页岩断层滑移量计算模型及影响因素研究

Study on Calculation Model of Shale Fault Slip and Its Influencing Factors

页岩气多级压裂中的断层滑移是导致页岩气水平井套管剪切变形的主要因素,严重影响了页岩气水平井的产能建设,但当前仍缺乏有效方法计算断层滑移量。鉴于此,分析了页岩气水平井多级压裂过程中断层受力状态,建立了一种考虑断层上、下部地层对断层影响的断层滑移模型及滑移量计算方法,并利用有限元软件研究了不同因素影响下断层滑移量的变化规律。研究结果表明:断层滑移过程中,由于地层存在弹性,断层顶部至底部滑移量逐渐减小,呈倒S形;断层面摩擦因数降低、断层岩石弹性模量减小、断层下部地层岩石弹性模量增加和水平最小地应力增大等因素均会增加断层滑移量,而断层岩石泊松比、下部地层岩石泊松比和地层垂向地应力等影响断层滑移量效果弱。研究结果可为页岩气水平井多级压裂施工的压裂参数控制提供参考。

Fault slip in multi-stage fracturing of shale gas is the main factor leading to the shear deformation of casing in shale gas horizontal wells,which seriously affects the productivity of shale gas horizontal wells.However,there is no effective method to calculate the fault slip at present.Accordingly,the stress state of the fault in the multi-stage fracturing process of shale gas horizontal wells was analyzed in this paper.A fault slip model and calculation method were established considering the influence of upper and lower strata on the fault.The change rule of the fault slip under the influence of different factors was studied by using finite element software.The results show that,in the process of fault slip,the slip from the top to the bottom of the fault decreases gradually due to the elasticity of the stratum,showing an inverted S shape.Factors such as the decrease of friction coefficient of fault plane,the decrease of elastic modulus of fault rock,the increase of elastic modulus of rock in the lower strata of the fault and the increase of horizontal minimum in-situ stress all increase the fault slip.While Poisson s ratio of fault rock,Poisson s ratio of rock in the lower strata and vertical in-situ stress have small influences on the fault slip.The research results provide a reference for the fracturing parameter control of shale gas horizontal wells.