Abstract:

Accurately monitoring the propagation of orthogonal fractures in shale reservoirs is of great significance for optimizing construction parameters and improving economic benefits. In response to the difficulty of evaluating the propagation of orthogonal fractures in on-site fiber-optic monitoring, a mechanical model for adjacent well fiberoptic monitoring orthogonal fracture propagation considering the tensile mechanical behavior during the fracture propagation process is established. Physical simulation experiments are conducted on horizontal well fracturing of shale specimens using fiberoptic monitoring. The mechanism of adjacent well fiber-optic monitoring orthogonal fractures is revealed, and the evolution characteristics of adjacent well fiber-optic strain induced by orthogonal fracture propagation are elucidated. A method for evaluating the propagation of orthogonal fractures based on adjacent well fiber-optic strain data was constructed. Research has shown that orthogonal fracture propagation induces five stages of strain enhancement stage, strain contraction convergence stage, strain linear stage, compressive strain contraction convergence stage, and strain stabilization stage in horizontal adjacent well optical fibers; orthogonal fractures induce three stages of strain enhancement stage, strain linear convergence stage, and strain divergence stage in vertical adjacent well optical fibers; the distance between the adjacent well optical fiber and the injection point determines the strength of the fiber-optic strain response signal. If the distance between the adjacent well optical fiber and the wellbore is too far, it will lead to the absence of the fiber-optic strain evolution stage. In physical simulation experiments, fiber-optic strain data can determine the number of hydraulic fractures and fractures initiation time. Competitive propagation phenomena may occur during orthogonal fracture propagation, and there is mutual influence between the vertical and horizontal sensing segments of the optical fiber. This study provides important reference for the effective monitoring and construction parameter optimization of orthogonal fractures in shale oil and gas reservoirs.

Key words: distributed fiber-optic sensing, fiber-optic strain, hydraulic fracturing, orthogonal fractures, fiber slippage

摘要：

准确监测页岩储层压裂正交裂缝的生成与扩展对于优化施工参数和提高经济效益具有重要意义。针对现场光纤监测正交裂缝扩展评价困难的问题，建立考虑裂缝扩展过程中的拉伸力学行为的邻井光纤监测正交裂缝扩展力学模型，开展光纤监测页岩试样的水平井压裂室内物理模拟试验，揭示了邻井光纤监测正交裂缝的力学机理，阐明了正交裂缝扩展诱发邻井光纤的应变演化特征，构建了根据邻井光纤应变数据评价正交裂缝扩展情况的方法。研究表明：正交裂缝扩展诱发水平邻井光纤应变响应会出现应变增强、应变收缩汇聚、应变直线状、压应变收缩汇聚及应变平稳五个阶段；正交裂缝诱发垂直邻井光纤应变响应会出现应变增强、应变直线状汇聚及应变发散三个阶段；邻井光纤与注入点的距离决定了光纤应变响应信号的强度，邻井光纤与井筒距离过远会导致光纤应变演化阶段的缺失；物理模拟实验中光纤应变数据可确定水力裂缝数量及起裂时间，正交裂缝扩展过程中会出现竞争扩展现象，光纤竖直传感段与水平传感段存在相互影响，本研究为页岩油气藏正交裂缝的有效监测和施工参数优化提供了重要参考。

关键词: 分布式光纤监测, 光纤应变, 水力压裂, 正交裂缝, 光纤滑移