An offshore carbonate oil field in the Arabian Gulf is exhibiting asphaltene deposition inside the tubing of production wells completed in one of two main producible limestone reservoirs. This problem significantly reduces well profitability because of production loss and frequent asphaltene-removal jobs (solvent soaking). Furthermore, future full-field enhanced-oil-recovery (EOR) development—namely gas injection—is now planned and might have a risk of enhancing the asphaltene problem. Therefore, comprehensive study has been carried out not only to establish a 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 of asphaltene properties collected during the 20 years of production history—saturates, aromatics, resins, and asphaltenes (SARA); asphaltene contents; and asphaltene-onset-pressure (AOP). Subsequently, the mathematical modeling analysis using those properties was incorporated into the study for better understanding/predicting of asphaltene-precipitation behavior. This paper describes the integration/optimization of the asphaltene-precipitation-envelope (APE) modeling on the basis of 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.

On the basis of the mathematical models established, several sensitivities (i.e., mixing with injection gas and blending oils produced from the two main producible reservoirs) were investigated to assess impacts of the future EOR on asphaltene risk from the subsurface and surface points of view. 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 influenced by gas injection.

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