Li Yang, Zhang Wenlong, Fei Yu, Lan Tianxiang, Wang Yongqian
School of Smart City Engineering, Qingdao Huanghai University, Qingdao, Shandong 266427, China.
College of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing 100083, China.
ACS Omega. 2025 Jun 13;10(25):26349-26367. doi: 10.1021/acsomega.4c09521. eCollection 2025 Jul 1.
The presence of bedding plane in laminated shale reservoir has an indelible impact on reservoir displacement, deformation, continuity of stress field, and mechanical perturbation among multiple fractures. Rational and thorough exploitation of the mechanical disturbance mechanism of the bedding surface in multistage hydrofracturing provides a shortcut for the production and efficiency increase of unconventional hydrocarbon reservoirs in practical engineering. Based on the framework of bidirectional mechanical coupling adaptive finite and discrete element method and referring to different vertical well fracturing schemes, this article evaluates the fracture evolution discipline after mechanical perturbation caused by multiple coin-shaped nonplanar hydrofractures and bedding planes. The numerical model integrates routinely obtained reservoir geomechanical data with physical properties of the bedding plane to quantify the complexity, mechanical behavior, and residual conductivity of the hydrofracture network. The numerical model is proven to be practical and reliable in theory and physical experiments. The local mesh refinement and coarsening technique around the fracture surface and on the bedding plane provide a reliable guarantee for improving the computation efficiency and evolution stability of nonplanar coin-shaped fractures. The mutual perturbation factor based on weight function theory and the statistical fracture surface area and volume are introduced to quantitatively evaluate and characterize the fracturing efficiency. Numerical experiments indicate that the fluctuation of stress value on the fracture surface is very sensitive to perforation spacing. The mutual disturbance factor and the statistical stimulated reservoir area and volume confirm that there is an optimal reorientation timing due to undirectional squeezing effect in sequential fracturing of a single vertical well and the bedding plane possesses a hurdle effect on unidirectional compressive pressure transmission and reservoir displacement, which makes it discontinuous, mitigates the optimal reorientation phenomena, and leads to a worse fracture network in the case of single vertical well fracturing with the bedding plane. Higher statistical fracture volume and higher pore pressure can be obtained by alternative fracturing with a bedding plane in twin vertical well fracturing. There is a conversion relationship between the statistical fracture area and volume in the specific case of multistage fracturing of the twin vertical well. Isosurface domain of differential vertical principal stress is intertwined in the whole fracturing process, resulting in a lower statistical reservoir area and pore pressure. However, the coverage disturbance domain of the stress field is not necessarily related to the pore pressure, and the disturbed global matrix may be more prone to damage and fractures.
层状页岩储层中层面的存在对储层位移、变形、应力场连续性以及多裂缝间的力学扰动有着不可磨灭的影响。合理深入地探究多级水力压裂中层面的力学扰动机制，为实际工程中非常规油气藏的增产提效提供了一条捷径。基于双向力学耦合自适应有限元和离散元方法框架，参考不同的垂直井压裂方案，本文评估了多个币形非平面水力压裂和层面引起的力学扰动后裂缝的演化规律。该数值模型将常规获取的储层地质力学数据与层面物理性质相结合，以量化水力压裂网络的复杂性、力学行为和残余导流能力。经理论和物理实验证明，该数值模型切实可靠。裂缝表面和层面周围的局部网格细化与粗化技术，为提高非平面币形裂缝的计算效率和演化稳定性提供了可靠保障。引入基于权函数理论的相互扰动因子以及统计裂缝表面积和体积，以定量评估和表征压裂效果。数值实验表明，裂缝表面应力值的波动对射孔间距非常敏感。相互扰动因子以及统计的增产储层面积和体积证实，单垂直井连续压裂中由于单向挤压效应存在一个最佳重新定向时机，且层面在单向压缩压力传递和储层位移方面具有阻碍作用，这使其不连续，减轻了最佳重新定向现象，导致在有层面的单垂直井压裂情况下裂缝网络更差。在双垂直井压裂中采用有层面的交替压裂可获得更高的统计裂缝体积和更高的孔隙压力。在双垂直井多级压裂的特定情况下，统计裂缝面积和体积之间存在转换关系。整个压裂过程中垂向主应力差等值面域相互交织，导致统计储层面积和孔隙压力较低。然而，应力场的覆盖扰动域不一定与孔隙压力相关，受扰动的整体基质可能更容易受损和产生裂缝。
