Abstract:
A subsea production system for producing petroleum by artificial elevation, assisted by submersible centrifugal pumps (SCPs) upstream of the WCT and installed on the seabed, includes a pumping module having one of more SCPs, installed in series or in parallel, with an inclination of up to 85 degrees in relation to the vertical, the module being connectible to a flow base to permit the “bypass” of production and wherein the pumping module and the flow base may be linked to installation and recovery by cable. A production line is connected upstream to the pumping module upstream and another production line is connected downstream to the pumping module. A method of installing the system in a new wellhead is described, as well as a method for installing the system in an existing wellhead. The uses of the subsea production system for boosting multiphase flow, injection of water in an injector well and the transfer of oil between two points of collection are also described.

Description:
[0001]     The present invention relates to the field of subsea systems of artificial lift for petroleum production.  
       BACKGROUND OF THE INVENTION  
       [0002]     The use of centrifugal pumps in the oil producing wells permits, when feasible, to boost flow of the well. When these systems and equipment are utilized in wet completion well installations the costs of intervention for maintenance are relatively high, since it entails: i) interruption of production, ii) retrieval of the production column, pump and related accessories of the well and iii) the presence of a drill for maintenance. In many cases these items represent an obstacle not only for production profits but also for the production process.  
         [0003]     An alternative solution for the described problem, the object of Brazilian application PI 0400926-6 under the title “Subsea Pumping System Module System and Installation Method” describes installing the pumping unit in an auxiliary or dummy well, where it is easier to retrieve the pumping unit in case of maintenance. However, it is necessary to construct one auxiliary or dummy well, which represents higher production costs. Even the construction of a hollow pile may represent an increase in costs.  
         [0004]     U.S. Pat. No. 6,508,308 describes methods for production in stages based on a wellhead which includes pumps operated sequentially during the life of the well. In the modalities described therein, production mountings are used for production processes in which the production column is bifurcated to provide a pair of legs. One of the legs includes a first pump which may be actuated in a selective manner to facilitate fluid flow through one of the legs. A sliding glove and a flapper valve diverter are also provided to block production flow through one or the other leg. A second fluid pump is lowered into the production column in order to pump fluid after the first pump ceases to operate.  
         [0005]     The above-mentioned North American patent discloses the possibility of producing oil without removing the production column from the well. The described systems include a “Y”-shaped block assembly with two legs. The “Y”-shaped assembly is suspended at the lower end of a production column. One of the legs supports a first fluid pump. One possible arrangement incorporates a diverter to selectively isolate the flow through one of the legs in order to permit the selective use of the first fluid pump.  
         [0006]     The first pump, positioned within the production column, is operated until it ceases operation. A second pump is introduced into the production column with the assistance of coiled tubing. The fluid is thereafter lifted to the surface using the second pump, which prevents removing the production column from the well, and the subsequent replacement of the first pump. When the second pump ceases to operate it may be easily removed and replaced without incurring the loss of time and costs associated with removing the production column from the well.  
         [0007]     Despite the technological advances in the art, there continues to be a need for an subsea petroleum production system in which one or more Submersible Centrifugal Pumps (SCPs), of the type utilized in the interior of subsea petroleum production wells, are equipped with a motor and accessories installed at an inclination of up to 85 degrees in a SCP pumping module, which may be installed and recovered by cable, the assembly being linked to installation on a flow base, so that a pig (line-cleaning device) can be passed through the flow lines, and provided with a skirt for stabilization on the seabed. Such system of petroleum production method and installation is described and claimed in the instant application.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     In a broad sense, the present invention relates to a subsea production system which includes a subsea pumping module with submersible centrifugal pumps (SCPs) downstream of a water Christmas Tree (WCT) installed on the seabed. The module is connectible with a flow base structure which permits a production bypass, and wherein the module and the flow base may be linked to installation and recovery by a cable.  
         [0009]     The invention provides a subsea production system which is installed by an anchoring vessel or a cable installation vessel, having low daily costs.  
         [0010]     The present invention provides a subsea production system which integrates dedicated technology including centrifugal pumps operating in the horizontal position, underwater engineering and installation technology.  
         [0011]     The present invention also provides a subsea production system which is quickly tested and replaced, sufficing to provide an associated backup.  
         [0012]     The present invention provides a subsea production system which permits performing pre-installation functional tests of the integration of pump/motor/electrical systems on land and offshore prior to their installation underwater.  
         [0013]     The invention also provides a subsea production system which enables the reuse of cables, electrical connectors, flying leads, etc., should a pump be replaced.  
         [0014]     The invention also provides a subsea production system which simultaneously reducing production shutdown time (time spent awaiting a rig plus actual work time), as well as cutting costs.  
         [0015]     The invention also provides a subsea production system which operates on the seabed and is subjected to temperature changes, including extreme low temperatures.  
         [0016]     The invention provides a subsea production system which enables the launch of the structure with the production line.  
         [0017]     The invention provides a subsea production system which contemplates the relocation of the flow base and the pumping module.  
         [0018]     The invention equally provides a subsea production system which boosts multiphase flow.  
         [0019]     The invention also provides a subsea production system which enables the injection of water in an injection well to sustain pressure in the reservoir while the production well produces the desired petroleum.  
         [0020]     The invention provides a subsea production system which permits the transfer of petroleum between points of collection, for example, between two production platforms or between a platform and a vessel.  
         [0021]     The invention provides a subsea production system to be utilized in series thus enabling long distance transport of multiphase fluid.  
         [0022]     The invention also provides a method of installing the subsea production system.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0023]      FIG. 1  is a schematic of the pumping module installed on the flow base in accordance with the instant invention.  
         [0024]      FIG. 2  shows the connection of the flow base with the centrifugal pumps.  
         [0025]      FIGS. 3A, 3B  and  3 C illustrate centrifugal pumps arranged in different configurations.  FIG. 3A  depicts a pair of centrifugal pumps arranged in an “X” (i.e., in series).  FIG. 3B  shows two centrifugal pumps arranged in parallel.  FIG. 3C  illustrates two pairs of centrifugal pumps in an X (series).  
         [0026]      FIGS. 4A through 4E  show a method of installation of system X-SCP in a new wellhead installation.  FIGS. 4A through 4E  show the steps of the method.  
         [0027]      FIGS. 5A through 5D  show a method of installation of system X-SCP in an existing well installation with a bundle.  FIGS. 5A through 5D  show the steps of the installation method. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     As is described herein, the present invention comprises one or more SCPs, of the type utilized in petroleum production subsea wells. In this configuration, one or more arrangements of SCPs (pump, motor and accessories), mounted with an inclination of up to 85 degrees in relation to the vertical, in a structure designated a SCPs pumping module, are installable and recoverable by cable. The SCPs pumping module is installed on a flow base so as that a pig (line-cleaning device) can be passed through the flowlines, which possesses a ground stabilizing skirt which is directly supported on the seabed. The flow base may be installed alone or together with a flexible pipe.  
         [0029]     In accordance with the architecture of the invention, in the case of the removal of the SCPs pumping module, the system enables production to continue through an alternative method, for example, a gas lift.  
         [0030]     The present concept utilizes a standard manufactured equipment/components from suppliers. Furthermore, the pump, motor and accessories are also conventional, commercially available equipment.  
         [0031]     Underwater mechanical and electrical connectors, as well, interface for a remote operated vehicle (ROV) and are also readily available.  
         [0032]     One of the important aspects of the invention is the installation and retrieval by cable that utilizes the method “buoy and chains,” pioneered by PETROBRAS, which avoids the need for a rig in the procedures.  
         [0033]     The present invention will be described following the numbers attached drawings.  
         [0034]      FIG. 1  illustrates a schematic view of the SCPs pumping module installed on the flow base according to the instant invention.  
         [0035]     Although  FIG. 1  depicts an embodiment involving two SCPs, the concept of the instant invention also contemplates an embodiment having a single centrifugal pump. It is also evident that modules with an odd number of pumps are also encompassed within the scope of the instant invention, for example a module having three SCPs.  
         [0036]     In  FIG. 1  the subsea production system ( 100 ) of the invention includes a flow base ( 10 ), a pumping module ( 20 ) and a structure ( 13 ) of the flow base ( 10 ) positioned between the flow base ( 10 ) and the pumping module ( 20 ).  
         [0037]     The flow base ( 10 ) is provided with an inlet connection (hub or flange) ( 12 ) for receiving the production line ( 31 ) upstream of the subsea production system ( 100 ) and a production line ( 32 ) downstream of the subsea production system ( 100 ). Control valves ( 14 ) permit the directing of inlet and outlet flows as it is deemed necessary.  
         [0038]     The pumping module ( 20 ) includes one or more centrifugal pumps ( 21 ) arranged in series or parallel, inclined up to 85 degrees in relation to the vertical. The pumping module ( 20 ) also includes a hydraulic connector ( 22 ) for connecting the pumping module ( 20 ) to the flow base ( 10 ). A base structure ( 23 ) protects the centrifugal pumps ( 21 ) from external impacts. The base structure ( 23 ) is provided with apparatus ( 25 ) which is compatible with installation tools. A panel ( 24 ) provides the requisite electrical connections.  
         [0039]      FIG. 2  shows the connection of the flow base ( 10 ) with the centrifugal pumps ( 21 ). On the flow base ( 10 ) are depicted the connection ( 12 ) (hub or flange), the exit connection ( 15 ) (hub or flange) of the flow base ( 10 ) and the hub ( 16 ) of the flow base ( 10 ) for the SCPs pumping module ( 20 ).  
         [0040]     The hydraulic connector ( 22 ) connects the centrifugal pumps ( 21 ) to the flow base ( 10 ) through the hub ( 16 ).  
         [0041]      FIG. 3A  shows the subsea production system in a typical centrifugal pump ( 21 ) in the form of an “X” configuration, designated “configuration X-SCPs.” In this configuration the pumps are connected in series.  
         [0042]     One notes that in  FIGS. 3A, 3B  and  3 C, the flow in the centrifugal pumps ( 21 ) is ascendant in order to avoid problems caused by the presence of gas in the system. For this reason, the pumps are always placed in an inclination of up to 85 degrees from the vertical position.  
         [0043]      FIG. 3B  depicts a configuration of centrifugal pumps ( 21 ) arranged in parallel in which it is possible to obtain a boosted flow while AP is maintained constant.  
         [0044]      FIG. 3C  shows a configuration of centrifugal pumps ( 21 ) of two sets of pumps in series in which it is possible to obtain an increase in the pressure while flow is maintained constant.  
         [0045]      FIGS. 4A through 4E  depict a method of installation of the underwater subsea production system ( 100 ) of the invention in a new wellhead ( 50 ).  
         [0046]      FIG. 4A  shows the installation of a new wellhead ( 50 ) with a production unit ( 51 ). The production unit ( 51 ) is a platform or any other type of production unit. A pile ( 52 ) is fixed in the seabed for positioning of the flow base ( 10 ) and the subsea production system ( 100 ) itself. The use of a pile is a conventional technique for positioning equipment on the seabed.  
         [0047]      FIG. 4B  illustrates the installation of the SCP by a vessel ( 53 ) which may be either a cable installation vessel or an anchor vessel. The transportation of the flow base ( 10 ) may be accomplished by the vessel itself, by a raft or by a tug.  
         [0048]      FIG. 4C  shows the flow base ( 10 ) installed with the line ( 32 ) and “pull-in” accomplished in the production unit ( 51 ).  
         [0049]      FIG. 4D  shows the installation of the SCP pumping module ( 20 ) on the flow base ( 10 ). An advantage of the herein described invention is that the flow base ( 10 ) may be installed together with the flow line. Alternatively, the flow base ( 10 ) is installed first, followed by the installation of the flow line ( 32 ). A flow line ( 31 ) connects the flow base ( 10 ) to the wellhead ( 50 ).  
         [0050]      FIG. 4E  depicts the subsea production system ( 100 ) installed in the depths of the ocean.  
         [0051]      FIGS. 5A through 5D  illustrate the method for installing this system in an existing wellhead ( 50 ).  
         [0052]      FIG. 5A  depicts an existing wellhead ( 50 ) with a bundle ( 60 ) defined as a set of lines. The bundle ( 60 ) is composed of three flow lines, a production line ( 61 ), a service line ( 62 ) and a control line ( 63 ).  
         [0053]      FIG. 5B  illustrates a vessel ( 53 ) that collects the production line ( 61 ) while the lines ( 62 ) and ( 63 ) remain connected to the production unit ( 51 ). The line ( 61 ) is carried by the vessel ( 53 ).  
         [0054]     In the succeeding stage of the installation method, the position of the line ( 61 ) where the flow base ( 10 ) will be positioned is determined by calculation. Thereafter, as is shown in  FIG. 5C , the procedure of lowering the flow base ( 10 ) to the seabed is initiated.  
         [0055]      FIG. 5D  shows the completion of the flow base ( 10 ) installation.  
         [0056]     The installation of the SCPs pumping module ( 20 ) is accomplished according to the method shown in  FIG. 4D .  
         [0057]     In conclusion, it may be said that the instant invention represents an alternative, among others, as to the employment of SCPs in auxiliary wells and as to the use of multiphase pumps up to the approximated limit of 60% of gas fraction present in the multiphase flow.  
         [0058]     It is important to appreciate that the description of the methods of installation of the subsea production system ( 100 ) of the invention contemplates various alternative embodiments, all of which are encompassed within the scope of the instant invention.  
         [0059]     The following are some aspects of the invention which distinguish the advantages of the invention over the sate of the art.  
         [0060]     The architecture of the present invention, with its two independent arrangements, provides for a continuity of production with a sole arrangement yielding a flow of more than fifty percent of production flow.  
         [0061]     The architecture of the present invention allows the entire system to be trial tested on land with all of the available resources and at a lower cost.  
         [0062]     In the present architecture the installation of the flow base may be accomplished together with the production line.  
         [0063]     There is more availability of resources to accomplish cable installation than for rig installation vessel length of resource use: the installation of the cable.  
         [0064]     With respect to the advantages to the rotodynamic multiphase pump, such as the pump marketed under the FRAMO brand, the market leader in this area, has a project of developing a 45 bar pump. In the future pumps of 100 bar, 110 bar, 150 bar and so forth will be required. The project will certainly require new alterations and specifications. SCPs, arranged in a series, provide increments on the order of approximately 80 bar for each pump positioned in the hydraulic series, without the need for a new project and new specifications. Therefore, when the system requires 160 bar, two pumps may be installed in series and so on.  
         [0065]     As related to in the state of art the following advantages of the subsea production system ( 100 ), are stressed: 
        a. Installation by an anchoring vessel of low daily operational cost.     b. Absence of technological barriers, since the invention system includes the integration of dedicated components and state of art, e.g., centrifugal transfer pumps operating in the horizontal position, underwater engineering and installation technologies;     c. No requirement for specific resources, which implies less shutdown time waiting for pump replacement resources;     d. Reduction in shutdown time for retrieving the pumping system for maintenance;     e. Testing and rapid substitution provided an available backup system;     f. Possibility of performance of land based, pre-installation, functional tests of the integration of pump/motor/electrical systems and offshore before the positioning of the underwater system on the sea floor.     g. Reuse of cables, connectors, flying leads, etc., in the event of pump replacement.     h. The operation of the subsea system on the seabed, being subjected to thermal changes effected with extreme low temperatures, translates into a better cooling of the electric motor;     i. Possibility of launching the structure together with the production line;     j. Possibility of relocating the flow base ( 10 ) and the pumping module ( 20 ); and     k. Component assembly of motor/pump/seals may be accomplished at the factory under ideal environmental conditions.