LAUSR

Abstract Injection pressure is one of the key parameters used in the design of shale gas reservoir stimulation. Higher injection pressure helps to initiate fractures, inject fracturing fluid and proppant smoothly and maximize the stimulated reservoir volume as soon as possible. If the injection pressure is too high, however, the risk of casing deformation is increased significantly. In this paper, the numerical calculation format of the injection pressure safety window while ensuring casing integrity (i.e., the maximum safety injection pressure) was proposed based on an example of an actual engineering project. Then, it was verified based on the actual situation of one shale gas well in Weiyuan. The numerical calculation format is as follows. First, a 3D finite element model of initial fine geostress field is established in the scale of block. Second, a primary submodel for introducing the asymmetric characteristics of reservoir stiffness to simulate the asymmetry of fracture distribution. Third, a secondary submodel containing the attributes of casing, cement sheath and reservoir material properties. Fourth, submodels are used to calculate the casing deformation generated by different injection loads and estimate the maximum allowable fracturing injection pressure (pj) while the safety requirement of casing deformation is satisfied. The calculation result of the case well shows that when the cementing quality is poor and fractures are distributed asymmetrically, the lateral and vertical displacements at the maximum displacement point of the casing under the injection pressure of 80 MPa are obviously lower than those under 90 MPa. According to the yield limit criterion of P-110 casing steel, the casing deformation in this case is elastic strain, so the injection pressure of 80 MPa is safe. In conclusion, this method has rational precision and accuracy, for its numerical result is consistent with the actual engineering phenomenon.