The Characteristics, Sources, and Geothermal Implications of Sulfur-Containing Nanoparticles in Deep High-Temperature Geothermal Fluids in the Jiyang Depression

Abstract

Rising global demand for clean energy has elevated the status of geothermal resources as a sustainable renewable energy. Nevertheless, high costs and environmental risks of deep drilling restrict the development of geothermal research. Recent advances in transmission electron microscopy (TEM) have opened new avenues for studying geothermal systems. This study focuses on the southeastern Jiyang Depression. The region’s unique geological structure features a composite hydrothermal system and distinct geothermal anomalies, providing an ideal case study. Geothermal fluid samples were collected from Well Dongying-1 at a depth of 4283.6 m and analyzed using TEM, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive X-ray spectroscopy (EDS). These techniques enabled comprehensive characterization of micro-nanoparticles, including their morphology, size, crystallinity, aggregation state, chemical composition, and elemental distribution. The results reveal abundant sulfur-bearing micro-nanoparticles in the Dongying geothermal fluids, primarily exhibiting spherical and plate-like morphologies. The spherical nanoparticles (~500 nm in diameter) consist of smaller gypsum nanocrystals with numerous defects, consistent with crystallization under geothermal conditions via an oriented attachment mechanism. In contrast, the plate-like particles are larger, highly crystalline, and coated with NaCl nanoparticles, suggesting their origin from the Shahejie Formation gypsum layer through water−rock interactions. Elemental analysis confirmed that magma is the primary source of sulfur in the spherical gypsum nanoparticles with regular morphology. These nanoparticles, due to their unique mobility and physicochemical properties, serve as effective tracers of deep geothermal activity, offering insights into tectonic controls on heat distribution. Additionally, the study identifies a potential mechanism for scale formation, where nanoparticles aggregate under specific conditions to create nanoscale deposits. This finding provides a new perspective for developing anti-scaling technologies and advances the sustainable utilization of geothermal resources. The research also contributes to understanding material transport in geothermal systems, offering theoretical foundations for future studies.