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

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.

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.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1illustrates an example well system for removing fluid from a subterranean zone. An articulated well bore430extends from surface414to subterranean zone415. In this embodiment, subterranean zone415comprises a coal seam, however subterranean zones in accordance with other embodiments may comprise other compositions, such as shale.

Articulated well bore430includes a substantially vertical portion432, a substantially horizontal portion434and a curved or radiused portion436interconnecting vertical and horizontal portions432and434. Horizontal portion434lies substantially in the horizontal plane of subterranean zone415. In particular embodiments, articulated well bore430may not include a horizontal portion, for example, if subterranean zone415is not horizontal. In such cases, articulated well bore430may include a portion substantially in the same plane as subterranean zone415. Articulated well bore430may be drilled using an articulated drill string. Articulated well bore430may be lined with a suitable casing438.

Articulated well bore430also includes an enlarged cavity420formed in substantially vertical portion432. In this embodiment, enlarged cavity420comprises a generally cylindrical shape; however, enlarged cavities in accordance with other embodiments may comprise other shapes. Enlarged cavity420may be formed using suitable underreaming techniques and equipment, as described in further detail below with respect toFIGS. 5-7. Articulated well bore430includes fluids450. Fluids450may comprise drilling fluid and/or drilling mud used in connection with drilling articulated well bore430, water, gas, for example methane gas released from subterranean zone415, or other liquids and/or gases. In the illustrated embodiment, methane gas452is released from subterranean zone415after articulated well bore430is drilled.

Enlarged cavity420acts as a chamber for the separation of gas and liquid since the cross-sectional area of enlarged cavity420is larger than the cross-sectional area of other portions of articulated well bore430. This allows gas452to flow through and up the articulated well bore430while 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 cavity420below a velocity at which the gas can entrain liquid, thus allowing for the separation of the gas and liquid at enlarged cavity420. This decrease in velocity results from the larger cross-sectional area of enlarged cavity420relative to the cross-sectional area of other portions of articulated well bore430through 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 unit440is disposed within articulated well bore430. In this embodiment, pumping unit440includes a bent sub section442and a pump inlet444disposed within enlarged cavity420. Pumping unit440is operable to drain liquid, entrained coal fines and other fluids from articulated well bore430. As discussed above, such liquid separates from the flow of gas452through articulated well bore430at enlarged cavity420. Bent sub section442of pumping unit440enables pump inlet444to be disposed within enlarged cavity420at a position that is horizontally offset from the flow of gas452through articulated well bore430at enlarged cavity420. In this embodiment, pump inlet444is horizontally offset from the longitudinal axis of vertical portion432of articulated well bore430. This position decreases the amount of gas452pumped through pump inlet444because gas452may bypass pump inlet444when it releases from subterranean zone430and flows through and up articulated well bore430where it may be flared, released or recovered. If pump inlet444was not horizontally offset from the flow of gas452through articulated well bore430at enlarged cavity420, gas452may flow into pump inlet444when it released from subterranean zone450. In that case the pump efficiency of the system would be reduced.

Thus, forming enlarged cavity420of articulated well bore430enables liquid of fluids450to separate out from the flow of gas452through the well bore. Enlarged cavity420also enables a user to position pump inlet444offset from the flow of gas452through articulated well bore430at enlarged cavity420. Thus, the fluids and entrained coal fines pumped from subterranean zone415through articulated well bore430will contain less gas, resulting in greater pump efficiency.

FIG. 2illustrates another example well system for removing fluid from a subterranean zone. An articulated well bore530extends from surface514to subterranean zone515. Articulated well bore530includes a substantially vertical portion532, a substantially horizontal portion534and a curved portion536interconnecting vertical and horizontal portions532and534. Articulated well bore530is lined with a suitable casing538. Articulated well bore530also includes an enlarged cavity520formed in substantially horizontal portion534.

Articulated well bore530includes fluids550. Fluids550may comprise drilling fluid and/or drilling mud used in connection with drilling articulated well bore530, water, gas, for example methane gas released from subterranean zone515, or other liquids and/or gases. In the illustrated embodiment, methane gas552is released from subterranean zone515after articulated well bore530is drilled. Enlarged cavity520acts as a chamber for the separation of gas and liquid much like enlarged cavity420ofFIG. 1discussed above.

A pumping unit540is disposed within articulated well bore530. In this embodiment, pumping unit .540includes a bent sub section542and a pump inlet544disposed within enlarged cavity520. Pumping unit540is operable to drain liquid, entrained coal fines and other fluid from articulated well bore530. As discussed above, such liquid separates from the flow of gas .552through articulated well bore530at enlarged cavity520. Bent sub section542of pumping unit540enables pump inlet544to be disposed within enlarged cavity520at a position that is vertically offset from the flow of gas552through articulated well bore530at enlarged cavity520. In this embodiment, pump inlet544is vertically offset from the longitudinal axis of horizontal portion534of articulated well bore530. This position decreases the amount of gas552pumped through pump inlet544because gas552may bypass pump inlet544when it releases from subterranean zone530and flows through and up articulated well bore530. If pump inlet544was not vertically offset from the flow of gas552through articulated well bore530at enlarged cavity520, gas552would likely flow into pump inlet544when it released from subterranean zone550. In that case the pump efficiency of the system would be reduced.

Enlarged cavity520also enables a user to position pump inlet544offset from the flow of gas552through articulated well bore530at enlarged cavity520. Thus, the fluids and entrained coal fines pumped from subterranean zone515through articulated well bore530will contain less gas, resulting in greater pump efficiency.

FIG. 3illustrates another example well system for removing fluid from a subterranean zone. An articulated well bore230extends from surface214to subterranean zone215. Articulated well bore230includes a substantially vertical portion232, a substantially horizontal portion234and a curved portion236interconnecting vertical and horizontal portions232and234.

Articulated well bore230includes an enlarged cavity220formed in curved portion236. Articulated well bore230includes fluids250. Fluids250may comprise drilling fluid and/or drilling mud used in connection with drilling articulated well bore230, water, gas, for example methane gas released from subterranean zone215, or other liquids and/or gases. In the illustrated embodiment, methane gas252is released from subterranean zone215after articulated well bore230is drilled. Enlarged cavity220acts as a chamber for the separation of gas and liquid much like enlarged cavity420ofFIG. 1discussed above.

A pumping unit240is disposed within articulated well bore230. Pumping unit240includes a pump inlet244disposed within enlarged cavity220. Pumping unit240is operable to drain liquid, entrained coal fines and other fluids from articulated well bore230. As discussed above, such liquid separates from the flow of gas252through articulated well bore230at enlarged cavity220. As illustrated, pump inlet244is offset from the flow of gas252through articulated well bore230at enlarged cavity220. This decreases the amount of gas252pumped through pump inlet244because gas252may bypass pump inlet244when it releases from subterranean zone230and flows through and up articulated well bore230.

Thus, forming enlarged cavity220of articulated well bore230enables liquids of fluids250to separate out from the flow of gas252through the well bore. Enlarged cavity220also enables a user to position pump inlet244offset from the flow of gas252through articulated well bore230at enlarged cavity220. Thus, the fluids and entrained coal fines pumped from subterranean zone215through articulated well bore230will contain less gas, resulting in greater pump efficiency.

FIG. 4illustrates another example well system for removing fluid from a subterranean zone. An articulated well bore130extends from surface114to subterranean zone115. Articulated well bore130includes a substantially vertical portion132, a substantially horizontal portion134, a curved portion136interconnecting vertical and horizontal portions132and134, and a branch sump137.

Articulated well bore130includes an enlarged cavity120. Enlarged cavity120acts a chamber for the separation of gas152and liquid153which are included in fluids released from subterranean zone115after articulated well bore130is drilled. This allows gas152to flow through and up the articulated well bore130while liquid153separates out from the gas and remains in enlarged cavity120and branch sump137for pumping. Branch sump137provides a collection area from which liquid153may be pumped.

A pumping unit140is disposed within articulated well bore130. Pumping unit140includes a pump inlet144disposed within branch sump137. Pumping unit140is operable to drain liquid153and entrained coal fines from articulated well bore130. As discussed above, such liquid153separates from the flow of gas152through articulated well bore130. Thus, forming enlarged cavity120of articulated well bore130enables liquid153to separate out from the flow of gas152through the well bore. Thus, the fluids and entrained coal fines pumped from subterranean zone115through articulated well bore130will contain less gas, resulting in greater pump efficiency.

As described above,FIGS. 1-4illustrate 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. 5illustrates an example underreamer610used to form an enlarged cavity, such as enlarged cavity420of FIG.1. Underreamer610includes two cutters614pivotally coupled to a housing612. Other underreamers which may be used to form enlarged cavity420may have one or more than two cutters614. In this embodiment, cutters614are coupled to housing612via pins615; however, other suitable methods may be used to provide pivotal or rotational movement of cutters614relative to housing612. Housing612is illustrated as being substantially vertically disposed within a well bore611; however, underreamer610may form an enlarged cavity while housing612is disposed in other positions as well. For example, underreamer610may form an enlarged cavity such as enlarged cavity520ofFIG. 2while in a substantially horizontal position.

Underreamer610includes an actuator616with a portion slidably positioned within a pressure cavity622of housing612. Actuator616includes a fluid passage621. Fluid passage621includes an outlet625which allows fluid to exit fluid passage621into pressure cavity622of housing612. Pressure cavity622includes an exit vent627which allows fluid to exit pressure cavity622into well bore611. In particular embodiments, exit vent627may be coupled to a vent hose in order to transport fluid exiting through exit vent627to the surface or to another location. Actuator616also includes an enlarged portion620which, in this embodiment, has a beveled portion624. 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. Actuator616also includes pressure grooves631.

Cutters614are illustrated in a retracted position, nesting around actuator616. Cutters614may have a length of approximately two to three feet; however the length of cutters614may be different in other embodiments. Cutters614are illustrated as having angled ends; however, the ends of cutters614in other embodiments may not be angled or they may be curved, depending on the shape and configuration of enlarged portion620. Cutters614include side cutting surfaces654and end cutting surfaces656. Cutters614may 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 surfaces656. Cutting surfaces654and656and 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 surfaces654and656configurations may be machined or formed on cutters614to enhance the cutting characteristics of cutters614.

In operation, a pressurized fluid is passed through fluid passage621of actuator616. Such disposition may occur through a drill pipe connector connected to housing612. The pressurized fluid flows through fluid passage621and exits the fluid passage through outlet625into pressure cavity622. Inside pressure cavity622, the pressurized fluid exerts a first axial force640upon an enlarged portion637of actuator616. Enlarged portion637may be encircled by circular gaskets in order to prevent pressurized fluid from flowing around enlarged portion637. The exertion of first axial force640on enlarged portion637of actuator616causes movement of actuator616relative to housing612. Such movement causes beveled portion624of enlarged portion620to contact cutters614causing cutters614to rotate about pins615and extend radially outward relative to housing612. Through the extension of cutters614, underreamer610forms an enlarged cavity as cutting surfaces654and656of cutters614come into contact with the surfaces of well bore611.

Housing612may be rotated within well bore611as cutters614extend radially outward to aid in forming an enlarged cavity642. Rotation of housing612may be achieved using a drill string coupled to the drill pipe connector; however, other suitable methods of rotating housing612may be utilized. For example, a downhole motor in well bore611may be used to rotate housing612. In particular embodiments, both a downhole motor and a drill string may be used to rotate housing612. The drill string may also aid in stabilizing housing612in well bore611.

FIG. 6is a diagram illustrating underreamer610ofFIG. 5in a semi-extended position. InFIG. 6, cutters614are in a semi-extended position relative to housing612and have begun to form an enlarged cavity642. When first axial force640(illustrated in FIG.5) is applied and actuator616moves relative to housing612, enlarged portion637of actuator616will eventually reach an end644of pressure cavity622. At this point, enlarged portion620is proximate an end617of housing612. Cutters614are extended as illustrated and an angle646will be formed between them. In this embodiment, angle646is approximately sixty degrees, but angle646may be different in other embodiments depending on the angle of beveled portion624or the shape or configuration of enlarged portion620. As enlarged portion637of actuator616reaches end644of pressure cavity622, the fluid within pressure cavity622may exit pressure cavity622into well bore611through pressure grooves631. Fluid may also exit pressure cavity622through exit vent627. Other embodiments of the present invention may provide other ways for the pressurized fluid to exit pressure cavity622.

FIG. 7is a diagram illustrating underreamer610ofFIG. 6in an extended position. Once enough first axial force640has been exerted on enlarged portion637of actuator616for enlarged portion637to contact end644of pressure cavity622thereby extending cutters614to a semi-extended position as illustrated inFIG. 6, a second axial force648may be applied to underreamer610. Second axial force648may be applied by moving underreamer610relative to well bore611. 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 force648forces cutters614to rotate about pins615and further extend radially outward relative to housing612. The application of second axial force648may further extend cutters614to a position where they are approximately perpendicular to a longitudinal axis of housing612, as illustrated in FIG.7. Housing612may include a bevel or “stop” in order to prevent cutters614from rotating passed a particular position, such as an approximately perpendicular position to a longitudinal axis of housing612as illustrated in FIG.7.

As stated above, housing612may be rotated within well bore611when cutters614are extended radially outward to aid in forming enlarged cavity642. Underreamer610may also be raised and lowered within well bore611to further define and shape cavity642. It should be understood that a subterranean cavity having a shape other than the shape of cavity642may be formed with underreamer610.

FIG. 8is an isometric diagram illustrating an enlarged cavity660having a generally cylindrical shape which may be formed using underreamer610ofFIGS. 5-7. Enlarged cavity660may be formed by raising and/or lowering the underreamer in the well bore and by rotating the underreamer. Enlarged cavity660is also an example of cavity420of 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.