Research on karst fissure development pattern of the Ordovician buried hills in Tianjin

Ordovician is a promising bedrock thermal reservoir in Tianjin Plain. However, during the process of development, it is found that the karst fractures in this stratum are very uneven and the aquosity is quite different, which may bring difficulties to the construction and seriously hinder the development of geothermal resources. Therefore, the data of nearly 100 Ordovician geothermal wells in this city were compared and analyzed, and the development of Ordovician type I and type II fractures and the original water output in different tectonic units were statistically analyzed to summarize the development law of the karst fissure. The results show that the karst fissures are mainly distributed in Majiagou Formation with relatively pure limestone, followed by Liangjiashan Formation and Yeli Formation with relatively developed argillaceous limestone. In the areas with burial depth less than 2 300 m, the fissure development of Ordovician System increases with the increasing of formation thickness. The thickness of karst fissures in the overlying strata of Neogene and Mesozoic is thicker than that in the overlying strata of Carboniferous. The karst fissures in Shuangyao and Panzhuang uplifts are well developed and water-rich. Karst fissures are most developed near tensional faults. According to this, karst fissures are mostly distributed near tensional faults and Majiagou Formation with pure limestone, mainly uplift areas with shallow burial depth and Neogene and Mesozoic overlying strata. These areas are rich in water, which can provide reliable basis for geothermal development.