Abstract:
The instant invention relates to a system for collecting and injecting water from a subterranean aquifer into hydrocarbon reservoirs, more specifically, the invention is directed to a system of water collection wells in aquifers and injector wells in oil reservoirs (petroleum) and one or more pumps. The invention finds application in production systems for hydrocarbons, where it is utilized for injecting water to maintain the pressure in a hydrocarbon reservoir (oil and gas), thereby enhancing oil recovery.

Description:
[0001]     This application claims priority to Brazilian Application No. PI0404603-0, filed Oct. 22, 2004, entitled “SISTEMA DE INJECÃO DE ÁGUA CAPTADA EM AQUIFERO SUBTERRÂNEO E POCOS INJETORES EM RESERVATÓRIO DE ÓLEO”, and incorporates the same herein by reference in its entirety.  
       TECHNICAL FIELD  
       [0002]     The present invention relates to a system for collecting and injecting water from a subterranean aquifer into hydrocarbon reservoirs, more specifically, the invention is directed to a system of water collection wells in subterranean aquifers and of injector wells in hydrocarbon (oil and gas) reservoirs, wherein one or more pumps may be utilized to improve injection rate. The invention finds application in hydrocarbon production systems, where water injection is utilized to maintain hydrocarbon (oil and gas) reservoir pressure, thereby enhancing oil recovery.  
       BACKGROUND OF THE INVENTION  
       [0003]     One of the principal methods of secondary recovery, known and employed in the art, especially in subsea petroleum systems, utilizes water injection to maintain the pressure in hydrocarbon producing reservoirs.  
         [0004]     Typically this water is collected and treated directly from the sea and/or from water produced jointly with the hydrocarbons.  
         [0005]     U.S. Pat. No. 4,234,047 (hereinafter “the &#39;047 Patent”) teaches the installation of a Submersible Centrifugal Pump (SCP) within a dummy well for injecting water into injector wells. The system described in the &#39;047 Patent has the following deficiencies. It requires the construction of a shallow well for installation of the pump. Furthermore, a water treatment plant is required to treat the water to be injected, which has been collected from the sea and/or produced jointly with the hydrocarbons.  
         [0006]     In Petrobras&#39; Brazilian Patent application PI 0400926-6 a method of installing a pump in a dummy well, in this case an oil production well, is also disclosed.  
         [0007]     The principal deficiencies in the current state of the art include the high cost of treating the collected water, as well as the reliability of the quality of the water being treated and injected into the well. Furthermore, the method presently utilized for collecting and injecting water results in the injected water having a temperature which approximates that of the low temperature water found at the ocean floor.  
         [0008]     For hydrocarbons, in general, and especially for heavy oils, it is highly desirable and advantageous that the water be injected at a temperature which is higher than that found at the ocean floor. Water, injected under these conditions, facilitates the dislodgement and scouring of the reservoir. Another difficulty in the current state of the art is the installation of a water injection pump.  
         [0009]     There exist some models of compact pumps that may be installed on the ocean floor in metal structure bases (skids) or may be integrated into the wellhead itself. However, utilizing submersible centrifugal pumps has certain advantages notably that this type of equipment is produced on a large scale and at a low cost. Furthermore, this type of equipment possesses a slender geometry which requires the drilling and construction of dummy wells for accommodating the equipment, as described in the patents above.  
         [0010]     The disadvantages in the state of art discussed above are remedied in the instant invention by an injection system which utilizes water collected from subterranean aquifers.  
         [0011]     More specifically, the present invention discloses a system of water collecting wells in aquifers and injector wells in oil (petroleum) reservoirs which provides a means of maintaining pressure in hydrocarbon reservoirs by injecting water, of higher quality (lower sulfite concentration) and at a higher temperature, into the reservoirs, thereby dispensing with the necessity of a water treatment plant and reducing the costs of installation and operation of stationary units in subterranean petroleum production fields.  
         [0012]     In this way, it is possible to maintain reservoir pressure using water having a higher quality and temperature than that presently achieved in the art, thereby increasing productivity and the oil recovery factor of the reservoir.  
         [0013]     Another application of the instant invention is in mature fields where there is no physical space available for the construction or enlargement of the existing water injection unit.  
       SUMMARY OF THE INVENTION  
       [0014]     The instant invention has the main objective of creating a system possessing an innovative concept and arrangement of wells to enable water collection from subterranean aquifers and the injection of that water into hydrocarbon producing wells for the purpose of maintaining pressure in those wells.  
         [0015]     The collection of water in subterranean aquifers is accomplished by using a system of water collecting wells. This collected water may be pressurized by means of a submarine pump and thereafter injected through injector wells, whose points of destination (targets) are located at the base of the oil (petroleum) reservoirs or in an active aquifer in the oil reservoir.  
         [0016]     The hydraulic connection for pumping between the collection well and the injector well may be accomplished in accordance with the following embodiments: 
        (1) at the seabed with underwater pipes linking at least one collection well with at least one injector well. In this case the pump may be installed at the seabed (the most basic embodiment), in a dummy well or on a metal structure. The pump may also be installed at the collection well itself, thereby reducing the necessary interfaces and underwater connectors,     (2) in the interior of a simple or multilateral well, with access to the collection zone and to the injection zone; and,     (3) at the exterior of a simple or multilateral well, with access to the collection zone and to the injection zone.        
 
         [0020]     In the first embodiment described above, the hydraulic interface occurs at the ocean floor through underwater pipes which link at least one collection well with at least one injector well and requires the construction of at least two independent wells: a first well (collection well) and a second well (injector well). This increases production costs and reduces the temperature of the water being injected, due to the substantial thermal exchange which occurs between the water and the sea water over the length of the submarine line which connects the wellheads of the wells (i.e., of the collection well and the injector well).  
         [0021]     The pumping unit maybe installed externally of the wells, thereby permitting it to be retracted and reinstalled by means of a cable from a low daily cost vessel.  
         [0022]     The solution herein described presents greater flexibility in the spacing between the point of collection and the point of injection. In this embodiment of the invention the design of the wellhead, collection column and injection column are conventional. Alternatively, the pumping unit may be installed at the collection well, utilizing a simplified and innovative design, thereby eliminating the need for a wet Christmas tree (WCT) installed at the collection well.  
         [0023]     In the second embodiment described above both the pump and the hydraulic connection between the collection and injector wells are located in the interior of a conventional or multilateral well which has access to the collection and injection zones. This arrangement eliminates the need for constructing two wells (for collecting and injecting) and maintains the injection water at a higher temperature by avoiding thermal exchange with sea water on the ocean floor, which is generally colder. In this case, with the pumping assembly being positioned in the interior of the well, maintenance will require the use of a rig, with its associated higher costs.  
         [0024]     In the third embodiment, the pump and the hydraulic connection, between the flows from the collection well and the injector well, are located externally to a conventional or multilateral well, thereby facilitating their being retrieved and re-installed via cable by a low daily cost vessel. There is a substantial reduction in costs with the construction of only one well with dual functions, i.e., collection and water injection, as opposed to constructing two wells. Furthermore, the temperature of the water being injected is higher because there will be no substantial thermal exchange with the water on the ocean floor, which is generally much colder. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  illustrates a basic embodiment of the invention wherein a conventional collection well is linked through submersible pipes to one or more injector wells, and a pump is installed externally between the collection well and the injector well on a metallic structure, a dummy well or other adequate means.  
         [0026]      FIG. 2  illustrates another embodiment of the invention wherein at least two wells (a collection well and an injector well) are externally linked. The pump is installed within the collection well, thereby avoiding the need for installing a wet Christmas tree (WCT)  
         [0027]      FIG. 3  illustrates another embodiment of the invention wherein the pump is installed within a multilateral well linking (communicating) the collection zone to the water injection zone.  
         [0028]      FIG. 4  illustrates another embodiment of the invention wherein a pump is installed externally from a multilateral well linking the collection zone to the water injection zone.  
         [0029]      FIG. 5  illustrates another embodiment of the invention wherein a pump is installed externally from a conventional well, linking the collection zone to the water injection zone.  
         [0030]      FIG. 6  illustrates another embodiment of the invention wherein a pump is installed within the interior of a conventional well, linking the collection zone to the water zone.  
         [0031]      FIG. 7  illustrates another embodiment of the invention wherein a pump is installed internally or externally of a multilateral well, permitting injection of the collected water at different locations within the injection zone. 
     
    
       [0032]     Summarizing:  
                                                                 Number               FIG.   of wells   Type of well   Pump location                                1   &gt;=2   Directional or Horizontal   External to the collection well       2   &gt;=2   Directional or Horizontal   Internal to the collection well       3   1   Multilateral   Internal to the well       4   1   Multilateral   External to the well       5   1   Directional or Horizontal   External to the well       6   1   Directional or Horizontal   Internal to the well       7   1   Multilateral   Internal or External                  
 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     In accordance with the invention, the specification and the claims of the instant application, the following terms are defined as follows:  
         [0034]      1 . Collection well  
         [0035]      2 . Injector well  
         [0036]      3 . Injection Pump  
         [0037]      4 . Directional or Horizontal (Conventional) well  
         [0038]      5 . Annular space  
         [0039]      6 . Multilateral well  
         [0040]      7 . Collection column  
         [0041]      8 . Injection column  
         [0042]      9 . Telescopic assembly (Tubing Seal receptacle (TSR))  
         [0043]      10 . Obturator (Tubing Packer Hanger)  
         [0044]      11 . Injection control element  
         [0045]      12 . Wellhead  
         [0046]      13 . Injection zone  
         [0047]      14 . Collection zone  
         [0048]      15 . Water collection line  
         [0049]      FIG. 1  is a general schematic view of an embodiment of the invention with a hydraulic connection positioned externally between the collection well  1  and one or more injector wells  2 . An injection pump  3  is installed externally to the two wells, either on a metallic structure or on a dummy well, coupled to the wellhead or alternatively secured by any other means. In this way the water collected from the collection well  1  is pressurized by the injection pump  3  and is injected into one or more of the injector wells  2 .  
         [0050]      FIG. 2  is a general schematic view of another embodiment of the invention wherein an injection pump  3  is installed internally in the collection well  1  and the hydraulic connection between the collection well  1  and the injector well  2  (not shown in the drawing) is external to those wells.  
         [0051]     In this simplified arrangement, there is no need to install a wet Christmas tree (WCT) in the collection well  1 . A collection column  7  is seated and positioned several hundred meters below the wellhead  12  by an obturator (tubing packer hanger)  10 .  
         [0052]     An injection pump  3 , encapsulated in a small section of mounting tubing, is installed between the tubing packer hanger  10  and the wellhead  12 . An injection control element  11 , such as a valve, is installed in a portion of the collection column  7 , below the tubing packer hanger  10 . The injection control element  11  may be operated remotely to blockade the collection well  1  in the event of an intervention. The injection control element  11  may be hydraulic or electric.  
         [0053]     In the event of a failure in the injection pump  3 , the pump may be retrieved without the necessity of retrieving the collection column  7 , since a telescopic assembly  9 , installed between the tubing packer hanger  10  and the injection pump  3 , facilitates the assembly and disassembly operation.  
         [0054]     Since safety concerns are less critical in the operation of a collection well  1 , the control of such a well may be accomplished by an injection control element  11 . This eliminates the need for installing a wet Christmas Tree (WCT) for this purpose, thereby reducing installation and maintenance costs. In this way, it is possible to connect the water collection line  15  directly to the wellhead  12 .  
         [0055]      FIG. 3  is a general schematic view of an embodiment of the invention wherein not only the injection pump  3  but also the hydraulic connection between the collection zone  14  and the injection zone  13 , are positioned within the interior of a multilateral well  6 . The collection column  7  is hydraulically linked to a suction orifice of the injection pump  3 . The discharge flow of the injection pump  3  is injected into the injection zone  13  through the injection column  8 .  
         [0056]      FIG. 4  is a schematic view of another embodiment of the invention wherein the hydraulic connection between the collection zone  14  and the injection zone  13  is located in the interior of a multilateral well  6  by means of an injection pump positioned externally of the multilateral well  6 .  
         [0057]     The existing water in the injection zone flows through the annular space  5  to the suction orifice of the injection pump  3  where it is pressurized and returns through the injection column  8  to the injection zone  13 .  
         [0058]      FIG. 5  illustrates an embodiment of the invention wherein an injection pump  3  is installed externally to a conventional well  4 , which interconnects (communicates) the collection zone  14  to the water injection zone  13 . The collected water flows through the annular space  5  to the suction orifice, where it is pressurized, thereafter returning through the injection column  8  to the injection zone  13 .  
         [0059]      FIG. 6  illustrates an embodiment of the invention wherein an injection pump  3  is installed in the injection column  8 , which itself is positioned in the interior of a conventional well  4 . The water collected in the collection zone  14  is pressurized by the injection pump  3  and flows through the injection column  8  until reaching the injection zone  13 .  
         [0060]      FIG. 7  illustrates an embodiment of the invention wherein a multilateral well  6  possesses an injection pump  3 . The injection pump  3  may be installed internally or externally (not shown in the drawing) to the multilateral well. In this embodiment of the invention, it is possible, with a single multilateral well  6 , to inject water into more than one injection zone  13 . In this arrangement, each injection zone  13  includes an injection control element, e.g., a type of valve. The collection of water may be done from one internal collection zone  14  to a multilateral well  6  or from another collection well (not shown in  FIG. 7 ) specified for this purpose.  
         [0061]     Although the present invention has been described herein according to its preferred embodiments, it should be obvious to one skilled in the art that various alterations and modifications are possible without departing from the scope of the instant invention, as defined by the claims appended hereto.