关键词: 页岩油, 自扩散, 两相流, 模型研究, 流动机理

Abstract: When the bottom hole pressure is lower than the saturation pressure in the exploitation of shale reservoir, the dissolved gas turns into free gas due to reservoir pressure depletion, and the flow law of reservoir fluids becomes more complex. Thus, the influence of dissolved gas drive in the early stage should be considered in oil production prediction. The essential law of oil flow relying on the expansion of free bubbles has not been clarified in previous domestic and foreign researches. Based on the fluid self-diffusion model, a mathematical model of self-diffused two-phase flow has been established considering the release of dissolved gas due to reservoir pressure depletion, by which the coupling diffusion-flow process jointly controlled by reservoir pressure depletion and dissolved oil drive is characterized. Then the model is verified by comparing the results with existing experimental data. In the process of oil flow during the primary exploitation of tight shale reservoirs dominated by self-diffusion, the flow capacity of oil driven by gas expansion is increased with the formation of free gas released from dissolved gas and the increase of gas saturation in crude oil. Through analyzing the influence of bubble point pressure and dissolved gas-oil ratio on oil flow, it is found that under the same production conditions, the higher bubble point pressure or dissolved gas-oil ratio can significantly improve the gas saturation in crude oil, so that a larger amount of oil can be squeezed out, thus increasing oil output. Finally, according to research results, reasonable suggestions are proposed for exploitation of shale reservoir.

Key words: shale oil, self-diffusion, two-phase flow, model study, flow mechanism