深层页岩在高水平应力差作用下压裂裂缝形态实验研究

Experimental research on the morphology of hydraulic fractures in deep shale under high difference of in-situ horizontal stresses

针对高水平地应力差下的深层页岩开展真三轴水力压裂物模实验,分析其裂缝形态和影响因素。实验结果表明:高水平地应力差下水力裂缝沿垂直最小主应力方向起裂并扩展成横切缝,受层理和天然裂缝的影响会发生穿透、沟通或转向行为,深层页岩裂缝形态可以分为4种:单一横切缝、伴随层理开启的多横切缝网,转向缝网和受天然裂缝影响的复杂缝网;水平地应力差的增大会增加水力裂缝的穿透能力;起裂压力越大,裂缝形态越复杂;先注入高黏度压裂液可以形成水平主缝,之后注入低黏度压裂液造分支缝,可以有效提升深层页岩改造体积。该实验结果可以为深层页岩压裂方案设计提供参考。

A series of hydraulic experiments are conducted to investigate the morphology of fractures in deep shale under high difference of horizontal in-situ stresses using a triaxial fracturing system. The results indicate that the hydraulic fractures always crack in the direction perpendicular to the minor principal stress,and extend,penetrate,connect or deflect when encounter the bedding planes and natural fractures. The fracture morphology have four categories：simple fracture,fractures with bedding planes opening,fractures with deflection and complex fractures affected by natural fractures. The increasing of horizontal stress difference leads to a higher penetrating ability of fractures. The higher the initial pressure,the more complex the fracture morphology. Stimulated reservoir volume can be improved by injecting the high viscosity fracturing fluid to generate the main fractures and by injecting the low viscosity fluid to open the branching fractures.