关键词: 特低渗透油藏, 天然气, 非混相驱, 采收率, 开发层系, 封堵

Abstract:

With a monolayer or two-layer physical model, a simulation experiment of the natural gas displacement in ultra-low permeability reservoirs was carried out. The results from the monolayer physical model showed that compared with water flooding, gas flooding in ultra-low permeability reservoirs might enhance not only the displacement efficiency but also the micro-sweep efficiency, increasing the recovery ratio by 4.5%. The subsequent natural gas injection after water flooding could gain a better effect of development, increasing the recovery ratio by 12.5%. Deliverability in oil wells kept high during the non-gas and low gas-liquid ratio stages, which were the major production period. The experimental results from the two-layer heterogeneous model indicated that since the real difference in interlayer permeability rates within reservoirs was much greater than that measured in laboratory, within the same suite of developed layers, the low permeable layer failed to inhale while the high permeable layer was well exploited due to gas flooding. The remaining oil would occur mainly in the low permeable layer as the high permeable layer was plugged with gel after a gas crossflow formed. After the plugging of the high permeable layer, the low permeable layer became active in gas-intake and could be completely exploited. The recovery ratio by the two-layer heterogeneous model was enhanced from 30.85% to 55.91%.

Key words: ultra-low permeability reservoir, natural gas, immiscible displacement, recovery ratio, layer system of development, plugging