Damage behavior and constitutive model of cement sheath under alternating temperature

Abstract

In this paper, an evaluation method for the mechanical properties of cement sheath is proposed to describe the real mechanical damage behavior of cement sheath under alternating temperatures. The mechanical properties of cement sheath under three types of alternating temperatures (25 °C–150 °C, 25 °C–200 °C, and 25 °C–250 °C) are investigated by using the full-scale experiment device of “production casing-cement sheath-intermediate casing” system, by which the damage law and mechanism of mechanical properties for cement sheath under alternating temperatures is revealed. Based on the test results, the uniaxial and triaxial damage constitutive models under alternating temperatures are established for future finite element simulations, and experimental results verify their reliability. The results show that the alternating temperature significantly damages the mechanical properties of the cement sheath, including the peak stress, elastic modulus, pore strain, elastic strain, and plastic strain. The damage mechanism under alternating temperatures includes thermal damage caused by uncoordinated thermal expansion of particles inside the cement sheath and free water evaporation, and additional damage resulting from inconsistent thermal expansion between the casing and the cement sheath, plastic accumulation and fatigue damage caused by alternating load, and chemical damage induced by changes in chemical substances. The research results could provide a reference and basis for cement sheath integrity theory in heavy oil wells.