Diverless Maintained Cluster (DMaC) Subsea Production System

Abstract

ABSTRACT This paper describes a significant research and development initiative by Esso Exploration and Production UK Limited for the development of low cost subsea production technology. The objective of this development program is to establish designs for a diverless maintained, clustered well, subsea production system suitable for deployment on small hydrocarbon accumulations in water depths from 100 to 1000 metres. Furthermore, the system is to be cost competitive compared with diver assist systems when deployed in water depths typical of central and northern North Sea locations. The Diverleas Maintained Cluster (DMaC) well development program, begun in 1989, is a four phase design development, component and prototype testing program, valued at two million pounds sterling. The first two phases of the program, completed in August 1990, resulted in the conceptual design of the DMaC system. The system centers on a simple gathering manifold which is 5 metres square and can be installed through the moonpool of a drilling rig. It supports up to eight producing wells with a combined capacity of 50,000 bbls/day exported through two 8-inch pipelines which form a pigging loop at the manifold. The wells are connected to the manifold by a spoolpiece comprising twin 4-inch flexible lines, for production and test, and by a control umbilical. The jumper spoolpiece and the control umbilical can be installed from a drill rig, with assistance from the drill support ROV, without interfering with the drilling or completion schedule. The Christmas tree has an ROV replaceable control pod and an ROV replaceable choke, utilising designs tested and proven during the earlier Esao Deepwater Integrated Production System (EDIPS) (1,2,3) program. Although suitable for deepwater application, the DMaC system is not designed to be exclusively maintained by diverless means. The system is versatile and provides a cost effective subsea production system in a wide range of water depths irrespective of whether a diverless or diver assist maintenance system is needed. INTRODUCTION The Diverless Maintained Cluster (DMaC) system development program, initiated in 1989, is managed and funded by Esso Exploration and Production UK Limited. It involves design development and prototype testing by several contractors with technical input and coordination provided by Exxon Production Research Company. A summary schedule illustrating the overall project plan is presented in Figure 1. DMaC combines the knowledge and experience gained by Esso from earlier deepwater studies and its association with the small manifolded cluster well concept at the Osprey field in the North Sea. The result is a subsea production system which is both low cost and suitable for deployment in deepwater. This paper overviews the DMaC system, describing the diverless installation method. It provides information about the key components including the provision for diverless maintenance. The paper also outlines ongoing feasibility and hardware development efforts. It is not the intent of the DMaC program to develop a fully optimised site specific design. Rather, the intent is to consider key issues in subsea production system design and to develop designs and prototype hardware which address those issues.