Characterization of rock thermophysical properties and factors affecting thermal conductivity−A case study of Datong Basin, China
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Abstract: Rock thermal physical properties play a crucial role in understanding deep thermal conditions, modeling the thermal structure of the lithosphere, and discovering the evolutionary history of sedimentary basins. Recent advancements in geothermal exploration, particularly the identification of high-temperature geothermal resources in Datong Basin, Shanxi, China, have opened new possibilities. This study aims to characterize the thermal properties of rocks and explore factors influencing thermal conductivity in basins hosting high-temperature geothermal resources. A total of 70 groups of rock samples were collected from outcrops in and around Datong Basin, Shanxi Province. Thermal property tests were carried out to analyze the rock properties, and the influencing factors of thermal conductivity were studied through experiments at different temperature and water-filled states. The results indicate that the thermal conductivity of rocks in Datong, Shanxi Province, typically ranges from 0.690 W/(m·K) to 6.460 W/(m·K), the thermal diffusion coefficient ranges from 0.441 mm2/s to 2.023 mm2/s, and the specific heat capacity of the rocks ranges from 0.569 KJ/(kg·°C) to 1.117 KJ/(kg·°C). Experimental results reveal the impact of temperature and water saturation on the thermal conductivity of the rock. The thermal conductivity decreases with increasing temperature and rises with high water saturation. A temperature correction formula for the thermal conductivity of different lithologies in the area is proposed through linear fitting. The findings from this study provide essential parameters for the assessment and prediction, development, and utilization of geothermal resources in the region and other basins with typical high-temperature geothermal resource.
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Figure 2. NW-SE geologic structure profile of Datong Basin (The profile position is shown in Fig. 1C, quated from Pan et al. 2022)
Notes: 1-Archaic Sanggan Group; 2-Cambrian; 3-Ordovician; 4-Carboniferous series; 5-Permian system; 6-Lower Jurassic cohorts; 7-Yungang Group of Middle Jurassic; 8-Neogene lower member of Kezhai Formation; 9-Neogene middle section of Kezhai Formation; 10-Neogene Kezhai Formation upper member; 11-Neogene Nanyulin Formation; 12-Quaternary system; 13-Reverse fault; 14-Normal fault; 15-Thermal reservoir
Figure 4. Thermal conductivity box patterns of different lithologies in Datong Basin
Notes: The serial number of horizontal coordinate is expressed respectively: 1-tuff; 2-tuffaceous breccia; 3-basalt; 4-diabase; 5-monzonitic granite; 6-granite; 7-metagranulite; 8-granulite; 9-schist; 10-gneiss; 11-marble; 12-metamorphic granite; 13-mudstone; 14-limestone; 15-siltstone; 16-shale; 17-marl; 18-sandstone; 19-pebbly sandstone; 20-dolomite; 21-Soil (dry); 22-Soil (saturated)
Figure 5. Box diagram of rock thermal diffusivity in Datong Basin.
Notes: The serial number of horizontal coordinate is expressed respectively: 1-tuff; 2-tuffaceous breccia; 3-basalt; 4-diabase; 5-monzonitic granite; 6-granite; 7-granulite; 8-metagranulite; 9-schist; 10-gneiss; 11-marble; 12-metamorphic granite; 13-mudstone; 14-limestone; 15-fine sandstone; 16-shale; 17-marl; 18-sandstone; 19-pebbly sandstone; 20-dolomite
Figure 7. Box diagram of specific heat capacity of rocks in Datong Basin.
Notes: The X axis represents: 1-tuff; 2-basalt; 3-diabase; 4-monzonitic granite; 5-granite; 6-granulite; 7-metagranulite; 8-schist; 9-gneiss; 10-metamorphic granite; 11-mudstone; 12-limestone; 13-fine sandstone; 14-shale; 15-marl; 16-sandstone; 17-dolomite
Figure 10. Relationship between thermal conductivity and temperature of CaM (Meng et al. 2022)
Figure 12. Thermal conductivity of rocks under dry and water-saturated conditions
Notes: The serial number of horizontal coordinate is expressed respectively: 1-schist; 2-gneiss①; 3-limestone①; 4-limestone②; 5-sandstone①; 6-monzonitic granite; 7-dolomite①; 8-gneiss②; 9-mudstone; 10-sandstone②; 11-sandstone③; 12-sandstone④; 13-pebbly sandstone; 14-dolomite② (The upper corner marks represent different rock samples of the same lithology)
Table 1. Comparison between thermal conductivity of different lithologies and other areas of North China Craton
Lithology Datong basin W/(m·K)
(This text)Ordos Basin
W/(m·K)
(Sun et al. 1996)Qingshui Basin
W/(m·K)
(Sun et al. 2006; Qi, 2021)Jizhong Depression
W/(m·K)
(Su, 2021; Gao, 2023)Mudstone 2.961(1) 1.984±1.032(20) 1.820±0.820(18) 2.350(15) Sandstone 3.375±0.593(9) 2.943±1.008(46) 2.440±0.280(16) 2.150 Limestone 2.968±0.676(9) 3.668±1.110(10) 3.350±0.490(8) 3.920(9) Dolomite 5.451±1.486(4) 3.345±1.120(7) — 5.670(10) Gneiss 2.632±0.663(9) 1.786(1) — 2.590(11) Fine sandstone 2.997(1) — 2.260±0.740(18) — Granite 3.120(1) — 2.715 — Notes: Number of samples is shown in brackets Table 2. Data of rock thermal conductivity at different temperatures
Sample Number Temperature/°C Lithology 25°C 30°C 60°C 90°C 120°C 150°C 180°C Reduction/% GLX-10 Dolomite 6.460 5.701 5.460 5.131 4.727 4.569 4.128 36 GLX-2 Shale 3.873 3.742 3.430 3.484 3.140 2.984 2.876 26 GLX-8 Limestone 2.947 2.947 2.911 2.741 2.624 2.539 2.446 17 TZX-5 Metamonzonite granite 3.055 3.001 2.996 2.892 2.733 2.603 2.554 16 DTA-6 Monzonitic granite 2.264 2.264 2.254 2.246 2.209 2.153 2.119 6 DTB-1 Gneiss 1.939 1.896 1.900 1.894 1.864 1.836 1.821 6 Table 3. Temperature correction formula of rock thermal conductivity in Datong Basin
Sample Number Lithology Correction formula R2 GLX-10 Dolomite λ(T) = −0.0163(T−T0)+λ(T0) 0.895 GLX-2 Shale λ(T) = −0.0069(T−T0)+λ(T0) 0.918 GLX-8 Limestone λ(T) = −0.0034(T−T0)+λ(T0) 0.981 TZX-5 Metamonzonite granite λ(T) = −0.0033(T−T0)+λ(T0) 0.965 DTA-6 Monzonitic granite λ(T) = −0.0008(T−T0)+λ(T0) 0.918 DTB-1 Gneiss λ(T) = −0.0008(T−T0)+λ(T0) 0.979 Note: λ(T0) refers to the thermal conductivity value at room temperature and pressure. -
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