West Seno: Facilities Approach, Innovations and Benchmarking
Authors: Wetch Stephen B. , Wybro Pieter G. 
Published: October 2008

Abstract
This paper summarizes key innovations of the overall approach of the installed system. Limited comparisons are offered to put this project in perspective. This paper introduces several system features many of which are further explained in the related papers.
Features include:TLP close coupled with tender-assisted surface drilling;Close coupled barge type FPU supporting the process and export SCRs;Simplified TLP ballast system using eductors with firepump;Simplified TLP hull configuration;Fixed tensioned risers serving for both drilling and production;First Deepwater EPIC for Asia.

Introduction

Project Challenge.
In the Fall of 1997, Unocal Indonesia had it's first significant deepwater discovery with Merah Besar off the east coast of Kalimantan. The following objectives were established. By the beginning of 1999, the West Seno field took priority for development. The objectives and challenges were basically the same, except that full offshore process was considered essential to handle the range of product composition with the distance to beach of about 60km.
The system developed from the following objectives:Provide oil and gas production facilities for 60kbopd and 150mmscfd in about 3300ft water depth with sales quality to existing shoreside infrastructure including tank farm;Develop a large number of wells (up to 28) with surface access with a lower cost tender assist rig that can be used in other fields and in shallow water operations;Build on the SX (Unocal developed) drilling program centered around a 13-3/8" riser system that allow full drill through capability with similar operations;Make surface operations similar to shallow water platforms with routine well interventions;Facilities for two distinct production areas;Use the benign environment which is current and not wave dominant to advantage in providing a low cost field and facility arrangement;Simplify to reduce cost as possible;Make floating systems in which at least a significant portion can be built in Indonesia, thus separate higher technology subsystems.

Convergence.
The objectives led to and included the replication of a surface well platform with a combined drilling/production riser. The operations were to be as seamless with the shallow water operations as possible. With a high percentage of national staff, the additional crossover training and staffing for deepwater operations should be simplified.
Subsea approaches were studied, but with the high number of well interventions, significant number of recompletions, the MODU costs at the time of concept selection (early 1999) increased the OPEX considerably.
Tradeoffs were not elaborate or complicated. By getting the "right" people with sufficient experience in the early conversation, clarity on what was needed took focus.
Looking for low cost approaches led to the following approach:close coupled TLP to a barge which supports the topsides and export lines;SCRs to shoreside infrastructure;Simplified TLP and barge hull types;Simplified marine ballast system;Simplified fixed tensioned riser system, which also contributes to overall mooring stiffness.