This paper presents the development of a completion and workover riser that incorporates a modified second-generation rotary-shouldered connection (RSC). This double-shouldered connection features a high-pressure, gas tight, metal-to-metal radial seal, a secondary back-up resilient sealing barrier and additional modifications to cope with subsea conditions. The comprehensive effort to design, test and qualify the completion and workover riser for offshore conditions in Australia and Africa is detailed. Results from extensive finite element analysis, laboratory tests, manufacturing processes and field results are presented.
The results of a 15-month project are the design, testing, manufacture and deployment of a performance validated, RSC completion and workover riser system. The riser was successfully placed into service and utilized on the Enfield and Chinguetti oil, gas and water injection wells located offshore Western Australia and West Africa.
The purpose of developing the RSC completion and workover riser was to create a cost effective and efficient riser system to meet the requirements of the innovative well completion system used on the Enfield and Chinguetti wells. The gas-tight, metal-to-metal seal RSC riser is robust, easy to handle, light weight and has a smaller deck footprint than conventional dual-bore risers.
Conventional dual-bore completion and workover risers can be costly to purchase, take up considerable amount of deck space and result in increased riser string weights reducing net lifting capacity when deploying tubing or a subsea tree. The weight of dual bore riser systems can preclude the use of smaller, lower cost drilling rigs on development well work, particularly in deeper water.
There are various designs of completion and workover riser connection systems, some of which require special, sometimes slow to operate, make-up spiders. Deployment of a tubing string or subsea tree requires both make up and break out of a large number of riser stands. Slow make-up and break out of joints can result in significant increased rig time particularly on a field development program comprising many subsea wells in deep water. In times of high rig rates, the cost associated with slow or non-optimized riser operations can be significant.
The Enfield oil field is located 40 km (25 miles) northwest of Exmouth, Western Australia (Figure 1), within 16 km (10 miles) of the Ningaloo Reef Marine Park. The field started production in July 2006 and comprises five subsea production wells, six water injection wells and two gas injection wells tied back via manifolds and flow lines to a floating production, storage and offtake vessel (FPSO). The water depth at Enfield ranges from 400 to 600 m (1,300 to 2,000 ft). The wells were drilled and completed from an anchored semi-submersible drill rig.
The Chinguetti oil field is located 80 km (50 miles) offshore Mauritania, west coast of Africa (Figure 2). The field started production in February 2006 and comprises six oil production wells, four water injection wells and one gas injection well tied back to an FPSO. The water depth at Chinguetti ranges from 700 to 850 m (2,300 to 2,800 ft). The wells were drilled and completed from a dynamic positioning (DP) drill ship. At this time Woodside no longer owns any assets in the Chinguetti field.