Synergistic flooding and gravity drainage by steam and gas (SFGD) is an innovative alternative to SAGD and SAGP, considering its potential to enhance oil recovery and improve oil production rate. This research presents 3D physical experiments and of numerical simulations of SFGD in offshore heavy oil reservoir in Bohai Oilfield, China.

3D physical experiments of SAGP and synergistic flooding and gravity drainage by steam and gas (SFGD) are carrird out. The expanding process of the steam chamber and the production performance in different stages are compared between SAGP and SFGD. And the mechanism of SFGD are analyzed. Then, through detailed reservoir numerical simulations of SFGD, the reasonable deployment modes of injection-production wells are given, and injection-production parameters such as gas-water ratio, and steam injection rate are optimized.

3D physical experiments results show that synergistic flooding and gravity drainage by steam and gas (SFGD) can greatly shoren the production time and redcce the cumulative steam injection compared with SAGP. The ultimate oil recovery rate of SFGD is 59.15%, 6.02% higher than that of SAGP (53.13%). The EOR mechanisms of SFGD mainly includes the synergistic effect of flooding and gravity drainage, increasing the velocity of heat conduction and increasing the sweep efficiency. Numerical simulations results show that the injection wells should be located in the upper middle of the reservoir during the development process of SFGD, so as to achieve maximum ultimate oil recovery and high oil production rate. For LD heavy oil reservoir with a formation depth of 1000 m, a thickness of 25 m and a viscosity of 21500 mPa·s, the vertical distance between the injection well and the production well is about 15 m, and the reasonable gas-water ratio of SFGD is 100-150 in condition of injection temperature of 300°Cand production pressure of 2 MPa, and the optimal steam injection rate is 100-120 m3/d.

Synergistic flooding and gravity drainage by steam and gas (SFGD) is a new and more effective method to develop heavy oil reservoir. The effective combination of displacement and gravity drainage can greatly improve oil production rate and recovery efficiency.

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