Study on the mechanical behavior and collapse resistance of double-casing under gypsum-salt layer

Abstract There are abundant oil and gas resources under the gypsum-salt layer, but its creep characteristics can easily lead to casing damage and affect the normal development of oil and gas wells. However, double-layer casing technology shows potential in dealing with gypsum-salt layer creep, but the in-depth study of its prevention mechanism is insufficient. Given this, a two-dimensional finite element analysis model of the casing, cement sheath, and gypsum-salt layer is constructed in this paper, and the mechanical properties and compressive strength of double casing in the gypsum-salt layer are compared, and the internal mechanism of effectively preventing gypsum-salt layer creep is revealed. Based on the above model, the influence of casing eccentricity on mechanical behavior and extrusion strength of double casing is discussed. The results show that double-layer casing has a better control effect on gypsum-salt layer creep than single-layer casing because double-layer casing can reduce the stress and stress non-uniformity of casing. The influence of casing eccentricity on double-layer casing is negligible, the maximum equivalent stress change is less than 1%, and the extrusion strength only decreases by 0.26% ~ 0.38%.