Abstract
When geothermal fluid flows to the wellhead along the wellbore, there is a thermal transfer from the high-temperature geothermal fluid to the low-temperature formation. This process can directly lead to the decrease of wellhead temperature and loss of geothermal energy. Even though previous studies have confirmed that reducing the thermal conductivity of cement could validly cut down the heat loss of geothermal fluid, the influence factors of thermal conductivity are limited. In this research, we conducted detailed studies of the influence factors of thermal conductivity and compressive strength for cement. The results show that with the increase of water-cement ratio and thermal insulation materials, thermal conductivity and compressive strength decline. Furthermore, curing temperature is another important factor to improve the thermal preservation effect, but the testing temperature has the opposite influence. Based on these results, the present study concluded that porosity, Skeleton ingredients, curing temperature, and test temperature are vital factors for thermal conductivity. This research provides theoretical guidance for increasing the wellhead temperature of geothermal fluid and enhancing the efficiency of geothermal energy.
Highlights
Geothermal energy is clean and sustainable and has been widely used for power generation, heating, and farming (Bildirici and Gökmenoğlu, 2017; Wang et al, 2017; Hamm and Metcalfe, 2019; Yang et al, 2021)
The compressive strength is 108.8, 87.8, and 63.9 MPa, which correspond with w/c ratio is 0.5, 0.6, and 0.7 respectively under curing temperature set at 120°C. These results show that the compressive strength increased 70.3%, 93.8%, and 63.0% compared with the curing temperature set at 60°C
The compressive strength of thermal insulation cement with 20% floating beads at different curing temperatures (i.e., 60°C, 90°C, and 120°C) are 22.5, 38.4, and 45.4 MPa, respectively, which are 42.6%, 14.7%, and 28.9% lower than pure cement under the same w/c ratio
Summary
Geothermal energy is clean and sustainable and has been widely used for power generation, heating, and farming (Bildirici and Gökmenoğlu, 2017; Wang et al, 2017; Hamm and Metcalfe, 2019; Yang et al, 2021). The wellhead temperature of the geothermal fluid is one of the most important parameters to determine the usage modes and applied efficiency for geothermal energy (Kanev et al, 1997; Tekin and Akin, 2011; Zhou and Zhang, 2013; Gorman et al, 2014). Elevating this temperature is vital for the exploration and utilization of geothermal energy. The theory that decreasing cement thermal conductivity can prominently reduce heat loss has been proposed
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