关键词: 陆相页岩油, 纳米束缚效应, 表观渗透率, 孔—缝组合方式, 数学模型

Abstract: Continental shale oil reservoirs in China are characterized with abundant clay minerals, well-developed laminae, and complex and diverse lithologies. The crude oil is accumulated in organic pores, inorganic pores, and bedding fractures, featuring multi-scale distributions. Therefore, it is very difficult to accurately characterize the flow mechanism of shale oil reservoirs and precisely predict their apparent permeability. Based on the nano-confinement effects and different flow boundary conditions, flow velocity equations were derived for organic pores, inorganic pores, and micro-fractures. Meanwhile, considering the distribution characteristics and arrangement-combination patterns of pores and fractures, a comprehensive apparent permeability prediction model for the fractured continental shale reservoirs was established. Taking the Jiyang depression shale oil reservoir as a case study, a systematical analysis was conducted on the effects of pore-fracture combination patterns, total organic carbon (TOC)content, nano-confinement effects, and fracture distribution characteristics on the apparent permeability of shale reservoirs. The results show that in continental shale oil, the low-velocity nonlinear flow behavior is mainly controlled by the liquid-solid interfacial slippage effects and adsorption boundary layer effects. The slippage effects in organic pores help increase the flow velocity, whereas the adsorption boundary layer effects in inorganic pores play a role in flow inhibition. The arrangement patterns of pores and fractures exert significant influences on the apparent permeability, with particularly pronounced nonlinear characteristics observed in serial arrangement, indicating the great impact of TOC content on flow behavior. Furthermore, under low-pressure gradient conditions, macropores such as inorganic pores and micro-fractures are the main flow channels, and the apparent permeability of micro-fractures increases nonlinearly with the increase in fracture density. The increase in fracture aperture significantly enhances its permeability, especially in laminated shale reservoirs.

Key words: continental shale oil, nano-confinement effect, apparent permeability, pore-fracture combination pattern, mathematical model