Research on the Properties of Cement Sheath for Heavy Oil Thermal Recovery

Abstract This study addresses the challenges associated with heavy oil extraction using steam stimulation. The injection of high-temperature steam severely tests the integrity of the cement sheath, leading to concerns such as alterations in cement hydration and strength degradation under elevated temperatures. Furthermore, thermal cycling can cause debonding of the cement sheath, potentially resulting in wellbore abandonment. Investigating the performance of the cement sheath under such extreme thermal conditions is essential to ensuring the safety and longevity of thermal recovery wells. To examine the behavior of the cement sheath under extreme thermal cycling, this study preliminarily investigates the physicochemical properties of cement specimens subjected to repeated temperature variations between 350°C and the bottom-hole formation temperature. The mechanical behavior, microstructural evolution, and compositional changes of the cement samples were systematically analyzed during the cyclic steam stimulation process to elucidate the impact of high-temperature cycles on the cement material. Experimental results indicate that the strength of the cement exhibits an initial decrease, followed by an increase, and ultimately stabilizes throughout the high-temperature cycles. In conventional-density cement, high temperatures cause the volatilization of internal components, resulting in increased porosity. However, in low-density, high-porosity cement, hydration at formation temperature followed by high-temperature curing induces crystallization within the pores, which enhances the density of the cement. The innovative aspect of this research lies in systematically revealing the mechanical performance evolution and microstructural response of cement under high-temperature cyclic conditions, and in comparing the different behaviors of conventional-density cement and low-density, high-porosity cement under thermal exposure.