James F. Ramsey, R. Michael Blincow, Robert D. Pickard
Enserch Exploration Inc.
Dallas
A deepwater project can be brought on-line more quickly because of stackable drilling and production templates.
Historically, one of the primary barriers to the economic development of deepwater reserves has been the long lead time from discovery to first production. Typically, production facilities must be built and often installed before development wells are drilled.
The use of three-slot drilling templates allows development drilling to proceed while the production templates, Christmas trees, flow lines, and production platform are constructed.
Thus, the time from initial investment to first revenue is reduced.
Enserch Exploration Inc., along with partners Petrofina Delaware Inc. and AGIP Petroleum, is using a "piggyback" or transportable stacked template system to develop deepwater gas reserves in Mississippi Canyon Block 441, approximately 50 miles south of Grand Isle, La. The discovery is located in 1,410-1,520 ft of water.
The Louisiana Offshore Oil Port (LOOP) safety fairway running north to south covers the eastern three fourths of Mississippi Canyon Block 441 and rules out surface production facilities over the well locations.
The fairway constraint has led to the development of special subsea well completions that will produce through flow line bundles to a fixed platform. The platform will be located in 380 ft of water on the adjacent Ewing Bank Block 482.
DEEPWATER PROJECT
The Mississippi Canyon Block 441 field will be developed using subsea-drilled and completed wells tied back to a shallow-water production facility (Fig. 1). Earl & Wright Consulting Engineers is providing project management and construction support. Three remote appraisal wells have been drilled recently in the field (Fig. 2). The field will be developed using each existing well as a production well, with four additional wells (two each at the A and B locations) to be drilled after subsea drilling templates have been installed.
The C location will be developed with a subsea template or a lay-a-way tree system with flexible flow lines. This depends on testing and evaluation results from the wells drilled at the A and B locations.
Processed gas will be exported to shore from the shallow-water platform via a wet gas pipeline system. All control and monitoring activities for the field will be conducted from the shallow-water platform. Distances from the well locations to the shallow-water facility are approximately 3, 4, and 6 miles. The flow lines and control umbilicals must traverse seabed irregularities, typical of the relatively steep slopes off the continental shelf along the Mississippi trough.
SUBSEA SYSTEM
The Mississippi Canyon Block 441 field subsea system consists of two three-well templates, subsea Christmas trees, control system, and associated equipment and running tools. All equipment is designed for diverless, or remotely operated vehicle, operations and for use with guidelines. The subsea equipment will be designed so it can be retrieved to the surface for maintenance and repair.
A unique two-piece template system has been developed for this project. Each template system consists of a drilling template with a production template that is later installed on top. In addition to allowing drilling while production templates are being fabricated and thoroughly tested, the system allows the existing wells to be easily incorporated into the template system. Fig. 3 shows a sequential stack of the templates on an existing wellhead.
The drilling template will be installed over and locked to the existing wellhead using an hydraulic wellhead connector with an integral tubing spool. The connection between the wellhead and template provides a rigid foundation for the drilling template, and the tubing spool provides a new wellhead profile for the existing well.
Two additional wells will be drilled through the conductor-housing receptacles located on either side of the existing well. These receptacles have a machined internal profile that provides a precise means of locating, locking, and supporting the 30-in. conductor housing on the drilling template. The 30-in. conductor will be control-jetted into each well slot, and 20-in. casing will be run and cemented back to the seafloor, providing additional structural support for the template.
The three wells on the template are located on 15-ft centers, which allows a blowout preventer (BOP) stack to be installed on one well without affecting the Christmas trees on the adjacent wells. A retrievable guide base provides guidance and orientation for the BOP stack during drilling operations.
The drilling template for the B location was installed in the middle of this year, and one of the two development wells was spudded shortly thereafter (Fig. 4). The drilling template for Location A should be installed around the fourth quarter of 1991.
After the four wells at the A and B locations are drilled, the production template will be installed over the drilling template at each location. The production template will be locked to the drilling template by four hydraulically activated latch mechanisms that stab into latch receptacles on the drilling template. The latch mechanisms are operated by the production template running tool, which is controlled from the surface by a control umbilical attached to and run on drill pipe.
The production template is a fully integrated structure with all flow line piping, control system piping, and the flow line connection base permanently installed.
The integral piping on the production template will provide a connection between the subsea trees and the flow line bundles.
After the production template is installed, the wells will be completed with a single string of 3 1/2-in. production tubing incorporating a single surface-controlled subsurface safety valve. A downhole chemical-injection valve for hydrate, paraffin, and corrosion control will also be provided.
Christmas trees for the template wells will be diverless with single master, wing, and swab valves in both the production and annulus bores. The trees will be remotely controlled from the shallow-water production platform by a piloted hydraulic control system. The piloted control system will minimize response times caused by the long distances from the subsea wells to the shallow-water platform.
FLOW LINE SYSTEM
Bundled flow lines will carry the production from the A and B locations to the platform in Ewing Bank Block 482. Two 3 1/2-in. diameter lines per well, along with one 34-hose umbilical, will be installed for each template. The steel lines and the umbilical will be housed in a 22-in. casing. The tie-in method at the C location will use either a flexible line or a flow line bundle, depending on the number of wells drilled at that location. R.J. Brown & Associates is providing the engineering design and support for the flow lines.
Two bundles, one to tieback each well cluster, will be built and pretested on Matagorda Peninsula, Tex. They will be transported from Matagorda to the Mississippi Canyon Block 441 field by bottom tow and tied-in at the production templates by diverless methods. The 450-mile tow route for the flow line bundles is shown in Fig. 5.
The 3 1/2-in. flow lines and the casing will be coated with a fusion-bonded epoxy. The casing will have an abrasion-resistant coating applied over the bottom half of the pipe to protect the corrosion coating during the tow. Cathodic protection will be provided by cast-on zinc sacrificial anodes.
The flow lines will have thermal insulation applied as they are pulled into the casing. The six flow lines and umbilical will be supported at regular intervals by spacers, which have wheels to facilitate the installation into the casing. Buoyant connector sleds will be attached to each end of the bundles to provide for flow line and umbilical connections, towing hardware, and deflection equipment. The bundles will be fully tested on land before they are launched.
The first end connection will be made at the template in deep water using the Cooper Oil Tool diverless McPac connector system and hardware. The connection at the production platform will involve the latching of the connector sled to the platform by diverless means and then using diver-installed spool pieces to join the flow lines and the riser piping. The deflect-to-connect method will be used for both the first and second end connections.
SHALLOW-WATER FACILITY
The shallow-water facility is a four-pile design, engineered by Petro-Marine Engineering of Texas Inc. It will be installed in the last half of 1992. The structure will be founded on four 72-in. diameter skirt piles with no main piles. This will maximize space for equipment while minimizing structural tonnage.
The deck structure will comprise a main deck, a cellar deck, and a subcellar deck with connecting stairways between levels. The majority of the processing system will be located on the cellar and subcellar decks. The process scheme is basically a three-phase separation to remove and treat produced water and to measure both the oil and gas streams before they are recombined in the wet gas pipeline leaving the platform.
The flow line bundle risers will connect with the flow line bundles to tie-in porches at the seabed. The risers are contained within casings and located sufficiently inside the jacket for protection and lateral support from environmental loading.
The shallow-water platform will be a manned facility capable of processing 150 MMcfd of gas and 1,500 b/d of condensate production. The wells should be on-line near the end of 1992 or early in 1993.
Copyright 1991 Oil & Gas Journal. All Rights Reserved.
