Abstract

With the growing significance of shale oil in the realm of oil and gas resources, there has been a heightened focus on the impact of the indeterminate oil–water two-phase flow behavior in shale reservoirs on the effective exploitation of shale oil. The utilization of FIB–SEM scanning on shale samples enables the establishment of the real pore network structure and facilitates the analysis of pore type, pore throat size and connectivity of shale reservoirs through the implementation of two-dimensional slices. Subsequently, the gridded connectivity-based pore network model is utilized to conduct oil–water two-phase flow simulation, wherein the L–S and N–S mathematical models are incorporated to quantitatively examine the correlation between the displacement pressure and wettability and the recovery degree and remaining oil, as well as the impact of throat size on pressure loss. The research findings indicate the emergence of five distinctive pore types in shale reservoirs, namely intergranular pores, dissolution pores, intercrystalline pores, intracrystalline pores, and microfractures. In shale reservoirs with poor connectivity, a significant quantity of nanometer-scale pores are generated, wherein the seepage capacity is primarily influenced by the size and connectivity of pore throats. The smaller the throat size is, the greater the displacement pressure will be and the greater the pressure drop will be after the throat is passed through. To prevent fingering and excessive pressure drop, it is necessary to maintain reasonable control over the displacement pressure. The displacement efficiency is optimal when the wall surface is in a water-wet state. Therefore, enhancing the wettability of the surface can facilitate the efficient recovery of the remaining oil in the microscopic pore throats. The research findings offer valuable theoretical insights for the efficient exploitation of shale oil resources.

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