Thermal performance and microstructure of oil well cement paste containing subsphaeroidal konilite flour in HTHP conditions

Konilite is a class of subsphaeroidal micro-crystallization quartzite. This study investigates the influence of konilite flour addition as mineral admixture on microstructure and hydration of oil well cement paste cured under high temperature and high pressure (HTHP) conditions, which is used for steam injection wells cementing. All of the pastes are subjected to the first stage thermal curing under 80 °C for 7 d, and then to the second stage HTHP conditions of 350 °C × 21 MPa for another 90 d. The compressive strength and permeability of the specimens are tested, and the hydration kinetics, chemical composition and microstructure of the pastes are characterized through ICC, XRD, TGA, MIP and SEM. The results show that konilite flour addition obviously increases the compressive strength of oil well cement pastes in both of the curing stages. Due to its pozzolanic activity, konilite flour slightly promotes the hydration of the pure cement pastes. The formed crystalline product of xonolite with net-structure morphology in the pastes is beneficial for the formation of finer pore structure, which also exhibits a lower permeability. Therefore, the replacement of konilite flour for silica flour as a mineral admixture in oil well cement should be a more suitable method for cementing of the steam injection wells.