关键词: 深层地热, 徐州地区, 岩溶热储, 聚热机制, 勘探有利区

Abstract: Xuzhou area features a widespread distribution of high-quality thermal reservoirs, such as carbonate and metamorphic rocks, indicating significant potential for deep geothermal resources. However, fundamental research on their formation conditions remains insufficient. This study, drawing on previous research and drilling data, provides a comparative analysis of the formation conditions for geothermal resources, including "source, pathway, reservoir, and caprock", across different tectonic units. It delineates prospective areas for deep geothermal resources, explores the accumulation mechanisms of deep geothermal energy, constructs a genetic model for deep geothermal systems, and identifies favorable areas for exploration. The research results show as follows. (1) The deep geothermal resource potentials across different tectonic units, from highest to lowest, are Fengpei fault block, Pizhou-Suining fault block, Tan-Lu fault zone, and Xuzhou-Jiawang fault block. (2) Geothermal temperatures in depressions are generally higher than those in the uplift areas within Xuzhou area. In the areas where Meso-Cenozoic fault depressions are developed, such as the Fengpei fault block and Tan-Lu fault zone, the geothermal gradient ranges from 2.0 ℃/hm to 3.2 ℃/hm. In contrast, the geothermal gradient is typically less than 2 ℃/hm in uplift areas including the Xuzhou-Jiawang and Pizhou-Suining fault blocks. The structural configuration alternating uplifts and sags within the depressions leads to the redistribution of heat flow, with the uplift areas exhibiting higher thermal conductivity and thus better conditions for heat accumulation. (3) Different types of reservoir-cap assemblages exhibit distinct heat accumulation conditions. Within the Fengpei fault block, the Huankou and Jing’an sags are characterized by dual caprock layers creating heat insulation, along with multiple stacked reservoirs (Neoarchean metamorphic rocks, Cambrian Zhangxia Formation and Ordovician Majiagou Formation carbonates), resulting in the most favorable heat accumulation conditions. In the Pizhou-Suining fault block, the Pantang and Sihu sags are characterized by reservoir-cap assemblages of Mesozoic-Cenozoic clastic rocks and Qingbaikou System dolomites. The significant differences in physical properties between the reservoir and caprock lead to heat concentration at their interface, yielding less favorable conditions for heat accumulation. (4) In the Fengpei fault block, crust-mantle uplift has occurred, and concealed magmatic bodies at depth provide a heat source. The intersection of deep major faults nearly EW-trending and NNW-trending forms efficient water-conducting channels. The reservoirs develop karst. The low thermal conductivity clastic rocks and coal measures have a strong insulation effect. These conditions result in a geothermal system predominantly driven by heat conduction, with thermal convection playing a supplementary role. (5) The northern Changdian Town, located within Huankou sag of the Fengpei fault block, sits atop an anticlinal structure bounded by normal faults. This area experiences heat flow convergence and sufficient groundwater recharge. The reservoir is buried at depths ranging from 3 000 to 4 000 meters, making it favorable for development and an advantageous area for deep geothermal resource exploration in Xuzhou area.

Key words: deep geothermal energy, Xuzhou area, karst geothermal reservoir, heat accumulation mechanism, favorable exploration area