| Title | Genetic Models and Distribution Characteristics of Hydro-geothermal Systems in Bohai Bay Basin |
|---|---|
| Authors | Xinwei Wang, Nan'an Gao, Tinghao Wang, Huiying Liu, Di Wang, Bingjie Wuchen, Hui Zhang, Lu Luo, Zixuan Cui |
| Year | 2023 |
| Conference | World Geothermal Congress |
| Keywords | geothermal system, carbonate geothermal reservoire, sandstone geothermal reservoir, genetic mode, distribution characteristics, Bohai Bay Basin |
| Abstract | The Bohai Bay Basin in North China is a vast geothermal geological unit surrounded by mountains on three sides and facing the sea on the east, covering an area of about 12×104 km2. It is a prominent area for geothermal heating in China, boasting over 3,000 geothermal wells with an outlet water temperature of 55-95℃ and a single well flow rate of 80-120m3/h. These wells are distributed across nearly 40 cities, covering a massive heating area of 150 million square meters. The basin's exploration efforts have identified two main types of geothermal reservoirs - the sandstone reservoir of the Neogene Guantao Formation(Ng) and the carbonate reservoir of the Late Paleozoic- Early Mesozoic (Pt2-3+Pz1). Understanding these reservoirs' formation model and distribution characteristics is crucial for exploring the accumulation system of geothermal resources and guiding the rapid development of geothermal resources. This paper utilizes the petroleum systems analysis approach-from source rock to trap- to study the genesis factors and geological processes of the two geothermal systems. While both the Ng and Pt2-3+Pz1 geothermal systems share the same heat source (crust/mantle conduction heating with an average heat flow value of 64 mW/m2), water source (atmospheric precipitation in surrounding mountainous areas), and regional thermal cap layer (400-600m thickness of the Quaternary), they have notable differences in reservoir spatial distribution, storage capacity, and geothermal water migration mode. The Ng geothermal system has a horizontal and well-connected reservoir with a bottom depth of 1500-2000m. The sandstone content is 40%-60%, and the cumulative thickness of the sand bodies is 160-300m with a high porosity of 25%～35%. Geothermal water in this system migrates slowly along the strata from west to east. Conversely, the Pt2-3+Pz1 geothermal system has a complicated structural deformation and segmented reservoir with a top depth of 1500-6000m. The weathered and karst reservoir has a fracture rate of 25%-50%, an average porosity of 3-9%, and a cumulative fracture thickness of 130-300m. Geothermal water migration in this system can be divided into five relatively independent but hydrologically connected subsystems. The central transverse-runoff subsystem and the eastern longitudinal-runoff subsystem are the most favorable exploration and development areas due to their shallow burial depth (1000-1500m) and low geothermal water mineralization (1-3g/L). |