Patent Publication Number: US-2012037376-A1

Title: System and Method For Well Clean-Up

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention is based on and claims the benefit of priority from U.S. Provisional Patent Application Ser. No. 61/150,831 of Yves Le Moign, entitled “ALTERNATIVE WELL CLEAN-UP SOLUTION,” filed on Feb. 9, 2009, the entire contents of the disclosure of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The invention generally relates to methods and systems for subsea well intervention, commissioning, extended well testing, and early production operations, and more particularly to a system and method for well clean-up and testing operations in subsea production. 
     DISCUSSION OF THE BACKGROUND 
     After the completion phase of subsea production wells, oil operators perform well clean-up and well test operations prior to beginning well production to determine the characteristics of the reservoir and prepare the well for the production phase. These operations typically last for a relatively short period of time (e.g., on order of a few days to 2 or 3 weeks). At times, such tests or production operations are carried out over longer or extended periods of time, either as required to better determine the characteristics of the reservoir, or simply to produce the well until alternative, permanent, production installations can be installed. 
     Clean-up and well test activities are typically carried out from a drilling rig, often the one that has been used to drill and/or complete the well, using a well test equipment set-up. Most of the time, the produced fluids, including gas and oil, are flared (e.g., burned), except where oil flaring is banned by law, in which case a barge typically is brought alongside the rig to store the produced oil. The gas produced in the process is however typically flared or, simply, vented. 
     When the subsea well is connected to a production line (or a flow line), some operators simply produce the well to the production platform or Floating Production Storage and Offloading (FPSO), often designated as the “Host,” and process the produced fluids with the production equipment. 
     When operators cannot or do not want to flow the well to the Host, they typically use a drilling rig plus additional equipment (e.g., test spread, well control equipment) to carry out such operations. However, this option can be very costly and also consumes precious rig time (e.g., typically 10 days or more per each well) that most operators would prefer to use for the drilling of additional wells. 
     In addition, when a rig is used, the produced fluids are treated and separated on the rig and, because the rig does not typically have sufficient or adequate storage facilities, the produced oil and gas are burned using a flaring system. Besides raising environmental, health and safety concerns, flaring introduces some limitations to such operations, because the capacity to flare large quantities of produced fluids is limited. 
     Some, seeking a cost-effective alternative to the use of drilling units to carry-out the above operations, have suggested the use of a relatively large monohull vessel equipped with a High Pressure tensioned riser (also referred to as a completion work-over riser, drill pipe riser, high pressure (HP) riser, or other terms known in the art) and test equipment similar to what is used on rigs. Such vessels, referred herein as “Testing Vessels,” are expected to be less costly than rigs, because they do not carry all the extra equipment and capacities required for the drilling of subsea wells, particularly in deep waters. 
     The same set of vessel and equipment could also be used to perform “through tubing” intervention operations, generally designated as “Light Well Intervention” (LWI). While such “Testing Vessels” may have the ability to perform LWI and well clean-up activities, they provide a solution that can still be rather costly, primarily because of the size of the vessel required to support such operations, and because of classification and other requirements placed on the vessel based on the well fluids returns and hydrocarbons processing activities on the vessel. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing disadvantages inherent in the known types of solutions present in the prior art, exemplary implementations of the present invention are directed to novel methods and systems utilizing an auxiliary barge, tanker or vessel (AV) in combination with a light well intervention (LWI) vessel, both being simultaneously and directly connected to a subsea well during operations. Advantageously, the novel methods and systems of the invention provide for cost effective, efficient, and environmentally friendly well clean-up, testing, production, and the like, operations, with many of the advantages of prior art system and methods, as well as several substantial additional benefits. Thus, the methods and systems of the present invention include many novel features, which are not anticipated, rendered obvious, suggested, or even implied by any of the prior art systems or methods, either alone or in any combination thereof. 
     According to an aspect of the present invention, there is provided a method and system utilizing an auxiliary barge, tanker or vessel (AV) in combination with a light well intervention (LWI) vessel. Advantageously, the auxiliary vessel (AV) can be used to take returns directly from a well, while the light well intervention (LWI) vessel performs other well intervention and testing operations, such as well control, in-well operations, handling and deployment of subsea equipment, including return lines used to flow the well to the auxiliary vessel (AV), and the like. 
     In one embodiment, there is provided a system for clean-up and subsea intervention operations in a subsea well or installation, which comprises a light well intervention vessel configured to deploy and connect a subsea well intervention package on a subsea well or installation, and configured to perform subsea intervention operations. The system also includes an auxiliary vessel directly coupled to the same subsea well or installation and configured to receive and treat returns from the subsea well. The light well intervention vessel and the auxiliary vessel can be connected substantially simultaneously to the subsea well or installation. 
     In another embodiment, there is provided a method for clean-up and subsea intervention operations in a subsea well or installation, which includes deploying and connecting a subsea well intervention package on a subsea well or installation with a light well intervention vessel, and performing at least one subsea intervention operation with the light well intervention vessel. The method also includes directly coupling an auxiliary vessel to the same subsea well or installation and receiving and treating returns from the subsea well with the auxiliary vessel. The method may also include substantially simultaneously connecting the light well intervention vessel and the auxiliary vessel to the subsea well or installation. 
     Although operations using an auxiliary vessel may have been carried out in the past, such operations were not carried out with an auxiliary vessel directly connected to a subsea well to process well returns. For example, in such operations, well returns were first sent to a surface platform, rig or installation, and from there to an auxiliary vessel. 
     Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrate a number of exemplary embodiments and implementations. The invention is also capable of other and different embodiments, and its several details can be modified in various respects, all without departing from the spirit and scope of the invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and aspects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description of the present invention is illustrated by way of example, and not by way of limitation, to the annexed pictorial illustrations, graphs, drawings, and appendices, in which like reference numerals refer to similar elements, and in which:. 
         FIG. 1  is used to illustrate an exemplary implementation of the well clean-up system on an auxiliary vessel (AV), in accordance with exemplary aspects of the present invention; 
         FIG. 2  is used to illustrate an exemplary auxiliary vessel (AV), including the exemplary well clean-up system of  FIG. 1 , in accordance with exemplary aspects of the present invention; and 
         FIGS. 3-12  are used to illustrate an exemplary well clean-up method, in accordance with exemplary aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments and aspects of the invention will now be described in detail with reference to the accompanying figures. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as “including,” “comprising,” “having,” “containing,” or “involving,” and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited. Further, whenever a composition, a group of elements or any other expression is preceded by the transitional phrase “comprising,” “including” or “containing,” it is understood that it is also contemplated the same composition, the group of elements or any other expression with transitional phrases “consisting essentially of,” “consisting,” or “selected from the group of consisting of,” preceding the recitation of the composition, the elements or any other expression. The term “system” may also be referred to herein as “apparatus.” 
     Whenever plural aspects of the invention are described herein, it is understood that we are also in possession of respective singular aspects and vice versa. Thus, if systems or methods are explicitly described, such description applies to a system or method. 
     The novel method and system described herein provide advantages over existing systems and methods. For example, the novel method and system are more economical, have greater operational flexibility, provide a significantly improved risk profile, and allow storing instead of burning of oil. 
     The present invention includes recognition that storing of well fluids can further allow operators to achieve greater testing flows, as is desirable, but hereinbefore unachievable, usually because of the difficulties faced trying to burn the large quantities of oil produced. Economically, the approach of the novel method and system has the benefit of a less costly system (e.g., less costly than employing rigs or even the more costly, larger “testing vessels”), and the additional benefit of recovering and not burning the oil (e.g., typically several tens of thousands of barrels are burned in a single operation). From an environmental point of view, such a novel approach avoids sizeable emissions, advantageously, which face increasing restrictions from governmental agencies, regulating agencies, and other regulatory bodies. In addition, the separation of the well testing operations from the other well activities, advantageously, reduces the overall level of risks of such combined operations. 
     Described herein are further details as to how well clean-up, testing, production, and similar, operations, can be performed by the novel system and method of the present invention, including a light well intervention (LWI) vessel employed with the assistance of a secondary auxiliary vessel (AV), as well as the novel combination of equipment packages, procedures, and similar items, employed for such operations. Such well flowing, testing and production capability need not be permanently associated with the light well intervention (LWI) vessel, advantageously, providing flexibility and the ability to revert when needed to a very cost-effective, stand alone, light well intervention (LWI) vessel configuration. 
     The light well intervention (LWI) vessel supports the installation of a well intervention package (WIP), which is employed to control a well, and also supports deployment of other subsea equipment, including coiled tubing, electric line and slick line services, and similar equipment and services, employed in connection with well testing operations, production operations, and similar operations. 
       FIG. 1  is used to illustrate an exemplary well clean-up system  100 , in accordance with exemplary aspects of the present invention.  FIG. 2  is used to illustrate an exemplary auxiliary vessel (AV)  200 , including the exemplary well clean-up system  100  of  FIG. 1 , in accordance with exemplary aspects of the present invention. 
     In  FIGS. 1-2  (and other FIGs., e.g.,  FIGS. 3-7 ), a return line  102  is provided and includes an upper, near vertical catenary riser section, which is suspended at the auxiliary vessel (AV)  200 , and a lower, compliant, flexible section attached to the well intervention package (WIP), itself installed over the well being produced. The return line  102  can include any combination of spoolable tubulars (e.g., such as a 3½″-4½″ coiled tubing made of steel or other suitable material), jointed tubulars (e.g., such as drill pipes) for the riser section, and can be made of any other suitable material or have any other suitable construction. For the lower section of the return line  102 , a flexible line that can be constructed of different materials and in different ways, fitted with buoyancy elements, and the like, can be employed. Such a flexible and compliant section at the lower end of the return line  102 , advantageously, facilitates the connection of the return line  102  to the well intervention package (WIP), provides marine compliance required to accommodate motions of the return line  102  relative to the well, motions of the light well intervention (LWI) vessel during installation, motions of the auxiliary vessel (AV)  200  during operations, and the like. The compliant shape given to the return line  102  can include any suitable shapes commonly employed in subsea operations to decouple surface vessel motions from bottom connections, such as a lazy wave shape, a steep wave shape, a lazy S shape, and the like. 
     The following example describes an exemplary application of the novel system and method, wherein the return line  102  is deployed by the light well intervention (LWI) vessel before being passed over (e.g., “cross hauled”) to the auxiliary vessel (AV)  200 . Advantageously, such an approach takes into account the economical benefits afforded by the use of the handling equipment already present on the light well intervention (LWI) vessel. However, other deployment procedures can be also employed, for example, including the return line  102  being deployed directly by a suitably equipped auxiliary vessel (AV)  200 , without the intervening step of the return line being initially deployed by the light well intervention (LWI) vessel, and then being passed to the auxiliary vessel (AV)  200 , and the like. 
     By way of example, the auxiliary vessel (AV)  200  can be a self-contained modified dynamically positioned (DP) tanker having suitable capacity to store the fluids produced during the well operations, e.g., 50,000 barrels (Bbls) of fluid. For example, the auxiliary vessel (AV)  200  can be configured as a 10,000 tons deadweight (DWT) tanker, having a 117 m centerline length, a 21 m beam width, approximately 50,000 bbls of storage capacity, and the like. However, a variety of other tankers and vessels can be employed to perform the novel methods and provide the novel systems of the present invention, as will be appreciated by those of ordinary skill in the relevant art(s). 
     Advantageously, the auxiliary vessel (AV)  200  carries the well test equipment and personnel, and includes facilities for the handling and support of the deployed return line  102 . The auxiliary vessel (AV)  200  further provides storage capacity for crude oil, other produced fluids, and the like. The auxiliary vessel (AV)  200  also allows for the export of stabilized crude oil. 
     Produced water can be treated to any applicable standard for oil in water content (e.g., less than 15 ppm) to allow environmentally safe disposal overboard or in properly configured facilities. In the exemplary application, the produced gases are flared off, cold vented, and the like. 
     In carrying out one embodiment of the present invention, the well flows into the return line  102  at the well intervention package (WIP) and from there to the auxiliary vessel (AV)  200 , where the hydrocarbons are processed. Upon reaching the auxiliary vessel (AV)  200 , the well fluids are handled and treated in a similar manner as in other production vessels and floating production facilities adapted for processing such produced fluids. 
     Typically, the well fluids flow from the return line  102  to the processing equipment via a choke manifold  104  functioning to control flowrate. The crude feed stream can be heated, e.g., by a steam generator  202 , coupled to a steam exchanger  106 , and then initially stabilized through a first stage separator  108  functioning for bulk water removal, bulk de-gassing, and similar operations. The first stage separator includes a high pressure (HP) gas flare  110 , which functions to bulk de-gas the crude feed stream. Further de-gassing and water removal can take place in a second stage separator  112  having a low pressure (LP) gas flare  114 . The processed crude then enters into a third stage separator  116  functioning to flash off any gas entrained in the feed, via a low pressure (LP) flare  114 , and the crude oil is finally stabilized. The stabilized crude from the third stage separator  116  is fed to a crude oil cooler  120 , which discharges the cooled oil to storage tank compartments  122  of the auxiliary vessel (AV)  200 . 
     Produced water from the separators  108 ,  112  and  116  can be directed to a light water treating unit (LWTU)  124 . Dispersed oil is removed by the light water treating unit (LWTU)  124  and the clean water stream is directed to a surge tank  126  for further de-gassing. The surge tank  126  is connected to the low pressure (LP) gas flare  128  and includes means  130  for sending treated water overboard. Such means can include a suitable pipe and associated piping. Accordingly, flash gas is removed in the surge tank  126  at near atmospheric pressure, and the clean water stream is disposed of overboard. The reject oil from the light water treating unit (LWTU)  124  and the skimmed oil from the surge tank  126  can be routed back to an inlet of the third stage separator  116  of the auxiliary vessel (AV), as needed. 
     Well clean-up fluids from the steam exchanger  106  are diverted through a surge tank  132  for temporary holding and for removing remaining flash gas (if any) from the well stream via the low pressure (LP) gas flare  114 . The clean-up fluids discharged from the surge tank  132  can be collected and stored in slop tanks  136  of the auxiliary vessel (AV)  200 . 
     The auxiliary vessel (AV)  200  can further include transfer pumps  204  for transferring fluids to the various system components, containers  206  for storing the various fluids, a basket  208  for holding system components, cabins  210 , a hang off  212  for the return line  102 , knock out (KO) drum pump  214  for the HP flare  110 , knock out drum pump  216  for the LP flare  114 , knock out drum  218  for the HP flare  110 , knock out drum  220  for the LP flare  114 , and flare boom  222 . Although  FIGS. 1-2  are used to illustrate the exemplary system and method, other equipment can also be employed to, for example, separate and handle solids, spent acid, other components of the well flow, and similar components of the well flow, as will be appreciated by those of ordinary skill in the relevant art(s). 
     Various systems, such as process control, emergency shutdown (ESD) and fire and gas systems can be selected and fitted to the auxiliary vessel (AV)  200 , for example, based on the application, overall system design, and any other relevant parameters or applications. Other systems can also be incorporated, as needed, such as an Emergency Quick Disconnect system (EQD) for allowing the auxiliary vessel (AV)  200  to close and disconnect the return line from the well intervention package (WIP) in case of loss of position, and other safety and communication systems employed on both the auxiliary vessel (AV)  200  and the light well intervention (LWI) vessel, and the like. Various types of production equipment are utilized on the auxiliary vessel (AV)  200 , which can include any suitable well test equipment used in standard or other well testing systems and methods, and the like. 
     Additional equipment can be used to process the crude oil for storage rather than to burn the crude oil. Testing equipment (e.g., testing equipment available from Schlumberger Technology Corporation or another Schlumberger entity) can be incorporated into the overall system, and other types of equipment can be employed to facilitate optimal and/or efficient equipment mobilization. In an exemplary embodiment, such equipment can be configured to handle flowrates on the order of 15,000 to 20,000 barrels of oil per day. By contrast, with conventional systems and methods, such flowrates would be very difficult, if not impossible, to achieve on a rig or vessel where burning of oil is employed. 
     In one aspect of the present invention, exemplary procedures for deploying the return line  102  and transferring the return line  102  to the auxiliary vessel (AV)  200  are described below and illustrated in  FIGS. 3-12 . In  FIGS. 3-12 , a transfer line can be deployed by a light well intervention (LWI) vessel  300 , and handed over to the auxiliary vessel (AV)  102 , once a well intervention package (WIP)  1002  has been deployed and tested. 
     In an alternative embodiment, a transfer line can be deployed by the auxiliary vessel (AV)  200  itself, before being connected to the well intervention package (WIP)  1002  by the light well intervention (LWI) vessel  300 . By employing such a compliant return line  102 , advantageously, the auxiliary vessel (AV)  200  can be positioned at a safe distance from the light well intervention (LWI) vessel  300  and at a chosen location in relation to a well  1004  and the light well intervention (LWI) vessel  300 . 
     In order to limit the handling and subsea operations of the light well intervention (LWI) vessel  300 , and considering that the light well intervention (LWI) vessel  300  is already equipped with a deployment spread for intervention operations, in an exemplary embodiment, the return line  102  can be deployed from the light well intervention (LWI) vessel  300 , before being handed over (e.g., “cross-hauled”) to the auxiliary vessel (AV)  200 , which can be a dynamically positioned (DP) tanker or a moored tanker, and then finally connected, subsea, to a return hub or port  1008  of the well intervention package (WIP)  1002 . 
     An outline of the exemplary operational sequence illustrated in  FIGS. 3-12 , will now be further described, as follows. 
     In  FIG. 3 , the light well intervention (LWI) vessel  300  is positioned away from the wellhead  1004 , after deployment and installation of the well intervention package (WIP)  1002  on a subsea tree  1006  of the well  1004 . The first end of a flexible jumper of the return line  102  is deployed over an aligner and through a moonpool of the light well intervention (LWI) vessel  300 . Buoyancy modules are attached at moonpool level, while lowering the flexible jumper of the return line  102 . In an alternative embodiment, the flexible jumper of the return line  102  can be deployed over a side or end of the light well intervention (LWI) vessel  300 . Once the second end of the flexible jumper of the return line  102  reaches deck level, the second end is hung-off, wherein a first extremity of a rigid pipe of the return line  102  is brought over the aligner, and connected to the flexible jumper of the return line  102 . 
     In  FIGS. 4-5 , a rigid line  404  connected to an auxiliary crane hook  304  of a main crane  306  of the light well intervention (LWI) vessel  300  is sent to working depth, and a remotely operated vehicle (ROV)  402  connects the auxiliary crane hook  304  to the first end of the flexible line  102 . The crane hook  304  is paid in to initiate a lazy wave shape on the flexible line  102  and provide additional seabed clearance. A second end of the rigid line  404  is lowered a predetermined distance (e.g., approximately 30 m) below the hull of the light well intervention (LWI) vessel  300 , and the crane hook  304  is lowered subsea with pick up rigging and cross-hauled to the second end of the rigid line  404 . The rigid line  404  is transferred to the main crane  306  portside of the light well intervention (LWI) vessel  300 . 
     In  FIGS. 6-9 , the auxiliary vessel (AV)  200  moves in and stabilizes itself approximately 30 m portside of the light well intervention (LWI) vessel  300 , for example, using dynamic positioning (DP, e.g., a fan beam) as a primary DP reference or mooring with cables, lines or anchors. The auxiliary vessel (AV)  200  lowers a wire  702  of a pulling winch  704  in the water and the ROV  402  of the LWI vessel swims to connect a recovery hook  706  of the pulling winch  704  to the second end of the rigid line  404 . The load is transferred from the main crane  306  of the light well intervention (LWI) vessel  300  to the winch  704  of the auxiliary vessel (AV)  200 , and the ROV  402  disconnects the main crane  306  from the winch  704  of the auxiliary vessel (AV)  200 . The line  702  is pulled onto the hang-off point  212  of the auxiliary vessel (AV)  200  and secured. 
     In  FIGS. 10-12 , the light well intervention (LWI) vessel  300  moves over to a location of the wellhead  1004 , and the auxiliary vessel (AV)  200  follows in relative dynamic positioning (DP) mode (e.g., in a fan beam mode). The light well intervention (LWI) vessel  300  lands the connector  302  onto a return hub or port  1008  of the well intervention package (WIP)  1002  and disconnects the rigging line  702 . The light well intervention (LWI) vessel  300  moves away to its normal operating position and can deploy a spoolable compliant guide (SCG)  1102 , and the like, as needed. The auxiliary vessel (AV)  200  then positions itself at a chosen, safe location on an opposite side of the well  1004 , and upstream of surface currents. 
     Advantageously, the novel methods and systems can be employed to perform normal light well intervention (LWI) operations, including spoolable compliant guide (SCG) operations. However, in further exemplary embodiments, the novel methods and systems can be employed to perform any suitable operations, for example, including wireline operations, coiled tubing operations, and the like, in open water or with any suitable guide, and the like. 
     While the inventions have been described in detail in connection with a number of exemplary embodiments, and implementations, the inventions are not so limited, but rather cover various modifications, and equivalent arrangements, which fall within the purview of the appended claims, as will be appreciated by those of ordinary skill in the relevant art(s).