THE TANGGU GEOTHERMAL RESERVOIR (TIANJIN, CHINA)

The Tanggu geothermal system is an extensive, highly permeable, horizo ntal sandstone reservoir, situated within the North China Sedimentary Basin. Twenty-three successful production wells, yielding water with a n average temperature of about 70 degrees C, have been drilled into th is reservoir since 1987, distributed over an area of some 330 km(2). T he hot water is mostly used for space heating. In 1995 the annual prod uction exceeded 5 million tons. Hot water extraction has caused the wa ter level to drop to a depth of 80 m in the production wells, and it c ontinues to decline at a rate of 3-4 m per year. This has raised the q uestion as to whether the reservoir may be overexploited. The main obj ective of a reservoir evaluation carried out in 1996 was to estimate t he long-term production potential of the Tanggu reservoir. Two simple models were developed for this purpose. The potential is determined by specifying a maximum allowable pump setting depth of 150 m. On this b asis the potential of the Tanggu reservoir is estimated to be about 10 million tons per year, for the next ten years. A comprehensive reserv oir management program must be implemented in Tanggu. The first priori ty of such a program should be to improve the energy efficiency of spa ce heating in the district, which should result in about 50% reduction in hot water consumption. Another management option is reinjection, w hich would counteract the water level draw-down. (C) 1998 CNR. Publish ed by Elsevier Science Ltd.