Investigation on Principles of Enhanced Offshore Heavy Oil Recovery by Coinjection of Steam with Flue Gas

Abstract

Abstract In consideration of the difficulty to setup conventional steam generator on offshore production platform, a compact steam and flue gas generator is developed to thermally stimulate offshore heavy oil reservoir, which consists of water treatment and injection unit, fuel injection unit, air injection unit, and metering and controlling unit. The temperature of steam and flue gas generated is usually 200-350°C with 13.1-28.3wt% flue gas, the injection pressure could be up to 20MPa, and steam injection rate is 80-270 m3/day. In past two years, cyclic steam-flue gas co-injection are applied to 8 offshore horizontal heavy oil wells completed thermally or non-thermally with screen pipe, and up to 3 times of oil production rate in average is observed compared to that of cold production, the peak oil production is more than 100 m3/day. In order to optimize the steam and flue gas co-injection strategy, laboratory experiments such as rheological characteristic measurement and PVT visualization of mixture of heavy oil and flue gas, 1D micro model displacement and 3D macro sandpack model stimulation, and numerical simulation are carried out to investigate the EOR principles. It shows significant synergistic EOR effect in steam and flue gas co-injection because of the foamy oil flow, improvement in heating and sweeping efficiency and gravity assisted drainage, besides of the combined reduction in oil viscosity by heating and gas solution. Flue gas plays an important role in co-stimulation of heavy oil with lower viscosity (500-2000mPa•s under reservoir condition) for the foamy oil flow and enlargement of heating and sweeping efficiency, at the same time, steam heating becomes more important for heavy oil with larger viscosity. At last, based on above researching results an empirical formula is developed to optimize ratio of flue gas to steam according to special reservoir conditions.