Research on thermal insulation cement for low/medium-temperature geothermal wells based on colloidal gas aphron fluid

Improving the water outlet temperature and heat recovery efficiency requires lowering the thermal conductivity of geothermal cement to reduce heat loss over the hundreds/thousands of metres of a wellbore. Microbubble insulation cement made with colloidal gas aphron (CGA) fluid was fabricated and tested. According to the results, the thermal conductivity of the CGA cement was reduced by 73.5% and the reduction in thermal conductivity was 12.07–68.69% higher than traditional insulation materials (perlite, vitrified microbeads). After curing at 60–100°C, the 10% CGA cement retained consistent compressive strength (10.41–13.43 MPa) and low thermal conductivity (0.118–0.155 W/m.K). This mix is also better suited for geothermal formations due to its increased fluidity and decreased density. Large-diameter pores appeared in the cured cement following CGA rupture. Additionally, the CGA prevented calcium silicate hydrate from forming, which prevented hydration products from filling the gaps and led to many micropores and microcracks. The heat transfer path was greatly expanded by the loose cement structure, which also decreased the total heat transmission per unit time. The results of this study offer fresh economic and environmental insights into the design of geothermal cements, considering the thermal conductivity, and lay a foundation for the efficient development of geothermal energy.