Patent Publication Number: US-6988548-B2

Title: Method and system for removing fluid from a subterranean zone using an enlarged cavity

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates generally to the recovery of subterranean deposits, and more particularly to a method and system for removing fluid from a subterranean zone using an enlarged cavity. 
   BACKGROUND OF THE INVENTION 
   Subterranean zones, such as coal seams, contain substantial quantities of entrained methane gas. Subterranean zones are also often associated with liquid, such as water, which must be drained from the zone in order to produce the methane. When removing such liquid, entrained coal fines and other fluids from the subterranean zone through pumping, methane gas may enter the pump inlet which reduces pump efficiency. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method and system for removing fluid from a subterranean zone using an enlarged cavity that substantially eliminates or reduces at least some of the disadvantages and problems associated with previous methods and systems. 
   In accordance with a particular embodiment of the present invention, a method for removing fluid from a subterranean zone includes drilling a well bore from a surface to the subterranean zone and forming an enlarged cavity in the well bore such that the enlarged cavity acts as a chamber to separate liquid from gas flowing from the subterranean zone through the well bore. The method includes positioning a pump inlet within the enlarged cavity and operating a pumping unit to produce the liquid through the pump inlet. 
   The well bore may comprise an articulated well bore. Positioning a pump inlet within the enlarged cavity may comprise positioning a pump inlet within the enlarged cavity such that the pump inlet is offset from the flow of gas through the well bore. Forming an enlarged cavity in the well bore may comprise forming an enlarged cavity in a substantially vertical portion of the articulated well bore. The pump inlet may be horizontally offset from a longitudinal axis of the substantially vertical portion of the articulated well bore. 
   In accordance with another embodiment, a system for removing fluid from a subterranean zone includes a well bore extending from a surface to the subterranean zone and an enlarged cavity formed in the well bore. The enlarged cavity is configured to act as a chamber to separate liquid from gas flowing from the subterranean zone through the well bore. The system includes a pumping unit having a pump inlet positioned within the enlarged cavity. The pumping unit is operable to produce the liquid through the pump inlet. 
   Technical advantages of particular embodiments of the present invention include forming an enlarged cavity of an articulated well bore that enables liquid to separate from gas in the flow of fluid from a subterranean zone through the well bore at the enlarged cavity. The enlarged cavity also enables a user to position a pump inlet offset from the flow of gas through the articulated well bore. Thus, fluids and entrained coal fines pumped from the subterranean zone through the articulated well bore will contain less gas, resulting in greater pump efficiency. 
   The enlarged cavity may be formed in a substantially horizontal portion or a substantially vertical portion of the articulated well bore. If the enlarged cavity is formed in a substantially horizontal portion of the articulated well bore, the pump inlet may be positioned within the enlarged cavity such that it is vertically offset from the longitudinal axis of the substantially horizontal portion. If the enlarged cavity is formed in a substantially vertical portion of the articulated well bore, the pump inlet may be positioned within the enlarged cavity such that it is horizontally offset from the longitudinal axis of the substantially vertical portion. Positioning the pump inlet in this manner allows gas of a subterranean zone to bypass the pump inlet when fluids and/or entrained coal fines are pumped through the articulated well bore. 

   
     Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some or none of the enumerated advantages. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of particular embodiments of the invention and their advantages, reference is now made to the following descriptions, taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  illustrates an example well system for removing fluid from a subterranean zone utilizing an enlarged cavity in a substantially vertical portion of an articulated well bore, in accordance with an embodiment of the present invention; 
       FIG. 2  illustrates an example well system for removing fluid from a subterranean zone utilizing an enlarged cavity in a substantially horizontal portion of an articulated well bore, in accordance with an embodiment of the present invention; 
       FIG. 3  illustrates an example well system for removing fluid from a subterranean zone utilizing an enlarged cavity in a curved portion of an articulated, well bore, in accordance with an embodiment of the present invention; 
       FIG. 4  illustrates an example well system for removing fluid from a subterranean zone utilizing an enlarged cavity and a branch sump of an articulated well bore, in accordance with an embodiment of the present invention; 
       FIG. 5  illustrates an example underreamer used to form an enlarged cavity, in accordance with an embodiment of the present invention; 
       FIG. 6  illustrates the underreamer of  FIG. 5  with cutters in a semi-extended position, in accordance with an embodiment of the present invention; 
       FIG. 7  illustrates the underreamer of  FIG. 5  with cutters in an extended position, in accordance with an embodiment of the present invention; and 
       FIG. 8  is an isometric diagram illustrating an enlarged cavity having a generally cylindrical shape, in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates an example well system for removing fluid from a subterranean zone. An articulated well bore  430  extends from surface  414  to subterranean zone  415 . In this embodiment, subterranean zone  415  comprises a coal seam, however subterranean zones in accordance with other embodiments may comprise other compositions, such as shale. 
   Articulated well bore  430  includes a substantially vertical portion  432 , a substantially horizontal portion  434  and a curved or radiused portion  436  interconnecting vertical and horizontal portions  432  and  434 . Horizontal portion  434  lies substantially in the horizontal plane of subterranean zone  415 . In particular embodiments, articulated well bore  430  may not include a horizontal portion, for example, if subterranean zone  415  is not horizontal. In such cases, articulated well bore  430  may include a portion substantially in the same plane as subterranean zone  415 . Articulated well bore  430  may be drilled using an articulated drill string. Articulated well bore  430  may be lined with a suitable casing  438 . 
   Articulated well bore  430  also includes an enlarged cavity  420  formed in substantially vertical portion  432 . In this embodiment, enlarged cavity  420  comprises a generally cylindrical shape; however, enlarged cavities in accordance with other embodiments may comprise other shapes. Enlarged cavity  420  may be formed using suitable underreaming techniques and equipment, as described in further detail below with respect to  FIGS. 5-7 . Articulated well bore  430  includes fluids  450 . Fluids  450  may comprise drilling fluid and/or drilling mud used in connection with drilling articulated well bore  430 , water, gas, for example methane gas released from subterranean zone  415 , or other liquids and/or gases. In the illustrated embodiment, methane gas  452  is released from subterranean zone  415  after articulated well bore  430  is drilled. 
   Enlarged cavity  420  acts as a chamber for the separation of gas and liquid since the cross-sectional area of enlarged cavity  420  is larger than the cross-sectional area of other portions of articulated well bore  430 . This allows gas  452  to flow through and up the articulated well bore  430  while liquid separates out from the gas and remains in the enlarged cavity for pumping. Such separation occurs because the velocity of the gas flowing up through the articulated well bore decreases at enlarged cavity  420  below a velocity at which the gas can entrain liquid, thus allowing for the separation of the gas and liquid at enlarged cavity  420 . This decrease in velocity results from the larger cross-sectional area of enlarged cavity  420  relative to the cross-sectional area of other portions of articulated well bore  430  through which the gas flows. An enlarged cavity having a larger cross-sectional area may lead to a greater reduction in velocity of the gas flowing up and through the well bore. 
   A pumping unit  440  is disposed within articulated well bore  430 . In this embodiment, pumping unit  440  includes a bent sub section  442  and a pump inlet  444  disposed within enlarged cavity  420 . Pumping unit  440  is operable to drain liquid, entrained coal fines and other fluids from articulated well bore  430 . As discussed above, such liquid separates from the flow of gas  452  through articulated well bore  430  at enlarged cavity  420 . Bent sub section  442  of pumping unit  440  enables pump inlet  444  to be disposed within enlarged cavity  420  at a position that is horizontally offset from the flow of gas  452  through articulated well bore  430  at enlarged cavity  420 . In this embodiment, pump inlet  444  is horizontally offset from the longitudinal axis of vertical portion  432  of articulated well bore  430 . This position decreases the amount of gas  452  pumped through pump inlet  444  because gas  452  may bypass pump inlet  444  when it releases from subterranean zone  430  and flows through and up articulated well bore  430  where it may be flared, released or recovered. If pump inlet  444  was not horizontally offset from the flow of gas  452  through articulated well bore  430  at enlarged cavity  420 , gas  452  may flow into pump inlet  444  when it released from subterranean zone  450 . In that case the pump efficiency of the system would be reduced. 
   Thus, forming enlarged cavity  420  of articulated well bore  430  enables liquid of fluids  450  to separate out from the flow of gas  452  through the well bore. Enlarged cavity  420  also enables a user to position pump inlet  444  offset from the flow of gas  452  through articulated well bore  430  at enlarged cavity  420 . Thus, the fluids and entrained coal fines pumped from subterranean zone  415  through articulated well bore  430  will contain less gas, resulting in greater pump efficiency. 
     FIG. 2  illustrates another example well system for removing fluid from a subterranean zone. An articulated well bore  530  extends from surface  514  to subterranean zone  515 . Articulated well bore  530  includes a substantially vertical portion  532 , a substantially horizontal portion  534  and a curved portion  536  interconnecting vertical and horizontal portions  532  and  534 . Articulated well bore  530  is lined with a suitable casing  538 . Articulated well bore  530  also includes an enlarged cavity  520  formed in substantially horizontal portion  534 . 
   Articulated well bore  530  includes fluids  550 . Fluids  550  may comprise drilling fluid and/or drilling mud used in connection with drilling articulated well bore  530 , water, gas, for example methane gas released from subterranean zone  515 , or other liquids and/or gases. In the illustrated embodiment, methane gas  552  is released from subterranean zone  515  after articulated well bore  530  is drilled. Enlarged cavity  520  acts as a chamber for the separation of gas and liquid much like enlarged cavity  420  of  FIG. 1  discussed above. 
   A pumping unit  540  is disposed within articulated well bore  530 . In this embodiment, pumping unit . 540  includes a bent sub section  542  and a pump inlet  544  disposed within enlarged cavity  520 . Pumping unit  540  is operable to drain liquid, entrained coal fines and other fluid from articulated well bore  530 . As discussed above, such liquid separates from the flow of gas . 552  through articulated well bore  530  at enlarged cavity  520 . Bent sub section  542  of pumping unit  540  enables pump inlet  544  to be disposed within enlarged cavity  520  at a position that is vertically offset from the flow of gas  552  through articulated well bore  530  at enlarged cavity  520 . In this embodiment, pump inlet  544  is vertically offset from the longitudinal axis of horizontal portion  534  of articulated well bore  530 . This position decreases the amount of gas  552  pumped through pump inlet  544  because gas  552  may bypass pump inlet  544  when it releases from subterranean zone  530  and flows through and up articulated well bore  530 . If pump inlet  544  was not vertically offset from the flow of gas  552  through articulated well bore  530  at enlarged cavity  520 , gas  552  would likely flow into pump inlet  544  when it released from subterranean zone  550 . In that case the pump efficiency of the system would be reduced. 
   Enlarged cavity  520  also enables a user to position pump inlet  544  offset from the flow of gas  552  through articulated well bore  530  at enlarged cavity  520 . Thus, the fluids and entrained coal fines pumped from subterranean zone  515  through articulated well bore  530  will contain less gas, resulting in greater pump efficiency. 
     FIG. 3  illustrates another example well system for removing fluid from a subterranean zone. An articulated well bore  230  extends from surface  214  to subterranean zone  215 . Articulated well bore  230  includes a substantially vertical portion  232 , a substantially horizontal portion  234  and a curved portion  236  interconnecting vertical and horizontal portions  232  and  234 . 
   Articulated well bore  230  includes an enlarged cavity  220  formed in curved portion  236 . Articulated well bore  230  includes fluids  250 . Fluids  250  may comprise drilling fluid and/or drilling mud used in connection with drilling articulated well bore  230 , water, gas, for example methane gas released from subterranean zone  215 , or other liquids and/or gases. In the illustrated embodiment, methane gas  252  is released from subterranean zone  215  after articulated well bore  230  is drilled. Enlarged cavity  220  acts as a chamber for the separation of gas and liquid much like enlarged cavity  420  of  FIG. 1  discussed above. 
   A pumping unit  240  is disposed within articulated well bore  230 . Pumping unit  240  includes a pump inlet  244  disposed within enlarged cavity  220 . Pumping unit  240  is operable to drain liquid, entrained coal fines and other fluids from articulated well bore  230 . As discussed above, such liquid separates from the flow of gas  252  through articulated well bore  230  at enlarged cavity  220 . As illustrated, pump inlet  244  is offset from the flow of gas  252  through articulated well bore  230  at enlarged cavity  220 . This decreases the amount of gas  252  pumped through pump inlet  244  because gas  252  may bypass pump inlet  244  when it releases from subterranean zone  230  and flows through and up articulated well bore  230 . 
   Thus, forming enlarged cavity  220  of articulated well bore  230  enables liquids of fluids  250  to separate out from the flow of gas  252  through the well bore. Enlarged cavity  220  also enables a user to position pump inlet  244  offset from the flow of gas  252  through articulated well bore  230  at enlarged cavity  220 . Thus, the fluids and entrained coal fines pumped from subterranean zone  215  through articulated well bore  230  will contain less gas, resulting in greater pump efficiency. 
     FIG. 4  illustrates another example well system for removing fluid from a subterranean zone. An articulated well bore  130  extends from surface  114  to subterranean zone  115 . Articulated well bore  130  includes a substantially vertical portion  132 , a substantially horizontal portion  134 , a curved portion  136  interconnecting vertical and horizontal portions  132  and  134 , and a branch sump  137 . 
   Articulated well bore  130  includes an enlarged cavity  120 . Enlarged cavity  120  acts a chamber for the separation of gas  152  and liquid  153  which are included in fluids released from subterranean zone  115  after articulated well bore  130  is drilled. This allows gas  152  to flow through and up the articulated well bore  130  while liquid  153  separates out from the gas and remains in enlarged cavity  120  and branch sump  137  for pumping. Branch sump  137  provides a collection area from which liquid  153  may be pumped. 
   A pumping unit  140  is disposed within articulated well bore  130 . Pumping unit  140  includes a pump inlet  144  disposed within branch sump  137 . Pumping unit  140  is operable to drain liquid  153  and entrained coal fines from articulated well bore  130 . As discussed above, such liquid  153  separates from the flow of gas  152  through articulated well bore  130 . Thus, forming enlarged cavity  120  of articulated well bore  130  enables liquid  153  to separate out from the flow of gas  152  through the well bore. Thus, the fluids and entrained coal fines pumped from subterranean zone  115  through articulated well bore  130  will contain less gas, resulting in greater pump efficiency. 
   As described above,  FIGS. 1-4  illustrate enlarged cavities formed in a substantially vertical portion, a substantially horizontal portion and a curved portion of an articulated well bore. It should be understood that embodiments of this invention may include an enlarged cavity formed in any portion of an articulated well bore, any portion of a substantially vertical well bore, any portion of a substantially horizontal well bore or any portion of any other well bore, such as a slant well bore. 
     FIG. 5  illustrates an example underreamer  610  used to form an enlarged cavity, such as enlarged cavity  420  of FIG.  1 . Underreamer  610  includes two cutters  614  pivotally coupled to a housing  612 . Other underreamers which may be used to form enlarged cavity  420  may have one or more than two cutters  614 . In this embodiment, cutters  614  are coupled to housing  612  via pins  615 ; however, other suitable methods may be used to provide pivotal or rotational movement of cutters  614  relative to housing  612 . Housing  612  is illustrated as being substantially vertically disposed within a well bore  611 ; however, underreamer  610  may form an enlarged cavity while housing  612  is disposed in other positions as well. For example, underreamer  610  may form an enlarged cavity such as enlarged cavity  520  of  FIG. 2  while in a substantially horizontal position. 
   Underreamer  610  includes an actuator  616  with a portion slidably positioned within a pressure cavity  622  of housing  612 . Actuator  616  includes a fluid passage  621 . Fluid passage  621  includes an outlet  625  which allows fluid to exit fluid passage  621  into pressure cavity  622  of housing  612 . Pressure cavity  622  includes an exit vent  627  which allows fluid to exit pressure cavity  622  into well bore  611 . In particular embodiments, exit vent  627  may be coupled to a vent hose in order to transport fluid exiting through exit vent  627  to the surface or to another location. Actuator  616  also includes an enlarged portion  620  which, in this embodiment, has a beveled portion  624 . However, other embodiments may include an actuator having an enlarged portion that comprises other angles, shapes or configurations, such as a cubical, spherical, conical or teardrop shape. Actuator  616  also includes pressure grooves  631 . 
   Cutters  614  are illustrated in a retracted position, nesting around actuator  616 . Cutters  614  may have a length of approximately two to three feet; however the length of cutters  614  may be different in other embodiments. Cutters  614  are illustrated as having angled ends; however, the ends of cutters  614  in other embodiments may not be angled or they may be curved, depending on the shape and configuration of enlarged portion  620 . Cutters  614  include side cutting surfaces  654  and end cutting surfaces  656 . Cutters  614  may also include tips which may be replaceable in particular embodiments as the tips get worn down during operation. In such cases, the tips may include end cutting surfaces  656 . Cutting surfaces  654  and  656  and the tips may be dressed with a variety of different cutting materials, including, but not limited to, polycrystalline diamonds, tungsten carbide inserts, crushed tungsten carbide, hard facing with tube barium, or other suitable cutting structures and materials, to accommodate a particular subsurface formation. Additionally, various cutting surfaces  654  and  656  configurations may be machined or formed on cutters  614  to enhance the cutting characteristics of cutters  614 . 
   In operation, a pressurized fluid is passed through fluid passage  621  of actuator  616 . Such disposition may occur through a drill pipe connector connected to housing  612 . The pressurized fluid flows through fluid passage  621  and exits the fluid passage through outlet  625  into pressure cavity  622 . Inside pressure cavity  622 , the pressurized fluid exerts a first axial force  640  upon an enlarged portion  637  of actuator  616 . Enlarged portion  637  may be encircled by circular gaskets in order to prevent pressurized fluid from flowing around enlarged portion  637 . The exertion of first axial force  640  on enlarged portion  637  of actuator  616  causes movement of actuator  616  relative to housing  612 . Such movement causes beveled portion  624  of enlarged portion  620  to contact cutters  614  causing cutters  614  to rotate about pins  615  and extend radially outward relative to housing  612 . Through the extension of cutters  614 , underreamer  610  forms an enlarged cavity as cutting surfaces  654  and  656  of cutters  614  come into contact with the surfaces of well bore  611 . 
   Housing  612  may be rotated within well bore  611  as cutters  614  extend radially outward to aid in forming an enlarged cavity  642 . Rotation of housing  612  may be achieved using a drill string coupled to the drill pipe connector; however, other suitable methods of rotating housing  612  may be utilized. For example, a downhole motor in well bore  611  may be used to rotate housing  612 . In particular embodiments, both a downhole motor and a drill string may be used to rotate housing  612 . The drill string may also aid in stabilizing housing  612  in well bore  611 . 
     FIG. 6  is a diagram illustrating underreamer  610  of  FIG. 5  in a semi-extended position. In  FIG. 6 , cutters  614  are in a semi-extended position relative to housing  612  and have begun to form an enlarged cavity  642 . When first axial force  640  (illustrated in FIG.  5 ) is applied and actuator  616  moves relative to housing  612 , enlarged portion  637  of actuator  616  will eventually reach an end  644  of pressure cavity  622 . At this point, enlarged portion  620  is proximate an end  617  of housing  612 . Cutters  614  are extended as illustrated and an angle  646  will be formed between them. In this embodiment, angle  646  is approximately sixty degrees, but angle  646  may be different in other embodiments depending on the angle of beveled portion  624  or the shape or configuration of enlarged portion  620 . As enlarged portion  637  of actuator  616  reaches end  644  of pressure cavity  622 , the fluid within pressure cavity  622  may exit pressure cavity  622  into well bore  611  through pressure grooves  631 . Fluid may also exit pressure cavity  622  through exit vent  627 . Other embodiments of the present invention may provide other ways for the pressurized fluid to exit pressure cavity  622 . 
     FIG. 7  is a diagram illustrating underreamer  610  of  FIG. 6  in an extended position. Once enough first axial force  640  has been exerted on enlarged portion  637  of actuator  616  for enlarged portion  637  to contact end  644  of pressure cavity  622  thereby extending cutters  614  to a semi-extended position as illustrated in  FIG. 6 , a second axial force  648  may be applied to underreamer  610 . Second axial force  648  may be applied by moving underreamer  610  relative to well bore  611 . Such movement may be accomplished by moving the drill string coupled to the drill pipe connector or by any other technique. The application of second axial force  648  forces cutters  614  to rotate about pins  615  and further extend radially outward relative to housing  612 . The application of second axial force  648  may further extend cutters  614  to a position where they are approximately perpendicular to a longitudinal axis of housing  612 , as illustrated in FIG.  7 . Housing  612  may include a bevel or “stop” in order to prevent cutters  614  from rotating passed a particular position, such as an approximately perpendicular position to a longitudinal axis of housing  612  as illustrated in FIG.  7 . 
   As stated above, housing  612  may be rotated within well bore  611  when cutters  614  are extended radially outward to aid in forming enlarged cavity  642 . Underreamer  610  may also be raised and lowered within well bore  611  to further define and shape cavity  642 . It should be understood that a subterranean cavity having a shape other than the shape of cavity  642  may be formed with underreamer  610 . 
     FIG. 8  is an isometric diagram illustrating an enlarged cavity  660  having a generally cylindrical shape which may be formed using underreamer  610  of  FIGS. 5-7 . Enlarged cavity  660  may be formed by raising and/or lowering the underreamer in the well bore and by rotating the underreamer. Enlarged cavity  660  is also an example of cavity  420  of FIG.  1 . 
   Although enlarged cavities having a generally cylindrical shape have been illustrated, it should be understood that an enlarged cavity having another shape may be used in accordance with particular embodiments of the present invention. Furthermore, an enlarged cavity may be formed by using an underreamer as described herein or by using other suitable techniques or methods, such as blasting or solution mining. 
   Although the present invention has been described in detail, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as falling within the scope of the appended claims.