From Passive to Controlled Injection: Managing the Risks of Water Injection in 40 Years Mature Field

Abstract Field B, with multiple stacked oil reservoirs having some highly depleted reservoirs, is introducing Sea Water Injection (WI) to expand existing dump flooding, to support planned infill wells that will significantly increase production. Natural dump flood projects have been successfully implemented since 2015, with replication across multiple areas within the field. Dump flooding has demonstrated positive results by increasing reservoir pressure and enhancing oil production at minimal cost. However, due to its reliance on differential reservoir pressure, natural dump flooding has limited injection rates, slow response and limited production impact. Key challenges in implementing sea WI include, 1) identifying a cost-effective water injection system for aging facilities with limited deck space, 2) understanding permeability pathways and distribution in target sands 3) mitigating risks associated with formation damage, 4) water injection facility performance and equipment reliability, 5) optimum infill well planning to ensure benefit from water injection. Mitigation strategies are described as following, 1) To minimize costs, a Portable Water Injection Module (PWIM) is being employed under a leasing model, thus reducing CAPEX exposure and associated economic risk. A modular design for the PWIM opted to fit into the limited available deck space thus avoiding the need for a separate injection platform or deck extension. Additionally, existing production wells with known performance are to be converted into injectors, eliminating the need for drilling injectors in new locations. 2) Dedicated special core-based studies were conducted to evaluate permeability contrast between key sands targeted for injection, capillary pressure for accurate saturation modelling, pore throat distribution, formation damage, and seawater compatibility to ensure effective and sustainable injection. 3) Comprehensive geomechanics study was conducted assessing waterflood performance incorporating advanced rock mechanics core testing results 4) A detailed water injection design, injection monitoring plan, and optimal PWIM specifications have been developed, incorporating lessons learned from existing dump flooding and water injection projects in neighboring fields. 5) Reservoir models have been refined and used to optimize the development strategy and infill locations. This paper presents a stepwise methodical approach to de-risk water injection projects in a mature asset by leveraging the success of dump flooding as a low-cost pressure maintenance method and systematically progressing into active sea water injection. This integrated approach evaluates subsurface and surface uncertainties, enables incremental investment, and ultimately enhances hydrocarbon recovery while reversing production decline to extend economic life.