Yu Chunlei, Zhang Shiming, Chen Ting, Sun Zhigang, Xu Jiaxiang
Exploration and Development Research Institute of Sinopec Shengli Oilfield Company, Dongying, China.
State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Efficient Development, Dongying, China.
Sci Rep. 2025 Jan 6;15(1):936. doi: 10.1038/s41598-024-84882-3.
The laminae of varying lithologies are characteristic of shale oil reservoirs, with their pronounced heterogeneity and fluid-solid coupling significantly impacting oil productivity. To this end, this study initially quantified the permeability and mechanical heterogeneity in lamina-developed shale through permeability tests and quasi triaxial mechanical experiments on shale cores from different orientations in the Jiyang Depression. These tests revealed marked brittleness in horizontally oriented cores and elasticity in vertically oriented cores. Subsequently, the strong fluid-solid coupling in lamina-developed shale formations was hereby investigated by permeability stress sensitivity experiments and CT scanning, which presented the dynamic opening and closing of laminae and strong fluid-solid coupling in horizontal direction during the fracturing shut-in and production (FSP). Based on online nuclear magnetic resonance (NMR), fluid migration in pores of different scales and laminae during the FSP was discovered. To detail the fluid seepage mode in lamina-developed shale oil reservoirs during FSP, an oil-water two-phase flow model coupling shale matrix, laminae, and hydraulic fractures was further simulated, based on the permeability heterogeneous and stress sensitivity, to delve into the variation in saturation, pressure, relative permeability, and streamlines of water in lamina-developed shale cores. The results showed that during the hydraulic fracturing, the horizontal brittleness, and vertical elasticity created a seepage channel composed of shale matrix, horizontal seams, and vertical hydraulic fractures. During the shut-in period, the expanded seepage area resulting from the opening of the laminae, combined with the extremely high pressure gradient from the seam to the matrix, facilitated the invasion of fracturing fluid into the matrix, displacing shale oil and gradually balancing the pressure among the three seepage media. During production, the extremely high pressure gradient shifted from the matrix to seams and hydraulic fractures, and oil and water were simultaneously extracted. However, due to stress sensitivity and variations in relative permeability, fracturing fluid remained trapped in the shale formation.
不同岩性的层理是页岩油储层的特征，其显著的非均质性和流固耦合对石油产能有重大影响。为此，本研究首先通过对济阳坳陷不同方向页岩岩心进行渗透率测试和准三轴力学实验，量化了层理发育页岩的渗透率和力学非均质性。这些测试表明，水平方向岩心表现出明显的脆性，垂直方向岩心表现出弹性。随后，通过渗透率应力敏感性实验和CT扫描研究了层理发育页岩地层中的强流固耦合现象，结果显示在压裂关井和生产（FSP）过程中层理的动态开合以及水平方向的强流固耦合。基于在线核磁共振（NMR），发现了FSP过程中不同尺度孔隙和层理中流体的运移情况。为详细描述FSP过程中层理发育页岩油储层的流体渗流模式，基于渗透率非均质性和应力敏感性，进一步模拟了耦合页岩基质、层理和水力裂缝的油水两相流模型，以深入研究层理发育页岩岩心中饱和度、压力、相对渗透率和水流线的变化。结果表明，在水力压裂过程中，水平脆性和垂直弹性形成了由页岩基质、水平缝和垂直水力裂缝组成的渗流通道。在关井期间，层理张开导致渗流面积扩大，加上从缝到基质极高的压力梯度，促使压裂液侵入基质，驱替页岩油并逐渐平衡三种渗流介质之间的压力。在生产过程中，极高的压力梯度从基质转移到缝和水力裂缝，油水同时被采出。然而，由于应力敏感性和相对渗透率的变化，压裂液仍滞留在页岩地层中。
