Tanggu is a harbor and industrial area and is the location of Tianjin Harbor, Tianjin Bonded Area and Tianjin Economic Development Area. It covers an area of 859 km2 and has a population of 430,000. Tanggu Geothermal Field is located at the western coast of Bohai Sea. This area belongs to the depression area of North China geologically. Neogene strata of Guantao Group is distributed widely in this region. Good permeability, large thickness, and high conductivity make it form a regional low-temperature porous reservoir. The reservoir is buried to a depth of 1,600 - 2,100 m. The total thickness of about 500 m can be divided into upper and lower sections including three aquifers. There are mudstone layers as aquicludes intercalated among aquifers. The Guantao I aquifer has a thickness 100 - 120 m. It is mainly a medium-fine sandstone with a porosity of 30 - 32% and water temperature of 55 - 65°C. The lower section includes two aquifers. The upper aquifer of Guantao III is a sandstone, about 100 m thick, with porosity of 28 - 30% and water temperature of 60 - 70°C. The lower aquifer of Guantao III is sandstone and conglomerate. Their porosity and permeability are 20% and 2,000 - 2,500 mm 2 respectively. Hot water has a temperature 65 - 78°C in this aquifer. This is the main aquifer presently exploited