Study and application of calculation method for in-situ stress of shale reservoir in southeast Chongqing

In-situ stress is an important parameter for drilling and fracturing reconstruction,but the shale reservoir heterogeneity in southeastern Chongqing is obvious,which makes the isotropic in-situ stress model unsuitable for shale formations,and it is necessary to re-establish a suitable stress calculation method for this type of formation.In response to the above problems,based on the mechanical properties of shale rock,this paper derives the lateral isotropic constitutive relationship of shale,and establishes a relational formula to obtain the lateral isotropic mechanical parameters of shale based on logging data.Also,combining the hydraulic fracturing data of adjacent wells,the structural strain coefficient of the area is reversed,and a method for calculating the horizontal isotropic in-situ stress of shale is jointly established.Using this method to calculate the in-situ stress at a depth of a shale gas well in the southeastern Chongqing,the calculation results were drawn into a continuously changing stress cross-section graph.The changing in-situ stress profile,and finally the inversion of the in-situ stress value at the corresponding depth through the acoustic emission experiments at the three depth points of the well are verified by the comparison with the calculation results.The results show that ① The horizontal isotropy of shale is obvious,the horizontal elastic modulus is generally greater than the vertical elastic modulus,the difference between the horizontal and vertical Poisson’s ratio is small,and there is no obvious rule;② The minimum horizontal in-situ stress calculated based on the lateral isotropic model is higher than the in-situ stress value calculated by the isotropic model,where the relative error between the calculation results based on the lateral isotropic model and the measurement results of the rock acoustic emission is less than 7%,with an average of 5.07%;③ The relative error between the calculation results of the combined spring model and the rock acoustic emission measurement results is greater than 15%.In this paper,the model is based on the structural characteristics of shale,which is more in line with the real situation of the formation.