层间应力差对水力裂缝扩展影响的大尺度实验模拟与分析

储隔层水平地应力差是水力裂缝高度延伸的主控因素,采用大尺寸全三维水力压裂实验系统模拟储隔层地应力条件,对长庆长6砂岩进行水力压裂裂缝垂向扩展模拟实验,并实现对大尺度岩样内部裂缝扩展的全三维实时声波监测。通过声波监测结果与实际裂缝形态对比,讨论了层间应力差、施工参数(排量、黏度)、施工压力对裂缝垂向延伸的影响。结果表明:缝高受层间应力差控制明显;同时施工参数也会影响裂缝的垂向延伸,高黏流体压裂有利于缝高延伸;对于均质致密砂岩岩样,实时声波监测技术能够对裂缝扩展动态进行有效监测。本研究为缝高延伸机理研究提供了实验手段,也为现场微地震监测提供参考。

Large scale experimental simulation and analysis of interlayer stress difference effect on hydraulic fracture extension

Horizontal geostress difference between reservoir and caprock is the main controlling factor for hydraulic fracturing height growth. A large scale full 3D hydraulic fracturing experiment system was used to simulate the geostress conditions of reservoir and caprock; simulation experiment was conducted to vertical growth of hydraulic fracturing for Chang-6 sandstone in Changqing Oilfield, and full 3D real-time acoustic monitoring was accomplished to internal fracture growth in large-size rock samples. A discussion was made regarding the effect interlayer stress difference, job parameters (flow rate, viscosity) and job pressure on vertical growth of fractures by comparing the results of acoustic monitoring and actual fracture geometry. The results show that fracture height is evidently controlled by interlayer stress difference; meanwhile, the job parameters will also affect the vertical growth of fractures, and fracturing with high-viscosity fluid is favorable for extension of fracture height; for homogeneous tight sandstone samples, real-time acoustic monitoring technique can effectively monitor the fracture growth conditions. This paper provides an experimental approach for the study on fracture height extension mechanism and also provides a reference for field micro-seismic monitoring.