Geothermal reservoir characteristics and geothermal resource evaluation of Guantao Formation in the Bohai Bay Basin

There are many sets of geothermal reservoirs of different types in the Bohai Bay Basin, and the sandstone geothermal reservoir of Neogene Guantao Formation is one of them which has moderate burial depth, large thickness and wide distribution. In the past, however, the Guantao Formation geothermal resources in the whole area were not evaluated systematically. Based on the research results of the present geothermal field characteristics in the whole basin, this paper systematically describes the areal distribution characteristics of the Guantao Formation geothermal reservoir by collecting and sorting out drilling, geological and geophysical data. Furthermore, the amount of geothermal resources of the Guantao Formation geothermal reservoir is evaluated, and the favorable areas of geothermal resources are delineated. And the following research results are obtained. First, the present average geothermal gradient of Quaternary-Paleogene in the Bohai Bay Basin is 34.7±3.5℃/km, while the average terrestrial heat flow is 64.4±8.1 mW/m2, which is the characteristics of the Cenozoic rift basin, indicating that there is geothermal setting for the formation of large geothermal fields with medium-low temperature. Second, the temperature of the Guantao Formation geothermal reservoir ranges from 19.6 to 96.2 ℃, with an average of 56.3 ℃. The relatively high temperature areas are mainly distributed in the Huanghua Depression, the Bozhong Depression and the Jizhong Depression, and the overall distribution trend is basically consistent with the present geothermal field pattern of the basin. Third, the amount of the Guantao Formation geothermal resources in 110 cities above the county level in the Bohai Bay Basin is equivalent to 99.6×108 t standard coal, and the average abundance of geothermal resources is 148.6×104 t/km2, so it is classified as the first-level oilfield geothermal resource with the best resource conditions. And 66.7% of them are concentrated in the North China oil area. Fourth, the amount of the Guantao Formation maximum probability geothermal resources in the Bohai Bay Basin is equivalent to 662.2×108 t standard coal, and the average abundance of geothermal resources is 72.4×104 t/km2. In conclusion, nine favorable areas of Guantao Formation geothermal resources can be delineated in the whole basin based on the geothermal reservoir characteristics and the ground and economic conditions, namely, Xingheng Uplift, Nangong Sag, Qiuxian Sag, Raoyang Sag, Wuqing Sag, Qikou Sag, Chengning uplift, Dongying Sag and Changwei Sag. © 2023 Natural Gas Industry Journal Agency. All rights reserved.