Study On Casing Loads In Creep Stratum

Casing loads in creep stratum under uniform in-situ stresses and non-uniform in-situ stresses are studied in this paper. It is one of the main factors to damage casings. Stress method is employed to analyze the casing loads with unifom in-situ stresses in the creep formations and the result is proved by displacement method. It is very hard to calculate the finally steady casing loads under non-uniform in-situ stresses in creep stratum. The casing is taken as the elastic foundation and the stratum as infinite viscoelastic foundation, then a Kelvin Model is built to analyze the casing loads under non-uniform in-situ stresses in creep stratum. By stresses methods and Laplace transform methods the distribution rules of casing loads are studied under non-uniform in-situ stresses in creep stratum. And based on the Viscoelastic theory, the formulas to calculate casing stresses are obtained. The results show that if the stiffness ratio is big enough, the casing loads will go to a stable and maximal loads distribution, and the value will approach the elastic solution with sufficient time duration. The conclusion is valuable to the selection of casing used in creep stratum.