Abstract:
A well fluid sampling tool is provided. The sampling tool includes at least one insulated sample chamber mounted in a tool collar. The tool collar may be coupled with a drill string such that, when the tool collar is deployed in a well bore, selected sample chambers may receive a fluid sample from outside the drill string without removing the drill string from the well bore (e.g., during measurement while drilling or logging while drilling operations). A heating module in thermal communication with at least one of the sample chambers is disposed to selectively heat the sample chambers in thermal communication therewith. The sampling tool may be particularly useful for acquiring and preserving substantially pristine formation fluid samples.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application Ser. No. 60/492,483 entitled  Apparatus for Obtaining High Quality Formation Fluid Samples , filed Aug. 4, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to the drilling of oil and gas wells, and more specifically, to a formation fluid sampling tool and method of use for acquiring and preserving substantially pristine formation fluid samples.  
       BACKGROUND OF THE INVENTION  
       [0003]     The commercial development of hydrocarbon (e.g., oil and natural gas) fields requires significant capital investment. Thus it is generally desirable to have as much information as possible pertaining to the contents of a hydrocarbon reservoir and/or geological formation in order to determine its commercial viability. There have been significant advances in measurement while drilling and logging while drilling technology in recent years (hereafter referred to as MWD and LWD, respectively). These advances have improved the quality of data received from downhole sensors regarding subsurface formations. It is nonetheless still desirable to obtain one or more formation fluid samples during the drilling and completion of an oil and/or gas well. Once retrieved at the surface, these samples typically undergo specialized chemical and physical analysis to determine the type and quality of the hydrocarbons contained therein. In general, it is desirable to collect the samples as early as possible in the life of the well to minimize contamination of the native hydrocarbons by drilling damage.  
         [0004]     As is well known to those of ordinary skill in the art, formation fluids (e.g., water, oil, and gas) are found in geological formations at relatively high temperatures and pressures (as compared to ambient conditions at the surface). At these relatively high temperatures and pressures, the formation fluid is typically a single-phase fluid, with the gaseous components being dissolved in the liquid. A reduction in pressure (such as may occur by exposing the formation fluid to ambient conditions at the surface) typically results in the separation of the gaseous and liquid components. Cooling of the formation fluid towards such ambient temperatures typically results in a reduction in volume (and therefore a reduction in pressure if the fluid is housed in a sealed container), which also tends to result in a separation of the gaseous and liquid components. Cooling of the formation fluid may also result in substantially irreversible precipitation and/or separation of other compounds previously dissolved therein. Thus it is generally desirable for a sampling apparatus to be capable of substantially preserving the temperature and/or pressure of the formation fluid in its primitive formation condition.  
         [0005]     Berger et al., in U.S. Pat. No. 5,803,186, disclose an apparatus and method for obtaining samples of formation fluid using a work string designed for performing other downhole work such as drilling, workover operations, or re-entry operations. The apparatus includes sensors for sensing downhole conditions while using a work string that permits working fluid properties to be adjusted without withdrawing the work string from the well bore. The apparatus also includes a relatively small integral sample chamber coupled to multiple input and output valves for collecting and housing a formation fluid sample.  
         [0006]     Schultz et al., in U.S. Pat. No. 6,236,620, disclose an apparatus and method for drilling, logging, and testing a subsurface formation without removing the drill string from the well bore. The apparatus includes a surge chamber and surge chamber receptacle for use in sampling formation fluids. The surge chamber is lowered through the drill string into engagement with the surge chamber receptacle, receives a sample of formation fluid, and then is retrieved to the surface. Repeated sampling may be accomplished without removing the drill string by removing the surge chamber, evacuating it, and then lowering it back into the well. While the Berger and Schultz apparatuses apparently permit samples to be collected relatively early in the life of a well, without retrieval of the drill string, they include no capability to preserve the temperature of the formation fluid. Further, it is a relatively complex operation to remove the formation fluid sample from the Berger apparatus.  
         [0007]     Brown et al., in U.S. Pat. No. 5,901,788 disclose a wire or slick line apparatus in which the sample chamber may be thermally insulated, given a high heat capacity, and/or provided with a heating source such as an electric heater, with the intent of maintaining the sample at a temperature similar to that of the formation. Corrigan et al., in PCT Publication WO 00/34624, disclose a slick line apparatus including a sample chamber contained within an evacuated jacket for maintaining the temperature of a formation fluid sample. The Corrigan apparatus further includes multiple heaters spaced along the sample chamber. One drawback of the Brown and Corrigan apparatuses is that they require the retrieval of the drill string from the well bore prior to being lowered therein, which typically involves significant cost and time, and increases the risk of subsurface damage to the formation of interest.  
         [0008]     Therefore, there exists a need for improved apparatuses and methods for obtaining samples of formation fluid from a well. In particular, an apparatus that does not require retrieval of the drill string from the well and that has the capability of preserving the sample of formation fluid in substantially pristine conditions is highly desirable.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention addresses difficulties in acquiring and preserving samples of pristine formation fluid, including those difficulties described above. Aspects of this invention include a sampling tool for obtaining samples of relatively pristine formation fluid without removing the drill string from the well bore. Sampling tools according to the invention may retrieve samples from both deep and shallow wells. Exemplary sampling tool embodiments of this invention are configured for coupling to the drill string and include one or more sample chambers. The sample chambers are typically insulated and/or provided with a heat source (also referred to as a heating module, e.g., an electric heater) for maintaining the temperature of the formation fluid. Sampling tool embodiments according to this invention typically further include on-board electronics disposed to collect multiple samples of pristine formation fluid at substantially any predetermined moment or time interval.  
         [0010]     Exemplary embodiments of the present invention may advantageously provide several technical advantages. For example, sampling tool embodiments according to this invention may advantageously provide for improved sampling of formation fluid from, for example, deep wells. In particular, embodiments of this invention are configured with the intent to try to maintain, for as long as possible, the fluid at about the same temperature and pressure conditions as found in the formation. A tool according to this invention, in combination with a logging while drilling (LWD) tool, is couplable to a drill string, and thus in such a configuration provides for sampling of formation fluid shortly after penetration of the formation of interest. Advantages are thus provided for the acquisition and preservation of relatively high quality formation fluid sample in substantially pristine conditions. These high quality samples may provide for more accurate determination of formation properties and thus may enable a better assessment of the economic viability of an oil and/or gas reservoir.  
         [0011]     In one aspect the present invention includes a downhole sampling tool. The downhole sampling tool includes a tool collar having at least one sample chamber deployed therein. Each sample chamber includes an insulating layer deployed thereabout. The tool collar is disposed to be operatively coupled with a drill string deployed in a well bore such that, when the tool collar is coupled to the drill string, sample chambers may be selectively placed in fluid communication with formation fluid drawn from outside the drill string without removing the drill string from the well bore. The sampling tool further includes a heating module in thermal communication with at least one of the sample chambers. The heating module is disposed to selectively heat the sample chambers in thermal communication therewith.  
         [0012]     In another aspect this invention includes a logging while drilling (LWD) tool. The logging while drilling tool includes a tool collar having at least one chamber mounted therein. Each sample chamber includes an insulating layer deployed thereabout. The tool collar is disposed to be operatively coupled with a drill string deployed in a well bore such that, when the tool collar is coupled to the drill string, sample chambers may be selectively placed in fluid communication with formation fluid drawn from outside the drill string without removing the drill string from the well bore. The LWD tool further includes a heating module in thermal communication with at least one of the sample chambers. The heating module is disposed to selectively heat the sample chambers in thermal communication therewith. The LWD tool still further includes at least one packer element. Each packer element is disposed to seal the wall of the well bore around the LWD tool. Each packer element is further selectively positionable between sealed and unsealed positions. The LWD yet further includes a sample inlet port connected to the at least one sample chamber via an inlet passageway.  
         [0013]     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
         [0015]      FIG. 1  is a schematic illustration of an offshore oil and/or gas drilling platform utilizing an exemplary embodiment of the present invention.  
         [0016]      FIG. 2  is a partially cutaway schematic representation of an exemplary sampling module embodiment according to the present invention.  
         [0017]      FIG. 3  is a partially cutaway schematic representation of an exemplary embodiment of a sample chamber insert for use with the exemplary sampling module of  FIG. 2 .  
         [0018]      FIG. 4  is a partially cutaway schematic representation of an exemplary sampling tool according to the present invention, including the exemplary sampling module of  FIG. 2 .  
     
    
     DETAILED DESCRIPTION  
       [0019]     Referring now to  FIG. 1 , one exemplary embodiment of sampling module  100  according to this invention is schematically illustrated in use in an offshore oil or gas drilling assembly, generally denoted  10 . A semisubmersible drilling platform  12  is positioned over an oil or gas formation  14  disposed below the sea floor  16 . A subsea conduit  18  extends from deck  20  of platform  12  to a wellhead installation  22 . The platform may include a derrick  26  and a hoisting apparatus  28  for raising and lowering the drill string  30  including drill bit  32 , sampling module  100 , and formation tester  200 . Drill string  30  may further include a downhole drill motor, a mud pulse telemetry system, and one or more sensors, such as a nuclear logging instrument, for sensing downhole characteristics of the well, bit, and reservoir.  
         [0020]     During a drilling, testing, and sampling operation, drill bit  32  is rotated on drill string  30  to create a well bore  40 . Shortly after the drill bit  32  intersects the formation  14  of interest, drilling typically stops to allow formation testing before contamination of the formation occurs, e.g., by invasion of working fluid or filter cake build-up. Expandable packers  220  are inflated to sealing engage the wall of well bore  40 . The inflated packers  220  isolate a portion of the well bore  40  adjacent the formation  14  to be tested. Formation fluid is then received at port  216  of formation tester  200  and may be pumped into one or more sample chambers  122  illustrated on  FIG. 2 . As described in more detail hereinbelow with respect to  FIG. 4 , embodiments of formation tester  200  may include a fluid identification module  210  including one or more sensors for sensing properties of the various fluids that may be encountered. Formation tester  200  may further pass fluid through a fluid passageway to one or more sample tanks housed in sample module  100 .  
         [0021]     It will be understood by those of ordinary skill in the art that the sampling module  100  and the formation tester  200  of the present invention are not limited to use with a semisubmersible platform  12  as illustrated on  FIG. 1 . Sampling module  100  and formation tester  200  are equally well suited for use with any kind of subterranean drilling operation, either offshore or onshore.  
         [0022]     Referring now to  FIGS. 2 and 3 , a schematic illustration of one exemplary embodiment of the sampling module  100  (also referred to herein as a sampling tool) according to this invention is shown. Sampling module  100  includes one or more sample tanks  120  disposed in a collar  110 . Collar  110  is typically configured for mounting on a drill string, e.g., drill string  30  ( FIG. 1 ), and thus may include conventional threaded connectors on the top and bottom thereof. While  FIGS. 2 and 3  show a sampling module including three sample tanks  120 , the artisan of ordinary skill will readily recognize that sampling module  100  may include substantially any number of sample tanks disposed in substantially any arrangement in the collar  110 .  
         [0023]     As described hereinabove, sample tanks  120  are configured to maintain the temperature of the formation fluid at a value substantially equal to that of the formation (e.g., formation  14  in  FIG. 1 ). In the embodiment of  FIG. 2 , sample tanks  120  include a sample chamber  122  surrounded by one or more insulating layers  124 . The sample chamber  122  may be fabricated from, for example, stainless steel or a titanium alloy, although it will be appreciated that it may be fabricated from substantially any suitable material in view of the service temperatures and pressures, exposure to corrosive formation fluids, and other downhole conditions. Insulating layer  124  may include substantially any suitable thermally insulating material, such as a polyurethane coating or an aerogel foam disposed on the sample chamber  122 . Insulating layer  124  may further include an evacuated annular region, the vacuum around the sample chamber  122  further enhancing the thermal insulation thereof. In one desirable embodiment insulating layer  124  is sufficient to substantially maintain the temperature of a sample at the formation temperature, the sample chamber  124  having an revalue of, for example, greater than or equal to about 12.  
         [0024]     With further reference to the embodiment of  FIG. 2 , the exterior of the sample chamber  122  is wound with an electrical resistance heating module  128  typically in the form of a tape, foil, or chain. Sample chamber  122  may alternately be coated with an electrically resistive coating. The heating module  128  is typically communicably coupled to a controller (shown schematically at  140 ) mounted inside the collar  110 . In embodiments in which the heating module  128  includes an electrical heating mechanism, electric power may be provided by substantially any known electrical system, such as a battery pack mounted in the tool body  110 , or elsewhere in the drill string, or a turbine disposed in the flow of drilling fluid. Alternately and/or additionally, the sample chamber may be heated using known chemical techniques, e.g., by a controlled exothermic chemical reaction in a separate chamber (not shown).  
         [0025]     Referring again to  FIG. 2 , the one or more sample chambers  122  are in fluid communication with a sample fluid passageway  130  including an inlet port  134  for receiving formation fluid (e.g. from an LWD tool). Passageway  130  is further in fluid communication with inlet valves  132  for controlling the flow of the formation fluid to the one or more sample chambers  122 . Inlet valves  132  are communicably coupled to the controller  140  and allow collection of separate fluid samples in each of the sample chambers  122  (e.g., at unique times or penetration depths). Multiple samples may also be collected simultaneously and optionally held at separate temperatures, thus providing additional information about the temperature and pressure stability of the formation fluid.  
         [0026]     With continued reference to  FIG. 2 , controller  140  may include a programmable processor (not shown), such as a microprocessor or a microcontroller, and may also include processor readable or computer readable program code embodying logic, including instructions for controlling the function of valves  132  and heating modules  128 . Controller  140  may be disposed in communication with one or more temperature probes (not shown) appropriately sized, shaped, positioned, and configured for providing temperature readings of the interior of the sample chambers  122 . The temperature probes may include, for example a thermistor or a thermocouple in thermal contact with the samples. Controller  140  may optionally be disposed in electronic communication with other sensors and/or probes for monitoring other physical parameters of the samples (e.g., a pressure sensor for measuring the pressure of the interior of the sample chamber  122 ). Controller  140  may also optionally be disposed in electronic communication with other sensors for measuring well bore properties, such as a gamma ray depth detection sensor or an accelerometer, gyro or magnetometer to detect azimuth and inclination. Controller  140  may also optionally communicate with other instruments in the drill string, such as telemetry systems that communicate with the surface. Controller  140  may further optionally include volatile or non-volatile memory or a data storage device. The artisan of ordinary skill will readily recognize that while controller  140  is shown disposed in collar  110  ( FIG. 2 ), it may alternately be disposed elsewhere, such as in identification module  210  of fluid tester  200 .  
         [0027]     In alternative embodiments, sampling module  100  may be configured to include a sample chamber insert  150  mountable in the collar  110  as illustrated on  FIG. 3 . The sample chamber insert  150  may, for example, include the one or more sample tanks  120 , the fluid passageway  130 , the inlet valves  132 , and the controller  140  disposed in a housing  152 . This embodiment may be advantageous in that the sample chamber insert  150 , including the sample tanks  120 , may be removed from the collar  110  and transported to a remote location for sample testing.  
         [0028]     Referring now to  FIG. 4 , another embodiment of the present invention includes a sample module  100  coupled to a formation tester  200  (e.g., a LWD tool). While sample module  100  and formation tester  200  are shown coupled at  235  (e.g., threaded to one another), the artisan of ordinary skill will readily recognize that consistent with the present invention they may also be fabricated as an integral unit. Formation tester  200  may be according to embodiments described and claimed in U.S. Pat. No. 6,236,620 to Schultz, et al. and typically includes one or more packer elements  220  for selectively sealing the wall of the well bore around formation tester  200 .  FIG. 4  illustrates two packer elements  220  for isolating a substantially annular portion of the well bore adjacent to a formation of interest. The packer elements  220  may comprise any type packer element, such as compression type or inflatable type. Inflatable type packer elements  220  may be inflated by substantially any suitable technique, such as by injecting a pressurized fluid into the packer. The packer elements  220  may further include optional covers (not illustrated on  FIG. 4 ) to shield the components thereof from the potentially damaging effects of the various forces encountered during drilling (e.g., collisions with the wall of the well bore).  
         [0029]     With further reference to  FIG. 4 , the formation tester  200  further includes at least one inlet port  216  disposed between packer elements  220 . In embodiments including only one packer element  220 , inlet port  216  is typically disposed therebelow (e.g., further towards the bottom of the well). Inlet port  216  is in fluid communication with a fluid identification module (shown schematically at  210 ) via fluid passageway  218 . Fluid identification module  210  typically includes instrumentation including one or more sensors for monitoring and recording properties of the various fluids that may be encountered in the well bore, from which a fluid type may be determined. For example, sensor measurements may distinguish between working fluid (e.g., drilling mud) and formation fluid. The fluid identification module  210  may include any of a relatively wide variety of sensors, including a resistivity sensor for sensing fluid or formation resistivity and a dielectric sensor for sensing the dielectric properties of the fluid or formation. Module  210  may further include pressures sensors, temperature sensors, optical sensors, acoustic sensors, nuclear magnetic resonance sensors, density sensors, viscosity sensors, pH sensors, and the like. Fluid identification module  210  typically further includes numerous valves and fluid passageways (not shown) for directing formation fluid to the various sensors and for directing fluid to, for example, a sample output passageway  214  or a fluid discharge passageway  212 , in fluid communication with output port  213 .  
         [0030]     Formation tester  200  typically further includes a control module (not shown) of analogous purpose to that described above with respect to controller  140 . The control module, for example controls the function of the various sensors described above and communicates sensor output with operators at the surface, for example, by conventional mud telemetry or electric line communications techniques. The control module may further be communicably coupleable with controller  140 .  
         [0031]     In operation, formation tester  200  is advantageously positioned adjacent a formation of interest in the well bore. The packer elements  220  are inflated, thereby isolating a substantially annular portion of the well bore adjacent the formation. One or more pumps  250  are utilized to pump formation fluid into the tool at port  216 . The pump  250  may include, for example, a bi-directional piston pump, such as that disclosed in U.S. Pat. Nos. 5,303,775 and 5,377,755 to Michaels et al., or substantially any other suitable pump in view of the service temperatures and pressures, exposure to corrosive formation fluids, and other downhole conditions. Fluid is typically pumped into the tool (rather than flowing by the force of the reservoir pressure) in order to maintain it above its bubble pressure (i.e., the pressure below which a single phase fluid becomes a two phase fluid). Sampled formation fluid then passes through the fluid identification module  210  where it is tested using one or more of the various sensors described above. Fluid is typically pumped in and then discharged from the tool via passageway  212  and output port  213  until it is sensed to have predetermined properties (e.g., a resistivity in a certain range) identifying it as likely to be a substantially pristine formation fluid. Typically, upon first pumping, the formation fluid is contaminated with drilling fluid. After some time, however, substantially pristine formation fluid may be drawn into the tool and routed to sampling module  100  via passageway  214 . Samples may be obtained using substantially any protocol (e.g., at a various time intervals or matching certain predetermined fluid properties measured by identification module  210 ).  
         [0032]     Referring now to  FIG. 2 , with further reference to  FIG. 4 , substantially pristine formation fluid may be received at inlet port  134 , which is in fluid communication with fluid passageway  214 , and routed to one or more sample chambers  122  through valves  132 . If the sample temperature falls, such a temperature change may be detected by the controller  140 , (e.g., using a thermistor or thermocouple in thermal contact with the sample). In response to the detected temperature drop, the control circuit may, for example, connect an electrical power supply (e.g., a battery source) with the electrical heating module  128  to heat the sample chamber  122  and thus stabilize the temperature of the sample.  
         [0033]     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.