Influence of shallow reservoir upon the components of brines in the Kunteyi playa

The Kunteyi playa located in the northwest Qaidam Basin is characterized by plentiful subsurface brines occurring in the shallow reservoir (salt deposits). The results suggest that the permeability of the salt reservoir is obviously different in space. The differentiation has a remarkable effect on the hydrochemical components of brines existing in the reservoir. By contrast, the brines bearing in reservoir of weaker permeability have relatively higher concentrations of Mg²⁺, K⁺ but lower values of pH and SO₄^2-. The concentrations of K⁺ and Mg²⁺ in the brines are 5.98~10.34 g/L and 6.08~13.98 g/L, respectively. The value of pH ranges from 6.8 to 7.2, while the concentration of SO₄^2- varies between 19.85 and 37.93 g/L. The brines in the reservoir with stronger permeability (K=134.78~198.89 m/d) and developed fractures are characterized by relatively higher concentrations of SO₄^2- (41.39~61.71 g/L) and pH (7.27~7.44) but lower concentrations of Mg²⁺ (4.18~6.24 g/L) and K⁺ (2.66~5.60 g/L). As a result, the low permeability of the reservoir shows a steady hydrochemical environment and a brine-salt equilibrium between the brines and the reservoir. These brines should probably be enclosed in the reservoir at the early hologenesis stage. On the contrary, the higher permeability of the reservoir indicates that the brines in it are hybrid waters comprised of primary brines and external saline waters. It is speculated that the resolution of lower concentrated waters enlarged small pores in the salts to be large ones and the permeability is thereupon enhanced. In a word, the mixing of different waters caused changes in the primary brines in nature.