Abstract:

Geothermal energy, considered as one of new and emerging energies, has attracted increasing attention from academia and industry recently, owing to its huge potential and desirable attributes. Regional geothermal characteristics and deep temperature estimation are of great significances for geothermal energy exploration and utilization. The lower reaches of the Yangtze River in Eastern China is a region with well-developed socio-economic conditions and extremely large energy demand. However, the current regional geothermal regime is not well understood and needs further update with newly acquired geothermal data to provide insights into energy potential assessment in the region. In this article, we outlined the present-day geothermal gradient and heat flow pattern of the Lower Yangtze and estimated the temperatures at 1000-5000 m depth by integrating previously available regional geothermal data and newly measured thermal properties. The results showed that the geothermal regime of the Lower Yangtze area is mainly controlled by the neo-tectonics within the area. The geothermal gradient ranged from 16 to 41 ℃/km, with most areas between 18-25 ℃/km and an exception of 28-35 ℃/km in the northern Jiangsu area. While the heat flow varied from 48 to 80 mW/m² with a mean value of 60 mW/m², high heat flow was also found in the northern Jiangsu area and near the Tan-Lu fault zone, indicating the Lower Yangtze area is of a moderate to high geothermal regime favorable for hydrocarbon generation and geothermal energy exploitation. The estimated temperatures-at-depth were 30-54 ℃ at 1000 m, 50-95 ℃ at 2000 m, 65-130 ℃ at 3000 m, 80-170 ℃ at 4000 m, and 100-210 ℃ at 5000 m. Generally, the geothermal gradient showed a remarkable SW-NE striking, with high temperature anomalies distributed in the southern Anhui and northeastern Jiangsu areas, suggesting potential targets of geothermal energy utilization in the two areas. In addition, we also determined the isothermal depth patterns at 60 and 120 ℃. On the basis of geological, geochemical and geothermal conditions, we propose that the Lower Cambrian Hetang Formation and the Permian Longtan Formation of the northern Jiangsu area are the preferable hydrocarbon targets. In terms of regional geothermal energy utilization, the shallow (1400-2100 m) and deep (2100-3000 m) geothermal energy in the northern Jiangsu area can be used for heating and power generation or other industrial utilizations, respectively.

Key words: the lower reaches of the Yangtze River, geothermal regime, deep temperature, geothermal resources