Brownfield Waterflood Management - Strategic Implementation of Field Trial Learning, South Oman

Abstract

Waterflood response in a brownfield with complex reservoir dynamics have significantly delayed the expected water injection response in Field ‘A’. The field is one of the highest oil producers in Oman South, spead over ~37 Km2, with more than 400 active wells, contributing > 90,000 BoE/d over the last 3 decades. The field is producing under strong bottom aquifer water drive and improved oil recovery waterflood. Current field development is focused in drilling horizontal in-fill wells and maximize recovery through well reservoir and facility management (WRFM). Production is from a combination of Mahwis aeolian and Al Khlata glacial reservoir formations. Sub-surface challenges are to arrest pressure decline, enhance sweep efficiency, ramp-up water injection (target > 440,000 BoE/d), and source additional water and manage complex operations. The produced water from oil producing wells post treatment gets re-injected into the aquifer ~100m below oil water contact (‘Deep Injection’) with 38 vertical injectors. This ‘Deep Injection’ albeit have prolonged water breakthrough has yet not delivered the optimum oil drive efficiency. One of the key subsurface challenge is the unfavorable mobility contrast between the oil and water causing early water breakthrough. Field wide variable mobility contrast, presence of intra reservoir baffles and enlarged size of the aquifer compared the legacy model assumptions triggered a transformation of the improved recovery strategy of the field – both short term and longer term. More effective injection strategy through ‘Field Trials’ have now been deployed (viz. ‘Water Re-Distribution’, ‘Make-up Water Diversion’ and ‘Shallow Injection’) over the last two years. Initial response from these trials shows encouraging results in terms of pressure support and sweep efficiency. Learning from the trails are incorporated in the future development and asset management strategy. This paper highlights the ‘Field Trials’ – practical approaches implemented to manage and optimize the field performamance. In a cost competitive low oil price time the team focused in enhancing efficient and impactful trials which yields short-term production gains keeping in mind the longer term persepective.