Abstract:

The eastern slope of Neihuang Uplift develops fault structures and abundant geothermal resources. The distribution of the high-quality karst geothermal reservoir in the Ordovician system matches the demand of urban heating. The refined evaluation of the geothermal resources in the study area will be beneficial to the efficient development and utilization of geothermal resources. In this study, we investigated the karst reservoir distribution, geothermal temperatures, physical properties and hydrochemistry, and the conceptual model of formation of the geothermal field. The amount of geothermal resources was carefully evaluated as well. The results show that (1) the Ordovician karst reservoirs are zoned in the plane and distributed in the northeast direction, with the characteristics of shallow burial in the middle and deep burial in the east and west, and the buried depth of the reservoir is 800-3,000 m. The reservoirs are layered in the longitudinal direction, and single well aquifers can be divided into 19-43 layers, and the accumulative water-bearing thickness is 26.3-137.2 m, mainly been distributed in Lower Majiagou Formation, Upper Majiagou Formation, and Fengfeng Formation, as the main aquifer; (2) the average porosity of the geothermal reservoir is 3.52%-15.45%, and the wellhead water temperature is 48-75 ℃, and the single well water volume is 55-160 m³/h, and the water chemistry type is SO₄·Cl-Ca·Na, and the salinity is 1,830-3,560 mg/L; (3) the geothermal reservoir volume method is used to evaluate the geothermal resources. The total amount of geothermal resources in the Nanle-Puyang section is 32.1 billion GJ, and the recoverable resources are 4.82 billion GJ, which is equivalent to 165 million tons of standard coal. The recoverable resources can satisfy a heating area of 57.94 million square meters. It is nearly fifteen times of the current development area of 3.93 million square meters, with a huge exploitation potential.

Key words: Neihuang Uplift, Ordovician, karst geothermal reservoir, formation and evolution, resourceevaluation