定向射孔水力压裂多裂缝形态实验研究

采用大型(试件尺寸：300 mm×300 mm×300 mm)真三轴水力压裂物理模拟实验系统,研究了定向射孔水力压裂人工水力裂缝起裂和形态的影响因素。研究结果表明：定向射孔方位角和水平地应力差对定向射孔水力压裂人工水力裂缝的起裂和形态影响巨大。定向射孔水力压裂形成的人工水力裂缝可能不是理想的平直双翼裂缝,而是双翼弯曲裂缝；在水平应力差和定向射孔方位角较大的情况下,容易形成由定向射孔方向和最大水平地应力方向多点同时起裂的非对称多裂缝系统或穿过微环面的双翼裂缝。提高原场地应力测量的精度和定向射孔的定向精度,将定向射孔方位角控制在较小角度,有利于避免产生形态复杂的人工水力裂缝,降低压裂施工难度和砂堵风险,改进压裂增产效果。

Experimental investigation of complex fracture geometries in hydraulic fracturing through orientated perforations

Hydraulic fracturing is used widely in petroleum industry,which plays an important role in the production of low permeability reservoir. Hydraulic fracture propagation behaviour and fracture geometry in perforated vertical wellbore are studied through a series of servo-controlled tri-axial fracturing experiments. The strata are simulated by a tri-axial rock mechanics test system on artificial specimens with size of 300 mm×300 mm×300 mm. Oriented perforation fracturing treatments are greatly affected by perforation parameters. The experimental results show that the main factors influence hydraulic fracture geometries are oriented perforation angle and the horizontal differential stress. The results also reveal that hydraulic fractures will not always initiate along perforations but micro-annulus near the wellbore, and usually the hydraulic fracture is non-planar. When the horizontal stress difference and the perforation angle are great, asymmetrical dual fractures will be generated along oriented perforation and the maximum horizontal stress directions. Improving the accuracy of in-situ stress measurement and orientated perforation can avoid the generation of complex-shaped hydraulic fractures.