Successful Wettability Alteration Pilot in Offshore Reservoir: Pilot Planning, Execution, Monitoring and Interpretation

Summary Surfactant injection as an EOR method is considered for a giant middle-eastern carbonate oilfield in offshore setting. The field is characterized by thin oil column, low permeability, and large lateral variations in fluid properties. Even after an extensive water-flood program, there are substantial amounts of oil left behind in the reservoir due to the mixed-wet to oil-wet nature of the Reservoir. An extensive surfactant-based wettability alteration EOR screening process was conducted to select the best surfactant for improving the oil recovery. After successful short surfactant injection trials, a long-term surfactant injection pilot was planned and executed. The pilot was supported by a comprehensive monitoring program. The pilot was conducted in an offshore environment involving very long horizontal well, which is unique in the industry and is first of its kind. A robust and comprehensive monitoring program is key to successfully evaluate the pilot performance and qualify the incremental oil production from the trial. A detailed monitoring program was prepared in advance before the pilot start-up, which involved internal and external parties. Monitoring plan consisted of high frequency monitoring of delivered surfactant quality, constant monitoring of surfactant injection concentration and injection rates. Plan involves high-frequency collection and monitoring of production samples with the aim of highlighting any changes compared to the base line measurement. External labs were also involved for precision monitoring of any surfactant breakthrough for pro-actively mitigating effects of any upset due to pre-mature surfactant breakthrough. For monitoring a dashboard has been created for identifying correlation between various processes. The pilot monitoring is still on-going and will continue for another 6 months. The comprehensive monitoring program has contributed to the successful conclusions from the pilot. The data gathered during the monitoring program will enable scale up of trial to other wells, qualification of incremental oil production, and to improve efficiency of the future implementation of surfactant injection on a greater number of wells. The paper presents the results planning of trial form lab to field, implementation of monitoring plan and results of the monitoring plan, which support the trial conclusions. The pilot and the monitoring program are unique in themselves as the scale of operations and number of stakeholders involved are large. The pilot demonstrates that it’s possible to implement an EOR project in a highly complex offshore carbonate field. The pilot was conducted in an offshore environment involving very long horizontal well and is first of its kind.