煤层水力裂缝扩展判定模型建立及验证

Establishment and Verification of the Evaluation Model of Hydraulic Fracture Propagation in Coal Seam

为解决煤层压裂裂缝扩展难以表征的问题,针对煤层压裂裂缝扩展难以表征的问题,根据岩石强度破坏准则,建立了水力裂缝扩展路径判定模型,通过室内试验验证了模型可靠性,结合矿场应用分析了水力裂缝与弱面相交后的扩展行为。结果表明:水平主应力差、弱面方位角、弱面摩擦系数是影响水力裂缝扩展的重要因素,在高主应力比、高方位角、高弱面摩擦系数条件下水力裂缝易直接穿过弱面,在低主应力比、低方位角、低弱面摩擦系数条件下水力裂缝易发生转向,并沿弱面走向扩展。研究结果对于认识煤层压裂裂缝形成机理,建立复杂裂缝表征模型及压裂设计提供了新思路。

In order to characterize fracture propagation in coal seam fracturing,It is difficult to characterize fracture propagation in coal seam fracturing.According to the rock strength damage criteria,the model of propagation when the hydraulic fractures came across the weak structural plane was studied,and laboratory experiments verified its reliability.The extending behavior of hydraulic fracture was analyzed when intersecting the weak surface using mine application.The results show that the important factors of impacting propagation are horizontal stress differential,azimuth of weak plane and coefficient of friction.It is easy for hydraulic fractures directly cross the weak plane under higher principal stress ratio,higher azimuth and higher coefficient of friction.By contrast,it is easy to propagate along the weak plane direction under the opposite condition.The research findings have great significance for understanding coal-seam complex fracture forming mechanism,establish the complex fracture forming model,and provide new ideas for fracturing design.