临兴区块石盒子组致密砂岩气储层压裂缝高控制数值模拟研究

Numerical modeling of hydraulic fracture containment of tight gas reservoir in Shihezi Formation,Linxing Block

对含上下隔层的致密砂岩进行水力压裂增产作业时,储隔层间应力差、物性差异等地质因素和压裂液黏度、施工排量、射孔位置等工程因素对水力裂缝延伸规律影响显著。针对鄂尔多斯盆地东缘临兴区块石盒子组致密气砂岩储层,基于ABAQUS有限元计算平台,建立三维层状介质的压裂缝高数值模型,研究各因素对裂缝高度控制的影响规律。研究结果表明:临兴区块石盒子组储层压裂施工产生垂直形态的水力裂缝,储隔层应力差是最关键控制因素,当大于4 MPa时可以有效控制缝高;弹性模量低的隔层对控制压裂缝高有利;泊松比对于压裂缝高几乎没有影响;高储隔层应力差(>4 MPa)下施工排量小于6 m^3/min时,裂缝延伸抑制作用明显;低储隔层应力差下(<2 MPa)施工排量越大,裂缝在隔层内延伸程度越大;压裂液黏度低于10 m Pa·s时对压裂缝高影响很小;射孔位置的不同对于裂缝起裂阶段影响显著,储层上部射孔时裂缝最终形态和压裂缝高较储层中部射孔和全井段射孔差异很大。开展室内试验研究施工排量、射孔位置等工程因素对裂缝穿层扩展的影响,试验结果与数值模拟结果吻合良好。研究结论可为油田现场预测裂缝形态,选择合适层位,优化压裂参数提供借鉴。

During the process of fracturing the layered tight gas reservoirs with shale seams,the propagation of hydraulic fractures can be significantly affected by the geological factors（ in-situ stress difference between inter-layers,rock deformability etc.）,and also some operation parameters（ injection rate,fracturing fluid viscosity,perforation positions etc.）.In this paper,a three-dimensional fracture height model of layered tight gas reservoirs has been constructed based on the ABAQUS software to investigate how these factors influence the propagation and geometry of hydraulic fractures.The data sample is from Linxing block on the east margin of Ordos Basin. The simulation result shows that many vertical fractures can be created during the treatment,and the fracture height is dominated by in-situ stress difference.In-situ stress difference higher than 4 MPa shows a great effectiveness in fracture height containment.In addition,the results indicate that lower elastic modulus is favorable for fracture height containment,while Possion＇s ratiohas almost no effect on it.The propagation of hydraulic fractures is strongly inhibited with in-situ stress difference higher than 4 MPa and injection rates lower than 6 m3/min.However,with the in-situ stress difference dropping to 2 MPa or even lower,the fracture height grows well with increasing injection rates.The simulation also finds that fracturing liquid with its viscosity lower than 10 m Pa·s has negligible impact on fracture height.Perforation position plays an important role in the fracture initiation stage.Fracture geometries differ a lot with different perforation schemes.Barring the numerical simulation,the authors have conducted many indoor experiments of which the results fits the simulation results well.The study of hydraulic fracture initiation and propagation in multi-layers reservoir can provide a reference for the field prediction of fracture geometry and optimization of pump injection program.