Subsea Trees and Controls for Australian Bass Strait Development
Authors: Gillette L.A. , Voss R.K. , Goggans T.A. 
Published: October 2008

This paper discusses the design, analysis, and performance requirements of the satellite sub sea trees and electro hydraulic controls equipment used in the development of small fields, considerably offset from existing platforms in the Bass Strait, Australia. The two initial systems were installed on previously drilled wells and permit connection of an additional well in a daisy chain manner.

INTRODUCTION

Offshore production from the Bass Strait has been ongoing sincen 1969 and has reached a relatively mature state, however, there are several small shallow water fields, with marginal economics, which have been considered for production. Two of these fields, Seahorse and Tar whine, were selected for initial development using electro hydraulically controlled single satellite trees which will produce to the existing Barracuda platform. Figure 1shows the relative location between the two development fields and the existing production platform.

This paper discusses the project approach, the design of the electro hydraulic control system, subentries, work over controls, the overall development arrangement, and the unique daisy chain or piggy back requirements of the system.

PROJECT APPROACH

Two primary objectives of the project were to minimize development costs and to obtain a quality product. Some of the items which contributed to meeting these objectives were:Development of simple contractual documents including equipment specifications, quality assurance requirements. and terms and conditions. These items were project specific and were reviewed in detail prior to initiation of work to ensure understanding and workability. This ultimately reduced administration costs.Establishment of clear communication lines which included dedicated project teams with clearly defined responsibilities and project seniority. Direct communication, including use of facsimile, was encouraged between team members which minimized turnaround time and misunderstandings and contributed to lower administration costs.Single source supply for both tree and controls equipment eliminated interface communications between different suppliers and provided a clear line of responsibility resulting in decreased contract administration and risk.Use of the daisy chain concept eliminated the requirement for a separate production flow line and control umbilical from the second well back to the production platform. Rather, short lines to the primary well only would be required reducing capital costs.Utilization of field-proven equipment, existing specific components or design features can and was achieved reducing design cost and increasing reliability and quality, which decreased manufacturing costs.Extensive acceptance and site integration testing and training prior to equipment installation contributed to reduced rig n installation time. The equipment design was based on a comprehensive customer specification Which required field-proven components and practices which emphasized simplicity and reliability. All designs passed through a customer review/approval cycle and the sub sea production equipment required an additional Third Party Certifying Authority Review.

General equipment design guidelines included: Sized to suit typical semi submersible moon pool dimensions and crane capacity; All equipment interchangeable between both existing wells; Installation with minimum diver assistance and subsequent intervention with ROV; Secondary mechanical overrides on the valves and connectors; Designed for 15 years of sub sea service; Material compatibility with environment, well fluid, injection chemical