An Integrated Towed Flowline Bundle Production System for Subsea Developments (1990)

ABSTRACT The concept of the INTEGRATED TOWED FLOWLINE BUNDLE PRODUCTION SYSTEM (ITFPS) is based on onshore construction and testing of a complete subsea system that consists of flowlines and control lines, as well as facilities for manifolding and, if so appropriate, for drillingand processing. The installation of such a system can be done by a pull or towing technique. The ITFPS is a concept designed for the development of subsea fields such as: satellites to existing offshore production facilities; a floating production development whereby the ITFPScan include the riser base on one end, as well as the production manifold on the other end; or for a 'near shore' subsea development that can be remotely operated from an onshore base. INTRODUCTION Subsea production dates from the mid sixties, when simple subsea trees were installed in shallow water depths, and possibly operated by divers. Ever since the subsea multiwell manifolding and floating production technologies have been developed to provide total subsea concepts that now operate satisfactorily, however, generally in diver accessible depths. The present research and development efforts of the oil majors aim for total remote production systems for developments in water depths beyond diver access by the mid 1990's. Major objectives in the design of such complex remote systems are to achieve the highest possible system reliability and to develop efficient procedures for installation, commissioning, operation and subsea intervention. A subsea satellite development typically involves a cluster of wells or a template structure and the connecting flowlines and control lines to the parent facility. This paper introduces theconcept of the INTEGRATED TOWED FLOWLINE BUNDLE PRODUCTION SYSTEM. This system combines all required flow and control lines within a bundled configuration, together with integrated facilities for manifolding and processing. It is based on onshore construction and testing of atotal system that can be installed offshore by using a towing technique, thereby minimising underwater activity during construction and operation. Installation of submarine pipelines by towing techniques are now an established and accepted method of installation. Pipelines can be installed by bottom tow (with or without added buoyancy), off bottom tow, near surface or surface tow, or towed at a controlled depth (see Figure 1). The CONTROLLED DEPTH TOW METHOD (CDTM) is particularly suitable for thetransportation of onshore fabricated and tested integrated systems (ITFPS). This relatively new technique for bundle transportation is outlined in the following section. GENERAL DESCRIPTION OF CDTM The principle of the Controlled Depth Tow Method (CDTM) involves the transportation of a pre-fabricated and fully tested flowline bundle suspended between two tugs (see Figure 2). To maintain control during the tow, the bundle has been designed and constructed within specific tolerances with respect to its submerged weight. In order to achieve sufficient buoyancy for the bundle, the flowlines, control lines etc are placed within a carrier pipe (see Figure 3). Chains are attached to provide additional weight in order to obtain a system which has a limited submerged weight. At rest the bundle floats at several metres above the seabed.