Hydrochemical characteristics and genesis of the subsurface brines in the Wolonghe brine-bearing structure of Sichuan Basin

Marine connate sedimentary brines occur in the carbonate rocks at the depth of approximately 2000 m in the Wolonghe brine-bearing structure (anticline) of western Sichuan Basin. Faults can be found in the depth of the brine-bearing structure, and fault zones occur on the western limb of the anticline, in which subsurface brines are concentrated. The brines range in TDS from 105.67g/L to 129.4g/L and are of the Cl-Na type. The comparison of the chemical compositions of the brines with those of evaporated Yellow Sea water indicates that the brines are rich in Br-, I-, Sr2+ and B2O3, but are poor in K+. The δD and δ18O of the brines show that they are of paleo-marine origin. Ratios of ions and compositions of the brines indicate that such evolution of chemical composition as desulphurization and dolomitization occurred in a sealed environment of high temperature and pressure during the evolution of the subsurface brines.