Abstract:
A method of performing a downhole well completion cleanup is provided. In a described embodiment, completion fluids from a first zone are flowed into a tubular string, and then the fluids are discharged into a second zone. An apparatus usable in the method is provided, in which a downhole pump is utilized to pump the fluids from one zone to the other. The pump may be operated in a variety of manners. The apparatus may also include fluid identification sensors and telemetry devices for monitoring the progress of the cleanup operation.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation-in-part of prior copending application Ser. No. 09/378,124, filed Aug. 19, 1999, the disclosure of which is incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a method and apparatus for performing a completion cleanup operation downhole. 
     Just prior to placing a well in production after a gravel packing operation or stimulation treatment therein, it is common practice to remove completion fluids from a hydrocarbon-bearing zone intersected by the well. In the usual situation, a substantial portion of the completion fluids in the zone are deposited there as a result of the gravel packing or stimulation treatment. If no gravel packing or stimulation treatments have been performed, then the completion fluids in the zone may be mud or other fluids introduced into the well during drilling or completion of the well. As used herein, the term “completion fluid” is used to indicate fluid which is introduced into a zone from a source other than the zone during drilling or completion of a well intersecting the zone. 
     Generally, the completion cleanup operation is accomplished by transporting an extensive amount of temporary production and fluid handling equipment to the well. This equipment may include temporary piping, manifolds, test heads, separators, line heaters, tanks, burner booms, etc. The temporary equipment is typically used because there is not yet any permanent production equipment installed at the well or the permanent production equipment is not designed to handle the cleanup operation. 
     The temporary equipment is rigged up on location and the well is flowed until all or most of the completion fluid has been removed from the hydrocarbon bearing zone. Any hydrocarbons produced in this operation may be burned off or otherwise disposed of, thereby creating safety and environmental problems. The completion fluids must also be disposed of, which is an additional environmental problem and adds to the expense of the operation. 
     From the foregoing, it can be seen that it would be quite desirable to provide an improved method of performing a completion cleanup operation. The improved method should not require that completion fluids and/or hydrocarbons be disposed of at the surface, and the method should be more economical, convenient to perform and safer than past cleanup operations. It is accordingly an object of the present invention to provide such an improved method, and an apparatus useful in performing the method. 
     SUMMARY OF THE INVENTION 
     In carrying out the principles of the present invention, in accordance with an embodiment thereof, a method is provided in which a completion cleanup operation is performed downhole. The method does not require an extensive amount of temporary equipment to be transported and installed at a well, does not require the burning of hydrocarbons at the surface, and does not require disposal at the surface of hydrocarbons and/or completion fluids. Apparatus which may be used in the method is also provided. 
     In one aspect of the present invention, a method is provided in which completion fluids are removed from a hydrocarbon-bearing producing zone and then injected into a disposal zone downhole. In this manner, no significant quantity of hydrocarbons or completion fluids are brought to the surface for disposal. The method may be performed conveniently and economically, with only a limited amount of equipment needed to perform the method. Additionally, the method is compatible with gravel packing, formation fracturing and other well completion operations. 
     In another aspect of the present invention, a method is provided in which fluid is pumped from a producing zone and into a disposal zone by a downhole pump. Various pumping methods may be utilized. For example, a hydraulic motor, which operates in response to fluid flowed therethrough, may be conveyed into the well by coiled tubing. The motor may be connected to a pump, so that when fluid is circulated through the coiled tubing, the pump pumps completion fluid from the producing zone and into the disposal zone. As another example, the downhole pump may be driven by an electric motor connected to a wireline or other electrical conductor. 
     In yet another aspect of the present invention, instead of pumping fluids from the producing zone to the disposal zone, the fluids are permitted to flow from the producing zone into a tubular string, and then the fluids are pumped from the tubular string into the disposal zone, for example, by a pump located at the surface. When the fluids are flowed into the tubular string, the fluids may be permitted to flow to the surface, where the fluids may be analyzed to determine whether the producing zone has been cleaned up. 
     In still another aspect of the present invention, an apparatus used in the method may include fluid sensors, including fluid identification sensors, and communication devices for transmitting fluid property information to the surface. In this manner, the fluids flowed from the producing formation may be analyzed downhole, without the need of bringing them to the surface. The communication devices may include telemetry devices, such as acoustic telemetry devices, mud pulse telemetry devices, electromagnetic telemetry devices, etc. 
     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 first well completion cleanup method embodying principles of the present invention; 
     FIG. 2 is an enlarged scale schematic cross-sectional view of an apparatus which may be used in the first method of FIG. 1; 
     FIG. 3 is a schematic partially cross-sectional view of an alternate configuration usable in the first method of FIG. 1; 
     FIG. 4 is a schematic partially cross-sectional view of another alternate configuration usable in the first method of FIG. 1; 
     FIG. 5 is a schematic partially cross-sectional view of another alternate configuration usable in the first method of FIG. 1; 
     FIG. 6 is a schematic partially cross-sectional view of a second well completion cleanup method embodying principles of the present invention; 
     FIG. 6A is an enlarged scale schematic cross-sectional view of an apparatus shown in FIG. 5; 
     FIG. 7 is a schematic partially cross-sectional view of a third well completion cleanup method embodying principles of the present invention; and 
     FIG. 8 is a schematic partially cross-sectional view of a fourth well completion cleanup method embodying principles of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in FIG. 1 is a completion cleanup 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. 
     The method  10  is depicted in FIG. 1 as being performed subsequent to a gravel packed completion, with gravel  12  having been placed about a well screen  14  according to conventional practices well known to those skilled in the art. However, it is to be clearly understood that the method  10  may be performed after other types of well completion operations, without departing from the principles of the present invention. 
     As representatively illustrated in FIG. 1, a well has been drilled with a wellbore  16  that intersects two zones  18 ,  20 . As used herein, the term “zone” is used to indicate a subterranean formation, or a portion thereof. Therefore, the zones  18 ,  20  may be portions of a single earth formation, or they may be located in separate formations. Note that a single zone may have hydrocarbon, as well as non-hydrocarbon, fluids therein, such as a zone in which a lower portion contains water and an upper portion contains oil. 
     In the method  10 , the upper zone  18  is a producing zone, that is, a hydrocarbon-bearing zone from which it is desired to produce fluids to the earth&#39;s surface. The lower zone  20  is a disposal zone, that is, a zone in which it is desired to dispose of completion fluids drained from the upper zone  18 . Of course, it is not necessary for the disposal zone  20  to be located below the producing zone  18 , but in the method  10  as depicted in FIG. 1, this configuration is convenient, since the disposal zone is intersected by the rathole  22  below a sump packer  24 . 
     The screen  14  is included in a production tubing string  26  installed in the well and stung into the sump packer  24 . The production tubing string  26  may also include another packer  28  above the screen  14 . Fluid flowing from the zone  18  into the wellbore  16  is, thus, contained between the packers  24 ,  28  prior to flowing into the production tubing string  26  through the screen  14 . Note that the well is preferably provided with protective casing  30 , but the method  10 , and other methods described herein, may be practiced in conjunction with an open hole completion, without departing from the principles of the present invention. 
     To pump completion fluids out of the producing zone  18  and into the disposal zone  20  prior to placing the well in production, a coiled tubing string  32  is lowered into the production tubing string  26 . The coiled tubing string  32  includes a pump apparatus  34 . However, it is to be understood that means of conveying the pump apparatus  34  other than coiled tubing may be utilized, without departing from the principles of the present invention. For example, segmented tubing may be used, or wireline could be used as described more fully below. 
     Upper and lower seals  36 ,  38  are also carried on the tubing string  32 . The upper seal  36  is preferably disposed about the pump apparatus  34 , and the lower seal  38  is preferably sealingly engaged within the sump packer  24 , or a packer bore receptacle attached thereto. The screen  14  is, thus, disposed between the seals  36 ,  38 , so that the pump apparatus  34  may draw fluid inwardly through the screen. If the well were not gravel packed, but had an opening through the production tubing string  26 , instead of the screen  14 , for receiving fluid from the zone  18 , the seals  36 ,  38  would preferably straddle the opening. 
     In one important aspect of the present invention, the pump apparatus  34  pumps completion fluid, which may comprise mud exclusively or as a portion thereof, from the upper zone  18  into the tubing string  32 , and then out of a lower end  39  of the tubing string and into the lower zone  20 . In this manner, no completion fluids or hydrocarbons are burned or otherwise disposed of at the surface. 
     Referring additionally now to FIG. 2, an enlarged cross-sectional view of the pump apparatus  34  is schematically illustrated. The pump apparatus  34  includes a pump  40 , an inlet passage  42  and a discharge passage  44 . The pump  40  draws fluid from the inlet passage  42 , which is in communication with an annular volume  45  between the production tubing  26  and the tubing string  32  below the seal  36 . The pump  40  pumps fluid into the discharge passage  44 , which is in communication with the interior of the tubing string  32  below the apparatus  34 . The discharged fluid eventually exits the lower end  39  of the tubing string  32  and flows into the lower zone  20  as described above. 
     The pump apparatus  34  may include a fluid property sensor  46  for detecting a property, such as resistivity, conductivity, pressure, temperature, etc., of the fluid being pumped by the pump  40 . The sensor  46  enables determination of, among other things, the point at which all or substantially all of the completion fluid has been pumped out of the upper zone  18 . The sensor  46  is depicted interconnected in the discharge passage  44 , but it could be otherwise positioned without departing from the principles of the present invention. 
     A communication device or transmitter  48  is connected to the sensor  46 . In this manner, indications of fluid properties sensed by the sensor  46  may be transmitted to a remote location, such as the earth&#39;s surface, for evaluation, monitoring, etc. For example, an operator at the earth&#39;s surface may monitor the fluid property indications and detect when all or substantially all of the completion fluid has been pumped out of the upper zone  18 . The operator may then stop the pumping operation, retrieve the tubing string  32  from the well and place the well in production. Alternatively, or in addition, the fluid property indications from the sensor  46  could be stored in a memory device for later retrieval and evaluation. 
     The communication device  48  may be any conventional type of transmitter known to those skilled in the art. For example, the communication device  48  may communicate with a remote location by acoustic telemetry, electromagnetic telemetry, mud pulse telemetry, etc. Additionally, the communication device  48  may communicate via one or more optional conductors  50 , shown in FIG. 2 in dashed lines, extending to a remote location. 
     The pump  40  is driven by a hydraulic motor  52  via a shaft  54 . An inlet passage  56  is in communication with the interior of the tubing string  32  above the apparatus  34 , and a discharge passage  58  is in communication with the annular volume  45  above the seal  36 . To operate the motor  52 , fluid is circulated through the tubing string  32 , through the inlet passage  56 , through the motor  52 , and through the discharge passage  58  into the annular volume  45  above the seal  36 . 
     Of course, other means of operating a motor to drive the pump  40  may be utilized, without departing from the principles of the present invention. For example, the motor  52  could be an electric motor connected to one or more conductors  60 . In that case, the seal  36  may not be needed to separate the fluid circulated to operate the motor  52  from the fluid pumped out of the zone  18 . 
     Additionally, other means of controlling the operation of the motor  52 , or at least operation of the pump  40 , may be used without departing from the principles of the present invention. For example, the sensor  46  may be interconnected to the motor  52  so that, when the sensor detects that all or substantially all of the completion fluid has been pumped out of the zone  18 , the motor stops automatically. 
     Furthermore, means other than the coiled tubing  32  may be used to convey a pump apparatus, such as the apparatus  34 , into the well. For example, as mentioned above, a wireline may be used to convey the apparatus  43 , in which case the motor  52  may be an electric motor connected to conductors  60  of the wireline and seal  36  would not be needed to separate fluid circulated through the tubing string  32  from fluid pumped from the zone  18 . FIG. 3 shows this alternate configuration for use in the method  10 , the pump apparatus being designated  34 a to indicate that it differs somewhat from the apparatus  34  described above. 
     Referring additionally now to FIGS. 4 and 5, alternate configurations of the tubing string  32  and production tubing  26  in the method  10  are representatively illustrated. In FIG. 4, the upper zone  18  has not been the subject of a gravel pack completion, and provision is made for closing off the production tubing  26  after the completion cleanup operation. Specifically, the lower end of the production tubing  26  is plugged by a plug  62 , and a sliding side door valve  64  selectively permits and prevents flow between the rathole  22  and the interior of the production tubing. During the completion cleanup operation, the valve  64  is open, permitting the pump apparatus  34  to pump completion fluid from the zone  18  to the rathole  22 . After the completion cleanup operation, the valve  64  may be closed to isolate the rathole  22  from the production tubing  26 . This configuration may be especially useful where the zone  18  is subjected to a stimulation operation, such as formation fracturing, prior to the completion cleanup operation. 
     In FIG. 5, the tubing string  32  includes a packer  68 , such as an inflatable packer, instead of the seal  38 . The packer  68  is set in the casing  30  below the production tubing  26  prior to pumping completion fluid out of the zone  18 . Additionally, FIG. 5 depicts the zones  18 ,  20  as portions of a single formation  66 . In this manner, completion fluid may be pumped from an upper zone  18  of the formation  66  and into a lower zone  20  of the formation. This may aid in recovery of hydrocarbons from the formation  66 , as in conventional water flood operations. 
     Referring additionally now to FIG. 6, another method  70  of performing a cleanup operation embodying principles of the present invention is representatively illustrated. The method  70  is an economical alternative for performing a cleanup operation in those cases in which a pump jack  72  will be used to produce the well. The pump jack  72  is used to pump completion fluid out of a hydrocarbon-bearing producing zone  74  and into a disposal zone  76  and then, after the cleanup operation, the pump jack is used to produce hydrocarbons from the producing zone. 
     In FIG. 6, the pump jack  72  is depicted connected by sucker rod  78  to a pump apparatus  80  sealingly disposed within a production tubing string  82 . The pump apparatus  80  is operated by the pump jack  72  to pump completion fluid out of the zone  74 , into the production tubing  82 , through the pump apparatus  80 , and out a lower end  84  of the production tubing and into the disposal zone  76 . An enlarged cross-sectional schematic view of the area encircled by dashed lines in FIG. 6 is shown in FIG.  6 A. 
     In FIG. 6A, it may be seen that the pump apparatus  80  includes a piston  86  connected to the sucker rod  78 . The pump jack  72  raises and lowers the sucker rod  78 , causing the piston  86  to reciprocate axially in the pump apparatus  80 . Valves  88 ,  90  are used to direct fluid displaced by the piston  86  to either the interior of the production tubing  82  below the apparatus  80 , or to the interior of the tubing above the apparatus. 
     When the piston  86  is displaced upwardly, fluid from the zone  74  is drawn into the production tubing  82  via openings  92 , and then into an inlet passage  94  of the pump apparatus  80 . A check valve  96  prevents the fluid from flowing back out of the inlet passage  94  when the piston  86  is displaced downwardly. 
     The fluid drawn into the pump apparatus  80  on the upward stroke of the piston  86  is retained in a cylinder  98  below the piston. When the piston  86  is displaced downwardly, this fluid is forced through a check valve  100  into the cylinder  98  above the piston. When the piston  86  again strokes upwardly, this fluid is forced either through the valve  88  or through the valve  90 , depending upon which valve is open. 
     If the valve  88  is open, the fluid is flowed through a discharge passage  102  when the piston  86  displaces upwardly. The discharge passage  102  extends through the piston  86  and is in communication with the interior of the production tubing  82  below the pump apparatus  80 . In this manner, the fluid is pumped through the lower end  84  of the production tubing  82  and outward into the disposal zone  76 . 
     A fluid property sensor  104  may be interconnected in the discharge passage  102  for sensing a property of the fluid pumped through the pump apparatus  80 . The sensor  104  may be similar to the sensor  46  described above, and the sensor  104  may be similarly connected to a communication device or transmitter (not shown in FIG. 6A) for communicating indications of fluid properties to a remote location. 
     If, instead of valve  88  being open, valve  90  is open lo when the piston  86  strokes upwardly, the fluid is discharged into the interior of the production tubing  82  above the apparatus  80 . The fluid is, thus, produced to the earth&#39;s surface through the production tubing  82  when the valve  90  is open. 
     Note that the valves  88 ,  90  may be otherwise configured, for example, as a combined three-way valve, etc., without departing from the principles of the present invention. Additionally, the valves  88 ,  90  may be interconnected to the fluid property sensor  104  so that, when all or substantially all of the completion fluid has been pumped out of the zone  74 , the valve  88  automatically closes and the valve  90  automatically opens. In this manner, the method  70  provides for automatic production from the zone  74  after the completion cleanup operation. 
     Referring additionally now to FIG. 7, another method  110  of performing a completion cleanup operation embodying principles of the present invention is representatively illustrated. In the method  110 , a downhole pump is not used to draw completion fluid from a hydrocarbon-bearing producing zone  112 . Instead, the completion fluid is permitted to flow into production tubing  114  from the zone  112  via a check valve  116 . This method  110  may be utilized where formation pressure in the zone  112  is sufficient to overcome hydrostatic pressure and force the fluid upward through the production tubing  114 . 
     When the completion fluid has flowed to the surface, or to another desired point, such as a subsea wellhead, a pump  118  is used to force the fluid back downwardly through the production tubing  114  and out through a check valve  120  into the rathole  122  below a sump packer  124 . From the rathole  122 , the fluid flows into a disposal zone (not shown in FIG. 7) as in methods described above. Thus, the method  110  permits use of a powerful surface pump, such as a rig pump, to dispose of the completion fluids in a downhole disposal zone. 
     A fluid property sensor  126  may be used to detect and monitor properties of fluid flowed through the check valve  116 , so that it may be determined when all or substantially all of the completion fluid has been removed from the zone  112 . The sensor  126  may be similar to the sensor  46  described above. Additionally, the sensor  126  may be connected to a communication device or transmitter  128  for transmitting fluid property indications from the sensor  126  to a remote location. 
     Alternatively, the properties or identity of the fluid flowed into the production tubing  114  may be physically checked at the earth&#39;s surface, for example, by taking a sample of the fluid, prior to using the pump  118  to pump the fluid back downwardly through the tubing. 
     The production tubing string  114  may include a valve  130 , such as a sliding side door valve, which may be opened to permit production therethrough when the completion cleanup operation is completed. The check valve  120  may be retrieved from the production tubing  114  and replaced with a plug (not shown) to close off the rathole  122  from the interior of the production tubing. Furthermore, the check valve  116 , sensor  126  and transmitter  128  may be retrieved from the production tubing  114  after the completion cleanup operation, for example, by initially installing the check valve, sensor and transmitter in a receptacle, such as a side pocket mandrel (not shown). 
     Referring additionally now to FIG. 8, another method  140  of performing a completion cleanup operation embodying principles of the present invention is representatively illustrated. In the method  140 , similar in many respects to the method  110  described above, a downhole pump is not used to draw completion fluid from a hydrocarbon-bearing producing zone  142 . Instead, the completion fluid is permitted to flow into production tubing  144  from the zone  142  and then into a tubing string  146 , such as a coiled tubing string, via a check valve  148 . As with the method  110 , the method  140  may be utilized where formation pressure in the zone  142  is sufficient to overcome hydrostatic pressure and force the fluid upward through the tubing string  146 . 
     The tubing string  146  is sealingly received in the production tubing  144  using seals  150 ,  152  carried externally on the tubing string. When positioned as shown in FIG. 8, the seals  150 ,  152  axially straddle one or more openings  154  permitting fluid communication through a sidewall of the production tubing  144 . Depending upon the well characteristics, the upper seal  150  on the coiled tubing string  146  and/or an upper packer  156  on the production tubing string  144  may not be needed in the method  140 . For example, the tubing string  146  may be sealingly received in the production tubing string  144  using only the seal  152  engaged with a conventional packer bore receptacle associated with a sump or production packer  158 . 
     The completion fluid flows into the tubing string  146  via the check valve  148  and then flows upwardly in the tubing string. When the completion fluid has flowed to the surface, or to another desired point, such as a subsea wellhead, a pump connected to the tubing string  146 , such as the pump  118  described above, is used to force the fluid back downwardly through the tubing string and out through a check valve  160  into the rathole  162  below the packer  158 . From the rathole  162 , the fluid flows into a disposal zone (not shown in FIG. 8) as in methods described above. Thus, the method  140  permits use of a powerful surface pump to dispose of the completion fluids in a downhole disposal zone. 
     A fluid property sensor  164  may be used to detect and monitor properties of fluid flowed through the check valve  148 , so that it may be determined when all or substantially all of the completion fluid has been removed from the zone  142 . The sensor  164  may be similar to the sensor  46  described above. Additionally, the sensor  164  may be connected to a communication device or transmitter  166  for transmitting fluid property indications from the sensor to a remote location. If the tubing string  146  is coiled tubing, then preferably the transmitter communicates with the remote location using one or more conductors, such as conductors  50  described above, or using acoustic or electromagnetic telemetry. 
     In addition to, or instead of, the sensor  164  and transmitter  166 , the tubing string  146  may include a fluid property sensor  168  to detect and monitor properties of fluid flowed through the lower check valve  160 . A communication device or transmitter  170  connected to the sensor  168  may be used to transmit fluid property indications to a remote location, as described above. The transmitter  170  may be a conventional mud pulse telemetry device, such as those generally used in MWD (Measurement While Drilling) systems, since fluid is being pumped outward through the tubing string  146  while the transmitter  170  is communicating the fluid property indications. 
     Alternatively, the properties or identity of the fluid flowed into the tubing string  146  may be physically checked at the earth&#39;s surface, prior to using the pump to pump the fluid back downwardly through the tubing string. This may be the preferred means of identifying the fluid flowed into the tubing string  146  when the tubing string is made up of segmented tubing. 
     After the completion cleanup operation is completed, the tubing string  146  may be retrieved from the well, the production tubing  144  may be plugged at its lower end, and the well may be placed in production. Thus, the method  140  as described above only requires that a coiled tubing rig be transported to the wellsite to perform the completion cleanup operation. If the tubing string  146  is made up of segmented tubing, the cleanup operation may only require the use of a workover rig. 
     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.