Like reference symbols in the various drawings indicate like elements.
Systems and methods of producing fluids from a subterranean zone can include downhole fluid heaters in conjunction with artificial lift systems. One type of downhole fluid heater is a downhole steam generator that generates heated steam or steam and heated liquid. Although “steam” typically refers to vaporized water, a downhole steam generator can operate to heat and/or vaporize other liquids in addition to, or as an alternative to, water. Some examples of artificial lift systems include pumps, such as electric submersible, progressive cavity, and others, gas lift systems, and other devices that operate to move fluids. Supplying heated fluid from the downhole fluid heater(s) to a target formation such as, a hydrocarbon-bearing formation or reservoir can reduce the viscosity of oil and/or other fluids in the target formation. To accomplish this process of combining artificial lift systems with downhole fluid heaters, a downhole cooling system can be deployed for cooling the artificial lift system and other components of a completion system. In some instances, use of a single multipurpose completion assembly allows for cyclical steam injection and production without disturbing or removing the well bore completion assembly. Such multipurpose completion assemblies can include a downhole heated fluid generator, an artificial lift system, and a production assembly cooling system that circulates surface cooled well bore water during the steam injection process.
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A well head 117 may be disposed proximal to a ground surface 116. The well head 117 may be coupled to a casing 115 that extends a substantial portion of the length of the well bore 114 from about the ground surface 116 towards the subterranean zone 110 (e.g., hydrocarbon-containing reservoir). The subterranean zone 110 can include part of a formation, a formation, or multiple formations. In some instances, the casing 115 may terminate at or above the subterranean zone 110 leaving the well bore 114 un-cased through the subterranean zone 110 (i.e., open hole). In other instances, the casing 115 may extend through the subterranean zone and may include apertures formed prior to installation of the casing 115 or by downhole perforating to allow fluid communication between the interior of the well bore 114 and the subterranean zone. Some, all or none of the casing 115 may be affixed to the adjacent ground material with a cement jacket or the like. In some instances, the seal 122 or an associated device can grip and operate in supporting the downhole fluid heater 120. In other instances, an additional locating or pack-off device such as a liner hanger (not shown) can be provided to support the downhole fluid heater 120. In each instance, the downhole fluid heater 120 outputs heated fluid into the subterranean zone 110.
In the illustrated embodiment, well bore 114 is a substantially vertical well bore extending from ground surface 116 to subterranean zone 110. However, the systems and methods described herein can also be used with other well bore configurations (e.g., slanted well bores, horizontal well bores, multilateral well bores and other configurations).
The tubing string 112 can be an appropriate tubular completion member configured for transporting fluids. The tubing string 112 can be jointed tubing or coiled tubing or include portions of both. The tubing string 112 carries the seal 122 and includes at least two valves 125, 126 bracketing the packer seal (e.g., valve 125 provided on one side of seal 122 and valve 126 provided on the other side of seal). Valves 125, 126 provide and control fluid communication between a well bore annulus 128 and an interior region 130 of the tubing string 112. When open, valves 125, 126 allow communication of fluid between the annulus 128 and tubing string interior 130, and when closed valves 125, 126 substantially block communication of fluid between the annulus 128 and tubing string interior 130. In this embodiment, the valves 125, 126 are electrically operated valves controlled from the surface 116. In other embodiments, valves 125, 126 can include other types of closure mechanisms (e.g., apertures in the tubing string 112 opened/closed by sliding sleeves and other types of closure mechanisms). Additionally, in other embodiments, the valves 125, 126 can be controlled in a number of other different manners (e.g., as check valves, thermostatically, mechanically via linkage or manipulation of the string 112, hydraulically, and/or in another manner).
The downhole fluid lift system 118 is operable to lift fluids towards the ground surface 116. In the illustrated embodiment, the downhole fluid lift system is an electric submersible pump 118 mounted on the tubing string 112. The electric submersible pump 118 has a pump inlet 132 which draws fluids from the well bore annulus 128 uphole of the packer seal 120 and a pump outlet 134 which discharges fluids into the interior region 130 of the tubing string 112. Power and control lines associated with electric submersible pump 118 can be attached to an exterior surface of tubing string 112, communicated through the tubing string 112, or communicated in another manner. In some embodiments, downhole fluid lift systems are implemented using other mechanisms such as, for example, progressive cavity pumps and gas lift systems as described in more detail below.
The downhole fluid heater 120 is disposed in the well bore 114 below the seal 122. The downhole fluid heater 120 may be a device adapted to receive and heat a recovery fluid. In one instance, the recovery fluid includes water and may be heated to generate steam. The recovery fluid can include other different fluids, in addition to or in lieu of water, and the recovery fluid need not be heated to a vapor state (e.g. steam) of 100% quality, or even to produce vapor. The downhole fluid heater 120 includes inputs to receive the recovery fluid and other fluids (e.g., air, fuel such as natural gas, or both) and may have one of a number of configurations to deliver heated recovery fluids to the subterranean zone 110. The downhole fluid heater 120 may use fluids, such as air and natural gas, in a combustion or catalyzing process to heat the recovery fluid (e.g., heat water into steam) that is applied to the subterranean zone 110. In some circumstances, the subterranean zone 110 may include high viscosity fluids, such as, for example, heavy oil deposits. The downhole fluid heater 120 may supply steam or another heated recovery fluid to the subterranean zone 110, which may penetrate into the subterranean zone 110, for example, through fractures and/or other porosity in the subterranean zone 110. The application of a heated recovery fluid to the subterranean zone 110 tends to reduce the viscosity of the fluids in the subterranean zone 110 and facilitate recovery to the ground surface 116.
In this embodiment, the downhole fluid heater is a steam generator 120. Gas, water, and air lines 136, 138, 140 convey gas, water, and air to the steam generator 120. In certain embodiments, the supply lines 136, 138, 140 extend through seal 122. In the embodiment of
In operation, well bore 114 is drilled into subterranean zone 110, and well bore 114 can be cased as appropriate. After drilling is completed, tubing string 112, downhole fluid heater 120, downhole fluid lift system 118, and seal 122 can be installed in the well bore 114. The seal 122 is then actuated to extend radially to press against and substantially seal with the casing 115. The valves 126, 125 are initially closed.
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The downhole fluid heater 120 can be activated, thus heating recovery fluid (e.g., steam) in the well bore. Because the apertures 126 in the downhole production sleeve are closed, the heated fluid passes into the target subterranean zone 110. The heated fluid can reduce the viscosity of fluids already present in the target subterranean zone 110 by increasing the temperature of such fluids and/or by acting as a solvent.
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As the subterranean zone 110 further cools and fluid viscosity in the reservoir further increases, production, even using the downhole fluid lift system, can slow. At this point, system 100 can be reconfigured for injection by closing valves 125, 126, and by activating the downhole fluid lift system 118 (to circulate cooling water) and the downhole fluid heater 120 to repeat the cycle described above. Such systems and methods can increase operational efficiencies because a single completion assembly can be installed in a well bore and remain in place during both injection and production phases of a cyclic production process. This reduces the number of trips in and out of the whole that would otherwise be required for systems and methods based on the use of separate injection and production assemblies.
The concepts described above can be implemented in a variety of systems and/or system configurations. For example, other approaches can be used to cool the downhole fluid lift system. Similarly, other downhole fluid lift systems can be used.
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A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.