A Ten Well Subsea Production System for the Enchova Field

ABSTRACT This paper describes the subsea equipment currently being designed and manufactured for production of the Brazilian Enchova Field. Six of ten wells will be located on a subsea unitized template. Up to four remaining wells are then connected through template piping to a subsea manifold also mounted on the template. A production riser is used to connect the subsea system to a semisubmersible floating production facility. Each well will produce through the subsea manifold and the production riser with an individual flowline. Raw crude is then processed on the semisubmersible and transferred down the center core of the production riser to an offshore loading system. All of the subsea equipment is controlled by a multiplexed control system with complete straight hydraulic back-up. Although components of this system do not require divers for running and retrieval, the system has been designed to interface with the "JIM" atmospheric diving system for subsea maintenance. INTRODUCTION The ten well subsea production system described comprises Phase II of-a three phase development program for the Enchova Field offshore Brazil. Although the emphasis of this paper is on the equipment required to bring the Enchova Field to Phase II status, it is important to briefly review all phases of field development. Phase I will have three wells producing to two semisubmersibles. Two of the three wells are produced through B.O.F. test: trees directly to the semisubmersibles; the third will produce through a subsea satellite tree. Currently, the first well is producing through a B.O.P. test tree to a semisubmersible. Oil is processed on the semi and routed (via a floating hose) to a tanker loading terminal. During early 1978, the second semisubmersible was contracted and the B.O.P. test tree, the satellite tree and the second tanker loading terminal ordered. Production will start from the second and third wells early in 1979 after the B.O.P. test tree and satellite tree are installed and flowlines are laid from the satellite well to the semi. Phase II will introduce a subsea template that accommodates the three Phase I wells plus up to seven additional wells for a total capacity of ten, all producing to one semisubmersible. (Refer to Figure I) Six wells can be located on the template. The current plan is for two template wells to be water injection wells, three to be producers and one a spare. The template has flowline connections for four satellite wells. The three Phase I wells will be tied to the template via flowlines, which leave the fourth connection as a spare. All wells then produce through satellite and template mounted flowlines to a retrievable subsea manifold on the template. Connecting the subsea manifold with the semisubmersible is a production riser system. Each well is produced through an individual flowline to the surface. The crude is processed there, routed down the riser core to the template and then through subsea pipelines to either of the two tanker loading terminals.