Enhancing Thermal Insulation of Geothermal Well Cement Using Alkali-Activated Straw Ash and Natural Zeolite

To improve the heat extraction efficiency from the wellbore fluids to the stratum in the geothermal well, thermal insulation cement, which is prepared by alkali-excited straw ash-natural zeolite, was based on the orthogonal test. The properties of thermal insulation cement, such as compressive strength, thermal conductivity and fluidity, were tested, and the comprehensive evaluation and range analysis of thermal insulation cement were carried out by using analytic hierarchy process (AHP) as a macro reference index. The results show that the alkali equivalent of natural zeolite and water glass are the two biggest factors affecting the properties of cement. The compressive strength of the optimal mixture at 38 °C and 60 °C for 8 h is 9.26 MPa and 24.46 MPa, respectively, and the thermal conductivity reduction rates at 30 °C, 60 °C and 90 °C are 42.41%, 50.29% and 54.03%, respectively. The initial consistency of the optimal mixture is 13.9 BC and the consistency time is 123 min, which can be used for engineering cementing. In addition, the thickening time of cement can be adjusted according to water-reducing agent and retarder to meet the actual construction requirements of cementing.