Enhanced cement formation for well completion in gas hydrates reservoirs

Abstract

Natural gas hydrates (NGHs) have abundant reserves and are greener energy source compared to petroleum resources. Intense heat release of cement slurry impacts the stability of NGHs during oil well cementing operations. Conventional low hydration-heat cement slurries significantly reduce the early-stage strength. In this paper, a novel strategy to optimize the exothermic and mechanical properties of cement slurry is proposed with the synergistic effects of various mineral admixtures and additives. The hydration heat and microstructure of cement with different admixtures were studied through isothermal calorimetry (IC), semi-adiabatic temperature test (ST), scanning electron microscopy (SEM), X-ray diffraction (XRD) and mechanical strength tests. The results indicate that the addition of nanosilica (NS) and C–S–H seeds lead to high early-stage strength for cement slurry substituted with high-volume fly ash (FA) and ground granulated blast furnace slag (GGBS), which meets the engineering performance for NGHs cementing. Compared with neat cement, blended cement designed with the new strategy has a 40.46% lower cumulative heat and a 56% higher compressive strength after 24 h. However, ST showed that the separated hydration heat rate peaks recombine together at higher temperature. The thermal storage performance of solid-solid phase change material (SSP) can effectively control the temperature rise due to cement hydration and maintain the separation of hydration heat rate peaks. This study provides novel ideas for the construction of low hydration heat and high early-stage strength cement slurry, and also provides key theoretical and methodological support for the performance control of cement slurry for NGHs cementing.