Performance study of modified aluminate cement under in-situ conversion conditions of shale oil

Abstract

The resource potential of in-situ conversion of shale oil is enormous, and it is a strategic alternative resource for China's oil and gas industry. However, extreme high temperatures under in-situ conversion conditions of low maturity shale oil can lead to a decline in the mechanical strength of cement. In this paper, the influence of modified sodium hexametaphosphate on the hydration behavior of aluminate cement and its application performance at 650 °C was systematically studied, and its macro performance and microstructure were deeply explored. As a result, it was found that the sodium hexametaphosphate can significantly reduce the permeability of aluminate mudstone, but not significantly improve the strength, at the same time, it was found that the permeability of aluminate mudstone modified by micro-silica composite sodium hexametaphosphate is significantly reduced, and the compressive strength is increased. After treated at 650 °C, the compressive strength of 5.0% sodium hexametaphosphate modified aluminate mudstone is the highest (47.19 MPa), while the compressive strength of micro-silica composite sodium hexametaphosphate modified aluminate mudstone shows a downward trend. The aluminate brine debris has obvious transformation of hydration products before and after treatment at 650 °C, including mainly C3AH6 and AH3 into C12A7 and CA. Among them, C3AH6 and AH3 mainly undergo thermal decomposition at 180–400 °C, and the pores of aluminate mudstone increase attribute to the transformation of crystal form. The C2ASH8 generated by aluminate mudstone at 50 °C due to micro-silica is helpful to improve the microstructure. But, the decomposition of C2ASH8 after 650 °C treatment will also lead to the increase of cement paste pores.