储/隔层岩石及层间界面性质对压裂缝高的影响

为评价储层和隔层岩石及层间界面性质对压裂缝高的影响,基于ABAQUS有限元计算平台,采用Cohesive单元研究了岩石弹性模量、地应力和抗拉强度等因素对压裂缝高的影响,并对各因素的影响程度进行了比较.通过数值模拟得出,弹性模量大的隔层在裂缝穿过界面时对其并无明显限制作用,反而会有利于隔层中缝高的增大;最小水平主应力大和抗拉强度高的隔层对缝高的扩展有显著限制作用;当储隔层界面的抗剪强度高出某一临界值时,压裂缝高急剧增大,小于该临界值时界面会发生滑移,裂缝被完全限制在储层内;在特定地层条件下,裂缝在储层中为垂直缝,扩展至界面处后开始沿界面扩展,形成T形缝.研究表明:弹性模量大的隔层对于控制压裂缝高不利;最小水平应力大和抗拉强度高的隔层有利于控制缝高,并且地应力的影响程度约为抗拉强度的1.6倍;界面抗剪强度越小,储/隔层界面就越容易发生滑移,越有利于控制压裂缝高. 

Effects of Reservoir Rock/Barrier and Interfacial Properties on Hydraulic Fracture Height Containment

In order to estimate effects of reservoir rock/barrier and interfacial properties on hydraulic fracture height control,studies were done to analyze and compare the effects of rock elastic modulus,in situ stress,and tensile strength on fracture height containment ability by Cohesive element based on the ABAQUS computing platform.Through numerical simulation,it was deduced that a barrier with high elastic modulus was not impeded when the fracture grows through the bonding interface,but was had an impact on the fracture height in the barrier.A barrier with minimum in situ stress and high tensile strength could significantly hinder the fracture height.The fracture height increased quickly when the interfacial shear strength of reservoir rock/barrier was beyond a critical value,and the fracture height was confined fully by the reservoir when the interfacial shear strength was lower than the critical value.Under proper conditions,the fracture propagated vertically in the reservoir and horizontally the interface,and thus develop into a T-shaped fracture.The research results showed that barrier with a high elastic modulus adversely affected fracture height containment.A barrier with minimum in situ stress and high tensile strength could strongly inhibit the fracture height propagation.The impact of in situ stress was about 1.6 times of tensile strength.The lower the shear strength of the interface,the easier for the reservoir rock/barrier to slip,which helped to contain the fracture height.