A High Thermal Conductivity Cement for Geothermal Exploitation Application
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Original Paper
A High Thermal Conductivity Cement for Geothermal Exploitation Application Sheng Wang ,1,2 Liming Jian,1 Zhihong Shu,1 Shaohua Chen,1 and Liyi Chen1 Received 4 March 2020; accepted 2 May 2020
In geothermal reservoir exploitation, the thermal conductivity of casing cement material is a key parameter that may affect the heat exchange and utilization efficiency of geothermal reservoirs. Based on a systematic approach of theoretical analysis, experimental research and microscopic analysis, this paper presents graphite composite cement (GC) with high thermal conductivity for potential application in geothermal reservoir exploitation. The GC consists of ordinary Portland cement (P.O 42.5), natural flake graphite, water-reducing agent (GB), early strength agent (CaCl2) and defoamer (HB-03). The physical properties of the GC, such as fluidity, pumpability, setting time, compressive strength and thermal conductivity, were obtained by carefully prepared laboratory tests that met our expectation. Finally, X-ray diffractometry and environmental scanning electron microscopy were used to analyze the micro-characteristics for an interpreted thermal conduction mechanism of GC. The results of analyses show that the formation of thermal conductivity network of natural flake graphite in cement is a key to improve thermal conductivity. The research results provide a new solution to the problems of low thermal energy extraction efficiency and poor cementing quality of geothermal reservoirs. KEY WORDS: Exploitation of geothermal reservoirs, High thermal conductivity, Casing cementing, Natural flake graphite.
INTRODUCTION Development and utilization of geothermal resources form a major frontier research topic in contemporary earth science and energy industry, which is of great significance to optimize energy supply structure and mitigate the impact of the global environmental problems (Lund and Boyd 2016; Zhang and Hu 2018). Ground source heat pump (GSHP) technology is one of the important ways to extract the renewable energy, and it has 1
State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China. 2 To whom correspondence should be addressed; e-mail: [email protected]
played an important role in the development of geothermal energy (Lund and Boyd 2016). Researchers have done a lot of research on the thermal extraction performance of the geothermal systems. It is generally accepted that coaxial borehole heat exchanger (CBHE) has higher thermal efficiency than traditional U-tube borehole heat exchange (Zhang and Hu 2018). Zhang et al. (2019b) established a three-dimensional unsteady heat transfer model for different working fluids of a downhole coaxial heat exchange and conducted field tests to verify their model. Wiktorski et al. (2019) analyzed the thermophysical parameters of working fluid, casing and formation to reduce costs and improve heat recovery efficiency. Song et al. (2018a, b) believed that thermal conductivity of insulation
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