煤层水力裂缝扩展判定模型建立及验证

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。研究显示：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。该研究对于认识煤层压裂裂缝形成机理,建立复杂裂缝表征模型,提供压裂设计新理念具有一定的指导意义。

Establishment and Verification of Hydraulic Fractures Propagation Model for Coal Seam

It is hard to describe the complex fracture types. According to the rock strength damage criteria, the model of propagation when the hydraulic fractures come across the weak structural plane was studied, and laboratory experiment verified the reliability. The extending behavior of hydraulic fracture was analyzed when intersecting the weak surface using mine application. The results shows 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. This study has the important significance to understand coal-seam complex fracture forming mechanism and establish the complex fracture forming model.