Terrestrial heat flow and geothermal field characteristics in the Bide-Santang basin, western Guizhou, South China

Chen Guo,Yong Qin,Lingling Lu

doi:10.1177/0144598717752364

Abstract

Geothermal fields in coal-bearing strata significantly influence coal mining and coalbed methane accumulation and development. Based on temperature data from 135 coalfield exploration boreholes and thermophysical tests of 43 rock and coal samples from the Upper Permian coal-bearing strata of the Bide-Santang basin in western Guizhou, South China, the distribution of terrestrial heat flow and the geothermal gradient in the study area are revealed, and the geological controls are analysed. The results show that the thermal conductivity of the coal-bearing strata ranges from 0.357 to 3.878 W (m K)−1 and averages 1.962 W (m K)−1. Thermal conductivity is controlled by lithology and burial depth. Thermal conductivity progressively increases for the following lithologies: coal, mudstone, siltstone, fine sandstone, and limestone. For the same lithology, the thermal conductivity increases with the burial depth. The present geothermal gradient ranges from 15.5 to 30.3°C km−1 and averages 23.5°C km−1; the terrestrial heat flow ranges from 46.94 to 69.44 mW m−2 and averages 57.55 mW m−2. These values are lower than the averages for South China, indicating the relative tectonic stability of the study area. The spatial distribution of the terrestrial heat flow and geothermal gradient is consistent with the main structural orientation, indicating that the geothermal field distribution is tectonically controlled at the macro-scale. This distribution is also controlled by active groundwater, which reduces the terrestrial heat flow and geotemperature. The high geothermal gradient in the shallow strata (<200 m) is mainly caused by the low thermal conductivity of the unconsolidated sedimentary cover. The gas content of the coal seam is positively correlated with terrestrial heat flow, indicating that inherited palaeogeothermal heat flow from when coalbed methane was generated in large quantities during the Yanshanian period due to intense magmatic activity.

Highlights

The earth’s geothermal field is produced by the effect of the earth’s internal heat on shallow crustal rocks with different heat conductivity (Chen et al, 1984), and it has been attracting increased attention from large institutional, industrial, and scientific interests in order to evaluate the potential and feasibility of geothermal energy production (Chelle-Michou et al, 2017; Galgaro et al, 2014; Gondal et al, 2017; Tsuchiya and Yamada, 2017; Walsh et al, 2017)
The burial depth and lithology are the key factors controlling rock thermal conductivity in the study area, which will be analysed in the following
Thermal conductivity is controlled by lithology and burial depth and increases in the lithologic order of coal/mudstone/siltstone/fine sandstone/limestone

Summary

Introduction

The earth’s geothermal field is produced by the effect of the earth’s internal heat on shallow crustal rocks with different heat conductivity (Chen et al, 1984), and it has been attracting increased attention from large institutional, industrial, and scientific interests in order to evaluate the potential and feasibility of geothermal energy production (Chelle-Michou et al, 2017; Galgaro et al, 2014; Gondal et al, 2017; Tsuchiya and Yamada, 2017; Walsh et al, 2017). Present-day geothermal research is focused on the factors controlling the distribution of formation temperature, geothermal gradient, and terrestrial heat flow (Deng et al, 2012; Jiang et al, 2016; Pascal, 2015; Reiter, 2014; Tanikawa et al, 2016) and has recently received considerable attention related to the exploration and exploitation of coal, petroleum, and natural gas (Feng et al, 2017; Isaev et al, 2014; Kuzielovaet al., 2017; Li et al, 2017; Liu et al, 2016; Safari et al, 2017). Guizhou Province is considered to be an important region for CBM development in South China, and the BideSantang basin is one of the most promising blocks with extremely abundant coal and CBM resources and reservoir physical properties (Qin et al, 2012a). Some CBM wells in the BideSantang basin have produced industrial-scale gas flow, indicating a considerable prospect for CBM development (Guo et al, 2017)

Results

Discussion

Conclusion