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

摘要： 中国陆相页岩油藏黏土矿物丰富且纹层发育显著,储层岩性复杂多样,原油赋存空间呈现有机孔、无机孔与层理缝等多种形态,并具有多尺度分布特征。因此,准确表征页岩油藏渗流规律并精确预测其表观渗透率十分困难。基于纳米尺度束缚效应以及不同流动边界条件,分别推导了有机孔、无机孔和微裂缝中的流速方程;同时,考虑孔—缝分布特征与排列组合方式,构建了适用于裂缝性陆相页岩油藏的综合表观渗透率预测模型。以济阳坳陷页岩油藏为例,系统阐明了孔—缝组合方式、总有机碳(TOC)含量、纳米束缚效应以及裂缝分布特征对页岩油藏表观渗透率的影响。研究结果表明,陆相页岩油藏低速非线性渗流特征主要受液—固界面滑移效应与吸附边界层效应制约,其中有机孔的滑移效应有助于提高渗流速度,而无机孔的吸附边界层效应则起到抑制作用。孔—缝排列方式对表观渗透率具有显著影响,尤其在串联排列中表现出明显的非线性特征,表明TOC含量对渗流特性影响显著。此外,在低压力梯度条件下,无机孔和微裂缝等大孔隙是主要流动通道,且微裂缝的表观渗透率随裂缝密度的增加呈现非线性增长趋势,裂缝开度的增大则显著提升其渗透率,尤以层状页岩油藏中的表现最为突出。

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