Use of a hydrogeochemical approach in determining hydraulic connection between porous heat reservoirs in Kaifeng area, Henan, China

In this paper a case study of hydraulic connectivity in a 300–1600 m deep, low temperature, sedimentary geothermal system in Kaifeng area, Henan province, China is presented. Based on lithologic data from 52 geothermal wells and chemical data on geothermal water (GW) from six depth-specific and representative wells, the system was chemically grouped into two main hot reservoirs (300–1300 m and 1300–1600 m deep), which were in turn, divided into six sub-reservoirs (SRs). Data on stable isotope (2H and 18O) ratios, radioactive isotope (14C) radiation in conjunction with computation of mineral–fluid chemical equilibria were used to establish the recharge source (a mountainous region in the southwestern part of Zhengzhou, 60 km away); evaluate groundwater age which varied with well depth from 15630 ± 310 a to 24970 ± 330 a; and assess the chemical equilibrium state within the system. The results of different analysis did not suggest an obvious hydraulic connection between the two main hot reservoirs. The location of the recharge zone and the geohydrologic characteristics of the study area demonstrate that the GW utilized from the system is mainly derived from confined waters of meteoric origin.