An offshore carbonate oil field in the Arabian Gulf is exhibiting asphaltene deposition problem mainly inside tubing of production wells completed in one of two main producible limestone reservoirs. This problem significantly reduces well profitability due to production loss and frequent asphaltene removal job (solvent soaking). Furthermore, future full-field EOR development, namely gas injection, is now planned and might have a risk to enhance the asphaltene problem. Therefore, comprehensive study has been carried out not only to establish less frequent and more effective remedy than the current action but also to evaluate a future risk of gas injection.
The study was initiated with careful review of the fundamental measurements, collected during the 20 years production history, of asphaltene properties, i.e. SARA (saturates, aromatics, resins and asphaltenes) analysis, asphaltene contents, AOP (asphaltene onset pressure) measurement, etc. Subsequently, the mathematical modeling analysis using those properties was incorporated into the study in order to develop APE (asphaltene precipitation envelope) for better understanding/predicting of asphaltene precipitation behavior. Therefore, this paper describes the integration/optimization of the APE modeling based on all available laboratory data, and consequently suggests representative APE. The APE model validity was evaluated by comparison with actual observation data in the problematic reservoir.
Based on the mathematical models once established, several sensitivities, namely mixing with injection gas and blending oils produced from two main producible reservoirs, were investigated in order to assess impacts of the future EOR on asphaltene risk from sub-surface and surface point of views. Several types of injection gas were examined, and their risks were compared and identified. Consequently, the surface facility design was adequately modified and optimized in order to minimize asphaltene risk assisted by gas injection.