Hydrogeochemical characteristics and evolution of formation water in the continental sedimentary basin: A case study in the Qaidam Basin, China

• Published in: The Science of the total environment 2024-12, Vol.957, p.177672, Article 177672
• Main Authors: Jiang, Wanjun, Sheng, Yizhi, Shi, Zheming, Guo, Huaming, Chen, Xianglong, Mao, Hairu, Liu, Futian, Ning, Hang, Liu, Nannan, Wang, Guangcai
• Format: Article
• Language: English
• Subjects: basins; case studies; China; environment; Evolution mechanism; Formation water; groundwater; Hydrogeochemical characteristics; hydrogeochemistry; oils; Qaidam Basin; salt lakes; seawater; tectonics; Water-rock interactions
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.177672

In deep formations, oil or gas reservoir rocks are generally accompanied by groundwater with high total dissolved solids (TDS), commonly referred to as “formation water”. The enrichment of trace and/or metallic elements such as K, B, Li, Br, Sr in this type of groundwater holds significant industrial values and socioeconomic benefits. However, the processes involved in the burial and generation of formation water remain not fully understood. In this study, totally 468 sets of major ions and trace elements were collected from current study and literatures to investigate the hydrogeochemical characteristics and evolution mechanisms of formation water from different regional geological structure units in Qaidam Basin, China. The results indicated that TDS of formation water in Western (QW), Central (QC) and Northern (QN) units of Qaidam basin ranged from 173 to 290 g/L, 101 to 152 g/L and 32 to 73 g/L, respectively, which were several to dozens of times higher than those of seawater, but lower than those of intercrystalline brine and salt lake water. The enrichment of Ca, Li, B, Br and depletion of Mg and SO42− were observed in the formation water in comparison to seawater and salt lake water. Formation water especially in QC and QW was identified as typical dissolved brine of terrestrial rock origin, experiencing prolonged water-rock interactions. However, the time and degree of water-rock interaction and metamorphism differed regionally due to the sedimentary history and patterns of Qaidam Paleolake. Overall, the large paleolake deposits under the control of multiple tectonic movements laid the material foundation for the burial and generation of the formation water, and a variety of fluids and deep faults became the sources and migration channels for formation water. It mainly experienced two stages, including the sedimentary process of saline strata and the transformation in the later period. [Display omitted] •Unique formation water hydrochemistry compared to seawater and salt lake water•Prolonged water-rock interactions govern sources and evolution of formation water.•The degree of water-rock interaction and metamorphism is controlled by structural unit.•Infiltration of freshwater or upwelling of hydrothermal fluid is possible sources.