Study On Gas - Assisted Gravity Driving Mechanism In Wangyuan Oilfield

Gas injection is one of the important methods to enhance the recovery of oil in the world, which has developed relatively late in China, but its application in low-permeability oil reservoir in China is not effective for poor miscibility and early gas breakthrough. As one of the successfully applied gas injection method, gas-assisted gravity drainage (GAGD) that takes advantage of the gravity difference of gas cap and oil can obtains sweep efficiency larger than90%for high dip oil reservoir or high permeability and thick oil reservoir. This technology is not well applied in the domestic, so matching relationships among oil reservoir, dip angle, gas injection rate, physical properties are worthy of further study.In this paper, starting from mechanism study of GAGD, based on the gas flooding experiment on the same natural cores taken from Wang Chang Oil Field under the conditions with and without dip angle, phase behavior of dry gas injection into reservoir oil and long core flooding is simulated in a phase behavior analysis software to provide the realistic basic seepage flow data for three-dimensional reservoir numerical simulation study. Applying numerical simulation theory and research technology, conceptual model is established to analyze the advantages of GAGD over water flooding, gas flooding and WAG. Then adaptability analysis of GAGD in oil reservoir (permeability, formation dip angle, formation thickness, porosity, heterogeneity and oil saturation) and injection-production parametric analysis (injection rate, production rate and pressure level) is carried out. Comparison and practical calculation of three oil recovery prediction method is conducted to lay a theoretical foundation for the production prediction of GAGD.The research result shows that, for the great difference of formation conditions and oil properties between domestic formation and the abroad, GAGD technology should be improved before being applied in China. GAGD is suitable for the light oil reservoir with oil viscosity lower than3.42mPa-s, permeability larger than100mD, dip angle larger than15°and thick formation, porosity smaller than25%. Stable displacement interface can be formed based on proper control of gas injection parameters. The above mentioned conclusions are of referential value for the screen of oil reservoir and determination of technological parameters for GAGD.