During offshore natural gas extraction, the formation of hydrates in the wellbore poses a crucial issue that affects flow safety. There is a need to find a reliable solution to establish a wellbore with excellent thermal insulation and stability to prevent wellbore blockage. 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-dimensional (2D) transient heat transfer 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·K) when the HGM (D51.8) content was 40 vol%. Compared to the traditional OWC (thermal conductivity ~ 0.889 W/(m·K)), 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 density of HGM/OWC LWTI composite material has been effectively reduced to a minimum of 1.31 g/cm3, 37% lower than that of pure cementing cement (2.08 g/cm3). The HGM/OWC LWTI composites exhibited good mechanical properties and low water absorption. This research can provide technical support for the efficient development of offshore natural gas.

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