砂泥互层储层条件下水力裂缝扩展实验研究

Hydraulic Fracture Propagation Experiment Under Sand Mud Interbedded Reservoir Conditions

鄂尔多斯盆地某区块发育丰富砂岩和泥岩多薄互层的页岩油资源,该区块层理、裂缝发育,非均质性特征显著,压裂改造中裂缝的扩展机理不明确,体积压裂改造难度较大。针对该区块开展了室内真三轴水力压裂物理模拟实验,探究了层理、地应力、排量等因素对裂缝穿层扩展的影响。研究结果表明:500 mm×500 mm×500 mm的天然露头砂泥夹层型岩样水力裂缝形态主要以复杂缝为主,层理发育程度越高,水力裂缝越偏向于水平方向;水平应力差的增大可以增加水力裂缝垂向穿层能力;高排量可以提高分支缝的开启概率,增大形成复杂缝网的概率。

A certain block in the Ordos Basin is rich in shale oil resources with alternating layers of thin sandstone and mudstone.This block is characterized by prominent bedding,fracturing,and heterogeneity,making it challenging to understand the mechanisms of fracture propagation during hydraulic fracturing and difficult to perform volumetric fracturing effectively.To address these issues,indoor true triaxial fracturing experi-ments were conducted in this block to explore the impact mechanisms of bedding,in-situ stress,and displacement rate on the cross-layer propagation of fractures.The results indicate that the hydraulic fracture patterns in the 500 mm×500 mm×500 mm natural sandstone-mudstone interlayer rocks are primarily complex fractures.The higher the degree of bedding development,the more the overall hydraulic fractures tend to be horizontally ori-ented.An increase in the difference between horizontal and vertical stress can increase the vertical deflection angle of hydraulic fractures.A higher displacement rate can enhance the probability of branch fracture initiation,also can enhance the likelihood of forming complex fracture networks.