Patent Publication Number: US-8109157-B2

Title: Methods and apparatus of downhole fluids analysis

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to co-pending and commonly owned U.S. patent application Ser. No. 11/203,932, filed Aug. 15, 2005, entitled “Methods and Apparatus of Downhole Fluid Analysis” and Ser. No. 11/858,138, filed Sep. 20, 2007, entitled “Circulation Pump for Circulating Downhole Fluids, and Characterization Apparatus of Downhole Fluids”, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The present invention relates to the field of sampling and analysis of downhole fluids of a geological formation for evaluating and testing the formation for purposes of exploration and development of hydrocarbon-producing wells, such as oil or gas wells. More particularly, the present disclosure is directed to methods and apparatus utilizing a downhole fluid sampling and analysis apparatus that is configured or designed for capturing formation fluids in a portion of a flowline utilizing, in part, a single valve apparatus, and characterizing the fluids downhole. 
     BACKGROUND 
     Downhole fluid sampling and analysis is an important and efficient investigative technique typically used to ascertain characteristics and nature of geological formations having hydrocarbon deposits. In this, typical oilfield exploration and development includes downhole fluid sampling and analysis for determining petrophysical, mineralogical, and fluid properties of hydrocarbon reservoirs. Fluid characterization is integral to an accurate evaluation of the economic viability of a hydrocarbon reservoir formation. 
     Typically, a complex mixture of fluids, such as oil, gas, and water, is found downhole in reservoir formations. The downhole fluids, which are also referred to as formation fluids, have characteristics, including pressure, temperature, volume, among other fluid properties, that determine phase behavior of the various constituent elements of the fluids. In order to evaluate underground formations surrounding a borehole, it is often desirable to obtain samples of formation fluids in the borehole for purposes of characterizing the fluids, including composition analysis, fluid properties and phase behavior. Wireline formation testing tools are disclosed, for example, in U.S. Pat. Nos. 3,780,575 and 3,859,851, and the Reservoir Formation Tester (RFT) and Modular Formation Dynamics Tester (MDT) of Schlumberger are examples of sampling tools for extracting samples of formation fluids from a borehole for surface analysis. 
     Formation fluids under downhole conditions of composition, pressure and temperature typically are different from the fluids at surface conditions. For example, downhole temperatures in a well could range from 300 degrees F. When samples of downhole fluids are transported to the surface, change in temperature of the fluids tends to occur, with attendant changes in volume and pressure. The changes in the fluids as a result of transportation to the surface cause phase separation between gaseous and liquid phases in the samples, and changes in compositional characteristics of the formation fluids. 
     Techniques also are known to maintain pressure and temperature of samples extracted from a well so as to obtain samples at the surface that are representative of downhole formation fluids. In conventional systems, samples taken downhole are stored in a special chamber of the formation tester tool, and the samples are transported to the surface for laboratory analysis. During sample transfer from below surface to a surface laboratory, samples often are conveyed from one sample bottle or container to another bottle or container, such as a transportation tank. In this, samples may be damaged during the transfer from one vessel to another. 
     Furthermore, sample pressure and temperature frequently change during conveyance of the samples from a wellsite to a remote laboratory despite the techniques used for maintaining the samples at downhole conditions. The sample transfer and transportation procedures currently in use are known to damage or spoil formation fluid samples by bubble formation, solid precipitation in the sample, among other difficulties associated with the handling of formation fluids for surface analysis of downhole fluid characteristics. 
     In addition, laboratory analysis at a remote site is time consuming. Delivery of sample analysis data takes anywhere from a couple of weeks to months for a comprehensive sample analysis. This hinders the ability to satisfy users&#39; demand for real-time results and answers (i.e., answer products). Typically, the time frame for answer products relating to surface analysis of formation fluids is a few months after a sample has been sent to a remote laboratory. 
     As a consequence of the shortcomings in surface analysis of formation fluids, recent developments in downhole fluid sampling and analysis include techniques for isolating and characterizing formation fluids downhole in a wellbore or borehole. In this, the MDT may include one or more fluid analysis modules, such as the Composition Fluid Analyzer (CFA) and Live Fluid Analyzer (LFA) of Schlumberger, for example, to analyze downhole fluids sampled by the tool while the fluids are still located downhole. 
     In downhole fluid sampling and analysis modules of the type described above, formation fluids that are to be sampled and analyzed downhole flow past a sensor module associated with the fluid sampling and analysis module, such as a spectrometer module, which analyzes the flowing fluids by infrared absorption spectroscopy, for example. In this, an Optical Fluid Analyzer (OFA), which may be located in the fluid analysis module, may identify fluids in the flow stream and quantify the oil and water content. U.S. Pat. No. 4,994,671 (incorporated herein by reference in its entirety) describes a borehole apparatus having a testing chamber, a light source, a spectral detector, a database, and a processor. Fluids drawn from the formation into the testing chamber are analyzed by directing the light at the fluids, detecting the spectrum of the transmitted and/or backscattered light, and processing the information (based on information in the database relating to different spectra), in order to characterize the formation fluids. 
     In addition, U.S. Pat. Nos. 5,167,149 and 5,201,220 (both incorporated herein by reference in their entirety) describe apparatus for estimating the quantity of gas present in a fluid stream. A prism is attached to a window in the fluid stream and light is directed through the prism to the window. Light reflected from the window/fluid flow interface at certain specific angles is detected and analyzed to indicate the presence of gas in the fluid flow. 
     As set forth in U.S. Pat. No. 5,266,800 (incorporated herein by reference in its entirety), monitoring optical absorption spectrum of fluid samples obtained over time may allow one to determine when formation fluids, rather than mud filtrates, are flowing into the fluid analysis module. Further, as described in U.S. Pat. No. 5,331,156 (incorporated herein by reference in its entirety), by making optical density (OD) measurements of the fluid stream at certain predetermined energies, oil and water fractions of a two-phase fluid stream may be quantified. 
     Conventionally, multiple valves are utilized in downhole fluid sampling and analysis modules of the type described above to control flow of formation fluids through the flowlines of the fluid analysis modules. For example, co-pending and commonly owned U.S. patent application Ser. No. 11/203,932, filed Aug. 15, 2005, entitled “Methods and Apparatus of Downhole Fluid Analysis”, discloses the use of a plurality of valves for isolating formation fluids in a part of the flowline of a downhole sampling and analysis module.  FIG. 7  schematically represents one example of a fluid sampling and analysis module with a flowline and multiple valve configuration for downhole characterization of fluids by isolating or capturing the formation fluids. In systems of the type depicted in  FIG. 7 , motors are provided downhole to actuate the valves, and a driver board is configured to control operation of the valves and associated motors. Typically, seal valves are employed for purposes of opening or closing the flowlines. The seal valves also may be used for directing fluids through the fluid sampling and analysis module. 
     The fluid control systems of the type described above have multiple components and operating parts, and require space in the downhole modules. In consequence, there is a need for a simple, yet reliable, fluid control system that provides the functionality described above, yet requires minimal space and downhole hardware for its operations. 
     SUMMARY 
     In consequence of the background discussed above, and other factors that are known in the field of downhole fluid sampling and analysis, applicants discovered methods and apparatus for downhole characterization of formation fluids by isolating the fluids from the formation and/or borehole in a flowline of a fluid sampling and analysis module. In some embodiments of the present disclosure, the fluids are isolated with a single valve flow control system that is integrated with the primary flowline and characteristics of the isolated fluids are determined utilizing, in part, a pressure and volume control unit (PVCU). 
     The applicants further discovered that when the isolated fluid sample is circulated in a closed loop line, accuracy of phase behavior measurements can be improved. Therefore, in order to circulate the sample in a closed loop line, a circulation pump is provided in the flowline of the apparatus. 
     According to one aspect of the present disclosure, there is provided a downhole fluid characterization apparatus configured for operation downhole, within a borehole. The apparatus includes a fluid sampling and analysis module having a primary flowline with a first end for formation fluids to enter and a second end for the fluids to exit the fluid sampling and analysis module. A bypass flowline in fluid communication with the primary flowline is provided, and a fluid control system interconnecting the primary flowline and the bypass flowline. The fluid control system has a first position interconnecting a first port of the primary flowline with a second port of the primary flowline for formation fluids to flow in the primary flowline, and a second position interconnecting the first port of the primary flowline with a first port of the bypass flowline and the second port of the primary flowline with a second port of the bypass flowline for formation fluids to flow, via the bypass flowline, in the primary flowline, wherein fluid flow in the primary flowline is maintained during operation of the fluid control system between the first position and the second position. In aspects of the present disclosure, in the first position of the fluid control system, the bypass flowline comprises a circulation flowline for captured formation fluids to circulate in a closed loop of the circulation flowline. 
     In other aspects herein, the fluid sampling and analysis module includes a circulation pump for circulating captured formation fluids in the closed loop of the circulation flowline. In other embodiments, the fluid sampling and analysis module includes at least one first sensor structured and arranged for measuring parameters of interest downhole, within a borehole, wherein the parameters of interest relate to captured formation fluids in the circulation flowline, and the at least one first sensor comprising one or more of a density/viscosity sensor; a pressure sensor; and an imager. In yet other aspects herein, the fluid sampling and analysis module includes a pump unit in fluid communication with the bypass flowline for varying pressure and volume of captured fluids. 
     Aspects of the present disclosure include a pressure compensation unit associated with the fluid control system, the pressure compensation unit being structured and arranged for balancing pressure at opposite ends of the fluid control system to borehole pressure. The fluid sampling and analysis module may further comprise a plurality of sensors structured and arranged for measuring parameters of interest relating to fluids withdrawn from the formation. The fluid control system may comprise a shaft structured and arranged for longitudinal movement in a housing; the shaft having a through hole extending longitudinally and three orifices; an annular space between the shaft and the housing, and four seals attached to the shaft in the annular space between the shaft and the housing, wherein the shaft and the inner wall of the housing being shaped so that in combination with the three orifices, through hole and annular space between the shaft and the housing fluid flow in the primary flowline is not blocked during operation of the fluid control system between the first position and the second position. 
     In certain embodiments, a tool configured to be located downhole for sampling and characterizing formation fluids located downhole in an oilfield reservoir includes a fluid analysis module, the fluid analysis module having a flowline for fluids withdrawn from a formation to flow through the fluid analysis module, the flowline having a first end for the fluids to enter and a second end for the fluids to exit the fluid analysis module; the flowline comprising a primary flowline and a bypass flowline; and the fluid analysis module further comprising a single valve interconnecting the primary flowline and the bypass flowline, the single valve being operable to a first position for formation fluids to flow in the primary flowline, and to a second position for formation fluids to flow, via the bypass flowline, in the primary flowline, wherein the bypass flowline comprises a closed loop flowline for captured fluids when the valve is in the first position. 
     In yet other embodiments, fluid flow in the primary flowline is maintained during operation of the valve between the first and the second positions. The fluid analysis module may further comprise a pressure compensation unit structured and arranged for balancing pressure at opposite ends of the valve so that operation of the valve between the first and the second positions is at a balanced borehole pressure. 
     Aspects herein provide a fluid flow control system structured to control flow of downhole fluids through a fluid sampling and analysis module configured for operation downhole, within a borehole, the fluid sampling and analysis module comprising a primary flowline and a bypass flowline, in fluid communication with the primary flowline, for downhole fluids withdrawn from a formation to flow through the fluid sampling and analysis module, the primary flowline having a first end for the fluids to enter and a second end for the fluids to exit the fluid sampling and analysis module. The fluid flow control system comprises a movable shaft configured and designed for operation downhole, within a borehole, the movable shaft being operable to selectively interconnect the primary flowline and the bypass flowline of the fluid sampling and analysis module, wherein the movable shaft has a first operating position interconnecting a first port of the primary flowline with a second port of the primary flowline, and a second operating position interconnecting the first port of the primary flowline with a first port of the bypass flowline and the second port of the primary flowline with a second port of the bypass flowline, wherein in the first position of the movable shaft downhole fluids flow in the primary flowline, and in the second position of the moveable shaft downhole fluids flow, via the bypass flowline, in the primary flowline; and fluid flow in the primary flowline is maintained during operation of the movable shaft between the first and the second operating positions. 
     In aspects herein, the fluid flow control system may include a housing; the movable shaft being structured and arranged in the housing for movement thereof in a longitudinal direction, wherein the movable shaft has a central through hole through which the downhole fluids flow in a longitudinal direction thereof; an annular space between an outer surface of the movable shaft and an inner surface of the housing; and three orifices for directing flow of downhole fluids in the primary flowline and the bypass flowline, wherein the shaft and the inner wall of the housing being shaped so that in combination with the three orifices, through hole and annular space between the shaft and the housing fluid flow in the primary flowline is not blocked during movement of the fluid control system between the first and the second operating positions. A pressure compensation unit is structured and arranged for balancing pressure at opposite ends of the movable shaft so that operation of the moveable shaft between the first and the second operating positions is at a balanced borehole fluid pressure. 
     Certain embodiments herein provide a method of downhole characterization of formation fluids utilizing a downhole tool comprising a fluid sampling and analysis module having a primary flowline, a bypass flowline and a single valve configured and designed for selectively interconnecting the primary flowline and the bypass flowline for flowing formation fluids through the fluid sampling and analysis module and for capturing formation fluids in a closed loop of the bypass flowline, the method comprising setting the valve in a first operating position so that formation fluids flow through the primary flowline; monitoring at least a first parameter of interest relating to formation fluids flowing in the primary flowline; when a predetermined criterion for the first parameter of interest is satisfied, setting the valve in a second operating position so that formation fluids flow, via the bypass flowline, in the primary flowline; capturing formation fluids in the closed loop of the bypass flowline by returning the valve to the first operating position; balancing pressure at opposite ends of the valve so that operation of the valve between the first and the second operating positions is at a balanced fluid pressure; and characterizing captured formation fluids by operation of one or more sensor structured and arranged on the bypass flowline. 
     In certain embodiments, a method includes characterizing captured formation fluids includes determining one or more fluid property of the captured fluids. In other aspects the method includes determining one or more fluid property comprises changing fluid pressure of the captured formation fluids by varying volume of the captured fluids before determining one or more fluid property. One or more fluid property may be determined after changing fluid pressure. 
     Additional advantages and novel features of the present disclosure will be set forth in the description which follows or may be learned by those skilled in the art through reading the materials herein or practicing the invention. The advantages of the invention may be achieved through the means recited in the attached claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate some of the embodiments disclosed herein and are a part of the specification. Together with the following description, the drawings demonstrate and explain principles of the present disclosure. 
         FIG. 1  is a schematic representation in cross-section of an exemplary operating environment of the methods and apparatus of the present disclosure. 
         FIG. 2  is a schematic representation of one embodiment of a system for downhole sampling and analysis of formation fluids according to the present disclosure with an exemplary tool string deployed in a wellbore. 
         FIG. 3  shows schematically one embodiment of a tool string according to the present disclosure with a fluid sampling and analysis module having a flowline and fluid flow control system for downhole sampling and analysis of formation fluids. 
         FIG. 4A  schematically represents one fluid sampling and analysis module with a flowline and single valve apparatus configuration according to one embodiment of the present disclosure for downhole characterization of fluids by isolating or capturing the formation fluids. 
         FIG. 4B  is a schematic depiction of the operations of a flowline and single valve apparatus configuration according to the present disclosure. 
         FIG. 5A  illustrates schematically one fluid sampling and analysis module with a flowline and single valve apparatus configuration and a pressure compensating system according to one embodiment of the present disclosure for downhole characterization of fluids by isolating or capturing the formation fluids. 
         FIG. 5B  illustrates schematically another fluid sampling and analysis module with a flowline and single valve apparatus configuration and a pressure compensating system according to another embodiment of the present disclosure for downhole characterization of fluids by isolating or capturing the formation fluids. 
         FIG. 5C  illustrates schematically one flowline and single valve apparatus configuration according to one embodiment of the present disclosure for a downhole fluid sampling and analysis module. 
         FIG. 5D  illustrates schematically fluid pressure conditions for the flowline and single valve apparatus configuration of  FIG. 5C  according to one embodiment of the present disclosure. 
         FIG. 6A  is a schematic depiction of the operations of a flowline and single valve apparatus configuration and pressure compensating system according to one embodiment of the present disclosure. 
         FIG. 6B  is a schematic depiction of the step-by-step operations of a flowline and single valve apparatus configuration and pressure compensating system according to one embodiment of  FIG. 6A . 
         FIG. 7  schematically represents an example of a fluid sampling and analysis module with a flowline and multiple valve configuration for downhole characterization of fluids by isolating or capturing the formation fluids. 
     
    
    
     Throughout the drawings, identical reference numbers indicate similar, but not necessarily identical elements. While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents and alternatives falling within the scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     Illustrative embodiments and aspects of the present disclosure are described below. In the interest of clarity, not all features of an actual implementation are described in the specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, that will vary from one implementation to another. Moreover, it will be appreciated that such development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having benefit of the disclosure herein. 
     The present disclosure is applicable to oilfield exploration and development in areas such as downhole fluid sampling and analysis using one or more fluid sampling and analysis modules in Schlumberger&#39;s Modular Formation Dynamics Tester (MDT), for example. 
       FIG. 1  is a schematic representation in cross-section of an exemplary operating environment of the present disclosure wherein a service vehicle  10  is situated at a wellsite having a borehole or wellbore  12  with a borehole tool  20  suspended therein at the end of a wireline  22 .  FIG. 1  depicts one possible setting, and other operating environments also are contemplated by the present disclosure. Typically, the borehole  12  contains a combination of fluids such as water, mud filtrate, formation fluids, etc. The borehole tool  20  and wireline  22  typically are structured and arranged with respect to the service vehicle  10  as shown schematically in  FIG. 1 , in an exemplary arrangement. 
       FIG. 2  is an exemplary embodiment of a system  14  for downhole analysis and sampling of formation fluids according to the one possible embodiment of the present disclosure, for example, while the service vehicle  10  is situated at a wellsite (note  FIG. 1 ). In  FIG. 2 , a borehole system  14  includes a borehole tool  20 , which may be used for testing earth formations and analyzing the composition of fluids from a formation. The borehole tool  20  typically is suspended in the borehole  12  (note also  FIG. 1 ) from the lower end of a multiconductor logging cable or wireline  22  spooled on a winch  16  (note again  FIG. 1 ) at the formation surface. The logging cable  22  typically is electrically coupled to a surface electrical control system  24  having appropriate electronics and processing systems for the borehole tool  20 . 
     Referring also to  FIG. 3 , the borehole tool  20  includes an elongated body  26  encasing a variety of electronic components and modules, which are schematically represented in  FIGS. 2 and 3 , for providing necessary and desirable functionality to the borehole tool  20 . A selectively extendible fluid admitting assembly  28  and a selectively extendible tool-anchoring member  30  (note  FIG. 2 ) are respectively arranged on opposite sides of the elongated body  26 . Fluid admitting assembly  28  is operable for selectively sealing off or isolating selected portions of a borehole wall  12  such that pressure or fluid communication with adjacent earth formation is established. The fluid admitting assembly  28  may be a single probe module  29  (depicted in  FIG. 3 ) and/or a packer module  31  (also schematically represented in  FIG. 3 ). Examples of borehole tools are disclosed in the aforementioned U.S. Pat. Nos. 3,780,575 and 3,859,851, and in U.S. Pat. No. 4,860,581, the contents of which are incorporated herein by reference in their entirety. 
     One or more fluid sampling and analysis modules  32  are provided in the tool body  26 . Fluids obtained from a formation and/or borehole flow through a flowline  33 , via the fluid analysis module or modules  32 , and then may be discharged through a port of a pumpout module  38  (note  FIG. 3 ). Alternatively, formation fluids in the flowline  33  may be directed to one or more fluid collecting chambers  34  and  36 , such as 1, 2¾, or 6 gallon sample chambers and/or six 450 cc multi-sample modules, for receiving and retaining the fluids obtained from the formation for transportation to the surface. Examples of the fluid sampling and analysis modules  32  are disclosed in U.S. Patent Application Publications Nos. 2006/0243047A1 and 2006/0243033A1, both incorporated herein by reference in their entirety. 
     The fluid admitting assemblies, one or more fluid analysis modules, the flow path and the collecting chambers, and other operational elements of the borehole tool  20 , are controlled by electrical control systems, such as the surface electrical control system  24  (note  FIG. 2 ). The electrical control system  24 , and other control systems situated in the tool body  26 , for example, may include processor capability for characterization of formation fluids in the tool  20 , as described in more detail below. 
     The system  14 , in its various embodiments, may include a control processor  40  operatively connected with the borehole tool  20 . The control processor  40  is depicted in  FIG. 2  as an element of the electrical control system  24 . Methods disclosed herein may be embodied in a computer program that runs in the processor  40  located, for example, in the control system  24 . In operation, the program is coupled to receive data, for example, from the fluid sampling and analysis module  32 , via the wireline cable  22 , and to transmit control signals to operative elements of the borehole tool  20 . 
     The computer program may be stored on a computer usable storage medium  42  associated with the processor  40 , or may be stored on an external computer usable storage medium  44  and electronically coupled to processor  40  for use as needed. The storage medium  44  may be any one or more of presently known storage media, such as a magnetic disk fitting into a disk drive, or an optically readable CD-ROM, or a readable device of any other kind, including a remote storage device coupled over a switched telecommunication link, or future storage media suitable for the purposes and objectives described herein. 
     In some embodiments of the present disclosure, the methods and apparatus disclosed herein may be embodied in one or more fluid sampling and analysis modules of Schlumberger&#39;s formation tester tool, the Modular Formation Dynamics Tester (MDT). In this, a formation tester tool, such as the MDT, may be provided with enhanced functionality for the downhole characterization of formation fluids and the collection of formation fluid samples. The formation tester tool may be used for sampling formation fluids in conjunction with downhole characterization of the formation fluids. 
       FIG. 4A  schematically represents one fluid sampling and analysis module with a flowline and single valve apparatus configuration according to one embodiment of the present disclosure for downhole characterization of fluids by isolating or capturing the formation fluids.  FIG. 4B  is a schematic depiction of the operations of a flowline and single valve apparatus configuration according to one embodiment of  FIG. 4A . 
     In  FIG. 4A , a fluid sampling and analysis module  32  has a flowline and single valve apparatus  100  for downhole characterization of fluids by isolating or capturing the formation fluids (note also  FIG. 3 ). In some embodiments, the apparatus  100  of  FIG. 4A  may be integrated with the primary flowline  33  of the module  32 . The apparatus  100  includes a bypass flowline  102  in fluid communication, via main flowline  33 , with a formation surrounding a borehole. The apparatus  100  may include a secondary flowline  115  for purposes of a backup flowline. 
     In the embodiment depicted in  FIG. 4A , the apparatus  100  includes a single valve apparatus  104  that interconnects the primary flowline  33  with the bypass flowline  102 . The single valve apparatus  104  is situated so as to control the flow of formation fluids in the bypass flowline segment  102  of the primary flowline  33  and to isolate or capture formation fluids in the bypass flowline  102 . The single valve apparatus  104  operates as a 4-way 2-position valve. In this, in one position of the single valve apparatus  104  (note  FIG. 4A ) a first port of the primary flowline  33  is connected with a first port of the bypass flowline  102  and a second port of the bypass flowline  102  is connected with a second port of the primary flowline  33  such that fluids flow in the primary flowline  33  via the bypass flowline  102 . Note  FIG. 4A . In another position of the single valve apparatus  104  (note  FIG. 4A ) a first port of the primary flowline  33  is connected with a second port of the primary flowline  33  and a first port of the bypass flowline  102  is connected with a second port of the bypass flowline  102  such that fluids flow in the primary flowline  33  and fluids are captured or isolated in the bypass flowline  102 . 
     A relief valve  106  may be situated on the primary flowline  33 . For example, if high pressure fluid were to be captured in the bypass flowline  102  due to failure of the valve apparatus  104  the high pressure can be released through relief valve  106  to prevent injury or safety issues after the tool returns to the surface. A check valve  121  may be provided for releasing unexpected high pressure in the primary flowline  33 , for example, due to any blockage or failure in the downhole fluid analysis module. However, the relief valve  106  and the check valve  121  are not required for fluid flow control between the primary and bypass flowlines. 
     A pressure/temperature gauge  108  may be provided on the bypass flowline  102  to acquire pressure and/or temperature measurements of fluids in the bypass flowline  102 . A density and viscosity sensor (vibrating rod)  110  also may be provided to measure characteristics of formation fluids flowing through or captured in the bypass flowline  102 . 
     A pump unit  111  may be arranged with respect to the bypass flowline  102  to control volume and pressure of formation fluids retained in the bypass flowline  102 . A scattering detector system  112  may be provided on the bypass flowline  102  to detect particles, such as asphaltene, bubbles, oil mist from gas condensate, that come out of isolated fluids in the bypass flowline  102 . A circulation pump  114  is provided on the bypass flowline  102  for circulating formation fluids that are isolated in the bypass flowline  102  in a closed loop formed by the bypass flowline  102  and the single valve apparatus  104 . 
     The bypass flowline  102  is looped, via the single valve apparatus  104 , and the circulation pump  114  is provided on the looped flowline so that formation fluids isolated in the bypass flowline  102  may be circulated, for example, during phase behavior characterization. When the isolated fluid sample in the bypass flowline  102  is circulated in a closed loop line, accuracy of phase behavior measurements can be improved. 
     Referring to  FIG. 4B , during the captured sample mode, formation fluids flow inside the primary flowline  33  with the single valve apparatus  104  in a first operating position. At this time, other fluid analysis modules analyze the characteristics of the sample flowing inside the primary flowline  33 . When the sample flow becomes stable, the sample contamination is sufficiently low, and sample is single phase, the formation fluids are flowed through the bypass flowline  102  by moving the single valve apparatus  104  from the first operating position to a second operating position. Then, the sample flows into the bypass flowline  102  for a few minutes, for example, and the single valve apparatus  104  is moved to the first operating position so that sample fluid is captured or isolated in a closed loop of the bypass flowline  102  and the single valve apparatus  104 . 
     The density and viscosity sensor  110  measures the sample density and the viscosity. The speed of the circulation pump  114  (sample flow rate) can be controlled by the surface positioned software based on the density and the viscosity measured by the density and viscosity sensor  110 . Next, the circulation pump  114  is started (note  FIG. 4A ). Then the pump unit  111  changes the pressure of the sample captured inside the bypass flowline  102  while the pressure/temperature gauge  108  measures the pressure change and the temperature of the sample. The scattering detector  112  monitors the solid (solid precipitation from liquid or oil coming out from condensate) or gas (bubble from liquid) coming out. 
     In certain aspects, the circulation pump  114  works as an agitator to mix the sample inside the bypass flowline  102  and to create bubbles or solids inside the bypass flowline  102 . With this function of the circulation pump  114 , bubbles and solids that are generated are carried to the scattering detector  112 . The pressure value is recorded when the scattering detector  112  detects the bubbles or solids. 
       FIG. 5A  is a schematic depiction of one fluid sampling and analysis module with a flowline and single valve apparatus configuration and a pressure compensating system according to one embodiment of the present disclosure for downhole characterization of fluids by isolating or capturing the formation fluids.  FIG. 5B  is a schematic depiction of another fluid sampling and analysis module with a flowline and single valve apparatus configuration and a pressure compensating system according to another embodiment of the present disclosure. In the apparatus of  FIG. 5B , a secondary flowline  115  is provided and additional details are provided with respect to the pump  111 , the valve  104 , and the circulation pump  114 . 
       FIG. 5C  illustrates schematically one flowline and single valve apparatus configuration according to one embodiment of the present disclosure for a downhole fluid sampling and analysis module.  FIG. 5D  illustrates schematically fluid pressure conditions for the flowline and single valve apparatus configuration of  FIG. 5C  according to one embodiment of the present disclosure. 
     In addition to the elements discussed above in connection with  FIG. 4A , the apparatus of  FIG. 5A  includes a pressure compensating system  130  having an oil line  132  that connects pressure compensation oil in a chamber  134  with a far end of the single valve  104 . Note also  FIGS. 6A and 6B . As depicted in  FIG. 5D , fluid pressure at ends of the single valve apparatus  104  is balanced by the pressure compensation oil  134 . In this, as depicted in  FIG. 6B , borehole pressure is equalized with the pressure of the oil  134  of the pressure compensating system  130  so that there is no differential pressure across the valve apparatus  104  to impede movement of the valve apparatus. Moreover, balancing pressure inside the apparatus  100  with borehole pressure prevents collapse of or damage to housing  119  of the apparatus  100 . 
     The configurations depicted in  FIGS. 5A and 5B  provide solutions to the issues identified above with respect to fluid flow control systems with multiple valves. In this, the single valve structure of the present disclosure eliminates the need for seal valves and simplifies the overall structure and configuration of the flowline of a sampling and analysis module. In particular, in contrast with a seal valve that is actuated by a DC motor wherein each seal valve of a fluid sampling and analysis module requires an associated motor for operation, the single valve structure of the present disclosure eliminates multiple valve and motor arrangements. By replacing seal valves with a single valve of the present disclosure, it is possible to reduce the electrical components and circuitry in the downhole sampling and analysis apparatus. 
     As depicted in  FIGS. 5A and 5B , the apparatus includes a closed loop circulation flowline  102 . In this, according to the configurations of  FIGS. 5A and 5B , the dead volume of the closed loop flowline is minimized to reduce the stroke of the pump  111  for depressurization. Furthermore, length of the sampling and analysis module  100  is reduced. In contrast with the structure depicted in  FIG. 7 , the configurations of the flowlines of  FIGS. 5A and 5B  reduce the dead volume. For example, a seal valve has a dead volume of 12 cc, whereas the single valve structure of the present disclosure has a dead volume of 1.6 cc. In consequence, the single valve structure minimizes fluid dead volume in the flowline and valve of the sampling and analysis module. 
     The single valve structures of  FIGS. 5A and 5B  provide replacement of a sample that is captured in the bypass flowline through a one way flow of fluids. Therefore, the structure of the single valve minimizes residual formation fluids in the closed loop circulation flowline. The single valve has a through hole extending longitudinally through the center of a piston shaft. Sampled formation fluids flow through the through hole during sample capture in the bypass flowline  102 . In this, the single valve structure eliminates the need for additional flowline hardware for formation fluids to flow through the primary flowline during sample capture in the bypass flowline. 
     In the embodiment depicted in  FIG. 5A , the apparatus  100  includes a housing  119  and a single valve apparatus  104  that interconnects the primary flowline  33  with the bypass flowline  102 . The single valve apparatus  104  is situated so as to control the flow of formation fluids in the bypass flowline segment  102  of the primary flowline  33  and to isolate or capture formation fluids in the bypass flowline  102 . The single valve apparatus  104  operates as a 4-way 2-position valve. The single valve apparatus  104  includes a valve actuator  118  and a valve shaft  107  (note also  FIG. 5C ) having, for example, four pressure seal points  109  located on the valve shaft  107 . The seal points  109  may be dynamic seals that are disposed on the valve shaft  107  and move with the shaft in valve housing  117 . The valve shaft  107  has a center through hole and three side holes or orifices  113 . The holes are in fluid connection with each other and with an annular space between the valve shaft  107  and the inner wall of the valve housing  117 . Note also  FIG. 5C . 
     In one position of the single valve apparatus  104  (note  FIG. 5A ) a first port of the primary flowline  33  is connected with a second port of the primary flowline  33  and a first port of the bypass flowline  102  is connected with a second port of the bypass flowline  102  such that fluids flow in the primary flowline  33  and fluids are captured or isolated in the bypass flowline  102 . Note  FIG. 5A . In another position of the single valve apparatus  104  a first port of the primary flowline  33  is connected with a first port of the bypass flowline  102  and a second port of the primary flowline  33  is connected with a second port of the bypass flowline  102  (note  FIG. 5C ) such that such that fluids flow in the primary flowline  33  via the bypass flowline  102 . As evident from  FIG. 5C , the inner wall of the valve housing  117  is contoured or shaped so that, in combination with the seal points  109  and orifices  113  fluid flow is maintained in the primary flowline  33  and the bypass flowline  102  during movement or operation of the single valve apparatus between the two above mentioned positions. 
     A pressure/temperature gauge  108  may be provided on the bypass flowline  102  to acquire pressure and/or temperature measurements of fluids in the bypass flowline  102 . A density and viscosity sensor (vibrating rod)  110  also may be provided to measure characteristics of formation fluids flowing through or captured in the bypass flowline  102 . 
     A pump unit  111  may be arranged with respect to the bypass flowline  102  to control volume and pressure of formation fluids retained in the bypass flowline  102 . The pump unit  111  has a piston actuator  124  that drives pump piston  126 . A scattering detector system  112  may be provided on the bypass flowline  102  to detect particles, such as asphaltene, bubbles, oil mist from gas condensate, that come out of isolated fluids in the bypass flowline  102 . A circulation pump  114  is provided on the bypass flowline  102  for circulating formation fluids that are isolated in the bypass flowline  102  in a closed loop formed by the bypass flowline  102  and the single valve apparatus  104 . An imager  116 , such as charge couple device or a CMOS, may be provided on the bypass flowline  102  to image fluid flowing in the bypass flowline  102 . 
     The bypass flowline  102  is looped, via the single valve apparatus  104 , and the circulation pump  114  is provided on the looped flowline so that formation fluids isolated in the bypass flowline  102  may be circulated, for example, during phase behavior characterization. When the isolated fluid sample in the bypass flowline  102  is circulated in a closed loop line, accuracy of phase behavior measurements can be improved. 
       FIG. 5B  is a schematic depiction of another fluid sampling and analysis module with a flowline and single valve apparatus configuration and a pressure compensating system according to another embodiment of the present disclosure. In the apparatus of  FIG. 5B , a secondary flowline  115  is provided and additional details are provided with respect to the pump  111 , the valve  104 , and the circulation pump  114 . For example, the pump unit  111  may have a piston actuator  124  that drives pump piston  126 . The actuator unit  124  may include an encoder  125  for monitoring rotations of, for example, a stepper motor  127  that is connected with, for example, a ball screw and nut assembly  129 , which converts rotary motion of the motor  127  to longitudinal motion of the pump piston  126 . In one embodiment of the present disclosure, the valve actuator  118  may comprise a brushless DC motor  131  that is connected with a ball screw and nut assembly  133  for controlling movement and position of the single valve apparatus  104 . Position switches  140  may be provided to monitor positions of the pump shaft  126  and the valve shaft  107 . In combination the aforementioned elements of the pump actuator unit  124  and the valve actuator  118  may be utilized for controlling movement and position of the piston  126  of the pump unit  111  and the valve shaft  107  of the single valve apparatus  104 . 
     In some embodiments, the circulation pump  114  may include a brushless DC motor  135  and a magnet coupler and impeller  137 , as described in detail in aforementioned U.S. patent application Ser. No. 11/858,138, previously incorporated herein by reference. 
     Although the exemplary embodiments depicted in  FIGS. 5A and 5B  show two actuators for the pump unit  111  and the single valve apparatus  104 , the present disclosure contemplates an actuating system having a single actuator for both the pump unit  111  and the valve apparatus  104 . In this, an actuating system having a single motor, for example, a brushless DC motor, with a suitable clutch connector assembly connected with the motor would provide drive and control functions for both pump unit  111  and the valve apparatus  104 . For example, a suitable clutch mechanism maintains position of the valve shaft  107  while sample fluids are replaced in the bypass flowline (note  FIG. 6B , Step  1 ). Then, the single motor releases the clutch so that the valve shaft  107  changes its position to the sample capturing position (note  FIG. 6B , Step  2 ). Next, the clutch holds the position until the next sample replacing sequence. While the valve shaft  107  is moved from the sample replacing position to the sample capturing position, another mechanism causes the pump shaft  126  to move backward so that space for pressurization is created in the pump unit  111 . After sample capture, the mechanism moves the pump shaft  126  forward to pressurize the captured fluids in the bypass flowline, and then moves the pump shaft backward to depressurize the captured fluids (note  FIG. 6B , Step  3 ). By use of a suitable clutch system it is possible to decouple the piston of the pump  111  and the valve shaft  107  while using a single motor. Moreover, movement of the pump piston  126  may be varied to a pressurize/depressurize configuration instead of a single depressurization movement. In this, it is possible to draw fluids into the bypass flowline, move the pump piston  126  in a forward direction to pressurize the captured fluids in the bypass flowline, and then move the pump piston  126  in a backward direction to depressurize the captured fluids in the bypass flowline. An actuating system with a single motor and a clutch system would utilize less space and require less power than a two actuator system depicted in  FIGS. 5A and 5B . However, the present disclosure contemplates use of both types of actuating systems. 
       FIG. 6A  is a schematic depiction of the operations of a flowline and single valve apparatus configuration and pressure compensating system according to one embodiment of the present disclosure. As previously discussed above in connection with  FIG. 4B , during the captured sample mode, formation fluids flow inside the primary flowline  33  with the single valve apparatus  104  in a first operating position. At this time, other fluid analysis modules analyze the characteristics of the sample flowing inside the primary flowline  33 . When the sample flow becomes stable, the sample contamination is sufficiently low, and sample is single phase, the formation fluids are flowed through the bypass flowline  102  by moving the single valve apparatus  104  from the first operating position to a second operating position. Then, the sample flows into the bypass flowline  102  for a few minutes, for example, and the single valve apparatus  104  is moved to the first operating position so that sample fluid is captured or isolated in a closed loop of the bypass flowline  102  and the single valve apparatus  104 . 
       FIG. 6B  is a schematic step-by-step depiction of the operations of a flowline and single valve apparatus configuration and pressure compensating system according to the present disclosure. Referring also to  FIG. 5A , the single valve  104  has a longitudinal valve shaft  107  that is movable in valve housing  117 . Four pressure seal points  109 , for example, dynamic seals are located on the valve shaft  107  and move with the shaft. The valve shaft  107  has a center through hole and three side holes or orifices  113 . The holes are in fluid connection with each other. As evident from  FIG. 5C , the inner wall of the valve housing  117  is contoured so that fluid flow in the primary flowline  33  and the bypass flowline  102  is not interrupted during movement of the valve shaft  107  from sample captured to sample replacing and vice versa. An actuator  118  is connected with the valve shaft  107  so as to move the valve shaft  107  in the housing  117  of the valve such that the position of the valve shaft  107  relative to the valve housing  117  is changed. 
     Referring to  FIG. 6B , for replacing the fluid in the bypass flowline, formation fluids flowing in the primary flowline are diverted to the bypass flowline. The formation fluids enter the loop of the bypass flowline and then return to the primary flowline. In this, a closed loop circulation flowline is provided by the interconnection of the single valve and the bypass flowline. Since the formation fluids reenter the primary flowline at the other end of the bypass flowline, sampled or captured fluids in the bypass flowline are replaced with fresh formation fluids. 
     The single valve system disclosed herein provides a closed loop circulation flowline for formation fluids that are isolated from the fluids in the primary flowline to undergo pressure changes in the circulation flowline. In this, the single valve  104  provides circulation of captured fluids in the bypass flowline  102  without interrupting fluid flow in the primary flowline  33 . A pressure balancing oil  134  (note  FIG. 6A ) is provided on both sides of the single valve piston shaft. The oil is in fluid communication with a pressure compensator system  130  to balance the pressure in the valve. Therefore, if pressure in the primary flowline fluctuates, or the pressure in the circulation flowline changes, the valve piston shaft can maintain its position relative to the housing of the single valve. An actuating force of 20 kgf is required for actuating the piston shaft of the single valve, which is sufficient to overcome the friction of the dynamic seals of the single valve. 
       FIG. 7  schematically represents an example of a fluid sampling and analysis module  32  with a flowline and multiple valve apparatus  70  for downhole characterization of fluids by isolating or capturing the formation fluids. Detailed description of the apparatus of  FIG. 7  may be found in co-pending and commonly owned U.S. patent application Ser. No. 11/203,932, filed Aug. 15, 2005, entitled “Methods and Apparatus of Downhole Fluid Analysis”, which discloses the use of a plurality of valves for isolating formation fluids in a part of the flowline of a downhole sampling and analysis module, and previously incorporated herein by reference. 
     The apparatus  70  includes a bypass flowline  35  and a circulation flowline  37  in fluid communication, via main flowline  33 , with a formation surrounding a borehole. In  FIG. 7 , the apparatus  70  includes two seal valves  53  and  55  operatively associated with the bypass flowline  35 . The valves  53  and  55  are situated so as to control the flow of formation fluids in the bypass flowline segment  35  of the main flowline  33  and to isolate formation fluids in the bypass flowline  35  between the two valves  53  and  55 . A valve  59  may be situated on the main flowline  33  to control fluid flow in the main flowline  33 . For example, each of the seal valves  53  and  55  may have an electrically operated DC brushless motor or stepping motor with an associated piston arrangement for opening and closing the valve. 
     One or more optical sensors, such as a  36 -channels optical spectrometer  56 , connected by an optical fiber bundle  57  with an optical cell or refractometer  60 , and/or a fluorescence/refraction detector  58 , may be arranged on the bypass flowline  35 , to be situated between the valves  53  and  55 . The optical sensors may be used to characterize fluids flowing through or retained in the bypass flowline  35 . U.S. Pat. Nos. 5,331,156 and 6,476,384, and U.S. Patent Application Publication No. 2004/0000636A1 (all incorporated herein by reference in their entirety) disclose methods of characterizing formation fluids. 
     A pressure/temperature gauge  64  and/or a resistance sensor  74  also may be provided on the bypass flowline  35  to acquire fluid electrical resistance, pressure and/or temperature measurements of fluids in the bypass flowline  35  between seal valves  53  and  55 . A chemical sensor  69  may be provided to measure characteristics of the fluids, such as CO2, H2S, pH, among other chemical properties. An ultra sonic transducer  66  and/or a density and viscosity sensor (vibrating rod)  68  also may be provided to measure characteristics of formation fluids flowing through or captured in the bypass flowline  35  between the valves  53  and  55 . U.S. Pat. No. 4,860,581, incorporated herein by reference in its entirety, discloses apparatus for fluid analysis by downhole fluid pressure and/or electrical resistance measurements. U.S. Pat. No. 6,758,090 and Patent Application Publication No. 2002/0194906A1 (both incorporated herein by reference in their entirety) disclose methods and apparatus of detecting bubble point pressure and MEMS based fluid sensors, respectively. 
     A pump unit  71 , such as a syringe-pump unit, may be arranged with respect to the bypass flowline  35  to control volume and pressure of formation fluids retained in the bypass flowline  35  between the valves  53  and  55 . A detailed description of the pump unit  71  is provided in the aforementioned U.S. patent application Ser. No. 11/203,932, previously incorporated herein by reference. 
     An imager  72 , such as a CCD camera, may be provided on the bypass flowline  35  for spectral imaging to characterize phase behavior of downhole fluids isolated therein, as disclosed in co-pending U.S. patent application Ser. No. 11/204,134, titled “Spectral Imaging for Downhole Fluid Characterization,” filed on Aug. 15, 2005. 
     A scattering detector system  76  may be provided on the bypass flowline  35  to detect particles, such as asphaltene, bubbles, oil mist from gas condensate, that come out of isolated fluids in the bypass flowline  35 . A circulation pump  78  is provided on the circulation flowline  37 . A detailed description of the circulation pump  78  is provided in the aforementioned U.S. patent application Ser. No. 11/858,138, previously incorporated herein by reference. 
     Since the circulation flowline  37  is a loop flowline of the bypass flowline  35 , the circulation pump  78  may be used to circulate formation fluids that are isolated in the bypass flowline  35  in a loop formed by the bypass flowline  35  and the circulation flowline  37 . 
     The preceding description has been presented only to illustrate and describe the invention and some examples of its implementation. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. Many modifications and variations are possible in light of the above teaching. The aspects herein were chosen and described in order to best explain principles of the invention and its practical applications. The preceding description is intended to enable others skilled in the art to best utilize the invention in various embodiments and aspects and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims.