Isotope Geochemistry of Geothermal Waters in Northern North China Basin: Implications on Deep Fluid Migration

Abstract

An isotope geochemical investigation was carried out on geothermal formation waters of the Jidong (Eastern Hebei) area in northern North China Basin. 11 water samples were collected from geothermal and non-thermal water wells located mainly in the Liuzhan region where the highest thermal gradient (7.5 ?C/100m) was found in North China Basin. Results confirmed that the extra-ordinary high thermal gradient is formed by upward migration of deeper, more saline and hotter geothermal fluid into the shallower aquifers. Interpretation of results supports a conceptual model to classify the system as a new type of geothermal systems in the sedimentary basins in China that is formed by migration of fluid from deeper aquifers into shallower ones. Furthermore, vertical fluid migration is probably also the reason for secondary oil reservoir being found in Ng formation. With rather low salinity (1-3 g/l), and relatively higher temperatures of 100-120 ?C at rather shallow depth (1000- 1500m), the thermal water in the Liuzhan system is the most favourable for exploitation in North China Basin.