Theoretical Modeling of Gas Exsolution and Liberation during Foamy-Oil Flow in Porous Media

Summary In the past, many coreflooding laboratory tests have been conducted to study foamy-oil flow in primary heavy oil production and solvent-based enhanced oil recovery processes (e.g., cyclic solvent injection). However, limited important technical data can be obtained from these experimental tests due to the complex nonequilibrium phase behaviors. In general, mathematical or numerical modeling is often performed to history match the experimental data and understand foamy-oil flow trends under different experimental conditions. Many important parameters need to be tuned and determined in the history matching processes, which could be time-consuming and possibly cause large errors. In this paper, we propose a novel and effective theoretical model to quantify the gas exsolution and liberation during foamy-oil flow in porous media. Experimentally, we conducted two laboratory tests in a 2D sandpack model to study the primary production of a heavy oil–methane (CH4) system by using a differential fluid production (DFP) method with two different pressure depletion step sizes. Theoretically, we developed a material-balance-based tank model to describe the foamy-oil productions in these two tests. In this model, the amounts of dissolved and evolved gases were determined directly from material-balance equations by using the measured production data. The subsequent gas-liberation process was modeled through a pressure-dependent relation with two adjustable parameters, which were determined using the measured free-gas–oil ratio (GOR) from the sandpack tests. The model was further used to generate the foamy-oil and free-gas relative permeabilities for the tests. Subsequently, numerical validation was performed against CMG-STARS simulations conducted under different depletion scenarios, which showed similar production trends. This comparison shows that the proposed theoretical model captures the essential features of foamy-oil flow and indicates its potential as a practical and efficient alternative for screening cold heavy oil production (CHOP) reservoirs.