Economically achievable oil recovery factors for offshore fields are typically lower than for similar onshore fields due to larger well spacing, inadequate reservoir characterization and shorter economic field life. The key challenge for mature offshore field development is to leverage on surface and subsurface assets by progressively evaluating field redevelopment opportunities and executing phased projects to mitigate risks. Applying appropriate EOR techniques will help to maximize economic oil recovery and tap the relatively large remaining oil volumes in these offshore mature fields. In addition, the synergies among “making the most of what you have” (facilities rejuvenation, asset integrity, production optimization and production enhancement), infill drilling campaigns, implementation of water and/or gas injection schemes and the design/execution of EOR field development schemes are critical success factors. These highly integrated and risk-based field redevelopment planning efforts have gained momentum worldwide and this paper describes the learnings from a mature oil field offshore Malaysia.
For the field under discussion, the current (primary) field development strategy of simultaneous production from multiple stacked reservoirs and continuous optimization of artificial lift will lead to modest oil recovery (30 to 35% average oil recovery factor). After more than 30 years on production and multiple previous infill drilling campaigns, the number of available drilling slots on the offshore platforms is limited, plus there are challenges in reaching attractive bypassed oil targets from existing platform/well locations. New well head platforms and intra-field pipelines are expensive, so the existing well drainage plan is compromised in terms of the number and location of production wells.
To achieve the desired step up in economic oil recovery, a field redevelopment plan is required that logically combines various risk-based strategies and value adding components. This paper describes the range of subsurface and field development studies that were required to define an effective field redevelopment plan including EOR (iWAG). Realizing an offshore EOR project with an attractive and robust unit development cost is challenging, especially in the current environment of softening oil prices. This paper also discusses the strategies of defining a field redevelopment plan in this mature oil field through integration/synergy between efforts to safeguard the NFA production (No Further Activity) and additional infill combined with realization of iWAG. It is fully understood that the timing of development project implementation is important for economic value and that it would normally not be prudent to exhaust primary and secondary development options before embarking on tertiary EOR techniques, but a synergistic and risk-mitigation (phased) approach is necessary in these high cost, mature offshore field environments.