A Systematic Approach in Delivering Infill and EOR Opportunities to Redevelop a Highly Complex Mature Field: A Case Study
Authors: Karim Rahimah Abd , Lee Heng Poh , Hong Chin Weng , Latif Mohd Anwar Mohamed , Anggono Hari , Husain Nik Hisham , Tayok Michael Collin Gerard , Tewari Raj Deo 
Published: March 2015

Abstract
This paper discusses about the systematic approach to identify and firm up the infill wells and EOR opportunities as part of the redevelopment strategy in a multilayered mature offshore oilfield which has been on production since the last 46 years. The field is located offshore East Malaysia at a water depth of 186 ft. Production performance of the field indicates the current development strategy and practices will yield a moderate recovery which is currently around 26%. It is in "mid-life crisis", facing problems of increasing water cut, high GOR, with bypassed/undrained oil areas and pressure depletion along with aging facilities.
In 2010, the study team embarked on full field redevelopment study to evaluate the infill and EOR opportunities. However, building dynamic model and identifying the remaining hydrocarbon from this area are very challenging due to its highly complex nature; thin oil-rims in over 200 multi-stacked reservoirs with individual thickness of 10 to 30ft, occurring at 2300 to 9800ft depth. The intensed faulting subdivides the field into hundreds of small reservoirs in numerous fault-blocks, with varying degree of fault-block communication and aquifer support. Limited reservoir data, including fluid contacts and fluid types, coupled with ambiguity in production allocation due to commingled production, further complicate dynamic modeling and history matching processes. These uncertainties will affect the remaining hydrocarbon volume and distribution, hence the success of redevelopment project through infill and EOR.
A systematic approach to evaluate infill opportunities and EOR performance using dynamic modeling, coupled with LTRO (Locate The Remaining Oil) studies will be discussed. The dynamic model captures the complex fluid movement due to heterogeneity and inter-fault block communications, whereas the LTRO provides an independent analysis on the current fluid contacts and remaining oil locations. Both methods complement each other, hence providing better understanding on the targeted reservoir and maturing the infill and EOR targets. Active surveillance and data gathering activities have also been lined up to reduce subsurface uncertainties. All these prove to be a comprehensive workflow to unlock the remaining oil in this complex field, resulting in several sizeable portfolios with potential to increase the recovery factor by 4 to 9%.

Introduction
The field is a geologically complex field, with hundreds of multilayered reservoirs consisting of sand-shale sequences, and heavily compartmentalized by antithetic faults (Figure 1). Throughout the production life, the field has undergone primary depletion with a peak production of around 64,000 bopd. Several phases of infill drilling campaigns have been executed to arrest production decline and developed the remaining hydrocarbon, however the average field recovery factor (RF) is only 26%.