Abstract:
An early formation evaluation tool is provided which includes formation fluid sampling capabilities. In one embodiment, fluid pressure in a drill string in which the tool is interconnected is utilized to operate packers of the tool and to operate fluid samplers of the tool. To successively control actuation of the samplers, a ratchet mechanism responsive to altering fluid pressures in the drill string aligns a piercing member with a series of frangible pressure barriers associated with the samplers.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to tools utilized in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides an early formation evaluation tool having formation fluid sampling capability. 
     It is well known that it is desirable to have the capability of evaluating characteristics of formations intersected by a wellbore before drilling operations are completed. This type of formation evaluation is known as “early” formation evaluation by those skilled in the art. For this purpose, tools have been developed which are interconnected in drill strings, and which are capable of performing tests on formations, such as pressure drawdown and buildup tests. These tests may be performed periodically during drilling operations. 
     However, it would also be advantageous to be able to collect samples of fluid from formations intersected by a wellbore during a drilling operation. Furthermore, it would be desirable to be able to collect such samples in conjunction with tests performed on formations, since this would be more economical and convenient than performing the formation tests and sample collections at different times, with separate tools, or on separate trips into the wellbore. Performing a formation test and a sample collection without moving the drill string between these operations would also aid in correlating the results of these operations to a particular location in the formation. 
     From the foregoing, it can be seen that it would be quite desirable to provide an early formation evaluation tool with the capability of collecting formation fluid samples. 
     SUMMARY OF THE INVENTION 
     In carrying out the principles of the present invention, in accordance with an embodiment thereof, an early formation evaluation tool is provided in which fluid samples may be conveniently collected therein. 
     In one aspect of the present invention, successive fluid samples are received in respective successive fluid samplers of a tool by alternately increasing and decreasing fluid pressure in a tubular string in which the tool is interconnected. The fluid samples may be received in the samplers either without repositioning the tool in the wellbore, or with the tool being repositioned in the wellbore between sample collections. 
     In another aspect of the present invention, fluid pressure in the tubular string may also be utilized to sealingly engage one or more packers of the tool with a wellbore. The fluid pressure used to operate the packers may be maintained in the tool while the fluid pressure in the tubular string is altered to operate the samplers. 
     In yet another aspect of the present invention, the tubular string to which fluid pressure is applied to collect fluid samples in the tool may also be manipulated to pump fluid from a formation into the tool. Thus, various operations of the tool may be conveniently and separately accomplished as desired by merely manipulating or applying fluid pressure to the tubular string. 
     In still another aspect of the present invention, the tool may include a ratchet mechanism responsive to fluid pressure applied to the tubular string. In one embodiment described herein, a J-slot is used to incrementally displace a piercing member relative to a series of pressure barriers. Fluid pressure applied to the tubular string may also be utilized to cause the member to pierce one of the barriers with which the member is aligned. 
     In a further aspect of the present invention, the tool includes at least one fluid sampler including an actuator. The actuator is placed in fluid communication with one fluid passage of the tool to thereby cause the sampler to receive a fluid sample therein from another fluid passage of the tool. In one embodiment described herein, the one fluid passage used to operate the actuator is placed in fluid communication with the interior of the tubular string in which the tool is interconnected. 
     These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of a representative embodiment of the invention hereinbelow and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic partially cross-sectional view of a method embodying principles of the present invention; 
     FIGS. 2A-V are quarter-sectional views of successive axial sections of an early formation evaluation tool which may be utilized in the method of FIG. 1; and 
     FIG. 3 is an elevational developed view of a J-slot member of the tool of FIGS. 2A-V. 
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in FIG. 1 is a method  10  which embodies principles of the present invention. In the following description of the method  10  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., without departing from the principles of the present invention. 
     In the method  10 , a formation testing system  12  is interconnected in a tubular string  14 , such as a drill string, and is positioned in a wellbore  16 . As depicted in FIG. 1, the formation testing system  12  is utilized as a part of the drill string  14  during drilling operations. Preferably, after a formation  18  of interest has been intersected by the wellbore  16 , drilling is momentarily halted while the formation testing system  12  is used to evaluate characteristics of the formation. However, it is to be clearly understood that principles of the present invention may be utilized in other methods, for example, after drilling operations have been completed, or wherein the formation testing system  12  is conveyed into the wellbore  16  as a part of another type of tubular string, etc. 
     The formation testing system  12  is similar in many respects to the formation testing system described in U.S. Pat. No. 5,791,414, the disclosure of which is incorporated herein by this reference. However, the present applicant has devised unique manners of adding fluid sampling capability to the formation testing system described in that patent, so that formation fluid samples may be collected in the system. Of course, principles of the present invention may be incorporated into other types of downhole systems, and it is not necessary for the present invention to be used in conjunction with the formation testing system of U.S. Pat. No. 5,791,414. 
     The formation testing system  12  used in the method  10  as depicted in FIG. 1 includes a valve actuating section, apparatus or tool  20  and a fluid sampling section, apparatus or tool  22 . Preferably, the valve actuating section  20  is similar to, or the same as, the valve actuating section described in the incorporated patent. The valve actuating section  20  includes a valve portion operative to selectively permit and prevent flow through a main axial flow passage of the drill string  14  in response to altering a fluid pressure differential between the interior and exterior of the drill string. Such fluid pressure differential changes are preferably caused by changing a rate of circulation of fluid through the drill string  14 . When the valve portion closes, the interior of the drill string  14  above the valve portion is placed in fluid communication with an internal inflation fluid passage of the fluid sampling section  22 , so that fluid pressure in the drill string above the valve portion may be used to inflate inflatable packers  24  of the fluid sampling section. The packers  24  sealingly engage the wellbore  16 , thereby isolating a portion of the formation  18  between the packers from the remainder of the wellbore. Fluid from the formation  18  may then be drawn into the fluid sampling section  22  by manipulating the drill string  14 , as described in further detail in the incorporated patent. 
     Referring additionally now to FIGS. 2A-V, a fluid sampling apparatus  30  embodying principles of the present invention is representatively illustrated. The apparatus  30  may be used for the fluid sampling section  22  of the fluid sampling system  12  in the method  10 , or the apparatus may be used in other systems or methods. 
     The apparatus  30  is similar in many respects to the fluid sampling section described in the incorporated patent. For example, fluid pressure applied to an internal fluid passage  32  of the apparatus  30  may be used to inflate axially spaced apart packers  34  carried on the apparatus. After the packers  34  have been sealingly engaged with a wellbore, such as the wellbore  16  in the method  10 , a pump assembly  36 , including a piston  38  and check valves  40 , may be operated by stroking the piston axially, such as by raising and lowering the drill string  14 , which is interconnected to the piston via an upper connector  42 . Such operation of the pump assembly  36  may be used to pump fluid from a formation into a crossover  44  positioned between the packers  34 , and thence into another internal fluid passage  46 . One or more instruments  48  in communication with the passage  46  may then be used to measure/record pressure drawdown and buildup, temperature, resistivity, etc., or other parameters useful in characterizing the formation and/or the fluid contained in the formation, etc. 
     However, in one unique aspect of the present invention, fluid pressure in the passage  32  may also be used in operating one or more actuators  50  of corresponding respective one or more fluid samplers  52 . The apparatus  30  representatively includes six circumferentially distributed and equally spaced apart samplers  52 . Only two of the samplers  52 , including one of the corresponding actuators  50 , are visible in FIG. 2J, but there may be any number of the samplers. 
     The samplers  52  are preferably, although not necessarily, of the type described in U.S. application Ser. No. 08/935,867, filed Sep. 23, 1997, the disclosure of which is incorporated herein by this reference. In the sampler described in that application, an actuator of the sampler includes a rupture disc which is broken to actuate the sampler to receive a fluid sample therein. The samplers  52  of the apparatus  30  depicted in FIG. 2J are somewhat modified from the sampler described in the incorporated application, however, in that their actuators  50  do not include the rupture disc. Instead, each actuator  50  is connected via an adapter  54  and conduit  56  to an internal fluid passage  58  of the apparatus  30 . For example, if there are six of the samplers  52  in the apparatus  30 , then there are correspondingly six of the adapters  54 , six of the conduits  56  and six of the passages  58 . Thus, when fluid pressure is applied to one of the passages  58 , the pressure is transmitted to the corresponding actuator  50 , which is thereby operated to cause the corresponding sampler  52  to receive a fluid sample therein. 
     As used herein, the term “sampler” is used to indicate a container in which a fluid sample may be retained, isolated from contamination, for retrieval and subsequent analysis. As used herein, the term “actuator”, when used in conjunction with a sampler, is used to indicate a mechanism or device of the sampler which is operated to cause the sampler to receive a fluid sample therein. It is to be clearly understood that principles of the present invention may be incorporated into apparatus which utilize samplers and actuators other than those described herein. 
     Fluid pressure is applied successively to the passages  58  by successively breaking corresponding respective frangible pressure barriers  60 . Only one of the pressure barriers  60  is shown in FIG. 2H, but it is to be understood that a pressure barrier is preferably associated with each of the passages  58  to initially isolate each of the passages from the passage  32 . Note that the passages  58  and pressure barriers  60  are circumferentially distributed and equally spaced apart in the apparatus  30 . 
     As used herein, the term “pressure barrier” is used to indicate any means of selectively permitting and preventing fluid pressure communication therethrough. For example, the pressure barrier  60  may be a pierceable disc or rupture disc as depicted in FIG. 2H, or the pressure barrier may be a valve, etc. 
     The pressure barriers  60  are opened to fluid pressure communication therethrough by successively piercing them with a penetrator or piercing member  62  attached to a ring  64 . The ring  64  is rotatably attached to a piston assembly  66 . A circular clip  70  axially retains the ring  64  relative to the piston assembly  66  while permitting rotation of the ring relative to the piston assembly. 
     Note that the passage  32  extends at least partially through the piston assembly  66  and acts on an upwardly facing differential area of the piston assembly. Fluid pressure in the passage  32  biases the piston assembly  66  axially downward against an upwardly biasing force exerted by a compression spring  68 . Thus, when a downwardly directed force on the piston assembly  66  (due to fluid pressure in the passage  32 ) exceeds the upwardly biasing force exerted on the piston assembly by the spring  68 , the piston assembly displaces downward, thereby displacing the penetrator  62  toward one of the barriers  60  with which the penetrator is axially and circumferentially aligned. 
     A pin  72  is attached to the ring  64  and extends inwardly therefrom. The pin  72  is received in a J-slot profile  74  formed externally on a generally annular-shaped internal portion  76  of an intermediate housing member  78  of an overall outer housing assembly  80 . The J-slot profile  74  extends circumferentially about the annular portion  76  and is continuous. 
     Referring additionally now to FIG. 3, a developed view of the J-slot profile  74  on the portion  76  is representatively illustrated with various positions of the pin  72  therein being shown in dashed lines. J-slot profiles such as the profile  74  are well known to those skilled in the art and, therefore, the manner in which the profile is used to incrementally rotate the ring  64  and thereby align the penetrator  62  with successive ones of the barriers  60  will be only briefly described herein. Those skilled in the art refer to such mechanisms as “ratchet” mechanisms, in which one member is displaced incrementally relative to another member of the mechanism. However, it is to be clearly understood that other types of ratchet mechanisms, and other displacement devices and mechanisms, may be utilized in the apparatus  30 , without departing from the principles of the present invention. 
     The J-slot profile  74  is depicted in FIG. 3 as if it were “unrolled”, that is, from a two-dimensional perspective, wherein the direction to the right in FIG. 3 is the downward direction as viewed in FIG.  2 H. Thus, when the pin  72  displaces downward due to the piston assembly  66  displacing downward in response to fluid pressure in the passage  32 , the pin correspondingly displaces to the right as viewed in FIG.  3 . For convenience, axially downwardly elongated portions  74   a  of the profile  74  have been numbered (1, 2, 3, 4, 5 and 6) adjacent the right-hand side of FIG. 3 to indicate the corresponding one of the pressure barriers  60  aligned with each of the portions  74   a.  The number  4  is repeated at the top and bottom of the figure, since the corresponding portion  74   a  is continuous between the top and bottom of the figure. 
     When the piston assembly  66  is in the position shown in FIGS. 2A-V, the pin  72  is upwardly disposed in the profile  74  in axially upwardly elongated portions  74   b  of the profile. When the piston assembly  66  is downwardly displaced (due to increased fluid pressure in the passage  32  overcoming the upwardly biasing force of the spring  68 ), the pin  72  displaces downwardly in the profile  74  (to the right in FIG. 3) and eventually enters one of the portions  74   a.  Of course, due to compression of the spring  68 , fluid pressure in the passage  32  sufficient to initiate downward displacement of the pin  72  in the profile  74  is thereafter increased further to displace the pin into one of the portions  74   a.  For example, approximately 800 psi in the passage  32  may be sufficient to initiate downward displacement of the pin  72  when it is at a position  72   b  as indicated in FIG. 3, and approximately 1,500 psi may be required to fully downwardly displace the pin to a position  72   a  as indicated in FIG.  3 . 
     Note that the pin  72  rotates when traversing from position  72   b  to position  72   a.  This is seen as an upward displacement of the pin  72  in FIG.  3 . Of course, by decreasing the pressure in the passage  32 , the pin  72  may be upwardly displaced in the profile  74  from a position  72   a  to a next adjacent position  72   b,  due to the spring  68  upwardly biasing the piston assembly  66 . Thus, it will be readily appreciated by one skilled in the art that the pin  72  may be sequentially and incrementally rotated with respect to the profile  74  by alternately increasing and decreasing the pressure in the passage  32 . In one embodiment of the apparatus  30 , fluid pressure in the passage  32  may be alternated between 1,000 and 1,500 psi to thereby incrementally rotate the pin  72  about the profile  74 . Other pressures may be utilized without departing from the principles of the present invention. A position  72   c  of the pin  72  is used when the apparatus  30  is initially assembled. 
     Referring again to FIG. 2H, the penetrator  62  is circumferentially offset relative to one of the barriers  60  when the piston assembly  66  is in its illustrated upwardly disposed position. When sufficient fluid pressure is applied to the passage  32  to downwardly displace the pin  72  into one of the portions  74   a,  the penetrator  62  will then be circumferentially and axially aligned with one of the barriers  60 , due to the fact that the profile  74  rotates the ring  64  as described above and each of the profile portions  74   a  is circumferentially aligned with one of the barriers. Downward displacement of the pin  72  to one of the positions  72   a  results in the penetrator  62  piercing one of the barriers  60  and thereby permitting fluid communication between the passage  32  and a corresponding one of the passages  58 . 
     Therefore, by alternately increasing and decreasing fluid pressure in the passage  32 , the penetrator  62  may be sequentially and incrementally aligned with successive ones of the barriers  60 , and each of the barriers may be opened by applying sufficient fluid pressure to the passage  32  when the penetrator is aligned with that barrier. Furthermore, since each barrier  60  is associated with a corresponding one of the passages  58  as described above, such altering of the fluid pressure in the passage  32  results in successive operation of the actuators  50  of the samplers  52 , thereby causing the samplers to successively receive fluid samples therein. 
     Referring specifically now to FIGS. 2I &amp; J, it may be seen that each sampler  52  has a conduit  82  providing fluid communication with the passage  46 . As described above, the passage  46  is the passage into which fluid is drawn from the formation when the pump assembly  36  is operated. Thus, when one of the samplers  52  is actuated, it receives fluid therein from the passage  46 , which passage preferably contains fluid pumped from a portion of a formation isolated between the packers  34  as described above. 
     Note that the passage  32  is also utilized for inflating the packers  34  as described above. In order to stabilize fluid pressure within the packers  34  after they have been inflated, the apparatus  30  includes a unique feature which isolates an internal fluid passage  84  leading to the packers from the passage  32  while fluid pressure in the passage  32  is alternately increased and decreased to actuate the samplers  52 . 
     Recall that the piston assembly  66  in one embodiment of the apparatus  30  begins to displace downwardly when fluid pressure in the passage  32  reaches approximately 800 psi. Referring specifically now to FIG. 2H, it may be seen that the passage  32  is initially in fluid communication with the passage  84 , that is, when the piston assembly  66  is in its upwardly disposed position. However, when fluid pressure in the passage  32  has been increased to approximately 1,000 psi, a seal  86  carried on the piston assembly  66  traverses an opening  88  formerly providing fluid communication between the passages  32 ,  84 . Thus, at approximately 1,000 psi (which pressure, in one embodiment of the apparatus  30 , is sufficient to inflate the packers  34  into sealing engagement with a wellbore), the passages  32 ,  84  are isolated from each other and that fluid pressure is “trapped” in the passage  84 , thereby maintaining inflation of the packers at a stable pressure. 
     When fluid pressure in the passage  32  is again decreased below approximately 1,000 psi, the seal  86  again traverses the opening  88  (albeit in an opposite direction) and thereby permits fluid communication between the passages  32 ,  84 . Thus, the packers  34  may be conveniently deflated when desired by merely decreasing fluid pressure in the passage  32 . 
     In order to fully appreciate the many benefits of the present invention, an exemplary operation of the apparatus  30  is described below. Operation of the apparatus  30  is described as if the apparatus were utilized for the fluid sampling section  22  in the method  10  depicted in FIG.  1 . However, it is to be clearly understood that the apparatus  30  may be otherwise utilized and operated, and that other apparatus may be constructed and other methods may be performed, without departing from the principles of the present invention. 
     The apparatus  30  is interconnected in the drill string  14  as the fluid sampling section  22  of the formation testing system  12 . The drill string  14  is conveyed into the wellbore  16  and drilling is commenced, for example, by rotating the drill string and circulating drilling mud therethrough. 
     When a formation of interest has been intersected, such as the formation  18 , drilling is ceased. The drill string  14  is raised or otherwise displaced to position the apparatus  30  opposite the formation  18 , so that inflation of the packers  34  will isolate a desired portion of the formation for analysis. 
     Fluid is circulated through the drill string  14  as described in the incorporated U.S. Pat. No. 5,791,414 to thereby close the valve portion of the valve actuating section  20  and provide fluid communication between the passage  32  of the apparatus  30  and the interior of the drill string above the valve portion. Fluid pressure applied to the drill string  14  at the surface may then be conveniently used to operate the apparatus  30  as described above. 
     Fluid pressure in the drill string  14  above the valve portion is increased to approximately 1,000 psi. This fluid pressure is transmitted to the passage  32  and results in inflation of the packers  34 , thereby sealingly engaging the packers with the wellbore  16  and isolating the desired portion of the formation  18  from the remainder of the wellbore. The 1,000 psi fluid pressure in the passage  32  also results in downward displacement of the piston assembly  66  and isolation of the passage  84  from the passage  32 . This traps the 1,000 psi in the packers  34 , maintains their inflation at a stable pressure and secures the apparatus  30  and drill string  14  therebelow relative to the wellbore  16 . 
     The drill string  14  above the apparatus  30  is manipulated by alternately raising and lowering it, thereby operating the pump assembly  36  of the apparatus. Fluid is pumped into the apparatus  30 , initially from the annular area radially between the apparatus and the wellbore and axially between the packers  34 , but eventually from the portion of the formation  18  isolated between the packers. In this manner, fluid is pumped from the formation  18 , through the crossover  44  of the apparatus  30  and into the passage  46 . The instruments  48  may be utilized to measure/record parameters such as fluid pressure, resistivity, etc. of the fluid in the passage  46 , internal and/or external to the apparatus  30 , etc. as described above and in the incorporated patent. 
     Fluid pressure in the passage  32  is then further increased to approximately 1,500 psi. This increase in fluid pressure further downwardly displaces the piston assembly  66 , thereby rotating the ring  64  and causing the penetrator  62  to become circumferentially and axially aligned with one of the barriers  60 . Such further downward displacement of the piston assembly  66  also causes the penetrator  62  to pierce the barrier with which it is aligned. 
     When the barrier  60  is pierced, fluid communication is permitted between the passage  32  and a corresponding one of the passages  58 . Fluid pressure in the passage  32  is thus communicated via the passage  58  to a corresponding one of the conduits  56  and to a corresponding one of the actuators  50 . Fluid pressure communicated to the actuator  50  causes a corresponding one of the samplers  52  to receive a fluid sample therein from the passage  46  via a corresponding one of the conduits  82 . 
     If it is desired to collect additional fluid samples from the same portion of the formation  18 , fluid pressure in the passage  32  may be decreased to approximately 1,000 psi and then increased again to approximately 1,500 psi. This causes the piston assembly  66  to displace upwardly and then downwardly, thereby rotating the ring  64 , aligning the penetrator  62  with the next successive barrier  60  and downwardly displacing the penetrator to pierce the barrier. Upon piercing of the barrier  60 , another fluid sample is collected in another corresponding one of the samplers  52  from the passage  46 . Between successive fluid sample collections, the drill string  14  above the apparatus  30  may be raised and lowered as desired to pump further fluid from the formation  18  into the passage  46 . 
     If it is desired to collect additional fluid samples from another portion of the formation  18 , or from another formation intersected by the wellbore  16 , the packers  34  may be deflated by decreasing fluid pressure in the passage  32  and the apparatus  30  may be repositioned in the wellbore. When fluid pressure in the passage  32  has been decreased below approximately 1,000 psi, fluid communication is again permitted between the passages  32 ,  84 . Fluid pressure in the packers  34  may then be bled off through the passage  32  to the drill string  14  above the valve portion of the valve actuating section  20 . The apparatus  30  is repositioned as desired and fluid pressure in the passage  32  is again increased to approximately 1,000 psi to inflate the packers  34 . The pump assembly  36  is operated to pump fluid from the formation into the passage  46  and fluid pressure in the passage  32  is again increased to approximately 1,500 psi to cause another of the samplers  52  to receive a fluid sample therein from the passage  46 . 
     Once the desired fluid samples are collected, fluid pressure in the passage  32  is relieved, thereby deflating the packers  34  as described above. The valve portion of the valve actuating section  20  is then opened as described in the incorporated patent and drilling may commence, or the apparatus  30  may be retrieved from the well for analysis of the fluid sample(s) contained therein. If, instead of retrieving the apparatus  30  from the well, further drilling is performed and another formation of interest or portion thereof is intersected by the wellbore  16 , the apparatus may again be operated to collect further fluid samples as described above. 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to these specific embodiments, and such changes are contemplated by the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.