四川省宜宾地区龙马溪组页岩水力裂缝形态实验研究

水力压裂技术是页岩储层开发中的关键技术之一，如何实现储层改造体积的最大化，是制约当前页岩储层高效开发的技术难题。通过开展水力压裂物理模拟实验，直接观察水力压裂裂缝扩展形态，有助于准确认识裂缝扩展机理。通过对762mm×762mm×914mm四川盆地龙马溪组页岩露头和人工样品开展针对性实验研究，分别考察了天然裂缝，泵注参数(排量、黏度)对该龙马溪组页岩水力压裂裂缝形态的影响，同时采用声发射监测技术，对页岩储层声发射事件分布规律进行分析。结果表明，天然裂缝的存在是实现储层复杂裂缝形态的必要条件之一，其分布形态又决定了水力裂缝形态的复杂程度；对水力裂缝形态的评估需要将施工净压力、排量、黏度三者结合考虑，提高施工净压力有利于形成复杂裂缝，随着施工排量或黏度的增长，净压力呈现先增大后减小的规律，即当排量或黏度过高时，裂缝形态又趋于单一化；声发射监测结果能够客观反映裂缝在三维空间内的扩展趋势，声发射率和振幅与泵注压力曲线趋势一致，出现多个峰值，表明页岩水力裂缝扩展具有明显的非连续特征。本工作为页岩压裂机理研究探索了实验方法，为该区块现场体积压裂工艺设计、改造后评估提供实验依据。

Laboratory study on hydraulic fracture geometry of Longmaxi Formation shale in Yibin area of Sichuan Province

Hydraulic fracturing is an important technology in shale gas reservoir development.Due to complex geological conditions,it is hard to know fracture propagation mechanism clearly and how to maximize the stimulated reservoir volume (SRV) is the key issue for hydraulic fracturing.A series of tests have been done with shale blocks from Longmaxi Formation outcrop to simulate hydraulic fracturing in field.The effect of natural fractures,in situ stress conditions,and pump injection parameters on hydraulic fracture geometry have been studied respectively.Meanwhile,fracture propagation in real time was analyzed by acoustic emission monitoring technology.The experimental results showed that the existence and distribution pattern of natural fracture system determine the hydraulic fracture geometry.The higher injection net pressure would result in more complex hydraulic fracture system.But the pumping rate and fluid viscosity were not always directly proportional to the injection net pressure.Hydraulic fracture system would be simpler when the pumping rate and fluid viscosity exceed a limited level.According to the location of acoustic events in space,it could reflect the hydraulic fractures distribution range.The changing coherence of acoustic frequency,amplitude and pressure curve also confirmed fracture discontinuous propagation in shale due to high rock brittleness.This work has explored experimental methods for the research of shale fracturing mechanism,and provided an experimental basis for volume fracturing process design in field.