Abstract
With huge reserves and wide distribution, tight oil and gas resources are the focus and hotspot of unconventional oil and gas research in recent years. In this paper, firstly, the multi-scale model of CO2 fracturing gas is established by considering the phase evolution characteristics of CO2. Secondly, considering the hydrophilicity of the tight reservoir, a microscale seepage model of CO2 under the adsorption condition of fracturing fluid is proposed. Again, considering the shrinkage effect of dense reservoir matrix, a dynamic coupling model of gas-liquid-solid under CO2 fracturing conditions is established. The results show that: (a) When the volume of the adsorbed layer of CO2 fracturing fluid accounts for 10% of the pore volume and the CO2 concentration is 20%, the fluid transport in the tight reservoir shows significant separation characteristics. (b) More CO2 enters the crude oil after considering the diffusion effect of CO2 body. The influence of CO2 diffusion mechanism on oil recovery should not be neglected. (c) Enhancement of elastic energy is one of the main mechanisms by which CO2 improves oil driving efficiency in tight reservoirs.
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