Influence of stress on the maximum shut-in pressure of double casing under non-uniform stress

Abstract

When the natural gas well overflows, if the well cannot be shut in time, the pressure in the casing will increase and may lead to the risk of blowout. In this paper, the finite element analysis method is used to study the influence of the physical properties and geometric defects of cement ring in the double-layer casing combination model on the maximum shut-in pressure. It is found that the increase of the elastic modulus of the inner cement ring will increase the maximum shut-in pressure, and it is less affected by Poisson’s ratio. The lack of geometry will lead to the uneven circumferential equivalent stress of the inner casing, cause stress concentration, and reduce the internal pressure strength and the maximum shut-in pressure of the inner casing. Through the analysis of a natural gas well in Shuiyu area of Sichuan Basin, it is proved that the maximum shut-in pressure can be determined more accurately by analyzing the change of internal pressure strength of casing. After considering the supporting effect of double-layer casing, the calculation error is only 1.87%. This result has important guiding significance for the formulation of well control measures in the field.