A Three-Dimensional Conceptual Model of the Yangyi Geothermal Reservoir Based on Integrated Data

The Yangyi geothermal field in central Tibet represents a structurally controlled high-temperature geothermal system that has been extensively investigated through geological, geochemical and geophysical exploration, resulting in a substantial body of multi-source datasets. Despite this wealth of information, previous studies have predominantly addressed individual methods or limited spatial scales, and a unified framework for interpreting reservoir architecture, fluid migration pathways, and spatial heterogeneity has remained absent. 

To address this limitation, this study integrates geological mapping, gravity and magnetotelluric surveys, borehole logging and well testing, together with short- and long-term tracer experiments, to construct a three-dimensional geological model of the Yangyi geothermal system within a consistent spatial framework. The model explicitly incorporates the major fault systems, deep and shallow stratifications constrained by the basement andesite layer, and the spatial distribution of low-resistivity zones. Productive geothermal wells, including ZK203, ZK208, and ZK403, are used to constrain the relationships between structural elements and observed hydraulic responses.

The results demonstrate that the spatial zonation of the Yangyi geothermal field is primarily governed by fault-controlled vertical structural differentiation. Shallow fracture networks spatially coincide with low-resistivity zones and constitute hydraulically efficient pathways that facilitate rapid tracer migration between wells. In contrast, the contribution of deep thermal fluids is mainly regulated by major fault structures and is progressively modified along structurally guided flow paths. Integrated geological, geophysical, and tracer evidence indicates that the parent geothermal fluid originates from deeply circulating meteoric water, ascending at depth predominantly along the F5 fault and migrating upward at shallower levels preferentially along the F3 fault. The development of low-resistivity zones reflects fracture enhancement and hydrothermal alteration within the shallow structural domain during this upflow process.

By integrating multi-source datasets within a three-dimensional geological modeling framework, this study provides a coherent structural interpretation for the coexistence of reservoir zonation and inter-well hydraulic connectivity in the Yangyi geothermal field, and offers robust structural constraints for identifying favorable reservoir configurations in fault-controlled geothermal systems.