sampler  12  is being run in a wellbore  14  that is depicted as having a casing string  16  secured therein with cement  18 . Although wellbore  14  is depicted as being cased and cemented, it could alternatively be uncased or open hole. Fluid sampler  12  includes a cable connector  20  that enables fluid sampler  12  to be coupled to or operably associated with a wireline conveyance  22  that is used to run, retrieve and position fluid sampler  12  in wellbore  14 . Wireline conveyance  22  may be a single strand or multistrand wire, cable or braided line, which may be referred to as a slickline or may include one or more electric conductors, which may be referred to as an e-line or electric line. Even though fluid sampler  12  is depicted as being connected directly to cable connector  20 , those skilled in the art the understand that fluid sampler  12  could alternatively be coupled within a larger tool string that is being positioned within wellbore  14  via wireline conveyance  22  including a tool string having multiple fluid samplers interconnected therein. 
         [0025]    In the illustrated embodiment, fluid sampler  12  includes an actuator assembly  24 , a sampler assembly  26  and a self-contained pressure source assembly  28 . Preferably, sampler assembly  26  includes multiple sampling chambers, two being visible in  FIG. 1 . In order to route the fluid samples into the desired sampling chamber, fluid sampler  12  includes a manifold assembly  30  positioned between actuator assembly  24  and sampler assembly  26 . Valving or other fluid flow control circuitry within manifold assembly  30  may be used to enable fluid samples to be taken in all of the sampling chambers simultaneously or to allow fluid samples to be sequentially taken into the various sampling chambers. In slickline conveyed embodiments, actuator assembly  24  preferably includes timing circuitry such as a mechanical or electrical clock which is used to determine when the fluid sample or samples will be taken. Alternatively, a pressure signal or other wireless input signal could be used to initiate operation of actuator assembly  24 . In electric line conveyed embodiments, actuator assembly  24  preferably includes electrical circuitry operable to communicate with surface systems via the electric line to initiate operation of actuator assembly  24 . 
         [0026]    After the fluid samples are taken, in order to route pressure into the desired sampling chamber, fluid sampler  12  includes a manifold assembly  32  positioned between sampler assembly  26  and self-contained pressure source  28 . Self-contained pressure source  28  may include one or more pressure chambers that initially contain a pressurized fluid, such as a compressed gas or liquid, and preferably contain compressed nitrogen at between about 10,000 psi and 20,000 psi. Those skilled in the art will understand that other fluids or combinations of fluids and/or other pressures both higher and lower could be used, if desired. Depending on the number of sampling chambers and the number of pressure chambers, valving or other fluid flow control circuitry within manifold assembly  32  may be operated such that self-contained pressure source  28  serves as a common pressure source to simultaneously pressurize all sampling chambers or may be operated such that self-contained pressure source  28  independently pressurizes certain sampling chambers sequentially. In the case of multiple sampling chambers and multiple pressure chambers, manifold assembly  32  may be operated such that pressure from certain pressure chambers of self-contained pressure source  28  is routed to certain sampling chambers. 
         [0027]    Even though  FIG. 1  depicts a vertical well, it should be noted by one skilled in the art that the fluid sampler of the present invention is equally well-suited for use in deviated wells, inclined wells, horizontal wells, multilateral wells and the like. As such, the use of directional terms such as above, below, upper, lower, upward, downward and the like are used in relation to the illustrative embodiments as they are depicted in the figures, the upward direction being toward the top of the corresponding figure and the downward direction being toward the bottom of the corresponding figure. 
         [0028]    Referring now to  FIG. 2 , therein is depicted a cross-sectional view of one embodiment of a sampler assembly of a fluid sampler embodying principles of the present invention that is generally designated  40 . In the illustrated portion, sampler assembly  40  includes two sampling chambers  42 ,  44 . As discussed above, valving or other fluid flow control circuitry within the manifold assembly between sampler assembly  40  and the actuator assembly may be used to enable fluid samples to be taken in sampling chambers  42 ,  44  simultaneously or sequentially. Likewise, valving or other fluid flow control circuitry within the manifold assembly between the pressure source and sampler assembly  40  may be used to enable simultaneous or independent pressurization of the fluid samples in sampling chambers  42 ,  44 . 
         [0029]    Sampler assembly  40  includes a support assembly  46  that may be in the form of a carrier assembly that extends longitudinally along a portion of or substantially the entire length of sampling chambers  42 ,  44 . Alternatively, support assembly  46  may be formed in discontinuous sections that are distributed at intervals along the length of sampling chambers  42 ,  44 . In the illustrated embodiment, support assembly  46  includes a chamber receiving assembly  48 , a retainer member  50  that is securably attachable to chamber receiving assembly  48  by mechanical means such as bolting and an outer housing  52 . In this configuration, chamber receiving assembly  48 , retainer member  50  and outer housing  52  provide longitudinal stability to sampling chambers  42 ,  44 . 
         [0030]    Referring now to  FIG. 3 , therein is depicted a cross-sectional view of one embodiment of a sampler assembly of a fluid sampler embodying principles of the present invention that is generally designated  60 . In the illustrated portion, sampler assembly  60  includes three sampling chambers  62 ,  64 ,  66 . As discussed above, valving or other fluid flow control circuitry within the manifold assembly between sampler assembly  60  and the actuator assembly may be used to enable fluid samples to be taken in sampling chambers  62 ,  64 ,  66  simultaneously or sequentially. Likewise, valving or other fluid flow control circuitry within the manifold assembly between the pressure source and sampler assembly  60  may be used to enable simultaneous or independent pressurization of the fluid samples in sampling chambers  62 ,  64 ,  66 . 
         [0031]    Sampler assembly  60  includes a support assembly  68  that may be in the form of a carrier assembly that extends longitudinally along a portion of or substantially the entire length of sampling chambers  62 ,  64 ,  66 . Alternatively, support assembly  68  may be formed in discontinuous sections that are distributed at intervals along the length of sampling chambers  62 ,  64 ,  66 . In the illustrated embodiment, support assembly  68  includes a chamber receiving assembly  70 , a plurality of retainer members  72  that are securably attachable to chamber receiving assembly  70  by mechanical means such as bolting and an outer housing  74 . In this configuration, chamber receiving assembly  70 , retainer members  72  and outer housing  74  provide longitudinal stability to sampling chambers  62 ,  64 ,  66 . 
         [0032]    Referring now to  FIG. 4 , therein is depicted a cross-sectional view of one embodiment of a sampler and pressure source assembly of a fluid sampler embodying principles of the present invention that is generally designated  80 . Unlike fluid samplers  12 ,  40  and  60  described above wherein the sampler assembly and pressure source assembly are longitudinally separated by a manifold, in fluid sampler  80 , the sampler assembly and the pressure source assembly occupy the same longitudinal portion of fluid sampler  80 . Specifically, in the illustrated portion, sampler and pressure source assembly  80  includes two sampling chambers  82 ,  84  and two pressure chambers  86 ,  88 . As discussed above, valving or other fluid flow control circuitry within the manifold assembly between sampler and pressure source assembly  80  and the actuator assembly may be used to enable fluid samples to be taken in sampling chambers  82 ,  84  simultaneously or sequentially. Likewise, valving or other fluid flow control circuitry within a manifold assembly functionally between sampling chambers  82 ,  84  and pressure chambers  86 ,  88  may be used to enable simultaneous or independent pressurization of the fluid samples in sampling chambers  82 ,  84 . 
         [0033]    Sampler and pressure source assembly  80  includes a support assembly  90  that may be in the form of a carrier assembly that extends longitudinally along a portion of or substantially the entire length of sampling chambers  82 ,  84  and pressure chambers  86 ,  88 . Alternatively, support assembly  90  may be formed in discontinuous sections that are distributed at intervals along the length of sampling chambers  82 ,  84  and pressure chambers  86 ,  88 . In the illustrated embodiment, support assembly  90  includes a chamber receiving assembly  92 , a plurality of retainer members  94  that are securably attachable to chamber receiving assembly  92  by mechanical means such as bolting and an outer housing  96 . In this configuration, chamber receiving assembly  92 , retainer members  94  and outer housing  96  provide longitudinal stability to sampling chambers  82 ,  84  and pressure chambers  86 ,  88 . 
         [0034]    Referring now to  FIGS. 5A-5B , an actuator for controlling fluid communication into a fluid sampler is generally designated  100 . Actuator  100  may be a part of an actuator assembly of a fluid sampler such as actuator assembly  22  of  FIG. 1 . Actuator  100  has an axially extending generally tubular body or housing assembly  102  including two housing members  104 ,  106  that are securably coupled together at a threaded coupling  108 . Housing member  106  includes a port  110  that is in fluid communication with the exterior of the fluid sampler and a fluid passageway  112  that is in fluid communication with one or more sampling chambers via the manifold. Slidably and sealingly disposed within housing member  106  is a piston  116  that initially blocks communication between port  110  and fluid passageway  112 , as best seen in  FIG. 5A . Piston  116  is biased to the left by pressure acting on a differential piston area  118 . Initially, displacement of piston  116  to the left is substantially prevented by a fluid  120  disposed within a fluid chamber  122 . Preferably, while fluid  120  prevents piston  116  from moving sufficiently to the left to open communication between port  110  and fluid passageway  112 , piston  116  is able to float as pressure differences between port  110  and fluid passageway  112  are balanced. 
         [0035]    Securably and sealingly positioned between housing member  104  and housing member  106  is a barrier assembly  124  that includes a barrier  126  and a support assembly  128  having a fluid passageway  130  defined therethrough. Barrier  126  initially prevents fluid  120  from escaping from chamber  122  into a chamber  132  of housing member  104 . Positioned within housing member  104  is a control system  134  that includes or is operably associated with a signal detector, a control circuit, a power supply, optional timing devices and an output signal generator or trigger depicted in  FIG. 5A  as a chemically initiated piercing assembly  136 . Chemically initiated piercing assembly  136  includes a chemical element or energetic material  138 , an ignition agent  140  and a piercing element  142  slidably disposed within a cylinder  144 . Chemical element  138  is preferably a combustible element such as a propellant that has the capacity for extremely rapid but controlled combustion that produces a combustion event including the production of a large volume of gas at high temperature and pressure. 
         [0036]    In an exemplary embodiment, chemical element  138  may comprises a solid propellant such as nitrocellulose plasticized with nitroglycerin or various phthalates and inorganic salts suspended in a plastic or synthetic rubber and containing a finely divided metal. Chemical element  138  may comprise inorganic oxidizers such as ammonium and potassium nitrates and perchlorates such as potassium perchlorate. It should be appreciated, however, that substances other than propellants may be utilized without departing from the principles of the present invention, including other explosives, pyrotechnics, flammable solids or the like. In the illustrated embodiment, ignition agent  140  is connected to the control circuit via an electrical cable  146  so that, when it is determined that actuator  100  should be operated, the control circuit supplies electrical current to ignition agent  140 . In slickline conveyed embodiments, actuator  100  may include one or more batteries to supply electrical energy to control system  134 . In electric line conveyed embodiments, electrical energy may be supplied to control system  134  from the surface. 
         [0037]    In operation, the signal detector of control system  134  receives the predetermined input signal that is verified by the control circuit. The input signal may be generated by a downhole timer operably associated with control system  134  or sent from the surface via the wireline or via wireless telemetry. If the control circuit determines that actuator  100  should be operated, electrical power is supplied from the power supply to ignition agent  140  to initiate the chemical reaction in chemical element  138 . The chemical reaction causes piercing element  142  to move to the right piecing barrier  126 , as best seen in  FIG. 5B . Fluid communication is thus established between chamber  122  and chamber  132  through opening  148 , which allows fluid  120  to exit chamber  122  as piston  116  is urged to the left by pressure from the exterior of the fluid sampler acting on differential piston area  118 . Fluid communication is now open between port  110  and fluid passageway  112 , as best seen in  FIG. 5B . Even though a particular actuator  100  has been depicted and described, those skilled in the art will understand that other types of actuators having other types of signal detectors, control circuits, power supplies, timing devices, output signal generators, triggers, pistons and the like may be used in the present fluid sampler without departing from the principle of the present invention. 
         [0038]    Referring now to  FIGS. 6A-6F  a fluid sampling chamber for use in a fluid sampler that embodies principles of the present invention is representatively illustrated and generally designated  200 . Preferably, one or more of sampling chambers  200  are positioned in a sampler assembly  24  that is coupled to an actuator assembly  22  and a self-contained pressure source assembly  26  as described above. 
         [0039]    As described more fully below, a passage  210  in an upper portion of sampling chamber  200  (see  FIG. 6A ) is placed in communication with fluid passageway  112  of the actuator (see  FIG. 5B ) when the fluid sampling operation is initiated using actuator  100 . Passage  210  is in communication with a sample chamber  214  via a check valve  216 . Check valve  216  permits fluid to flow from passage  210  into sample chamber  214 , but prevents fluid from escaping from sample chamber  214  to passage  210 . 
         [0040]    A debris trap piston  218  is disposed within housing  202  and separates sample chamber  214  from a meter fluid chamber  220 . When a fluid sample is received in sample chamber  214 , debris trap piston  218  is displaced downwardly relative to housing  202  to expand sample chamber  214 . Prior to such downward displacement of debris trap piston  218 , however, fluid flows through sample chamber  214  and passageway  222  of piston  218  into debris chamber  226  of debris trap piston  218 . The fluid received in debris chamber  226  is prevented from escaping back into sample chamber  214  due to the relative cross sectional areas of passageway  222  and debris chamber  226  as well as the pressure maintained on debris chamber  226  from sample chamber  214  via passageway  222 . An optional check valve (not pictured) may be disposed within passageway  222  if desired. In this manner, the fluid initially received into sample chamber  214  is trapped in debris chamber  226 . Debris chamber  226  thus permits this initially received fluid to be isolated from the fluid sample later received in sample chamber  214 . Debris trap piston  218  includes a magnetic locator  224  used as a reference to determine the level of displacement of debris trap piston  218  and thus the volume within sample chamber  214  after a sample has been obtained. 
         [0041]    Meter fluid chamber  220  initially contains a metering fluid, such as a hydraulic fluid, silicone oil or the like. A flow restrictor  234  and a check valve  236  control flow between chamber  220  and an atmospheric chamber  238  that initially contains a gas at a relatively low pressure such as air at atmospheric pressure. A collapsible piston assembly  240  includes a prong  242  which initially maintains check valve  244  off seat, so that flow in both directions is permitted through check valve  244  between chambers  220 ,  238 . When elevated pressure is applied to chamber  238 , however, as described more fully below, piston assembly  240  collapses axially, and prong  242  will no longer maintain check valve  244  off seat, thereby preventing flow from chamber  220  to chamber  238 . 
         [0042]    A piston  246  disposed within housing  202  separates chamber  238  from a longitudinally extending atmospheric chamber  248  that initially contains a gas at a relatively low pressure such as air at atmospheric pressure. Piston  246  includes a magnetic locator  247  used as a reference to determine the level of displacement of piston  246  and thus the volume within chamber  238  after a sample has been obtained. Piston  246  included a piercing assembly  250  at its lower end. In the illustrated embodiment, piercing assembly  250  is spring mounted within piston  246  and includes a needle  254 . Needle  254  has a sharp point at its lower end and may have a smooth outer surface or may have an outer surface that is fluted, channeled, knurled or otherwise irregular. As discussed more fully below, needle  254  is used to actuate the pressure delivery subsystem of the fluid sampler when piston  246  is sufficiently displaced relative to housing  202 . 
         [0043]    Below atmospheric chamber  248  and disposed within the longitudinal passageway of housing  202  is a valving assembly  256 . Valving assembly  256  includes a pressure disk holder  258  that receives a pressure disk therein that is depicted as rupture disk  260 , however, other types of pressure disks that provide a seal, such as a metal-to-metal seal, with pressure disk holder  258  could also be used including a pressure membrane or other piercable member. Rupture disk  260  is held within pressure disk holder  258  by hold down ring  262  and gland  264  that is threadably coupled to pressure disk holder  258 . Valving assembly  256  also includes a check valve  266 . Valving assembly  256  initially prevents communication between chamber  248  and a passage  280  in a lower portion of sampling chamber  200 . After actuation the pressure delivery subsystem by needle  254 , check valve  266  permits fluid flow from passage  280  to chamber  248 , but prevents fluid flow from chamber  248  to passage  280 . Preferably, passageway  280  is placed in fluid communication with pressure from the self-contained pressure source via the manifold therebetween. 
         [0044]    Once the fluid sampler has been run downhole via the wireline conveyance to the desired location and is in its operable configuration, a fluid sample can be obtained into one or more of the sample chambers  214  by operating actuator  100 . Fluid from passage  112  then enters passage  210  in the upper portion of each of the desired sampling chambers  200 . For clarity, the operation of only one of the sampling chambers  200  after receipt of a fluid sample therein is described below. The fluid sample flows from passage  210  through check valve  216  to sample chamber  214 . It is noted that check valve  216  may include a restrictor pin  268  to prevent excessive travel of ball member  270  and over compression or recoil of spiral wound compression spring  272 . An initial volume of the fluid sample is trapped in debris chamber  226  of piston  218  as described above. Downward displacement of piston  218  is slowed by the metering fluid in chamber  220  flowing through restrictor  234 . This prevents pressure in the fluid sample received in sample chamber  214  from dropping below its saturation pressure. 
         [0045]    As piston  218  displaces downward, the metering fluid in chamber  220  flows through restrictor  234  into chamber  238 . At this point, prong  242  maintains check valve  244  off seat. The metering fluid received in chamber  238  causes piston  246  to displace downwardly. Eventually, needle  254  pierces rupture disk  260  which actuates valving assembly  256 . Actuation of valving assembly  256  permits pressure from the self-contained pressure source to be applied to chamber  248 . Specifically, once rupture disk  260  is pierced, the pressure from the self-contained pressure source passes through passage  280  and valving assembly  256  including moving check valve  266  off seat. In the illustrated embodiment, a restrictor pin  274  prevents excessive travel of check valve  266  and over compression or recoil of spiral wound compression spring  276 . Pressurization of chamber  248  also results in pressure being applied to chambers  238 ,  220  and thus to sample chamber  214 . 
         [0046]    When the pressure from the self-contained pressure source is applied to chamber  238 , pins  278  are sheared allowing piston assembly  240  to collapse such that prong  242  no longer maintains check valve  244  off seat. Check valve  244  then prevents pressure from escaping from chamber  220  and sample chamber  214 . Check valve  216  also prevents escape of pressure from sample chamber  214 . In this manner, the fluid sample received in sample chamber  214  is pressurized such that the fluid sample may be retrieved to the surface without degradation by maintaining the pressure of the fluid sample above its saturation pressure, thereby obtaining a fluid sample that is representative of the fluids present in the formation. 
         [0047]    While this invention has been described with a reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.

Summary:
An apparatus ( 10 ) for obtaining fluid samples in a subterranean well ( 14 ). The apparatus ( 10 ) includes a wireline conveyance ( 22 ) and a fluid sampler ( 12 ) supported by and positioned with the wireline conveyance ( 22 ) in the well ( 14 ). The fluid sampler ( 12 ) includes an actuator ( 24 ) operable to establish a fluid communication path between an exterior and an interior of the fluid sampler ( 12 ), a plurality of sampling chambers ( 26 ) operable to receive fluid samples therein and a self-contained pressure source ( 28 ) in fluid communication with the sampling chambers ( 26 ) operable to pressurize the fluid samples obtained in the sampling chambers ( 26 ) to a pressure above saturation pressure, thereby preventing phase change degradation for the fluid samples during retrieval of the fluid sampler ( 12 ) to the surface.