Construction and application of favorable target evaluation system for hot dry rock

Abstract

China has abundant resources of hot dry rocks. However, due to the fact that the evaluation methods for favorable areas are mainly qualitative, and the evaluation indicators and standards are inconsistent, which restrict the evaluation efficiency and exploration process of dry hot rocks. This paper is based on the understanding of the geologic features and genesis mechanisms of hot dry rocks in China and abroad. By integrating the main controlling factors of hot dry rock formation, and using index grading and quantification, the fuzzy hierarchical comprehensive method is applied to establish an evaluation system and standards for favorable areas of hot dry rocks. The evaluation system is based on four indicators: heat source, thermal channel, thermal reservoir and cap rock. It includes 11 evaluation parameters, including time of magmatic/volcanic activity, depth of molten mass or magma chamber, distribution of discordogenic faults, burial depth of thermal reservoir, cap rock type and thickness, surface thermal anomaly, heat flow, geothermal gradient, Moho depth, Curie depth, Earthquake magnitude and focal depth. Each parameter is divided into 3 levels. Applying this evaluation system to assess hot dry rock in central Inner Mongolia revealed that Class I favorable zones cover approximately 494 km², while Class II favorable zones span about 5.7×10⁴ km². The Jirgalangtu Sag and Honghaershute Sag in the Erlian Basin, along with Reshuitang Town in Keshiketeng Banner, Reshui Town in Ningcheng County, and Reshuitang Town in Aohan Banner of Chifeng City, are identified as Class I favorable zones for hot dry rock resources. These areas are characterized by high-temperature subsurface molten bodies or magma chambers serving as high-quality heat sources, shallow thermal reservoir depths, and overlying thick sedimentary rock layers acting as caprock. The establishment and application of the evaluation system for favorable areas of hot dry rock are expected to provide new approaches and scientific basis for guiding the practice of selecting hot dry rock areas in China.