基于声波监测技术的长庆砂岩裂缝扩展实验

Experimental study of Changqing sandstone fracture propagation based on acoustic monitoring

针对在全三维水力压裂物理模拟实验中,水力裂缝实时扩展形态无法准确描述的问题,利用被动声波监测技术,研究水力裂缝在超大型(762cm×762cm×914cm)天然砂岩岩样中的扩展机理.结果表明:水力压裂裂缝呈经典的径向形态扩展,与实际裂缝形态一致;实验条件下,径向裂缝延伸净压力受断裂韧性的控制,与通常现场裂缝延伸净压力受流体黏性控制有很大区别.为与现场裂缝扩展进行相似对比,建议物模实验参数设计应适当提高液体黏度及排量,同时降低岩样断裂韧性.声波监测技术在超大尺寸水力压裂实验中的应用,可为现场水力压裂裂缝微地震监测技术应用提供指导.

How to describe fracture propagation in real-time precisely in the physical simulation is still big challenge.It's the first time to use acoustic monitoring technology to investigate the mechanism of fracture propagation in large-scale(762 cm×762 cm×914 cm)sample.The results show correctly that the fracture is propagating in radial shape.Based on acoustic data,we have probed into the fracture propagation mechanism.The results show that in lab conditions radial fracture propagating net pressure was controlled by fracture toughness instead of fluid flowing that controls fracture propagation in field.In order to meet the fracture propagation similarity between field and lab,it is advised to design experiment with low fracture toughness,higher injection rate and higher fluid viscosity.The application of acoustic monitoring to the hydraulic fracturing experiment successfully will supply valuable conclusions to guide the seismic monitoring in field.