定向射孔对水力裂缝起裂与延伸的影响

 射孔孔眼是沟通井筒和地层的通道，压裂施工中射孔参数影响施工效果。采用大尺寸真三轴水力压裂物理模拟实验系统，研究定向射孔方位角、水平应力差和微环隙对裂缝起裂、延伸、转向、破裂压力及形态的影响，并建立了射孔直井在地应力条件下产生垂直裂缝的破裂压力预测模型。实验结果表明：利用定向射孔压裂技术可以在地层中形成双翼弯曲水力裂缝；随着定向射孔方位角的增大，破裂压力越来越高，转向距离也越来越大；且水平最大主应力与水平最小主应力之间的应力差对裂缝的转向距离有很大影响；微环隙对裂缝形态及破裂压力也有影响，其使得破裂压力较从射孔孔眼起裂所需压力大幅降低，且裂缝形态与裸眼井起裂类似。结论对于实际的射孔参数优化设计和水力压裂施工具有参考意义。

IMPACT OF ORIENTED PERFORATION ON HYDRAULIC FRACTURE INITIATION AND PROPAGATION

Hydraulic fracturing is used widely in petroleum industry，which plays an important role in the production of low permeability reservoir. And hydraulic fracturing treatments are greatly affected by the selected perforation parameters. The geometric configuration is a key problem in hydraulic fracturing. The strata are simulated by a triaxial rock mechanics test system on artificial specimens with size of 300 mm×300 mm×300 mm. The fracture propagation mechanism of hydraulic fracturing is studied. Experiments are designed to investigate hydraulic fracture initiation sites，breakdown pressure and geometries，specially the tortuous fracture geometries resulting from fracture initiation and propagation through perforated vertical wellbore. The experimental results show that the tortuous fracture can be generated by using oriented perforation fracturing technology. And a model for prediction of hydraulic fracture initiation pressure from vertical wellbores with perforations has been presented under given in-situ stress condition. To investigate the sensitivity of the results to variable conditions，by changing the perforation angle and the horizontal stress difference，it is found that the breakdown pressure and hydraulic fracture reorientation path are functions of the perforation orientation. To reduce the breakdown pressure and reorientation path，the perforations should be placed with a smaller perforation angle. The effect of micro-annulus near the wellbore on the fracture initiation and its geometry is also discussed；it makes the fracture initiation as from an open-hole and the fracture geometry very simple. The conclusions drawn above provide valuable guidance to the design of hydraulic fracturing treatment and oil engineering practice.