Mechanical properties of low-density cement under shale oil in-situ conversion conditions

Abstract

This paper is devoted to study the mechanical behavior of a low-density cement (with a density of 1.3 g/cm3) under shale oil in-situ conversion conditions. A series of tests were conducted to determine the physical and mechanical properties of the low-density cement, including water and gas permeability, uniaxial compressive strength and triaxial compressive strength, under various temperatures and pressures to simulate shale oil in-situ conversion conditions. Furthermore, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) tests were conducted on the low-density cement for composition evaluations after being exposed to high temperatures. The results showed that the strength of the cement was mostly stabilized after 7 days of curing at 50 °C, while it deteriorated significantly after being exposed to high temperatures (especially when the temperature reached 380 °C and above). The TGA and XRD results showed that the degradation of mechanical behavior after being exposed to high temperatures was related to the decomposition of hydration products. The triaxial test results showed that mechanical properties of the low-density sample were sensitive to the level of confining pressure (especially when the confining pressure was higher than 10 MPa). The pore water pressure and the pore collapse both have a detrimental effect on the mechanical properties, and the pore collapse was the main reason that caused the failure patterns to change from brittle to ductile..