页岩气储层变排量压裂的造缝机制

裂缝性页岩储层压裂时,如何通过调节压裂泵排量,使水力裂缝沟通更多天然裂缝,是缝网压裂的关键。选取龙马溪组页岩露头开展真三轴水力压裂试验,压裂过程中以逐步阶梯式方式提高排量,实时分析变排量压裂时水力裂缝扩展行为以及与天然裂缝的沟通情况。试验结果表明：采用变排量压裂,初始阶段,随着压力逐渐升高,会在井筒周围的弱面附近产生多个待破裂点,随排量突然提高会使水力裂缝沿着多个破裂点动态分叉扩展。随着排量阶梯式升高,泵压明显升高,排量越大,泵压波动越大,水力裂缝与天然裂缝沟通形态越复杂,天然裂缝产状和缝内净压力等影响到水力裂缝进一步沟通程度。试验结果证实,变排量压裂可以激活更多天然裂缝,有助于形成复杂裂缝网络。

Fracturing mechanism of shale gas reservoir with variable pump rates

Strengthening the interaction between hydraulic fractures and natural fractures by the adjustment of pump pressure is the key of fracture network. Longmaxi shale outcrops are selected to study the propagation of hydraulic fractures and the interaction between hydraulic fractures and natural fractures by utilizing tri-axial fracturing test system. The pump pressure increases in a step-wise manner during the tests. The experimental results indicate that the variable pump rates can gradually build the pressure, which generates many under-fracture points in weak planes around the wellbore. Hydraulic fractures will have dynamic extension along these under-fracture points when there is a sudden increase of pump rate. As the pump rate increases in a step-wise manner, the pump pressure significantly increases. Higher pump rate leads to a more fluctuant pump pressure and a more complex fracture network. The occurrence and geometric distribution of natural fractures and net pressure can influence the degree of further interaction. The results prove that the variable pump rates can activate more natural fractures, which contributes to form complex fracture network.