Abstract:
In selected aspects, the present invention provides methods and systems for recovering hydrocarbons from a reservoir involving gravity-dominated recovery processes, such as steam assisted gravity drainage (SAGD). Aspects of the invention involve the use of multilateral wells in staged production processes, so that alternative segments of wells may be used in alternative ways during a recovery process, for example repurposing sections of an injection well as a production well at a stage in a recovery process when there is surplus injection well infrastructure in place.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority of U.S. Provisional Patent Application No. 61/904,380, entitled “MULTIPURPOSING OF MULTILATERAL INFILL WELLS FOR BYPASS HYDROCARBON RECOVERY” filed Nov. 14, 2013, the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates to methods, systems and well configurations for in situ recovery of hydrocarbons from hydrocarbon deposits. 
       BACKGROUND 
       [0003]    Among the deeper, non-minable deposits of hydrocarbons throughout the world are extensive accumulations of viscous hydrocarbons. In some instances, the viscosity of these hydrocarbons, while elevated, is still sufficiently low to permit their flow or displacement without the need for extraordinary means, such as the introduction of heat or solvents. In other instances, such as in Canada&#39;s bitumen-containing oil sands, the hydrocarbon accumulations are so viscous as to be practically immobile at native reservoir conditions. As a result, external means, such as the introduction of heat or solvents, or both, are required to mobilize the resident bitumen and subsequently harvest it. 
         [0004]    A number of different techniques have been used to recover these hydrocarbons. These techniques include steam flood, (i.e., displacement), cyclic steam stimulation, steam assisted gravity drainage (SAGD), and in situ combustion, to name a few. Each of these techniques uses distinctive key mechanisms to produce hydrocarbons. There are for example a wide range of gravity-dominated recovery techniques, such as SAGD, including adjunct or related gravity-dominated techniques which are not confined to steam as the mobilizing fluid. An example of such a related technique is the steam/solvent process, one embodiment of which is the Solvent Aided Process (SAP). Other gravity-dominated in situ recovery processes may include, either individually or in combination, injection of solvents and solvent mixtures, non-condensing oxidizing gases, non-condensing non-oxidizing gases, or surfactants. 
         [0005]    Gravity-dominated techniques such as SAGD generally create and then take advantage of a highly efficient fluid density segregation, or gravity drainage, mechanism in the reservoir to produce oil. A traditional system which is a concomitant of the SAGD process is the SAGD well pair. It typically consists of two generally parallel horizontal wells, with the injector vertically offset from and above the producer. 
         [0006]    Aspects of SAGD are described in Canadian Patent No. 1,130,201 issued Aug. 24, 1982. Numerous other patents pertaining to aspects and variations of SAGD have been issued. Also, many technical papers have been published on this topic. The SAGD process, as embodied in the operation of a well pair, and as applied in an oil sand, typically involves first establishing communication between the upper and lower horizontal wells. There are well known techniques, both thermal and non-thermal, for establishing this inter-well communication. Subsequently, steam is injected into the overlying horizontal well on an ongoing basis. Due to density difference, the steam tends to rise and heat the oil sand, and thereby mobilizes the resident bitumen. The mobilized bitumen is denser than the steam, and tends to move downward towards the underlying horizontal well from which it is produced. By operating the injector and the producer under appropriately governed conditions, it is possible to use the density difference to counteract the tendency of more mobile fluids to channel or finger through the less mobile fluids and overwhelm the producing well. Thus, in traditional SAGD operations, each well in the well pair has a specific and distinctive role in ensuring that the efficiencies which can be achieved with a gravity-dominated process are realized. 
         [0007]    In a typical SAGD process, as adjacent SAGD steam chambers develop, ascend to the top of the reservoir and spread laterally, they will eventually merge. Under these circumstances, a group of merged chambers will function in certain respects as a hydraulic unit operating under a gravity-dominated recovery process. Once the adjacent chambers coalesce as a hydraulic unit, alternative approaches to recovery may be employed, as for example described in Canadian Patent No. 2,591,498. 
       SUMMARY 
       [0008]    In selected aspects, the present invention provides methods and systems for recovering additional hydrocarbons, or for recovering hydrocarbons more efficiently, from a reservoir which is to undergo, is undergoing, or has undergone a gravity-dominated recovery process. In selected embodiments, the invention makes use of the merger of mature SAGD chambers into a single hydraulic merged chamber, leaving a pattern of well pairs within which there is an excess of exchangeable steam injection capacity. That is, within mature chambers, steam injectivity is high and, with the advent of the merger, that injectivity is sufficient to provide the steam requirements of the merged plurality of chambers with fewer steam injection wells than are typically present in that plurality of well pairs. 
         [0009]    In aspects of the present invention, after merger of two or more adjacent steam chambers, one or more of the previously existing steam injectors may no longer be required to maintain a steam injection rate that will service the production capacity associated with the merged steam chamber. To take advantage of the excess injection capacity while addressing the need for infill wells to harvest otherwise by-passed oil in a gravity-dominated recovery process, the trajectory of a surplus injector is modified, or multiplied, via multilateral drilling such that a horizontal portion of the new multilateral well trajectory forms the wellbore of a multilateral infill well at an appropriate selected location, or over an appropriate selected locus, between adjacent patterns. Thus, a surplus horizontal injector is transformed into a horizontal producer by means of drilling and completion re-configuration, so that ultimately the original injection well is re-located and re-purposed as a production well. 
         [0010]    In various aspects, the invention provides methods and systems that may be employed following a period of operating adjacent horizontal well pairs under a gravity-dominated recovery process in a viscous hydrocarbon reservoir. The period of operation will generally have been sufficient to allow the formation of adjacent steam chambers associated with the adjacent well pairs and to allow their eventual hydraulic merger. Following the merger of the steam chambers, aspects of the invention involve the following steps. At least one of the injector wells in the group of merged chambers may be re-purposed by drilling out a new trajectory that branches off from some point along the existing injector well, so that its trajectory includes an appreciable horizontal length which is suitably located as an infill producer well. In this way, aspects of the invention involve the use of multilateral wells. The re-purposed well may be reconfigured so that it is capable of operating as an infill producer well. The re-configured well may then be operated as an infill producer well. 
         [0011]    In selected embodiments, the invention provides methods and systems for producing hydrocarbons from a subterranean reservoir which involve operating a first injector-producer well pair under a substantially gravity-dominated recovery process, to form a first mobilized fluid zone in the subterranean reservoir. A second injector-producer well pair is similarly operated under a substantially gravity-dominated recovery process, to form a second mobilized fluid zone in the subterranean reservoir. The first injector-producer well pair and the second injector-producer well pair together being adjacent well pairs, which are operated to form a bypassed hydrocarbon region between the adjacent well pairs, defined by a common mobilized fluid zone formed when the first mobilized fluid zone and the second mobilized fluid zone merge. A multilateral infill well may be provided in the bypassed hydrocarbon region, for example as an arm of a multilateral injector well of the first or second injector-producer well pair. The multilateral infill well and the adjacent well pairs may be operated to increase the mobility of hydrocarbons in the bypassed hydrocarbon region. The multilateral infill well and the adjacent well pairs may also be operated under a substantially gravity-dominated recovery process to enlarge the common mobilized fluid zone, and to produce mobilized hydrocarbons from the bypassed hydrocarbon region through the multilateral infill well. In aspects of the invention, the common mobilized fluid zone may for example be enlarged by injecting a mobilizing fluid through at least one active injection well of the first or second injector-producer well pair. 
         [0012]    Multilateral wells of the invention may be adapted to alternative uses. For example, in alternative embodiments, the multilateral injector well may function as an active injection well, or it may be repurposed so that it is not an active injection well. In selected embodiments, mobilizing fluid may be: injected through the multilateral injector well; circulated through the multilateral infill well arm of the multilateral injector well; diverted at a multilateral injector well junction to an injection arm of the multilateral injector well; and, injected into the common mobilized fluid zone through the injection arm of the multilateral injector well. 
         [0013]    In further selected embodiments, the multilateral injector may be repurposed so that it functions concurrently as an injector along one or more branches and a producer along one or more branches. In alternative embodiments, multiple infill wells are provided between adjacent well pairs, with one or more of the injector branches continuing to serve as injectors while the producer branches are produced concurrently as infill or multiple infill wells. 
         [0014]    In a further alternative embodiment, the injector may be redrilled and repurposed as a multilateral well such that it serves in a production function as a vent well for removal of gases from the reservoir. 
         [0015]    In a further alternative embodiment, the injector may be re-drilled and re-purposed such that it serves in a bitumen production function, or as a non-condensing gas vent well, in a zone or reservoir that is hydraulically isolated, either in part or in whole, from the reservoir in which it was originally drilled. In this way, an injector located in one reservoir may be re-drilled and re-purposed for use in another zone or reservoir. 
         [0016]    In various embodiments, the mobilizing fluid may for example include steam, and/or hot water and/or a light hydrocarbon, such as a C3 to C10 alkane, or mixtures thereof. 
         [0017]    Mobilized hydrocarbons may be produced from the multilateral infill well to assist in establishing fluid communication between the multilateral infill well and the common mobilized fluid zone. In selected embodiments, a bypass mobilizing fluid, such as steam or a light hydrocarbon (C3-C10 alkane), may be injected into the multilateral infill well to mobilize hydrocarbons in the bypassed hydrocarbon region. 
         [0018]    In selected embodiments, the gravity-dominated recovery process used in alternative aspects of the invention may be SAGD. The conformation of well trajectories may accordingly be in keeping with typical implementations of SAGD, with the multilateral infill well and the adjacent well pairs being substantially horizontal and having approximately parallel segments. The multilateral infill well and the adjacent well pairs, constituting a well group, may similarly be provided in a field pattern that is repeated longitudinally or laterally or both, to form a multiple of well groups in the field pattern. 
         [0019]    The foregoing description of the invention has generally been expressed in retrospective terms. That is, for simplicity, it has characterized embodiments in which SAGD operations, and eventual merger of the chambers, occurs first, after which the multilateral well is created as an offshoot of a surplus injector. An alternative sequence of operations can involve a prospective approach. This entails drilling the multilateral well at the outset, or at some earlier stage of operations, for example prior to merger of steam chambers, in anticipation of its eventual function, either exclusively or additionally, as an infill producer. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]    The present methods and systems disclosed herein will be described with reference to the following drawings, which are illustrative and not limiting: 
           [0021]      FIG. 1  shows a prior art well configuration for a gravity-dominated process, such as SAGD, that employs well pairs. Also shown are the associated chambers which are depicted as having merged. 
           [0022]      FIG. 2  depicts the same situation as  FIG. 1  but, in accordance with current industry practice, including infill production wells. 
           [0023]      FIG. 3  illustrates an embodiment of the method and system of the present invention. 
           [0024]      FIG. 4  illustrates an alternative embodiment. 
           [0025]      FIG. 5  depicts schematically wells that have been redrilled and repurposed as multilateral wells to permit concurrent injection and production, and to permit multilateral production branches which serve as multiple infill wells. 
           [0026]      FIG. 6  depicts schematically a well that has been re-drilled beginning at some selected location along the well trajectory. 
           [0027]      FIG. 7  is a sectional view of a partially completed multilateral well. 
           [0028]      FIG. 8  is a sectional view of the multilateral well of  FIG. 7 , further along in the completion process. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    In selected aspects, the present invention provides methods and systems for coordinating the advent of surplus injection capacity (well injectivity) which has evolved in the course of a gravity-dominated recovery process with the opportunity to activate one or more infill wells at that same stage of operation so as to enhance performance. 
         [0030]      FIG. 1  depicts schematically three adjacent merged chambers in a gravity-dominated recovery process employing horizontal well pairs. The typical embodiment of this configuration involves SAGD. In a SAGD operation, this situation would typically occur once the chambers have ascended to the top of the reservoir and have spread laterally, eventually merging at or near the top of the reservoir and forming a hydraulic unit with adjacent chambers. 
         [0031]      FIG. 2  shows this same configuration but with the inclusion of infill producers  8 . This configuration reflects the now common practice of activating infill producers which have been located within the wedge-like portion  7  of the reservoir whose hydrocarbons might otherwise be bypassed. Typically, in a thermal recovery process such as SAGD, the infill wells are located within a zone which has been mobilized to some degree so that they are capable of production while requiring little or no thermal treatment at their wellbores. 
         [0032]    After merger of the chambers, and the consequent formation of a single hydraulic entity among a group of adjacent well pairs, changes in pressure in one chamber are communicated to other chambers within the merged aggregate. This fact, combined with the high injectivity of the injectors—a reflection of their location within a high mobility medium—permits the following re-configuration and re-purposing of certain wells. 
         [0033]    Specifically, as illustrated in  FIG. 3  by way of example, the surplus well injectivity which occurs at this mature stage of operations affords the operator the option of discontinuing the use of some of the injection wells. In this illustration, injection at wells  1  and  5  are discontinued, while injection continues at well  3 . 
         [0034]    However, again referring to  FIG. 3 , inasmuch as this same stage of operations corresponds to the stage of operations where one would normally elect to activate infill wells, the surplus injectors  1  and  5 , rather than being suspended, are re-drilled along a new trajectory and are re-purposed for infill service. When referring to re-purposing of a well, we are indicating that the re-purposed well assumes an entirely different function or role from that of the original well, or alternatively retains some of the functions of the original well while including an enlarged functionality. 
         [0035]    There are many possible configurations involving injectors which are discontinued and then re-purposed as infill producers.  FIG. 4  presents one such alternative embodiment. 
         [0036]    It is also feasible to redrill and repurpose the original injectors so that they continue to function as injectors along one or more branches while also functioning as single or multiple infill wells along one or more other branches. This is illustrated in  FIG. 5  where, in this example, each injector is repurposed so that it possesses at least one infill production well branch, and so that instead of dedicating one injector within a group of merged chambers for injection purposes only, each injector may function concurrently as as both an injector and an infill producer. In the example presented in  FIG. 5 , there are multiple infill wells between adjacent well pairs. 
         [0037]    In  FIG. 6 , for simplicity, a single re-drill trajectory is shown. In practice, it is entirely feasible to drill multiple offshoots from the same original wellbore and to orient those offshoots along distinctive trajectories. These offshoot wells are often referred to as multi-lateral wells. 
         [0038]    In alternative embodiments, the multilateral well junction, multilateral infill well and parent injection well may be completed so that steam or an alternative injection fluid may be circulated within the infill well, prior to initiating infill production, with the injection fluid returning from the infill arm then diverted at the multilateral junction to the injection well arm of the multilateral well. In this way, initial heating of the infill well region may be accomplished with steam or alternative fluid circulation, in conjunction with the continued use of the injector well to introduce steam to the steam chamber. In similar fashion, alternative heavy oil well startup techniques may be applied to the multilateral injection well, for example involving the use of solvents as injection fluids or line heaters for mobilizing bitumen in the vicinity of the well bore. 
         [0039]    In alternative embodiments, multilateral wells may be provided with downhole control systems, such as chokes or valves that may be operated to selectively manage the production and injection of fluids using the multilateral well. In addition, sensors may be provided in the multilateral well, for example to monitor pressure, temperature, flow rate and fluid composition. 
         [0040]      FIGS. 7 and 8  illustrate aspects of completed multilateral wells, which involve deploying multiple pipes to form seals with inlet portion  63  of dual crossover  60  and liner  92  of lateral bore  90 . A completion of this kind may for example be deployed as follows. First, hollow deflector  110  may be run down main bore  22  and coupled to whipstock packer  98 . A hydraulic set liner hanger assembly  112  may then be introduced into main bore  22 . Inlet pipe string  126  may be coupled to an inlet portion of the dual crossover and pipe assembly  114  and pipe assembly  116  may be extended in a downhole direction. Pipe assembly  114  includes a third seal  118  coupled to a distal end of pipe  120 , and pipe assembly  116  includes seal  122  coupled to a distal end of pipe  124 . As illustrated, pipe  124  may be longer than pipe  120 , and seal  122  may include a larger outer diameter than seal  118 . 
         [0041]    Referring now to  FIG. 8 , as hydraulic set liner hanger assembly  112  is advanced through a main bore, a downhole end of the pipe assembly  114  is deflected by hollow diverter  110  into lateral bore  90  and seal  122  is received in polished bore receptacle  108  to provide a seal between liner  92  and pipe  124 . As hydraulic set liner hanger assembly  112  advances, seal  118  passes through hollow diverter  110  and is received in a polished bore receptacle (not shown) in dual crossover  60  to provide a seal between hydraulic set liner hanger assembly  56  and pipe  120 . Hydraulic set liner hanger assembly  112  may then be set in main bore. Tubing may then be deployed to the lateral bores of the completed multilateral well. 
         [0042]    Although various embodiments of the invention are disclosed herein, many adaptations and modifications may be made within the scope of the invention in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way. Numeric ranges are inclusive of the numbers defining the range. The word “comprising” is used herein as an open-ended term, substantially equivalent to the phrase “including, but not limited to”, and the word “comprises” has a corresponding meaning. As used herein, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a thing” includes more than one such thing. Citation of references herein is not an admission that such references are prior art to the present invention. Any priority document(s) and all publications, including but not limited to patents and patent applications, cited in this specification are incorporated herein by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein and as though fully set forth herein. The invention includes all embodiments and variations substantially as hereinbefore described and with reference to the examples and drawings.