Hydrogeochemistry of Formation Water in the Northern Songliao Basin, China

Abstract

The Songliao basin is one of the largest Mesozoic continental rifting basins in China, dominated by Cretaceous fluvial and lacustrine strata. Based upon 2433 pressure data and 6270 water sample data around the basin, it is shown that, not only the abnormal pressures exist in the different formations and structural zones, but also the underpressure coexists with the overpressure within a single geological formation. Besides, the pressure coefficients change gradually from 1.02~1.30 in the western Central Depression to 1.05~0.5 in the eastern Central Depression, and then become 0.65~0.9 in the east Uplift zone, especially in the Quantou formation (K2q). The analysis of hydrochemistry data reveals a distinct compositional variation in the different pressured systems. Water composition is dominated by water type of NaHCO3 but varies greatly in salinity (1.0 ~ 20 g/L) and ionic ratios in the different areas. The origin of formation water may be attributed to the dissolution of silicate minerals and halite, the interplay of clay dehydration due to compaction, topographydriven meteoric water recharge as well as diagenesis alteration such as cation exchange by albitization of plagioclase, the dissolution or precipitation of calcite and gypsum. Their impacts differ greatly in the different hydrochemical and abnormal pressured environments.