Optimization of Water Injection in a Giant Carbonate Reservoir: Lessons, Challenges and Solutions

Abstract Water injection is used to improve the overall efficiency of hydrocarbon recovery while prolonging the productive life of the reservoir. It is imperative to have an efficient and optimized water injection system to maximize the value of water injected. This paper summarizes the challenges, learnings, and short- and long-term solutions for optimizing the water injection system in a giant, saturated carbonate reservoir in the Middle East which has been in production for over 60 years. Overhauling the existing decades old system is difficult and needs a coordinated team effort. This paper discusses a multi-pronged effort for water injection optimization. A robust reservoir surveillance plan coupled with in-house AI-ML based tools helps to evaluate performance and identify issues. System inefficiencies were identified proactively through regular inspection and real time data. To arrest the reservoir pressure depletion, production rebalancing was envisaged to increase production from healthy areas. Water injection optimization along with ramp up water injection volumes was undertaken. MRC (maximum reservoir contact) wells and lower completion were proposed to reduce surface congestion while improving accessibility and conformance. Several short- and long-term solutions have been developed which are in different phases of implementation. The field suffers from a lack of water required for injection resulting in a gradual drop in reservoir pressure. Also, the increased withdrawal is causing gas cap gas cusping in attic wells, thus constraining surface facilities. Employing conventional and AI-based analysis tools, efforts have been made to increase the value of injected water while limiting the reservoir pressure drop by identifying the right locations and correct quantities for injection. Simplified clusters with low turn-around time along with few conventional clusters have helped to add significant volumes. Proactive stimulation, production-injection rebalancing, MRC wells, smart completions and innovative artificial lift ideas have helped in arresting pressure decline, improving well accessibility for logging, and reducing carbon footprint. Over the long-term, seawater will replace the current aquifer water injection which will help in increasing injection capacity. Injection along the gas-cap fence is under implementation to minimize gas migration to oil zone. These initiatives are expected to add significant reserves and achieve ~60% RF by the end of the concession. The current paper showcases the need for adopting a multipronged strategy covering all aspects of water injection management for unlocking potential while maintaining reservoir health of a brownfield. The lessons learned and the improvised solutions utilized in the field can be utilized for other water-deficient fields for maximizing the value of injected water while minimizing pressure loss in the short term while deploying long term solutions for improving water injection volumes.