An Experimental Study on Creep Characteristics of Salt Rock and Gypsum-salt Rock in Puguang Gas Field

Abstract

Through the determination of mineralogical compositions of the salt rock and gypsum-salt rock in Puguang gas field and the creep experiments on these rocks, the authors analyze the impacts of mineralogical compositions, deviatoric stress, temperature, and confining pressure on creep behavior and proposes the constitutive equation of steady-state creep rate by combining with the creep curve and rock parameters obtained by the experiments. The experiment results indicate that the main mineralogical compositions of the salt rock and gypsum-salt rock in Puguang gas field are sodium chloride and calcium sulfate, where the content of sodium chloride can be up to more than 93%; the inherent mineralogical compositions are the internal factors that impact the creep characteristics of rock, along with the content of sodium chloride increasing, the rates of transient creep and steady-state creep increase accordingly; and as the deviatoric stress and temperature increase, the steady-state creep rate increases too. However, the impact of confining pressure is very small. The authors obtain the parameters of Heard's creep constitutive equation by fitting test data, working out the steady-state creep rates of salt rock and gypsum-salt rock under different deviatoric stresses and temperatures, which provides the theoretical basis of the calculation of safe mud density window and the analysis of abnormal casing deformation for the formations of salt rock and gypsum-salt rock in Puguang gas field.