Mechanisms Underlying the Bromine Anomaly in the Brine of the Jingbian Gas Field, Ordos Basin, Northwestern China

Abstract

Bromine (Br) is a vital chemical raw material primarily obtained from marine brine. The bromine/chlorine (Br/Cl) ratio serves as a crucial indicator for predicting marine potash mineralization in evaporites. As salinity increases, bromine gradually accumulates through evaporation in residual brine. During the process of brine evaporation to the potassium salt stage, the bromine content in the brine can exceed 1000 ppm. The marine brine sourced from the weathering crust reservoir at the top of the Ordovician Majiagou Formation in the Jingbian gas field, Ordos Basin, in northwestern China, displays an exceptionally high bromine content (averaging 1590 ppm), surpassing levels found in contemporary seawater. Based on analysis of major compositions, only brine evaporates to the gypsum stage. Despite extensive exploration in the region, large-scale potassium salt deposits have not been identified. This heightened concentration of bromine in low salinity brine suggests supplementation from additional organic bromine sources. The strata adjacent to the high-bromine oil field water in the Jingbian gas field, Ordos Basin, consist of the Ordovician marine evaporite strata of the Majiagou Formation and the overlying Carboniferous and Permian marine and continental deposits rich in fossil algae. Interactions between hydrocarbons and oilfield water contribute to the notable bromine anomaly observed in the Jingbian gas field in the Ordos Basin. Elevated bromine levels have also been noted in brine from various oil fields worldwide. Through an analysis of the major compositions of brines and bromine, this study will elucidate the reasons behind the presence of high bromine brines.