东营凹陷页岩油储层层间干扰及裂缝扩展规律研究

Research on Interlayer Interference and the Fracture Propagation Law of Shale Oil Reservoirs in the Dongying Sag

东营凹陷页岩油储量丰富,但储层物性差,纵向含油层系多而薄,多为灰泥岩互层。为了准确描述东营凹陷页岩油储层层间应力干扰机理及水力压裂裂缝的扩展规律,利用非线性有限元法建立了基于渗流–应力–损伤耦合的多薄互层分层压裂模型,模拟分析了不同排量、压裂液黏度及不同上、下隔层厚度下的裂缝扩展形态、规律和诱导应力场,研究了裂缝扩展形态与诱导应力场的关系,并对压裂施工参数进行了优化。模拟结果表明:随着水力裂缝扩展,应力干扰区域越来越大;当排量为9~12 m^(3)/min、黏度为20 mPa·s时,裂缝尖端诱导应力大,易连通天然裂缝,压裂改造效果明显;上部隔层厚度大于2.50 m、下部隔层厚度大于4.50 m时,极少出现穿层现象。研究结果可为东营凹陷页岩油储层后续的水力压裂施工提供理论支撑。

The Dongying Sag is rich in shale oil reserves,but poor in reservoir physical properties.The sag has many thin oil-bearing layer sequences in the vertical direction,which are mostly interlayered with limestone and mudstone.To precisely describe the law for the interlayer interference and the fracture propagation of the shale oil reservoirs in the Dongying Sag,a separate-layer fracturing model based on seepage-stress-damage coupling was built with the nonlinear finite element method.The morphology and law for fracture propagation,and induced stress field were analyzed considering different flow rates and viscosities of fracturing fluid,and different thicknesses of the upper and lower isolation layers.On this basis,the fracturing parameters were optimized.Simulation results show that the stress interference area grows along with the propagation of hydraulic fractures.When the flow rate is 9–12 mm^(3)/min and the viscosity is 20 mPa·s,the induced stress at the tips of fractures is high.In this case,natural fractures are prone to be connected and good stimulation results can be achieved.In addition,layer crossing is rare when the thickness of the upper isolation layer is greater than 2.5 m and that of the lower one is greater than 4.5 m.The results can provide theoretical support for the subsequent hydraulic fracturing of shale oil reservoirs in the Dongying Sag.