The Research of Creep Property of Deep Shale Rock and Its Influence on Casing Loading

Abstract

In recent years, shale oil and gas exploitation has attracted much attention, and the problems of borehole shrinkage and casing damage due to creep property of deep shale rock cannot be ignored. Especially, deep shale rock under the condition with containing water behaves shows stronger creep mechanical behavior. The creep mechanical behavior has direct influence on borehole shrinkage and casing load. The potential engineering risks need mechanism explanation and quantitative assessment. The creep mechanical behavior of deep shale rocks was studied by experiments, meanwhile the creep rate of shale with the condition of containing water was measured. The creep parameters were fitted according to the power-law model, and the parameter of A and n in the model can be obtained. On the basis of experiments, a three-dimensional multilayer wellbore model is established to numerically simulate the creep behavior of shale rock and the influence on the casing loading. In the experiment of our study, the shale under the condition of containing water content accelerates elastic and creep deformation about 1.5 times larger than the one under the condition without containing water. Through the numerical calculation, after one week, in deep layer the casing loading can reach about 158.9MPa when shale rock under the condition of containing water and it can reach about 146.3Pa without containing water. After one year, the casing loading can reach about 548.8MPa when shale rock under the condition of containing water and und it can reach about 517.9MPa without containing water. Creep property of shale rock will lead to the increase of casing loading and damage risk obviously, and it should be taken into consideration for the design of casing.