Integrated experimental and simulation study of asphaltene precipitation during miscible-rich gas injection in heavy oil reservoirs

Miscible hydrocarbon gas injection can lead to asphaltene precipitation by altering the fluid phase equilibrium. The present study characterizes oil samples using SARA (Saturates, Aromatics, Resins, and Asphaltenes) analysis. An average colloidal instability index of 1.02 and 5.2 wt% asphaltene content confirmed severe instability. These results were verified by field observations in Well-7, where miscible gas injection triggered asphaltene deposition and flow restriction. Using a flow assurance device, the asphaltene onset pressure for the live oil at reservoir temperature was determined to be 382 bar. To tackle precipitation risks, two distinct hydrocarbon gases with liquid-to-gas ratios of 2.13 and 2.53 L/m 3 were used. The experimental measurements indicated that the leaner gas (2.13 L/m 3 ) is more effective, resulting in a lower asphaltene onset pressure of 447 bar compared to 521.2 bar for the richer gas (2.53 L/m 3 ). To evaluate the deposition propensity, high-pressure, high-temperature filtration tests were performed by maintaining reservoir temperature while systematically reducing pressure from above the bubble point to well into the two-phase flow regime. By coupling detailed live-oil PVT analysis with a solid-model-enhanced Peng-Robinson EOS, this study quantifies the onset and magnitude of asphaltene precipitation. The findings reveal the critical role of injected gas enrichment in altering fluid equilibrium and triggering asphaltene destabilization within the live oil system.