Characteristics and Development Potential Evaluation of Geothermal Resources in Lanzhou Basin

This paper is the result of geothermal exploration engineering.

Objective  The study on the formation and evolution of the geothermal system in the Lanzhou Basin and the factors for their heat generation are significant support and guidance for both the overall development planning of geothermal resources and the understanding the different distribution patterns of geothermal resources in faulted basins.

Methods Based on the previous research results and the latest data from 11 geothermal wells, the geothermal geological conditions in the Lanzhou geothermal system, including the stratigraphic structure, geological structure, geothermal field characteristics, and thermal reservoir characteristics are analyzed to reveal the characteristics of geothermal resource occurrence in the Lanzhou Basin. In addition, the conceptual model of the geothermal system is established in this area. Based on this foundation, an evaluation of the development potential of geothermal resources and a planning framework for their utilization direction were both conducted.

Results The geological conditions for heat generation are excellent in the Lanzhou geothermal field. The heat source is derived from the heat conduction of geothermal heat flow. Affected by the faulted basin movement, the geothermal gradient, reservoirs, and thermal reservoir temperatures exhibit a various distribution on the plane, generally showing higher (thicker) values both in the central and eastern regions and lower values in the western regions. The geothermal water in the Lanzhou Basin originates from the atmospheric precipitation in the bedrock mountainous area northwest of the urban area, which migrates along the strata and fractures, absorbing the heat from the rock matrix, and eventually forms geothermal water resources in the deeply buried Paleogene Xiliugou Formation strata.

Conclusions Based on the analysis of the thermal reservoir conditions in the area, an evaluation for the Lanzhou Basin was conducted of the geothermal resource potential and development prospects. The assessment results for the Lanzhou Basin illustrate that the geothermal resource volume, the geothermal fluid heat content, recoverable geothermal fluid volume, the exploitable geothermal fluid heat, and the geothermal field capacity were 7241.05×10⁶ GJ, 2039.98×10⁶ GJ, 381,185.78 m³/d, 22.21×10⁶ GJ/a, and 705.04 MW, respectively. It belongs to a large-scale medium-low temperature geothermal field, which is suitable for heating applications with thermal reservoirs exceeding 60°C for a total building heating area of 10,861,000 m². The development and utilization directions for the three types of reservoirs are planned in the three geothermal fields. Both the high-permeability reservoirs in the Xigu geothermal field and the medium-high permeability reservoirs in the Qilihe geothermal field belong to the hot water of low-temperature geothermal resources (Class III) , which can be applied for heating, physiotherapy, bathing, and greenhouse planting.