In recent years, gas reservoirs containing high levels of hydrogen sulfide have been found in salinized lacustrine carbonate rocks in the upper member of the Lower Ganchaigou Formation (E₃²) in the Yingxiongling area of the western Qaidam Basin. This poses great safety risks to drilling and development. To clarify the genetic mechanisms of hydrogen sulfide, we have analyzed the geochemical characteristics and sulfur isotopes of natural gas and predicted the distribution of hydrogen sulfide. The results show that (1) natural gas in the Yingxiongling area is dominated by wet gas, with relatively high nonhydrocarbon content. The gas is E₃²oil-type gas in a mature stage. (2) Hydrogen sulfide in natural gas reservoirs is less likely to originate from biological and volcanic geneses, and it is primarily a product of thermochemical sulfate reduction. The high-quality Oligocene source rocks distributed across a large area, the saline-deposit formations widely distributed in the western Qaidam Basin, and the high geothermal gradients and large numbers of developed pore-type reservoirs, all combine to provide favorable conditions for the formation of hydrogen sulfide reservoirs. (3) During the E₃² deposition period, rock salt developed in the center of the lake basin, the sealing conditions for oil and gas were favorable, and the formation temperature was high during the reservoir formation period. Development of subsalt porous reservoirs is conducive to enrichment of hydrogen sulfide, and comprehensive prediction indicates that the subsalt formation in the Central Yingxiongling-Ganchaigou area is an enrichment zone for hydrogen sulfide. The research results are of considerable significance for the exploration and deployment, and the production safety, of hydrogen sulfide-containing reservoirs.

For insight into the productive and storage mechanisms of biogas in the Qaidam Basin, efforts were made to investigate the groundwater recharge and the processes of hydrocarbon generation by CDOM-EEM (fluorescence excitation-emission matrix of Chromophoric dissolved organic matter) spectrum, hydrogen and oxygen isotopes, and geochemical characters in the central depression of the Qaidam Basin, China. The samples contain formation water from three gas fields (TN, SB, and YH) and surrounding surface water (fresh river and brine lake). The results indicate that modern precipitation significantly controls the salinity distribution and organic matter leaching in the groundwater system of the central depression of the Qaidam Basin. Higher salinity levels inhibit microbial activity, which leads to organic matter degradation and to gas generation efficiency being limited in the groundwater. The inhabitation effect is demonstrated by the notable negative correlation between the extent of organic matter degradation and its concentration with hydrogen and oxygen isotopes. The conclusion of this study indicated that modern precipitation emerges as a crucial factor affecting the biogas production and storage in the Qaidam Basin by influencing the ultimate salinity and organic matter concentration in the formation, which provides theoretical insight for the maintenance of modern gas production wells and the assessment of gas production potential.

S-wave seismic data are unaffected by natural gas trapped in strata, making them a valuable tool to study evaporite facies comparing to P-wave data. S-wave seismic data were utilized to construct an isochronous framework and analyze evaporite facies by seismic sedimentology methods in the Quaternary biogenic gas-bearing Taidong area, Sanhu Depression, Qaidam Basin, NW China, with calibration from wireline logs, geochemical evidences, and modern analogs. Techniques of phase rotation, frequency decomposition, R (Red), G (Green), B (Blue) fusion, and stratal slices were integrated to reconstruct seismic geomorphological features. Linear and sub-circular morphologies, resembling those observed in modern saline pans such as Lake Chad, were identified. Observations from Upper Pleistocene outcrops of anhydrite and halite at Yanshan (east of the Taidong area), along with lithological and paleo-environmental records from boreholes SG-5, SG-1, and SG-1b (northwest of the Taidong area), support the seismic findings. The slices generated from the S-wave seismic data indicate a progressive increase in the occurrence of evaporite features from the K2 standard zone upwards. The vertical occurrence of evaporite facies in the Taidong area increases, which coincides with the contemporary regional and global arid paleo-environmental changes. The interpretation of Quaternary stratal slices reveals a transition from a freshwater lake to brackish, saline, and finally, a dry saline pan, overlaid by silt. This analysis provides valuable insights into locating evaporites as cap rocks for biogenic gas accumulation and also into mining the evaporite mineral resources in shallow layers of the Taidong area.

S-wave seismic data are unaffected by natural gas trapped in strata, making them a valuable tool for seismic sedimentology. In this study, S-wave seismic data were utilized to construct an isochronous framework and analyze evaporative facies in the Quaternary biogenic gas-bearing Taidong area, Sanhu Depression, Qaidam Basin, NW China, with calibration from wireline logs and modern analogs. Techniques of phase rotation, frequency decomposition, R (Red), G (Green), B (Blue) fusion, and stratal slices were integrated to reconstruct seismic geomorphological features within the isochronous framework. Linear and sub-circular morphologies, resembling those observed in modern saline pans such as Lake Chad, were identified. Observations from Upper Pleistocene outcrops of anhydrite and halite at Yanshan, east of the Taidong area, salinity measurements from Well TX1 to the north, and lithological and paleo-environmental records from boreholes SG-5, SG-1, and SG-1b to the northwest support the seismic findings. The RGB-fused slices generated from the S-wave seismic data in Taidong area indicate a progressive increase in the occurrence of evaporative features from the K2 standard zone upwards. The vertical occurrence of evaporative facies in the Taidong area mirrors the contemporary regional and global paleo-environmental changes. The interpretation of Quaternary stratal slices from seismic sedimentology—spanning K2, K1, and K0 standard zones—reveals a transition from a freshwater lake to brackish, saline, and finally, a dry saline pan, overlaid by silt. This analysis provides valuable insights into locating evaporites as cap rocks for biogenic gas accumulation and also into mining the evaporite resources in shallow layers of the Taidong area.

Against the global low-carbon transition drive, mudstone biogas represents a vital unconventional natural gas resource. Yet unclear micro-scale gas-displacing-water mechanisms hinder its productive exploitation. This work combines multi-pressure NMR displacement tests and mono-multifractal coupling analysis to quantify dynamic pore evolution, overcoming limits of conventional static pore characterization. Mudstone core samples from the Sanhu area of Qaidam Basin are analyzed to decode biogas charging controls and build a multi-factor coupling model. Results reveal that micro–mesopores dominate reservoirs; brittle minerals form rigid pore frameworks, while water-wet clays impede gas flow. Gas–water displacement proceeds in staged preferential flow, with two threshold pressures (8 MPa, 15 MPa) slowing efficiency gains. Fractal indices reliably reflect gas–water partitioning. Pore geometry and mineral assemblages jointly govern biogas accumulation; intervals with well-connected pores, weak water wettability and low clay content favor gas charging. The findings support the exploration of analogous continental mudstone gas reservoirs.