PSI - Issue 58

Heng Yang et al. / Procedia Structural Integrity 58 (2024) 144–149 H. Yang et al./ Structural Integrity Procedia 00 (2022) 000–000

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2.2. FEM model of the casing-cement sheath-formation combination The casing-cement sheath-formation combination in the salt rock formation with a depth of 2500m in the underground gas storage can be simplified as a plane strain model (Chu and Shen et al., 2015; Zhang and Shen et al., 2018). ABAQUS is used to establish the FEM model of the combination, as shown in Fig. 2. The elastic and geometric parameters of the model are shown in Table 1. In addition, the cohesion of the cement sheath is 14.37 MPa, and the internal friction angle is 16.43°. The yield strength of the casing is 758 MPa. The formation creep model is: ε .�� = 3.743e -10 ∙ q 1.876 . Table 1. Elastic and geometric parameters of the FEM model. Material Elastic modulus (GA) Poisson’s ratio Inner diameter (mm) Outer diameter (mm) Casing 210 0.3 247.94 282.58 Cement sheath 9 0.2 282.58 320 Formation 1.8 0.38 320 3200*3200

Fig. 2. FEM model of the casing–cement sheath formation combination.

3. Results and discussion 3.1. Failure of cement sheath Integrity under salt rock creep

The integrity failure of cement sheath can be evaluated by the following methods. When the equivalent plastic strain (PEEQ) of the cement sheath >0, shear failure of the cement sheath occurs (Yang and Bu et al., 2021). When the circumferential stress of the cement sheath 0, the