Accumulation conditions and exploration potential of deep natural gas in the Qaidam Basin

Abstract

This paper examines the enrichment conditions of deep natural gas reservoirs in the Qaidam Basin and delineates the exploration potential utilizing seismic, geological, geochemical, well-logging, and drilling data. The findings indicate the presence of two high-quality gas source formations, namely the Jurassic and Paleogene formations, along the northern margin and the western part of the basin, respectively. The formations both exhibit advanced evolution and robust gas-generating capacity. The deep layers along the northern margin consist of bedrocks and Paleogene clastic reservoirs, while the western deep layers feature Paleogene lacustrine carbonate reservoirs. The reservoirs west of Qaidam Basin are widely distributed on the plane and vertically form multiple reservoir cap combinations. The primary pores, dissolution pores, fractures, and other pore types developed in the reservoirs are considered as the storage space for deep gas accumulation. The continuous active deep faults serve as high-quality channels for deep gas sources; furthermore, the formation of deep structures is well-matched with natural gas generation. The deep hydrocarbon source rocks in the western Qaidam Basin are characterized by early and continuous hydrocarbon generation. Early-generated liquid hydrocarbons undergo high-temperature cracking into gas during later burial, resulting in a robust gas-generating capacity and significant potential for deep resources. The widely developed salt rocks, argillaceous rock, and abnormally high-pressure layers in the deep Qaidam Basin contribute to preserving deep natural gas. In conclusion, it is believed that deep gas reservoirs in the Qaidam Basin are enriched in the traps around hydrocarbon-generating sags with developed faults. Key favorable areas for deep-seated natural gas exploration include the basement rocks of the ancient piedmont uplift in the northern margin of Qaidam, the Paleogene clastic rocks in the central structural belt, and the carbonate rocks along the Yingxiongling structural belt in the western part of the basin.

Keywords

• deep gas reservoir
• accumulation conditions
• exploration potential
• lacustrine carbonatite
• qaidam basin