Formation conditions, resource potential, and utilization prospects of cretaceous thermal groundwater in the Zharkent artesian basin

Abstract

This study examines the formation conditions and resource potential of the Cretaceous thermal aquifer system of the Zharkent Artesian Basin, located in the eastern part of the Ili intermontane basin within the Panfilov District of the Zhetysu Region, Kazakhstan. The study is based on drilling and testing data from 18 deep wells completed between 1957 and 2016, supplemented by industrial hydrogeological reports and published results from previous investigations. The methods included structural-geological analysis, hydrodynamic delineation of the groundwater recharge area, and a groundwater-balance approach in which subsurface inflow was calculated using Darcy’s law. The Upper Cretaceous aquifer occurs at depths of 1680-3702 m and, within the most prospective right-bank sector of the basin, at 2670-3702 m. The water-bearing sequence is 54-130 m thick. Wellhead water temperatures range from 74 to 103°C, free-flow discharge rates from 22 to 75 L/s, and excess wellhead pressures from 1.4 to 53.5 kgf/cm². The groundwater has low mineralization of 0.26-0.90 g/dm³, is alkaline, and is predominantly of the Na–Cl–HCO₃ hydrochemical type, with elevated fluoride and dissolved silica concentrations. The recharge balance of the Cretaceous aquifer comprises four principal components: infiltration of surface runoff, 2.05 m³/s (43.6%); infiltration of atmospheric precipitation, 0.107 m³/s (2.3%); subsurface inflow from fractured Paleozoic rocks, 0.534 m³/s (11.3%); and inflow along tectonic fault zones, 0.635 m³/s (13.5%). Total recharge within the territory of Kazakhstan is estimated at 3.326 m³/s. When transboundary groundwater inflow from the territory of China, estimated at 1.377 m³/s, is included, total recharge reaches 4.703 m³/s, equivalent to 406.3×10³ m³/day. The approved exploitable groundwater reserves of the Zharkunak geothermal field, amounting to 12960 m³/day under categories B+C₁, represent only about 3.2% of the estimated natural groundwater resources. This ratio indicates substantial remaining potential for further development of the basin. The thermal-energy potential of the approved reserves is estimated at 3524.1 GJ/day, corresponding to an average thermal capacity of 40.8 MW, an annual thermal-energy output of 357.6×10³ MWh, and an equivalent replacement of 43.9×10³ tonnes of standard fuel per year. Potential pathways for cascading utilization of the geothermal resource are proposed, and two prospective development projects for the Zharkent Basin are considered.