Abstract:

Based on the analysis of Shahejie Formation water in Huimin Sag，the geochemical characteristics and origin of formation water were analyzed. The results show that these waters are of CaCl₂ type with main chemical composition of anion Cl^- and cation (Na⁺+K⁺).Vertically，the chemical composition of these waters alternately increased and decreased. The water chemistry parameters reflect the Member 2 and Member 4，the middle and lower Member 3 of Shahejie Formation have good sealing. The formation water was saturated by CaCO₃，but not vet saturated by CaSO₄. The degree of ions' enrichment and deletion can be presented by using of the composition contrasting with the seawater and lacustrine saline-water evaporation trajectory. Thereby，the origin of formation water was analyzed based on ions' enrichment and deletion，and the result indicates the appearance of concentration of Cl^- and Na⁺，enriohment of cazenrichment of Ca²⁺，deletion of Mg²⁺ and SO₄^2- are owing to the combine effects of evaporation，dolomitization，desulfitation and hydrocarbon generation. Moreover，the lower-salinity areas in which each formation above the Member 4 of Shahejie Formation has lower-salinity water all occur in Linnan sag，and the clay mineral dehydration in Linnan sag can be used to interpret this phenomenonin the plane.

Key words: Huimin Sad, geochemical characteristics of formation water, origin of formation water, evaporating concentration, albitization