基于结构弱面及缝间干扰的页岩缝网压裂技术

Network fracturing technique in shale reservoirs based on weak discontinuity and fracture interaction

为明确页岩储层中层理、天然裂缝等结构弱面和缝间干扰对缝网压裂效果的影响机制,根据全三维物模实验所观察到的裂缝扩展现象,理论分析了结构弱面控制下和缝间干扰影响下复杂裂缝的形成机制,并结合数模研究对现场有助于形成复杂裂缝的多种施工工艺和方法进行了探讨。最终得出:结构弱面可使与之相遇的水力裂缝停止、转向或产生新缝,结构弱面发生剪切错动或张开后均可成为页岩气流动通道;此外,缝间干扰会影响后续裂缝的几何形态,从而改变其与结构弱面的逼近角;2级主裂缝间可以产生分支缝,有利于增加裂缝复杂度,适当降低裂缝间距可在一定程度上增强缝间干扰。目前已进行矿场试验的大排量低黏压裂液、暂堵转向、平台"拉链式"压裂等措施取得了较好的监测结果,作业方式的改进和不同压裂技术的综合应用也是增加裂缝复杂度的有效途径。

Network fracturing technique is important for the development of shale gas.To investigate the influence of weak discontinuities and fracture interaction on network fracturing result,the formation of complex fractures under weak plan and fracture interaction was analyzed theoretically on the basis of full threedimensional physical simulation experiments.With combination of numerical simulation,several methods contributing to complex fractures were discussed.The results show that the hydraulic fracture may stop extension,swerve or initiate new fracture when it intersects with the plan.The weak discontinuity can become effective channel for gas to flow after it was opened or was shear dislocated.The hydraulic fracture occurring afterwards was influenced by the fracture generating beforehand due to the fracture interaction and then its approaching angle with weak plan changed.Branch crack occurred between two principle fractures and that was helpful to the formation of complicated fracture network.Proper reduction of fracture interval is in favor of enhancing the interaction at some extent.Some methods that had been tested in the field have obtained satisfactory monitoring results.The change of fracturing process and the combination of different techniques can be effective ways to enhance the fractures complexity.