Sinoprobe and parameters study on deep karst geothermal reservoir in the Donglihu Area, Tianjin and its exploitable potential analysis

This paper is the result of geothermal resource survey engineering.

Objective Tianjin is abundant in geothermal resources with high utilization level, and section 4-3 in Wumishan Formation of Jixian system is the main development dolomite reservoir at present. With the development intensity of geothermal fluid increasing, the exploitation potential of some areas has reached the limit. Exploring the deep geothermal resources and increasing the allowable productions have become one of the effective ways to ensure the sustainable development of geothermal resources in Tianjin.

Methods Donglihu area is the key research region in this study. Deep geophysical detection had been carried out and geothermal scientific exploration well CGSD-01 had been drilled.

Results The main results are listed as follows: (1)CGSD-01 drilling encountered the section 2 of Wumishan Formation at 3715 m, a set of purplish red argillaceous dolomite with light gray fine-grained dolomite is developed at the bottom of the section 3 of Wumishan Formation overlying, the thickness is about 73 m, and the fissures are not developed, which can be considered as aquiclude or aquitard; (2)The completion depth of CGSD-01 is 4051.68 m, and the bottom temperature is 106℃, specific field is 1.53 m³/h·m, permeability is 0.40 m/d, conductivity is 48.69 m²/d; (3)The geothermal fluid type of the section 2 of Wumishan Formation is Cl·SO₄·HCO₃-Na, salinity is 1.7 g/L. It is preliminarily inferred that the geothermal water is originated from atmospheric precipitation, and mainly occurs mixing, cation alternating adsorption, carbonate dissolution, sulfate reduction, and does not reach equilibrium state; (4)The maximum outflow rate of CGSD-01 can be reach to 130 m³/h, and the temperature is 100℃, which can meet the heating load of 300 thousand square meters building area.

Conclusions The high-yield new reservoir section 2 in Wumishan Formation of Jixian system was exposed for the first time in the second space of deep thermal reservoir in Tianjin area, and the thermal reservoir structure and main parameters of the reservoir were proved up, showing a good resource prospect.