Abstract:
Techniques for reduced contamination formation evaluation are provided. The techniques relate to drawing fluid into a downhole tool positionable in a wellbore penetrating a subterranean formation having a virgin fluid and a contaminated fluid therein. Fluid is drawn into at least two inlets for receiving the fluids from the formation. At least one evaluation flowline is fluidly connected to at least one of the inlets for passage of the virgin fluid into the downhole tool. At least one cleanup flowline is fluidly connected to the inlets for passage of the contaminated fluid into the downhole tool. At least one fluid circuit is fluidly connected to the evaluation flowline and/or cleanup flowlines for selectively drawing fluid therein. At least one fluid connector is provided for selectively establishing a fluid connection between the flowlines. At least one sensor is provided for measuring downhole parameters in one of the flowlines. Fluid may be selectively pumped through the flowlines to reduce the contamination in the evaluation flowline.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to techniques for performing formation evaluation of a subterranean formation by a downhole tool positioned in a wellbore penetrating the subterranean formation. More particularly, the present invention relates to techniques for reducing the contamination of formation fluids drawn into and/or evaluated by the downhole tool.  
         [0003]     2. Background of the Related Art  
         [0004]     Wellbores are drilled to locate and produce hydrocarbons. A downhole drilling tool with a bit at and end thereof is advanced into the ground to form a wellbore. As the drilling tool is advanced, a drilling mud is pumped through the drilling tool and out the drill bit to cool the drilling tool and carry away cuttings. The fluid exits the drill bit and flows back up to the surface for recirculation through the tool. The drilling mud is also used to form a mudcake to line the wellbore.  
         [0005]     During the drilling operation, it is desirable to perform various evaluations of the formations penetrated by the wellbore. In some cases, the drilling tool may be provided with devices to test and/or sample the surrounding formation. In some cases, the drilling tool may be removed and a wireline tool may be deployed into the wellbore to test and/or sample the formation. In other cases, the drilling tool may be used to perform the testing or sampling. These samples or tests may be used, for example, to locate valuable hydrocarbons.  
         [0006]     Formation evaluation often requires that fluid from the formation be drawn into the downhole tool for testing and/or sampling. Various devices, such as probes, are extended from the downhole tool to establish fluid communication with the formation surrounding the wellbore and to draw fluid into the downhole tool. A typical probe is a circular element extended from the downhole tool and positioned against the sidewall of the wellbore. A rubber packer at the end of the probe is used to create a seal with the wellbore sidewall. Another device used to form a seal with the wellbore sidewall is referred to as a dual packer. With a dual packer, two elastomeric rings expand raidally about the tool to isolate a portion of the wellbore therebetween. The rings form a seal with the wellbore wall and permit fluid to be drawn into the isolated portion of the wellbore and into an inlet in the downhole tool.  
         [0007]     The mudcake lining the wellbore is often useful in assisting the probe and/or dual packers in making the seal with the wellbore wall. Once the seal is made, fluid from the formation is drawn into the downhole tool through an inlet by lowering the pressure in the downhole tool. Examples of probes and/or packers used in downhole tools are described in U.S. Pat. Nos. 6,301,959; 4,860,581; 4,936,139; 6,585,045; 6,609,568 and 6,719,049 and U.S. Patent Application No. 2004/0000433.  
         [0008]     Formation evaluation is typically performed on fluids drawn into the downhole tool. Techniques currently exist for performing various measurements, pretests and/or sample collection of fluids that enter the downhole tool. However, it has been discovered that when the formation fluid passes into the downhole tool, various contaminants, such as wellbore fluids and/or drilling mud, may enter the tool with the formation fluids. These contaminates may affect the quality of measurements and/or samples of the formation fluids. Moreover, contamination may cause costly delays in the wellbore operations by requiring additional time for more testing and/or sampling. Additionally, such problems may yield false results that are erroneous and/or unusable.  
         [0009]     It is, therefore, desirable that the formation fluid entering into the downhole tool be sufficiently ‘clean’ or ‘virgin’ for valid testing. In other words, the formation fluid should have little or no contamination. Attempts have been made to eliminate contaminates from entering the downhole tool with the formation fluid. For example, as depicted in U.S. Pat. No. 4,951,749, filters have been positioned in probes to block contaminates from entering the downhole tool with the formation fluid. Additionally, as shown in U.S. Pat. No. 6,301,959 to Hrametz, a probe is provided with a guard ring to divert contaminated fluids away from clean fluid as it enters the probe.  
         [0010]     Despite the existence of techniques for performing formation evaluation and for attempting to deal with contamination, there remains a need to manipulate the flow of fluids through the downhole tool to reduce contamination as it enters and/or passed through the downhole tool. It is desirable that such techniques are capable of diverting contaminants away from clean fluid. It is further desirable that such techniques be capable of one of more of the following, among others: analyzing the fluid passing through the flowlines, selectively manipulating the flow of fluid through the downhole tool, responding to detected contamination, removing contamination and/or providing flexibility in handling fluids in the downhole tool.  
       SUMMARY OF THE INVENTION  
       [0011]     In at least one aspect, the present invention relates to a reduced contamination formation evaluation system for a downhole tool positionable in a wellbore penetrating a subterranean formation having a virgin fluid and a contaminated fluid therein. The system is provided with  
         [0012]     at least two inlets for receiving the fluids from the formation, at least one evaluation flowline fluidly connected to at least one of the at least two inlets for passage of the virgin fluid into the downhole tool, at least one cleanup flowline fluidly connected to at least one of the inlets for passage of the contaminated fluid into the downhole tool, at least one fluid circuit fluidly connected to the evaluation and/or cleanup flowlines for selectively drawing fluid therein, at least one fluid connector for selectively establishing a fluid connection between the evaluation and/or cleanup flowlines and at least one sensor for measuring downhole parameters in the evaluation and/or cleanup flowlines.  
         [0013]     In another aspect, the invention relates to a reduced contamination formation evaluation tool positionable in a wellbore penetrating a subterranean formation having a virgin fluid and a contaminated fluid therein. The tool is provided with a fluid communication device extendable from the housing for sealing engagement with a wall of the wellbore and having at least two inlets for receiving the fluids from the formation, at least one evaluation flowline positioned in the housing and fluidly connected to at least one of the inlets for passage of the virgin fluid into the downhole tool, at least one cleanup flowline fluidly connected to the inlets for passage of the contaminated fluid into the downhole tool, at least one fluid circuit fluidly connected to the evaluation and/or cleanup flowline for selectively drawing fluid therein, at least one fluid connector for selectively establishing a fluid connection between the evaluation and/or cleanup flowline and at least one sensor for measuring downhole parameters in the evaluation and/or cleanup flowlines.  
         [0014]     In yet another aspect, the invention relates to a method of evaluating a subterranean formation having a virgin fluid and a contaminated fluid therein. The method involves a downhole tool having at least two inlets adapted to draw the fluids into at least one evaluation flowline and at least one cleanup flowline in the downhole tool. The tool is positioned in a wellbore penetrating the formation, fluid is selectively drawn into the evaluation and/or cleanup flowlines, a fluid connection is selectively established between the evaluation and the cleanup flowlines and downhole parameters of the fluids in the evaluation and/or cleanup flowlines are measured.  
         [0015]     Finally, in another aspect, the invention relates to a method of drawing fluid into a downhole tool positionable in a wellbore penetrating a formation having a virgin fluid and a contaminated fluid therein. The method involves positioning a fluid communication device of the downhole tool in sealing engagement with a wall of the wellbore, establishing fluid communication between at least one evaluation flowline of the fluid communication device and the formation, establishing fluid communication between at least one cleanup flowline of the fluid communication device and the formation, pumping fluid into the cleanup flowline at a cleanup pump rate, pumping fluid into the evaluation flowline at an evaluation pump rate, selectively altering the cleanup pump and/or evaluation pump rate for a discrete time interval and performing formation evaluation of the fluid in the evaluation and/or cleanup flowline after the time interval. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     So that the above recited features and advantages of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof that are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0017]      FIG. 1  is a schematic view, partially in cross-section of downhole formation evaluation tool positioned in a wellbore adjacent a subterranean formation.  
         [0018]      FIG. 2  is a schematic view of a portion of the downhole formation evaluation tool of  FIG. 1  depicting a fluid flow system for receiving fluid from the adjacent formation.  
         [0019]      FIG. 3  is a schematic, detailed view of the downhole tool and fluid flow system of  FIG. 2 .  
         [0020]      FIG. 4A  is a graph depicting the flow rates of fluid through the downhole tool of  FIG. 2  using unsynchronized pumping. FIGS.  4 B 1 - 4  are schematic views of fluid flowing through the downhole tool of  FIG. 2  at points A-D, respectively, of  FIG. 4A .  
         [0021]      FIG. 5A  is a graph depicting the flow rates of fluid through the downhole tool of  FIG. 2  using synchronized pumping. FIGS.  5 B 1 - 4  are schematic views of fluid flowing through the downhole tool of  FIG. 2  at points A-D, respectively, of  FIG. 5A .  
         [0022]      FIG. 6A  is a graph depicting the flow rates of fluid through the downhole tool of  FIG. 2  using partially synchronized pumping. FIGS.  6 B 1 - 4  schematic views of fluid flowing through the downhole tool of  FIG. 2  at points A-D, respectively, of  FIG. 6A .  
         [0023]      FIG. 7A  is a graph depicting the flow rates of fluid through the downhole tool of  FIG. 2  using offset synchronized pumping. FIGS.  7 B 1 - 5  are schematic views of fluid flowing through the downhole tool of  FIG. 2  at points A-E, respectively, of  FIG. 7A .  
         [0024]      FIG. 8A  is a graph depicting the flow rates of fluid through the downhole tool of  FIG. 7A  further depicting flow into a sample chamber. FIGS.  8 B 1 - 5  are schematic views of fluid flowing through the downhole tool of  FIG. 2  at points A-E, respectively, of  FIG. 8A . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Presently preferred embodiments of the invention are shown in the above-identified figures and described in detail below. In describing the preferred embodiments, like or identical reference numerals are used to identify common or similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.  
         [0026]      FIG. 1  depicts a downhole tool usable in connection with the present invention. Any downhole tool capable of performing formation evaluation may be used, such as drilling, coiled tubing or other downhole tool. The downhole tool of  FIG. 1  is a conventional wireline tool  10  deployed from a rig  12  into a wellbore  14  via a wireline cable  16  and positioned adjacent a formation F. The downhole tool  10  is provided with a probe  18  adapted to seal with the wellbore wall and draw fluid from the formation into the downhole tool. Dual packers  21  are also depicted to demonstrate that various fluid communication devices, such as probes and/or packers, may be used to draw fluid into the downhole tool. Backup pistons  19  assist in pushing the downhole tool and probe against the wellbore wall.  
         [0027]      FIG. 2  is a schematic view of a portion of the downhole tool  10  of  FIG. 1  depicting a fluid flow system  34 . The probe  18  is preferably extended from the downhole tool for engagement with the wellbore wall. The probe is provided with a packer  20  for sealing with the wellbore wall. The packer contacts the wellbore wall and forms a seal with the mudcake  22  lining the wellbore. The mudcake seeps into the wellbore wall and creates an invaded zone  24  about the wellbore. The invaded zone contains mud and other wellbore fluids that contaminate the surrounding formations, including the formation F and a portion of the clean formation fluid  26  contained therein.  
         [0028]     The probe  18  is preferably provided with at least two flowlines, an evaluation flowline  28  and a cleanup flowline  30 . It will be appreciated that in cases where dual packers are used, inlets may be provided therebetween to draw fluid into the evaluation and cleanup flowlines in the downhole tool. Examples of fluid communication devices, such as probes and dual packers, used for drawing fluid into separate flowlines are depicted in U.S. Pat. No. 6,719,049 and US Published Application No. 20040000433, assigned to the assignee of the present invention, and U.S. Pat. No. 6,301,959 assigned to Halliburton.  
         [0029]     The evaluation flowline extends into the downhole tool and is used to pass clean formation fluid into the downhole tool for testing and/or sampling. The evaluation flowline extends to a sample chamber  35  for collecting samples of formation fluid. The cleanup flowline  30  extends into the downhole tool and is used to draw contaminated fluid away from the clean fluid flowing into the evaluation flowline. Contaminated fluid may be dumped into the wellbore through an exit port  37 . One or more pumps  36  may be used to draw fluid through the flowlines. A divider or barrier is preferably positioned between the evaluation and cleanup flowlines to separate the fluid flowing therein.  
         [0030]     Referring now to  FIG. 3 , the fluid flow system  34  of  FIG. 2  is shown in greater detail. In this figure, fluid is drawn into the evaluation and cleanup flowlines through probe  18 . As fluid flows into the tool, the contaminated fluid in the invaded zone  24  ( FIG. 2 ) breaks through so that the clean fluid  26  may enter the evaluation flowline  28  ( FIG. 3 ). Contaminated fluid is drawn into the cleanup line and away from the evaluation flowline as shown by the arrows.  FIG. 3  depicts the probe as having a cleanup flowline that forms a ring about the surface of the probe. However, it will be appreciated that other layouts of one or more intake and flowlines extending through the probe may be used.  
         [0031]     The evaluation and cleanup flowlines  28 ,  30  extend from the probe  18  and through the fluid flow system  34  of the downhole tool. The evaluation and cleanup flowlines are in selective fluid communication with flowlines extending through the fluid flow system as described further herein. The fluid flow system of  FIG. 3  includes a variety of features for manipulating the flow of clean and/or contaminated fluid as it passes from an upstream location near the formation to a downstream location through the downhole tool. The system is provided with a variety of fluid measuring and/or manipulation devices, such as flowlines ( 28 ,  29 ,  30 ,  31 ,  32 ,  33 ,  35 ), pumps  36 , pretest pistons  40 , sample chambers  42 , valves  44 , fluid connectors ( 48 ,  51 ) and sensors ( 38 ,  46 ). The system may also provided with a variety of additional devices, such as restrictors, diverters, processors and other devices for manipulating flow and/or performing various formation evaluation operations.  
         [0032]     Evaluation flowline  28  extends from probe  18  and fluidly connects to flowlines extending through the downhole tool. Evaluation flowline  28  is preferably provided with a pretest piston  40   a  and sensors, such as pressure gauge  38   a  and a fluid analyzer  46   a . Cleanup flowline  30  extends from probe  18  and fluidly connects to flowlines extending through the downhole tool. Cleanup flowline  30  is preferably provided with a pretest piston  40   b  and sensors, such as a pressure gauge  38   b  and a fluid analyzer  46   b . Sensors, such as pressure gauge  38   c , may be connected to evaluation and cleanup flowlines  28  and  30  to measure parameters therebetween, such as differential pressure. Such sensors may be located in other positions along any of the flowlines of the fluid flow system as desired.  
         [0033]     One or more pretest piston may be provided to draw fluid into the tool and perform a pretest operation. Pretests are typically performed to generate a pressure trace of the drawdown and buildup pressure in the flowline as fluid is drawn into the downhole tool through the probe. When used in combination with a probe having an evaluation and cleanup flowline, the pretest piston may be positioned along each flowline to generate curves of the formation. These curves may be compared and analyzed. Additionally, the pretest pistons may be used to draw fluid into the tool to break up the mudcake along the wellbore wall. The pistons may be cycled synchronously, or at disparate rates to align and/or create pressure differentials across the respective flowlines.  
         [0034]     The pretest pistons may also be used to diagnose and/or detect problems during operation. Where the pistons are cycled at different rates, the integrity of isolation between the lines may be determined. Where the change in pressure across one flowline is reflected in a second flowline, there may be an indication that insufficient isolation exists between the flowlines. A lack of isolation between the flowlines may indicate that an insufficient seal exists between the flowlines. The pressure readings across the flowlines during the cycling of the pistons may be used to assist in diagnosis of any problems, or verification of sufficient operability.  
         [0035]     The fluid flow system may be provided with fluid connectors, such as crossover  48  and/or junction  51 , for passing fluid between the evaluation and cleanup flowlines (and/or flowlines fluidly connected thereto). These devices may be positioned at various locations along the fluid flow system to divert the flow of fluid from one or more flowlines to desired components or portions of the downhole tool. As shown in  FIG. 3 , a rotatable crossover  48  may be used to fluidly connect evaluation flowline  28  with flowline  32 , and cleanup flowline  30  with flowline  29 . In other words, fluid from the flowlines may selectively be diverted between various flowlines as desired. By way of example, fluid may be diverted from flowline  28  to flow circuit  50   b , and fluid may be diverted from flowline  30  to flow circuit  50   a.    
         [0036]     Junction  51  is depicted in  FIG. 3  as containing a series of valves  44   a, b, c, d  and associated connector flowlines  52  and  54 . Valve  44   a  permits fluid to pass from flowline  29  to connector flowline  54  and/or through flowline  31  to flow circuit  50   a . Valve  44   b  permits fluid to pass from flowline  32  to connector flowline  54  and/or through flowline  35  to flow circuit  50   b . Valve  44   c  permits fluid to flow between flowlines  29 ,  32  upstream of valves  44   a  and  44   b . Valve  44   d  permits fluid to flow between flowlines  31 ,  35  downstream of valves  44   a  and  44   b . This configuration permits the selective mixing of fluid between the evaluation and cleanup flowlines. This may be used, for example, to selectively pass fluid from the flowlines to one or both of the sampling circuits  50   a, b.    
         [0037]     Valves  44   a  and  44   b  may also be used as isolation valves to isolate fluid in flowline  29 ,  32  from the remainder of the fluid flow system located downstream of valves  44   a, b . The isolation valves are closed to isolate a fixed volume of fluid within the downhole tool (i.e. in the flowlines between the formation and the valves  44   a, b ). The fixed volume located upstream of valve  44   a  and/or  44   b  is used for performing downhole measurements, such as pressure and mobility.  
         [0038]     In some cases, it is desirable to maintain separation between the evaluation and cleanup flowlines, for example during sampling. This may be accomplished, for example, by closing valves  44   c  and/or  44   d  to prevent fluid from passing between flowlines  29  and  32 , or  31  and  35 . In other cases, fluid communication between the flowlines may be desirable for performing downhole measurements, such as formation pressure and/or mobility estimations. This may be accomplished for example by closing valves  44   a, b , opening valves  44   c  and/or  44   d  to allow fluid to flow across flowlines  29  and  32  or  31  and  35 , respectively. As fluid flows into the flowlines, the pressure gauges positioned along the flowlines can be used to measure pressure and determine the change in volume and flow area at the interface between the probe and formation wall. This information may be used to generate the formation mobility.  
         [0039]     Valves  44   c, d  may also be used to permit fluid to pass between the flowlines inside the downhole tool to prevent a pressure differential between the flowlines. Absent such a valve, pressure differentials between the flowlines may cause fluid to flow from one flowline, through the formation and back into another flowline in the downhole tool, which may alter measurements, such as mobility and pressure.  
         [0040]     Junction  51  may also be used to isolate portions of the fluid flow system downstream thereof from a portion of the fluid flow system upstream thereof. For example, junction  51  (i.e. by closing valves  44   a, b ) may be used to pass fluid from a position upstream of the junction to other portions of the downhole tool, for example through valve  44   j  and flowline  25  thereby avoiding the fluid flow circuits. In another example, by closing valves  44   a, b  and opening valve d, this configuration may be used to permit fluid to pass between the fluid circuits  50  and/or to other parts of the downhole tool through valve  44   k  and flowline  39 . This configuration may also be used to permit fluid to pass between other components and the fluid flow circuits without being in fluid communication with the probe. This may be useful in cases, for example, where there are additional components, such as additional probes and/or fluid circuit modules, downstream of the junction.  
         [0041]     Junction  51  may also be operated such that valve  44   a  and  44   d  are closed and  44   b  and  44   d  are open. In this configuration, fluid from both flowlines may be passed from a position upstream of junction  51  to flowline  35 . Alternatively, valves  44   b  and  44   d  may be closed and  44   a  and  44   c  are open so that fluid from both flowlines may be passed from a position upstream of junction  51  to flowline  31 .  
         [0042]     The flow circuits  50   a  and  50   b  (sometimes referred to as sampling or fluid circuits) preferably contain pumps  36 , sample chamber  42 , valves  44  and associated flowlines for selectively drawing fluid through the downhole tool. One or more flow circuits may be used. For descriptive purposes, two different flow circuits are depicted, but identical or other variations of flow circuits may be employed.  
         [0043]     Flowline  31  extends from junction  51  to flow circuit  50   a . Valve  44   e  is provided to selectively permit fluid to flow into the flow circuit  50   a . Fluid may be diverted from flowline  31 , past valve  44   e  to flowline  33   a   1  and to the borehole through exit port  56   a . Alternatively, fluid may be diverted from flowline  31 , past valve  44   e  through flowline  33   a   2  to valve  44   f . Pumps  36   a   1  and  36   a   2  may be provided in flowlines  33   a   1  and  33   a   2 , respectively.  
         [0044]     Fluid passing through flowline  33   a   2  may be diverted via valve  44   f  to the borehole via flowline  33   b   1 , or to valve  44   g  via flowline  33   b   2 . A pump  36   b  may be positioned in flowline  33   b   2 .  
         [0045]     Fluid passing through flowline  33   b   2  may be passed via valve  44   g  to flowline  33   c   1  or flowline  33   c   2 . When diverted to flowline  33   c   1 , fluid may be passed via valve  44   h  to the borehole through flowline  33   d   1 , or back through flowline  33   d   2 . When diverted through flowline  33   c   2 , fluid is collected in sample chamber  42   a . Buffer flowline  33   d   3  extends to the borehole and/or fluidly connects to flowline  33   d   2 . Pump  36   c  is positioned in flowline  33   d   3  to draw fluid therethrough.  
         [0046]     Flow circuit  50   b  is depicted as having a valve  44   e ′ for selectively permitting fluid to flow from flowline  35  into flow circuit  50   b . Fluid may flow through valve  44   e ′ into flowline  33   c   1 ′, or into flowline  33   c   2 ′ to sample chamber  42   b . Fluid passing through flowline  33   c   1 ′ may be passed via valve  44   g ′ to flowline  33   d   1 ′ and out to the borehole, or to flowline  33   d   2 ′. Buffer flowline  33   d   3 ′ extends from sample chamber  42   b  to the borehole and/or fluidly connects to flowline  33   d   2 ′. Pump  36   d  is positioned in flowline  33   d   3 ′ to draw fluid therethrough.  
         [0047]     A variety of flow configurations may be used for the flow control circuit. For example, additional sample chambers may be included. One or more pumps may be positioned in one or more flowlines throughout the circuit. A variety of valving and related flowlines may be provided to permit pumping and diverting of fluid into sample chambers and/or the wellbore.  
         [0048]     The flow circuits may be positioned adjacently as depicted in  FIG. 3 . Alternatively, all or portions of the flow circuits may be positioned about the downhole tool and fluidly connected via flowlines. In some cases, portions of the flow circuits (as well as other portions of the tool, such as the probe) may be positioned in modules that are connectable in various configurations to form the downhole tool. Multiple flow circuits may be included in a variety of locations and/or configurations. One or more flowlines may be used to connect to the one or more flow circuits throughout the downhole tool.  
         [0049]     An equalization valve  44   i  and associated flowline  49  are depicted as being connected to flowline  29 . One or more such equalization valves may be positioned along the evaluation and/or cleanup flowlines to equalize the pressure between the flowline and the borehole. This equalization allows the pressure differential between the interior of the tool and the borehole to be equalized, so that the tool will not stick against the formation. Additionally, an equalization flowline assists in assuring that the interior of the flowlines is drained of pressurized fluids and gases when it rises to the surface. This valve may exist in various positions along one or more flowlines. Multiple equalization valves may be put inserted, particularly where pressure is anticipated to be trapped in multiple locations. Alternatively, other valves  44  in the tool may be configured to automatically open to allow multiple locations to equalize pressure.  
         [0050]     A variety of valves may be used to direct and/or control the flow of fluid through the flowlines. Such valves may include check valves, crossover valves, flow restrictors, equalization, isolation or bypass valves and/or other devices capable of controlling fluid flow. Valves  44   a - k  may be on-off valves that selectively permit the flow of fluid through the flowline. However, they may also be valves capable of permitting a limited amount of flow therethrough. Crossover  48  is an example of a valve that may be used to transfer flow from the evaluation flowline  28  to the first sampling circuit and to transfer flow from the cleanup flowline to the second sampling circuit, and then switch the sampling flowing to the second sampling circuit and the cleanup flowline to the first sampling circuit.  
         [0051]     One or more pumps may be positioned across the flowlines to manipulate the flow of fluid therethrough. The position of the pump may be used to assist in drawing fluid through certain portions of the downhole tool. The pumps may also be used to selectively flow fluid through one or more of the flowlines at a desired rate and/or pressure. Manipulation of the pumps may be used to assist in determining downhole formation parameters, such as formation fluid pressure, formation fluid mobility, etc. The pumps are typically positioned such that the flowline and valving may be used to manipulate the flow of fluid through the system. For example, one or more pumps may be upstream and/or downstream of certain valves, sample chambers, sensors, gauges or other devices.  
         [0052]     The pumps may be selectively activated and/or coordinated to draw fluid into each flowline as desired. For example, the pumping rate of a pump connected to the cleanup flowline may be increased and/or the pumping rate of a pump connected to the evaluation flowline may be decreased, such that the amount of clean fluid drawn into the evaluation flowline is optimized. One or more such pumps may also be positioned along a flowline to selectively increase the pumping rate of the fluid flowing through the flowline.  
         [0053]     One or more sensors, such as the fluid analyzers  46   a, b  (i.e. the fluid analyzers described in U.S. Pat. No. 4,994,671 and assigned to the assignee of the present invention) and pressure gauges  38   a, b, c , may be provided. A variety of sensors may be used to determine downhole parameters, such as content, contamination levels, chemical (e.g., percentage of a certain chemical/substance), hydro mechanical (viscosity, density, percentage of certain phases, etc.), electromagnetic (e.g., electrical resistivity), thermal (e.g., temperature), dynamic (e.g., volume or mass flow meter), optical (absorption or emission), radiological, pressure, temperature, Salinity, Ph, Radioactivity (Gamma and Neutron, and spectral energy), Carbon Content, Clay Composition and Content, Oxygen Content, and/or other data about the fluid and/or associated downhole conditions, among others. Sensor data may be collected, transmitted to the surface and/or processed downhole.  
         [0054]     Preferably, one or more of the sensors are pressure gauges  38  positioned in the evaluation flowline ( 38   a ), the cleanup flowline ( 38   b ) or across both for differential pressure therebetween ( 38   c ). Additional gauges may be positioned at various locations along the flowlines. The pressure gauges maybe used to compare pressure levels in the respective flowlines, for fault detection, or for other analytical and/or diagnostic purposes. Measurement data may be collected, transmitted to the surface and/or processed downhole. This data, alone or in combination with the sensor data may be used to determine downhole conditions and/or make decisions.  
         [0055]     One or more sample chambers may be positioned at various positions along the flowline. A single sample chamber with a piston therein is schematically depicted for simplicity. However, it will be appreciated that a variety of one or more sample chambers may be used. The sample chambers may be interconnected with flowlines that extend to other sample chambers, other portions of the downhole tool, the borehole and/or other charging chambers. Examples of sample chambers and related configures may be seen in U.S. Patent/Application No. 2003042021, U.S. Pat. Nos. 6,467,544 and 6,659,177, assigned to the assignee of the present invention. Preferably, the sample chambers are positioned to collect clean fluid. Moreover, it is desirable to position the sample chambers for efficient and high quality receipt of clean formation fluid. Fluid from one or more of the flowlines may be collected in one or more sample chambers and/or dumped into the borehole. There is no requirement that a sample chamber be included, particularly for the cleanup flowline that may contain contaminated fluid.  
         [0056]     In some cases, the sample chambers and/or certain sensors, such as a fluid analyzer, may be positioned near the probe and/or upstream of the pump. It is often beneficial to sense fluid parameters from a point closer to the formation, or the source of the fluid. It may also be beneficial to test and/or sample upstream of the pump. The pump typically agitates the fluid passing through the pump. This agitation can spread the contamination to fluid passing through the pump and/or increase the amount of time before a clean sample may be obtained. By testing and sampling upstream of the pump, such agitation and spread of contamination may be avoided.  
         [0057]     Computer or other processing equipment is preferably provided to selectively activate various devices in the system. The processing equipment may be used to collect, analyze, assemble, communicate, respond to and/or otherwise process downhole data. The downhole tool may be adapted to perform commands in response to the processor. These commands may be used to perform downhole operations.  
         [0058]     In operation, the downhole tool  10  ( FIG. 1 ) is positioned adjacent the wellbore wall and the probe  18  is extended to form a seal with the wellbore wall. Backup pistons  19  are extended to assist in driving the downhole tool and probe into the engaged position. One or more pumps  36  in the downhole tool are selectively activated to draw fluid into one or more flowlines ( FIG. 3 ). Fluid is drawn into the flowlines by the pumps and directed through the desired flowlines by the valves.  
         [0059]     FIGS.  4 A- 8 B 5  depict the flow of fluid into a probe having multiple flowlines, such as in the fluid flow system of FIGS.  2  and/or  3 . These figures demonstrate techniques for manipulating the flow of fluid into the tool to facilitate the flow of clean fluid into the evaluation flowline and reduce contamination. In each figure, the flow of fluid into the probe  18  and through evaluation flowline  28  and cleanup flowline  30  are depicted. Pumps  60 ,  62  are schematically depicted as being operatively connected to flowlines  28 ,  30 , respectively for drawing fluid therethrough. Pump  62  is depicted as operating at a higher rate than the evaluation pump  60 . However, it will be appreciated that the pumps may be operated at the same rate, or the cleanup pump may be operated at a higher rate than the evaluation pump. For depiction purposes, only one pump is shown for each flowline. However, any number of pumps across either flowline may be used. These pumps may be the same as the pumps  36  of  FIG. 3 .  
         [0060]     Referring to FIGS.  4 A- 4 B 4 , pumps  60 ,  62  are depicted as operating in an unsynchronized mode.  FIG. 4A  shows a graph of the flow rate Q (y axis) versus time t (x axis) of fluid passing through the evaluation flowline  28  and the cleanup flowline  30 , represented by lines  66  and  64 , respectively. FIGS.  4 B 1 -B 4  depict the operation of the pumps and the flow of fluid into the probe at points A-D, respectively, of the graph of  FIG. 4A .  
         [0061]     At point A on  FIG. 4A , the pumps are both operating and drawing fluid into the respective evaluation and cleanup flowlines. As depicted in  FIG. 4A   1 , a portion of the formation fluid passes into the evaluation flowline, and a portion of the fluid passes into the cleanup flowline. Preferably, the contaminated fluid  24  is drawn into the cleanup flowline so that only clean fluid  26  flows into the evaluation flowline as indicated by the arrows.  
         [0062]     At point B in  FIG. 4A , the cleanup pump is stopped, but the evaluation pump continues pumping. The corresponding flow rates of the pumps at Point B show that the flow rate ( 64 ) through the cleanup flowline has dropped, while the flow rate ( 66 ) through the evaluation flowline continues. As shown in  FIG. 4B   2 , contaminated fluid is no longer being drawn into the cleanup line and away from the evaluation flowline. In this case, both contaminated and clean fluid may be drawn into the evaluation flowline as indicated by the arrows.  
         [0063]     At point C in  FIG. 4A , both pumps are pumping and the flow rate  64  of the cleanup line increases. As shown in  FIG. 4A   3 , the pumps return to operation as previously described with respect to point A.  
         [0064]     At point D in  FIG. 4A , the cleanup pump is pumping, but the evaluation pump is stopped. The corresponding flow rates of the pumps at Point D show that the flow rate ( 64 ) through the cleanup flowline continues, while the flow rate ( 66 ) through the evaluation flowline has dropped. As shown in  FIG. 4B   4 , fluid is no longer being drawn into the evaluation flowline. In this case, both contaminated and clean fluid may be drawn into the cleanup flowline as indicated by the arrows.  
         [0065]     Referring to FIGS.  5 A- 5 B 4 , the pumps  60 ,  62  are depicted operating in a synchronized mode. These Figures are the same as FIGS.  4 A- 4 B 4 , except that both pumps are turned off at points B and D. At points B and D of  FIG. 5A , the flow rates  64   a ,  66   a  both drop as the pumps are stopped. As shown in FIGS.  5 B 2  and  4 , fluid stops flowing into either flowline when the pumps are stopped.  
         [0066]     Referring to FIGS.  6 A- 6 B 4 , the pumps  60 ,  62  are depicted operating in a partially synchronized mode. These Figures are the same as FIGS.  4 A- 4 B 4 , except that both pumps are turned off at point B. At point B of  FIG. 6A , the flow rates  64   b ,  66   b  both drop as the pumps are stopped. As shown in  FIG. 6B   2 , fluid stops flowing into either flowline.  
         [0067]     Referring to FIGS.  7 A- 7 B 5 , the pumps  60 ,  62  are depicted operating in an offset synchronized mode. FIGS.  7 A- 7 B 5  are the same as FIGS.  4 A- 4 B 4 , except that at point B, the cleanup pump is on and the evaluation pump is off, at point C both pumps are off, and at point D the cleanup pump is on and the evaluation pump is off. Additionally, an additional point E is depicted with both pumps on. The resulting curves  64   c ,  66   c  in  FIG. 7A  show that the flow rate through the cleanup flowline drops at point C, while the flow rate through the evaluation flowline drops for an extended time from points B to D.  
         [0068]     Referring to FIGS.  8 A- 8 B 5 , a pumping and sampling operation is depicted. In this case, the pumps  60 ,  62  are depicted operating in the offset synchronized mode of FIGS.  7 A- 7 B 5 . However, the sampling operation may be performed with any of the modes described. These Figures are the same as FIGS.  7 A- 7 B 5 , except that a sample chamber  42  is connected to the evaluation flowline in FIGS.  8 B 1 - 5 . Valves  66  and  68  are depicted along flowline  28  to selectively divert fluid to the sample chamber.  
         [0069]     The valves are preferably activated and/or fluid is delivered into the sample chamber at a point when clean fluid is present in the evaluation flowline. In the mode described in FIGS.  8 A- 8 B 5 , sampling is performed after the pumps have been cycled to assure the flow of clean fluid into the evaluation flowline  28 . As shown in FIGS.  8 B 1 - 3 , the valve  66  is closed and valve  68  is open at points A-C of the pumping operation. As shown in  FIG. 8B   4 , at point D, valve  66  is opened and valve  68  is closed to permit fluid to start to flow into sample chamber  42 . As shown at point E and in  FIG. 8B   5 , fluid begins flowing into the sample chamber.  
         [0070]     FIGS.  8 A- 8 B 5  depict a given sampling operation used in combination with a pumping mode. The sampling operation may also be used in combination with other pumping modes, such as those depicted in  FIGS. 4-6 . It is preferred that such pumping and sampling be manipulated to draw clean fluid into the sample chamber and/or contaminated fluid away therefrom. Fluid may be monitored through the flowlines to detect contamination. Where contamination occurs, fluid may be diverted from the sample chamber, for example to the wellbore.  
         [0071]     Pressure in the flowlines may also be manipulated using other device to increase and/or lower pressure in one or more flowlines. For example, pistons in the sample chambers and pretest may be retracted to draw fluid therein. Charging, valving, hydrostatic pressure and other techniques may also be used to manipulate pressure in the flowlines.  
         [0072]     It will be understood from the foregoing description that various modifications and changes may be made in the preferred and alternative embodiments of the present invention without departing from its true spirit. The devices included herein may be manually and/or automatically activated to perform the desired operation. The activation as desired and/or based on data generated, conditions detected and/or analysis of results from downhole operations.  
         [0073]     This description is intended for purposes of illustration only and should not be construed in a limiting sense. The scope of this invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. “A,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded.