STUDY ON THE THERMAL RESERVOIR CHARACTERISTICS OF KARST GEOTHERMAL FIELDS IN TIANJIN CITY

The characteristics of karst thermal reservoir are analyzed comprehensively based on the geotectonic characteristics and stratigraphic distribution of Tianjin City. It is believed that the main tectonic framework are Central Hebei depression, Cangxian uplift and Huanghua depression from northwest to southeast, with the major faults of NE-trending Cangdong fault, Tianjin fault and NW Ninghe-Baodi fault. The karst geothermal fields are mainly distributed on the Cangxian uplift where geothermal fields are developed in Wangcaozhuang, Dacheng, Panzhuang, Shuangyao and Xiaohanzhuang salients. The research suggests that the Jixianian Wumishan Formation, composed of dark gray coarse-grained dolomite and chert banded dolomite, is widely distributed throughout Tianjin with developed crevice karst and good porosity-permeability, which serves as the main thermal reservoir. The thermal current value of Cangxian uplift is higher than that of the surrounding areas. The main source of geothermal water is the mountainous area of Jixian county in the north with the major fault and unconformity as the most important migration channel.