Genetic Mechanism of Xiwenzhuang Geothermal Field in Taiyuan Basin

The study of the genetic mechanism of geothermal field is beneficial to the fine evaluation and effective development of geothermal field resources. On the basis of previous research results and the latest geothermal drilling data, the conceptual model of the formation of Xiwenzhuang geothermal field is established through analysis of main factors of "source, reservoir, migration channel and cover" of the karst geothermal system in Taiyuan Basin, and geothermal resources are carefully evaluated. It is considered that the Xiwenzhuang geothermal field formatted a middle-low temperature conducting geothermal system whose heat source results from the high terrestrial heat flow of asymmetric rift basin, whose recharge water source comes from the atmospheric precipitation in the exposed area of Ordovician karst reservoir in Dongshan and Xishan, and whose migration channels are the karst unconformity surface and fractures by which karst water migrated through the boundary faults of Dongshan and Xishan into the deep geothermal reservoir of the basin from Dongshan and Xishan bidirectional recharge, and after endothermic and temperature-increasing, gradually enriched and confined in the Ordovician karst reservoir of the Xiwenzhuang uplift in the central part of the basin. This geothermal system is characterized by better sealing performance, more aquifers of geothermal reservoir, faster recharge speed and higher geothermal gradient. In detail, the Ordovician karstic reservoir's cap rocks resulting in the buried depth of 800-1 700 m constitute of Carboniferous, Permian, Triassic and Quaternary. From top to bottom, the four main aquifers of Fengfeng Formation, Upper Majiagou Formation, Lower Majiagou Formation and Liangjiashan Formation are developed in turn. The average effective thickness of the thermal reservoir is 184.6 m in total, the migration age from the recharge source area to the confined area of basin is about 2 000 a, the average geothermal gradient of the overlying strata of the Ordovician geothermal reservoir is 3.0-4.0 ℃/100 m, and the geothermal water temperature range is 55-75℃. According to the fine evaluation results of geothermal resources of Ordovician karstic reservoir, the total geothermal reserve is 33.53×108 GJ, which is equivalent to 1.14×108 t of standard coal. The annual exploitation of geothermal resources can meet the demand of indoor heating area of 6.07 million square meters with huge potential for development. © 2019, Editorial Department of Earth Science. All right reserved.