四川盆地永川区块五峰组—龙马溪组深层页岩可压性评价

Evaluation on the fracability of deep shale in Wufeng-Longmaxi Formation,Yongchuan block,Sichuan Basin

为了开展四川盆地永川区块3500 m以深页岩气储层的可压性评价,以该区块上奥陶统五峰组—下志留统龙马溪组深层页岩储层岩心为研究对象,研究了页岩岩心的单轴岩石力学性能参数、三轴岩石力学性能参数、X射线衍射成分分析,以及脆性指数、水平差应力系数、成岩作用、断裂韧性对深层页岩可压性的影响,并且通过层次分析法确定了4个主要影响因素的权重值,建立了永川区块五峰组—龙马溪组深层页岩可压性评价模型;进而利用永川区块5口页岩气井压裂施工过程中的停泵压力对模型进行验证,并运用该模型指导了YY5-2井现场24段压裂施工。研究结果表明:①基于脆性指数、水平差应力系数、成岩作用、断裂韧性建立的可压性评价模型能够较好地反映永川区块深层页岩的可压性,利用该模型进行页岩储层可压性分级对现场压裂施工具有指导作用;②基于脆性指数、水平差应力系数、成岩作用、断裂韧性建立的可压性评价模型与停泵压力的相关性仅为83.13%,为提高永川区块五峰组—龙马溪组深层页岩可压性模型的预测精度,还需要进一步考虑其他因素对于可压性的影响。

In order to evaluate the fracability of some shale reservoirs with burial depth over 3500 m,many cores sampled from deep shale reservoirs of Wufeng-Longmaxi Formation in Yongchuan block were taken as objectives to analyze the uniaxial and triaxial rock mechanical parameters,and X-diffraction composition and study the effects of brittleness index,horizontal stress difference coefficient,diagenesis,and fracture toughness on this fracability.The weight of these four affecting factors was determined by means of analytical hierarchy process(AHP).And one model to evaluate the fracability was established and then verified by using pump-off pressure in five shale gas wells during fracturing.Furthermore,this model was used to guide a 24-staged fracturing for YY5-2 well.Results show that(1)this established model based on brittleness index,horizontal stress difference coefficient,diagenesis,and fracture toughness can not only better reflect the fracability of deep shale in Yongchuan block but also be used to classify the fracability so as to guide on-site fracturing;and(2)it is only 83.13% correlated with the pump-off pressure.Therefore,in order to improve its accuracy to evaluate the fracability in Wufeng-Longmaxi Formation,it is necessary to further consider other factors affecting the fracability.