天然页岩压裂裂缝扩展机理试验

采用大尺寸真三轴试验系统对页岩露头开展了水力压裂裂缝扩展模拟试验,并利用高能CT扫描观测压后岩心内部裂缝形态,研究了多种因素对页岩水平井压裂裂缝扩展规律的影响。试验条件下的研究结果表明:排量对裂缝复杂度的影响存在一定的范围;当水平地应力差小于9 MPa时,水力裂缝易沿天然裂缝转向,形成网状缝。随着应力差的增加,主裂缝(横切缝)的产生有利于沟通更多的天然裂缝,形成相对更复杂的裂缝;相同水平应力差条件下,水平应力差系数大于0.25时,有明显形成单一主裂缝的趋势;排量和压裂液黏度对水力裂缝几何形状的影响可用参数qμ表达,该值较低或较高都不利于缝网的产生;页岩层理的发育和胶结强度严重影响压裂缝网的复杂度。

Fracture propagation mechanism experiment of hydraulic fracturing in natural shale

Hydraulic fracturing simulation experiments of shale outcrops were carried out by a true triaxial test system. The effects of multiple factors on fractures propagating law of horizontal well in shale formation were studied, and fracture morphology were observed by high-energy CT scanning. The results show that there is a certain range for the effects of delivery rate on fracture complexity. When the horizontal stress difference is less than 9 MPa, hydraulic fracture easily propagates along the natural fractures, forming fracture network. In this range, when the stress difference is increased, the main hydraulic fracture (transverse fracture) can be formed more easily and communicate more natural fractures, forming a relatively more complex fracture system. Under the condition of the same horizontal stress difference, if the stress difference coefficient is greater than 0.25, the obvious single main fracture will form. The effects of viscosity of fracturing fluid and delivery rate on fracture propagation can be expressed by the parameter qμ. Too small or too large value show that fracture network is not easy to produce. The development and cementation intensity of shale depositional bedding seriously affect the fracture propagating complexity of hydraulic fracturing.