射孔参数对硬质岩石起裂压力的影响规律研究

Study on the Influence of Perforation Parameters on the Initiation Pressure of Hard Rock

BZ气田中深部地层以硬质岩石为主,储层起裂压力大,压裂作业的难度与危险性大。射孔孔道是传递压裂动力的通道,合理的射孔参数设计能够降低储层的起裂压力。基于断裂相场理论,结合压裂液流动-岩石应力损伤耦合方程,建立基于相场法的裂缝扩展模型,并通过现场数据验证模型的可靠性。结合BZ气田岩石力学数据及射孔弹打靶试验,采用压裂数模软件模拟不同射孔方案下硬质岩石的起裂压力变化规律。研究结果表明:定向射孔时,沿水平最大主应力方向射孔岩石的起裂压力最小;螺旋射孔时,相位越大,孔密越小,起裂压力越大;不考虑孔道摩阻的影响,孔径对起裂压力影响较小;起裂压力随着穿深的增加而降低,且穿深小于100 mm时起裂压力的降低幅度最大。建议BZ气田采用定向射孔,射孔方向沿水平最大主应力方向,射孔孔密大于每米16孔,射孔弹穿深大于100 mm,孔径尽量大;如果采用螺旋射孔,则射孔相位要小于60°。该研究成果为BZ等硬质岩石油气田储层压裂改造射孔参数优选提供参考,可提升储层压裂效果。

The middle and deep layer of BZ gas field are mainly hard rocks,and the reservoir fracturing pressure is high,which increases the difficulty and risk of fracturing operation.Perforating channel is the passageway to transmit fracturing power,thus optimizing perforating parameters is an important measure to reduce rock fracture pressure.Based on the theory of fracture phase field and the coupling equation of fracturing fluid flow and rock stress damage,fracture extending model based on phase field method is established,and the reliability of the model is verified by field data.Combined with the rock mechanics interpretation data of BZ gas field and the shooting test of perforating charge,fracturing software is used to simulate the variation law of hard rock fracturing pressure under different perforation schemes.When the perforation is in the direction of the maximum horizontal principal stress,the rock initiation pressure is the smallest.In spiral perforation,when the phase gets larger,the hole density and the maximum fracturing pressure are getting smaller.The influence of pore diameter on the initiation pressure is small without considering the influence of pore friction.With the increase of penetration depth,the crack initiation pressure decreases,and when the penetration depth is less than 100 mm,the decrease is large.It is recommended to adopt directional perforation in BZ gas field.The perforation direction is along the direction of maximum principal stress,the perforation density is greater than 16 holes/m,the perforation depth is greater than 100 mm,and the aperture is as large as possible.If spiral perforation is used,the perforation phase is less than 60°.The research results provide a reference for the optimization of perforation parameters of hard rock in BZ gas field.