陆相页岩储层水力裂缝穿层扩展规律

Through-layer propagation laws of hydraulic fractures in continental shale reservoirs

赵彦昕 许文俊 王雷 张光明 赵金洲

ZHAO Yanxin XU Wenjun WANG Lei ZHANG Guangming ZHAO Jinzhou

长江大学石油工程学院 油气钻采工程湖北省重点实验室 油气藏地质及开发工程国家重点实验室 · 西南石油大学

College of Petroleum Engineering, Yangtze University, Wuhan 430100, Hubei, China Hubei Key Laboratory of Oil & Gas Drilling and Production Engineering, Wuhan 430100, Hubei, China State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, Sichuan, China

陆相页岩储层垂向非均质性强，层间岩性与应力差异大，层间弱界面发育，水力裂缝穿层扩展困难，导致压裂改造效果不佳。基于有限元+黏聚力单元法建立了陆相页岩水力裂缝穿层扩展流固耦合模型，与解析解和室内实验结果对比验证了模型的准确性。基于此模型，采用单因素和正交实验分析法开展算例研究，揭示了各项地质与工程参数对陆相页岩储层水力裂缝穿层扩展行为的控制机理与影响规律。研究结果表明，层间界面剪切滑移改变水力裂缝垂向扩展路径，限制缝高增长；水力裂缝宽度较大，削弱缝高扩展能力。高层间界面胶结强度、高垂向应力差、低层间应力差、低抗拉强度差、低弹性模量差、高压裂液黏度、高注入排量，有利于水力裂缝实现穿层扩展，各因素影响程度的主次顺序为层间界面胶结强度＞层间应力差/抗拉强度差＞压裂液黏度/注入排量＞垂向应力差＞弹性模量差。研究成果进一步完善了陆相页岩储层水力压裂穿层扩展基础理论，为陆相页岩储层水力压裂选井、选层和施工方案优化设计提供了理论依据。

Continental shale reservoirs are characterized by strong vertical heterogeneity, large inter-layer lithological and stress differences and developed weak interfaces, which make through-layer propagation of hydraulic fractures difficult, leading to poor fracturing stimulation effects. In this paper, a fluid-solid coupling model of through-layer propagation of hydraulic fractures in continental shale was established based on finite element + cohesive unit method, and its accuracy was verified by comparing the analytical solution with the laboratory experimental result. Based on this model, a case study was carried out by means of single factor and orthogonal experiment analysis method, and the control mechanisms and influence laws of geological and engineering parameters on through-layer propagation behaviors of hydraulic fractures in continental shale reservoirs were clarified. It is indicated that the main mechanisms hindering the through-layer propagation of hydraulic fracture are that interface shear slide changes the vertical propagation path of hydraulic fracture, so as to restrict the increase of fracture height, and hydraulic fracture is wider, leading to the weakening of fracture height expansion capacity. High interface bonding intensity, vertical stress difference, and fracturing fluid viscosity and injection rate, and low inter-layer stress difference, tensile strength difference and elastic modulus difference are favorable for the through-layer propagation of hydraulic fracture, and their influence degree is ranked as interface bonding intensity > inter-layer stress difference > tensile strength difference > fracturing fluid viscosity/injection rate > vertical stress difference > elastic modulus. The research results further improve the basic theories on through-layer propagation of hydraulic fractures in continental shale reservoirs, and provide a theoretical basis for well and layer selection and construction scheme optimization design of hydraulic fracturing of continental shale reservoirs.

10.13639/j.odpt.2023.01.010