Conceptual Design of a Turret-Moored Production System (TUMOPS)

ABSTRACT A project was initiated in 1987 to develop the Turret Moored Production System (TUMOPS) concept for:developing offshore fields in remote locations where in-field storage with shuttle tanker export is required,early/phased developments, andshort-term field developments, where relocation is possible. During the first phase of the project, alternate configurations for the system with varying water depths, number of wells, storage capacities, and drilling/workover facilities were investigated [1]. This paper provides a follow-up to [1] and describes the second phase of project which focused on further defining key system components, including the subsea system, the turret and fluid transfer systems, and the combination mooring/thruster stationkeeping system, for one set of field parameters; and culminated in the development of a conceptual design for an example field offshore Norway. INTRODUCTION TUMOPS represents the combination of technologies developed during years of industry experience with ship-based floating production systems, turret-moored drillships, and the existing turret-moored production test ship [2]. The basic system arrangement consists of a production ship, which supports a full drilling/workover system and process facilities, positioned over subsea template wells, as shown in Figure 1. Flexible risers connect the production ship to the subsea wells. The turret mooring system allows the vessel to maintain the best heading relative to the wind, wave, and current conditions, thereby providing good motion characteristics for both production and drilling/workover operations. The ship also provides crude oil storage for up to seven days of production. The produced crude is offloaded to a shuttle tanker for transportation to shore. During Phase I of the project, various configuration alternatives of the system were developed for water depths of 125, 300, and 500 meters, and production rates of 25,000, 50,000 and 75,000 barrels of oil per day (BOPD). Subsea systems for both a manifolded subsea and a non-manifolded subsea case were designed. Facilities required for a range of drilling/workover capability, from "light" workovers (wireline and coiled tubing) to a fully equipped drilling facility, were also investigated. The main conclusions of Phase I were as follows [1]:The basic TUMOPS concept is technically feasible.Full drilling capability can be supported by the production ship.The turret can support up to 20 flexible risers.Further work is justified to refine designs and confirm costs for key system components. The second phase of the project focused on the design of key system components, including the subsea system, the turret and transfer systems, and the stationkeeping system, for a given set of field parameters. Additionally, offshore installation activities and operation of TUMOPS were investigated. Completion of the Phase II work, as described herein, provided a conceptual design basis for an example field offshore Norway. TUMOPS CONCEPTUAL DESIGN BASIS The Phase II TUMOPS conceptual design is based on development of a representative oil field offshore Norway in a water depth of 125 meters. The production ship will accommodate the facilities to support simultaneous production, drilling/workover, and offloading operations for up to 42 subsea wells.