Occurrence Mechanism of Convective Geothermal Systems in Jiaodong Peninsula, China

Abstract

Previous studies have shown that on the surface, Jiaobei uplift and Weihai uplift have higher heat flow values than Jiaolai depression. However, the mechanism by which the deep heat flow migrates and the exposure of geothermal resources are still unclear. In this study, the geothermal field distribution, thermal conductivity, temperature logging data, and chemical composition of the geothermal fluid in the Jiaodong Peninsula were analyzed. Regarding the thermal field’s characteristics and their controlling factors, a conceptual model of heat flow diversion-accumulation between the uplift and basin areas in the Jiaodong Peninsula is proposed. The lithology of the uplift area is mainly composed of intrusive rocks and metamorphic rocks with high thermal conductivities. The lithology of the basin mainly consists of sandstone with a low thermal conductivity. The bottom of the basin, which has a low thermal conductivity and low permeability, serves as a heat insulation and water insulation roof, which causes the heat flow and the heat-carrying fluids and gases from the deep crust to be refracted and redistributed at the bottom of the basin area. As a result, the bottom of the uplift areas has a higher heat flow. In particular, the axial position in the uplift area has the highest heat flow. In addition, the geothermal resources in the Jiaodong Peninsula are mainly distributed in the V-shaped area where the upper block of the NE- and NW-trending faults intersect, and the scope of the exposure of the geothermal resources is very limited.

Genesis of Geothermal Waters in Zhongshan City, China: Hydrochemical and H-O-C Isotopic Implications

“…The desulfuration coefficient, γSO 4 2− /γCl − , can reflect the oxidation-reduction environment of underground water: The smaller γSO 4 2− /γCl − is, the more the underground water environment is reduced [55]. The range of variation for γSO 4 2− /γCl − in geothermal water is 0.019 to 0.051 (0.029 on average, much less than the mean value (0.1) for seawater) [56], which indicates that geothermal water is in a highly reduced environment.…”

“…The research on the geothermal reservoir temperature is critically important for establishing a conceptual model and a formation mechanism of geothermal reservoirs in geothermal fields. At present, the geothermometers used to estimate the geothermal reservoir temperature mainly include a cation geothermometer, SiO 2 geothermometer, gas geothermometer, and isotope geothermometer [50][51][52][53][54][55][56][57][58][59][60][61][62][63] These geothermometers have different application conditions, so it is necessary to select a suitable geothermometer according to the specific conditions of a geothermal system to obtain optimal estimates of the geothermal reservoir temperature [64]. In this study, a cation geothermometer and a SiO 2 geothermometer were used to calculate the geothermal reservoir temperature in the study area.…”

Hydrochemical Characteristics and Indication to Geothermal Genesis of Low–Medium-Temperature Convection Geothermal Field in Yanshan Orogenic Basin, China

“…In the early years of this subject's discovery, studies of hydrogen and oxygen isotopes in geothermal fluids in Tibet helped to identify their possible flow directions and sources of recharge [18]. Later on, the relationship between ion ratio and salinity was used to analyze the hydrodynamic environment of geothermal fluid in the Jiaodong area and its relationship with seawater recharge [19]. Studies on the distribution of environmental isotopes and hydrochemistry, including 14 C, can clarify key geothermal cycle information such as residence time and circulation depth of conductive geothermal fluids in subsidence basins in the Gansu region [20].…”