Abstract:

In Tianjin Banqiao depression, the Dongying Formation contains abundant ground pressure-type geothermal fluid resources. Because the exploitable water level is deep, both survey and development of the resource are difficult for local government. Combining with the pore structure and ground pressure of Dongying Formation, the authors analyzed the data of the pumping test of well TR21 and suggested that Dongying Formation is in overpressure condition, having a starting hydraulic gradient. By iterative fitting of the data from 0 and 3 stage drawdown pumping test, the calculated starting hydraulic gradient is 1.16（1 160‰）and the overpressure coefficient of permeability is 1.896 m/d. These data indicate that the geothermal fluid of Dongying Formation receives  recharged from the underlying overpressure Shahejie Fomation. Dongying Formation can trap underlying strata overpressure of 5.12-6.25 MPa which provides the probability for the formation of overpressure of underlying strata and the preservation of overpressure of the Dongying Formation. The overpressure coefficient of permeability is higher than the one obtained（1.392 m/d）by permeability, suggesting that the coefficient of permeability of geothermal reservoirs increases under overpressure conditions. The overpressure and increase of coefficient of permeability of the reservoir facilitate the exploitation of the resources.

Key words: geothermal energy, reservoir overpressure；pumping test；hydraulic gradient；mining conditions；Dongying Formation；Banqiao depression