Effects of in-situ stress and elastic parameters of cement sheath in salt rock formation of underground gas storage on seal integrity of cement sheath

Abstract

The cement sheath seal integrity is crucial for a safe operation of underground gas storage. Owing to its creep characteristics, the salt formation squeezes the cement sheath, which may cause failure of the cement sheath’s seal integrity and pose risks to the safe operation of underground gas storage. In this study, the experimentally obtained salt rock creep law and finite-element software ABAQUS were used to verify the adaptability of the salt rock creep in ABAQUS. In addition, a model of casing–cement sheath formation combination under creep formation conditions was developed. The effects of the in-situ stress (ISS) and cement sheath’s elastic parameters on the seal integrity of the cement sheath were studied in the salt rock layer. The creep of the salt rock increased the stress acting on the cement sheath over time and caused shear failure of the cement sheath. A larger uniform horizontal ISS led to a shorter time period for shear failure of the cement sheath, larger equivalent plastic strain (PEEQ), and larger yield area. A larger maximum horizontal ISS led to a shorter time period for shear failure of the cement sheath, larger PEEQ, and larger yield area. The yield area was concentrated in the direction of the maximum and minimum horizontal ISSs. Uniform and non-uniform horizontal ISS creeps did not cause tensile failure of the cement sheath. The reduction in the elastic modulus of the cement sheath and increase in the Poisson’s ratio of the cement sheath could reduce the shear failure risk of the cement sheath in salt rock formation. The influences of the ISS and cement sheath elastic parameters in the salt rock layer on the seal integrity of the cement sheath obtained in this study can provide references for the seal integrity failure of the cement sheath in the creep formation.