Immiscible Water-Alternate-Gas (iWAG) EOR Field Development in Mature Offshore Reservoirs: Planning, Execution, and Surveillance

Abstract This paper presents a case study detailing the planning, execution, and surveillance of the Immiscible Water Alternate Gas (iWAG) EOR technique. Field B, located in the East Malaysia Region, has opted for iWAG EOR, with a comprehensive Field Development Planning (FDP) formulated for implementation to improve the recovery. The paper will delve into EOR planning and strategies, the surveillance plan, and a chronological overview of the execution process. Additionally, the paper highlights observations and results obtained post execution. Through the utilization of the 3D Dynamic model and lab analysis, various production strategies were examined across multiple scenarios to pinpoint the most effective approach, ultimately maximizing recovery and additional reserves. Sensitivities were performed on factors such as iWAG cycle ratio, injection days per cycle, injection rates and timing of injection. In ensuring the success of the implementation, a comprehensive surveillance plan has been developed. The critical focus area covered pressure monitoring, saturation distribution, water and gas breakthrough, injection and production profiling, wells’ connectivity, wellbore integrity and production chemistry. Prior to full commencement of injection, Water to Gas and Gas to Water switching exercise as well as water and gas injectivity testing was conducted with main objective to evaluate injectivity index, ICV choke performance and to estimate the maximum injection rate and pressure. Following a comprehensive analysis, optimal strategies have been identified for the field. This includes an iWAG cycle ratio of 1:3, with injections occurring over 120 days per cycle. Effective injection rates of 18 MMscfd and 33 kbwpd water were determined to yield the best results. Subsequently, these strategies were executed, and surveillance plan including baseline monitoring was executed to ensure the success of the implementation. The digital monitoring platform has been effectively deployed, enabling real-time monitoring of critical parameters for both injector and benefiter wells. These parameters include tubing head pressure, annulus pressure, PDG gauge pressure and injection rates. Additionally, regular data acquisition via permanent fiber optics and conventional slickline were executed. Throughout the implementation phase, several challenges were identified, primarily on the reliability of the surface equipment, hindering the project’s full implementation. Injection was delayed by three years compared to the initial plan, resulting in a decline in reserves and the economic value of the project, which necessitated constant improvements. This presentation and discussion centers on optimization techniques, surveillance planning, observations, results, and the challenges faced during implementation, aiming to advance EOR practices within the oil and gas industry.