Lightweight insulating oil-well cement filled with hollow glass microspheres and numerical simulation of its unsteady heat transfer process

Abstract

Abstract During subsea natural gas extraction, the free water and gas molecules present in the reservoir and the low-temperature and high-pressure conditions of the subsea environment cause the formation of hydrates; the blockage of the wellbore due to these hydrates is a critical issue that affects flow safety. Located between the wellbore and casing, well cement plays an important role in strengthening the wellbore and sealing off the oil, gas, and water layers. A cement that exhibits optimal mechanical strength and enhanced thermal insulation properties can contribute to preventing hydrate formation. However, research on such materials is rare. In this study, lightweight and thermally insulated (LWTI) composites with the desired mechanical strength for deep-sea natural gas development were prepared using oil-well cement (OWC) as the matrix and hollow glass microspheres (HGM) as the filler. A two-phase mathematical model of the HGM/OWC LWTI composites was developed using the COMSOL Multiphysics software and solved using the finite element method. A transient heat transfer analysis of the HGM/OWC LWTI composites was performed. The effective thermal conductivities (keff) of the HGM/OWC LWTI composites were measured and the values agreed well with the simulation results. The keff of the composites was approximately 0.371 W/(m·℃) when the HGM (D51.8) content was 40 vol.%. Compared to the traditional OWC (thermal conductivity ~ 0.889 W/(m·℃)), the thermal insulation performance of the HGM/OWC LWTI composites was significantly improved. In addition, the density, mechanical properties, and water absorption of the HGM/OWC LWTI composites were investigated. The densities of the HGM/OWC LWTI composites were found to be low, ranging from 1.31 to 1.94 g/cm3. The HGM/OWC LWTI composites exhibited good compressive strength and low permeability. Thus, HGM/OWC LWTI has promising applications in the thermal insulation of cemented wellbores for deep-sea natural gas development.