昆特依盐湖浅部储卤层对卤水组成的影响

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

昆特依干盐湖位于柴达木盆地北部,浅部石盐沉积层储存着丰富的地下卤水。研究表明,研究区石盐储层渗透性存在明显的空间分布差异,这种差异对储层中卤水的水化学组成产生显著影响。渗透性较弱的储卤层,卤水赋存于石盐之间的孔隙中,其渗透系数K值为0.01~8.64 m/d,卤水中K+浓度为5.98~10.34 g/L,Mg2+浓度为6.08~13.98 g/L,pH值介于6.8~7.2,SO2-4浓度为19.85~37.93 g/L;说明低渗透性的储卤层具有稳定的水化学环境,且卤水与介质之间基本达到了水-盐作用平衡,应该为早期成盐时圈闭的残余卤水。而渗透性较强的储卤层,K为134.78~198.89 m/d,卤水中K+浓度为2.66~5.60 g/L,Mg2+浓度为4.18~6.24 g/L,pH为7.27~7.44,SO2-4浓度为41.39~61.71 g/L;说明渗透性较强的储卤层,卤水具有较高的SO2-4浓度及pH值和较低的K+、Mg2+浓度,推测由于低盐度水流溶解作用促使储卤层微小孔隙形成大的溶孔,使储层渗透性增强,水体混合导致卤水水化学特性发生改变。

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 SO2-4. The concentrations of K＋and Mg2 ＋in the brines are 5. 98 ~ 10. 34 g/L and 6. 08 ~ 13. 98 g/L,respectively. Thevalue of pH ranges from 6. 8 to 7. 2,while the concentration of SO2-4 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 SO2-4（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.