Garden Banks 388 Subsea Production Control System
Authors: Goggans Tim , MacNeill John , Blincow Mike 
Published: October 2008

This paper discusses the design, analysis and performance requirements of an electro hydraulic production control system for a 24 well deepwater development controlled from a Floating Production Facility (FPF) in the Gulf of Mexico. The controls include not only topside FPF installed equipment, but subsea template and tree mounted equipment, including control umbilical?s.

INTRODUCTION

Garden Banks 388 is a deepwater development in the Gulf of Mexico. Garden Banks Block 388 is located in 2,190 feet of water approximately 120 miles south of Grand Island Louisiana. The field will be produced via a converted semisubmersible drilling rig, Enserch Garden Banks FPF (formerly the Glomar Biscay 1). The FPF will maintain full drilling capabilities while simultaneously accommodating production. Production facilities are rated for 40,000 BOPD and 120 MMCFD. A 24-slot production template is installed on-site, and can accommodate both template wells and satellite wells. Production is piped through the template and up the free standing production riser to the FPF for processing. Oil and gas will be processed on board the rig and exported via the production riser and export lineswithin the template. Two 12-inch gathering lines run from the FPF site to a purpose-built shallow water processing facility located 54 miles away in Eugene Island Block 315.

PROJECT APPROACH

Two primary objectives of the project were to minimize development costs and obtain a flexible control system. Some of the items which contribute to meeting these objectives were:Development of pertinent contractual documents including equipment specifications, quality assurance requirements, and terms and conditions. These items were job specific and were reviewed in detail prior to initiation of work to insure understanding and workability. This ultimately reduced administration costs.Establishment of clear communication lines which included a dedicated project team with clearly defined responsibilities. Direct communication was encouraged between team members which minimized t.urnaround time and misunderstanding and contributed to lower administration costs.The template mounted hydraulic/chemical injection manifold pods utilized in this project are redundant and allow single well isolation without affecting other wells. This allows the addition of new completion or rerouting of template hydraulic or chemical supplies without losing production. These manifold pods allow operator flexibility without the use of subsea valving.By mounting a control pod on a tree verses the template, the system is more flexible, allowing incorporation of future modifications like changing the number of functions to be operated and/or adding down hole monitoring.Each christmas tree is controlled by redundant electrical quads to prevent the use of a subsea electrical distribution system. This was economically achievable due to the short offset. With the use of a surface electrical distribution network as opposed to asubsea electrical distribution system, the system reliability is enhanced by avoiding electrical problems that could jeopardize the entire development.Utilization of field proven equipment, existing specific components or design features was achieved, reducing design cost and increasing reliability and quality, which decreased manufacturing costs.Extensive acceptance and integration testing and training prior to equipment installation should contribute to reduced rig installation time.