Characteristics and development potential evaluation of geothermal resources in the Lanzhou Basin

This paper is the result of geothermal geological survey engineering.

Objective  The paper aims to study the formation and evolution of geothermal system and evaluate geothermal potential in the Lanzhou Basin to stipulate an overall development and utilization planning. This can strengthen understanding the differentiated distribution pattern of geothermal resources in rifted basins, which has great support and guidance for promoting development and utilization of geothermal resources.

Methods Based on the previous research results and the latest data from 11 geothermal wells, the geothermal geological conditions in 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 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 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 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, the geothermal resources volume and development potential was evaluated, with geothermal resource volume of 7241.05×10⁶ GJ, the geothermal fluid heat content of 2039.98×10⁶ GJ, recoverable geothermal fluid volume of 381 185.78 m³/d, the exploitable geothermal fluid heat of 22.21×10⁶ GJ/a, and the geothermal field capacity were of 705.04 MW. All these data suggest that the Lanzhou geothermal field belongs to a large-scale medium-low temperature geothermal field. 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.