Wet christmas tree

Abstract: A wet Christmas tree (20), utilized particularly in subsea production systems, includes:- at the bottom a connector (22) for the purpose of locking to the wellhead; a guide structure (24) consisting of a central ring attached to said connector (22), supporting arms (26) and guide funnels (28); a valve block (30); a re-entry mandrel (32); hydraulically driven gate-type lateral valves (46, 48, 50, 52) with metal/metal sealing and with spring-type return flow lines with loops (54, 56, 58) and piping for the crossover line; hydraulically adjustable chokes (60, 62); a flow line terminal (36); a re-entry pole (42); and a control system.

Description: This invention relates to a Wet Christmas Tree (WCT) which is particularly useful for application in a subsea petroleum production system and which presents a considerably simplified and more reliable manifold. The subsea production systems for petroleum originating from wells located at great depths utilize subsea completion, since that is the most feasible option, both technically and economically. One such subsea production systems is the template-manifold which includes among other components a template structure, a manifold, and wet Christmas trees. The subsea production systems known so far present as their major characteristic the provision, either in the template-manifold or in the manifold itself, of active elements, such as chokes, manoeuvre valves and control modules. This leads to both an increased number of recoverable modules and a reduced system reliability. With the purpose of reducing the number of recoverable modules arranged in a template-manifold of a subsea production system, and thus improving the reliability of the system, this invention provides a wet Christmas tree having as its major characteristic the inclusion of active elements such as chokes, manoeuvre valves and control modules, thus simplifying the template-manifold of the subsea production system. This invention relates to a wet Christmas tree (WCT) for utilization in subsea production systems of the type described in our EP-A-0480772. The WCT of this invention is characterised by the features of claim 1. In a preferred embodiment of the WCT:- the re-entry mandrel is adapted to receive the WCT running tool, the tree cap, a secondary unlocking tool of the WCT connector, and a handling tool; the flow line terminal has the purpose of enabling connection of the flow lines (production, production testing and annulus) and the hydraulic control lines between the WCT and the manifold; the re-entry pole is integrated to the assembly of the WCT by means of an orientation key; and the control module includes a control system responsible for the activation of WCT functions during the installation and operating phases. In order that the present invention may more readily be understood the following description is given, merely by way of example, with reference to the accompanying drawings, in which:- FIGURE 1 is a front view of the WCT of this invention; FIGURE 2 is an overview of the WCT of Figure 1; and FIGURE 3 is a lateral view of the WCT of Figures 1 and 2. As may be inferred from Figures 1 to 3, in which like reference numerals identify corresponding parts, the wet Christmas tree (WCT) generally designated 20 includes:- at the bottom a connector 22 for locking to the wellhead, with a visual indicator of the locked/unlocked position and with secondary mechanical unlocking with extension up to the top of the WCT for driving by means of a tool to be run with a drill string; a guide structure 24 consisting of: a central ring attached to the connector 22, guide funnels 28 with portholes for guide cable passage, and arms 26 for supporting the guide funnels; a valve block 30 adapted at the top to receive the re-entry mandrel, and at the bottom for coupling to the connector 22 or to a spacing spool; a re-entry mandrel 32 which is adapted at top to receive the WCT running tool, a tree cap, a tool for secondary unlocking of the connector 22, and a handling tool and is adapted at the bottom for assembly to the block 30, the extension of the vertical access passages to the production and to the annulus, and connectors of the hydraulic lines for the installation tool and for the WCT cap; a WCT cap 34 of blank type and pressure-tight for the passages so as to work as a second protection barrier during production and to be installed, preferably by the same WCT installation tool; hydraulically actuated normally closed gate-type lateral access valves with metal/metal sealing and with spring-biased return; flow lines with loops having a flexibility compatible with the travel required by the connection system and the piping for the crossover line; hydraulically adjustable chokes incorporated in the WCT arrangement; a flow line terminal 36 consisting basically of the terminal itself, of the device 38 for retraction of the loops and unlocking of the terminal, and of a protection structure 40 (to prevent damage to the terminal during the transportation and handling operations, and which is to be run prior to running the (WCT) ; a re-entry pole 42 with an orientation key and having the function of guiding and orienting the WCT/WCT-cap installation tool, the tool for secondary unlocking of the connector, and the installation tool of a control module 44; and a control module 44, preferably of electrohydraulic multiplexed type, which is the assembly responsible for the activation of the WCT functions during the installation and operating phases. The valve block 30 includes a vertical passage for production, with (i) two normally closed gate-type valves (one master and one for swabbing) which present metal/metal sealing and are hydraulically driven with a spring-biased return action, and are equipped with an override mechanism for ROV (remotely operated vehicle) tool driving, and (ii) lateral accesses to the two control lines of a secondary system and sub-surface safety valve (SCSSV), provided with isolating valves prepared for ROV operation. The above-mentioned lateral access valves include valves 46, 48 for the production line and the testing and production line, and valves 50, 52 for the annulus line and crossover line, equipped with an override mechanism for ROV tool driving. The flow lines consist of (i) loops 54, 56 for the production and production testing lines, and a loop 58 for the annulus line, with a flanged end for assembly at the outlet of the valve block 30 (or at a crosspiece), and another bevelled end for the purposes of welding to the flow line terminal 36, and also (ii) piping for the crossover line, making the connection between the annulus and production lines. The chokes incorporated in the arrangement of the WCT 20 include a choke 60 for the production line and a choke 62 assembled on the annulus line (for lift gas control). The choke 60 will have the upstream and downstream flanges equidistant in relation to the body centrelines, so as to allow for its assembly in an inverted position (for assembly in either production or injection trees). As can be also seen in the Figures, the Christmas tree 20 includes:- a panel of ROV operated valves 64, pins 66 for secondary unlocking of the connector, a base 68 for a control module, a structure 70 for ROV anchoring, crosspieces 72, 74 and 76, and an impact flange 78. It must be pointed out that the valves 46, 48, for the production and production testing lines, and also the valves 50, 52 for the annulus and crossover lines, have their actuators facing the external surface of the template-manifold and are equipped with an interface for secondary ROV operation. In addition, the WCT 20 can be converted from production to water injection by merely inverting the choke 60 for the production line, with allowance for the utilization in the WCT 20 of a control system of electrohydraulic multiplexed type. It must be pointed out also that a wet Christmas tree according to this invention can be used both in the structure of the template-manifold and in the structure of the manifold itself.

Claims: A wet Christmas tree characterized by including:- a connector (22) for the purposes of locking it to the wellhead; a guide structure (24) consisting of a central ring attached to said connector (22), supporting arms (26), and guide funnels (28); a re-entry mandrel (32); a valve block (30) adapted at the top to receive the re-entry mandrel and adapted at the bottom for coupling to said connector (22) or to a spacing spool; a protection cap (34); a first pair (46,48) and a second pair (50,52) of hydraulically driven gate-type lateral access valves with metal to metal sealing and with spring-biased return; flow lines with loops (54,56, 58) and piping forming a crossover line; hydraulically adjustable chokes (60, 62) incorporated in the arrangement of the WCT (20); a flow line terminal (36); a re-entry pole (42); and a preferably electrohydraulically multiplexed control module (44). A wet Christmas tree according to claim 1, characterized in that said re-entry mandrel (32) is (i) adapted at the top to receive the WCT running tool, the cap (34), the tool for secondary unlocking of said connector (22), and the handling tool; and (ii) adapted at the bottom for assembly to said valve block (30), extensions of the vertical passages which give access to the production and to the annulus, and connectors of the hydraulic lines for the installation tool and for said WCT cap (34). A wet Christmas tree according to claim 1 or 2, characterized in that said valve block (30) includes vertical passages for production and access to the annulus with hydraulically driven gate-type valves presenting metal to metal sealing. A wet Christmas tree according to any one of claims 1 to 3, characterized in that two (46, 48) of the valves are valves for the production and production testing lines, respectively, and two more (50, 52) of the valves are respective valves for the annulus and crossover lines, and are equipped with an override mechanism for ROV tool operation. A wet Christmas tree according to any one of claims 1 to 4, characterized in that two (54, 56) of said loops are respective production and production testing loops, and the third loop (58) is a loop for the annulus line with a flanged end for assembly at the outlet of said valve block (30) and another bevelled end for the purpose of welding to the flow line terminal (36). A wet Christmas tree according to any one of claims 1 to 5, characterized in that said chokes (60, 62) are a choke for the production line and a choke assembled on the annulus line respectively, of which one choke (60) has its upstream and downstream flanges equidistant in relation to the centrelines of the body, thus allowing its assembly in an inverted position for operation in both production and injection modes. A wet Christmas tree according to any one of claims 1 to 6, characterized in that said flow line terminal (36) includes a device (38) for retraction of said loops (54, 56, 58) and for locking of said terminal (36), and a protection structure (40). A wet Christmas tree according to any one of claims 1 to 7, characterized in that said connector (22) is equipped with secondary mechanic unlocking with extension up to the top of the WCT (20) for operation by a tool to be run with drill string, said tool engaging pins (66). A wet Christmas tree according to any one of claims 1 to 8, characterized in that said valves (46, 48, 50, 52 and 64) have their actuators facing towards the external surface of the template-manifold and are equipped with an interface for ROV operation. A wet Christmas tree according to any one of claims 1 to 9, characterized in that said WCT (20) can be converted from production to water injection by inversion of said choke (60).

Inventors: DA SILVA JOSE EDUARDO MENDONCA, PAULO CEZAR AUGUSTO SILVA, DA SILVA, JOSE EDUARDO MENDONCA, PAULO, CEZAR AUGUSTO SILVA, Da Silva, José Eduardo Mendonça
Applicants: PETROLEO BRASILEIRO SA, PETROLEO BRASILEIRO S.A. - PETROBRAS
Application year: 1992
Main classification: E21B43
IPC codes: E21B33, E21B34