Distribution and Origin of Underground Water Chemical Fields in Songliao Continental Oil-Bearing Sedimentary Basin

There are many factors affecting underground water chemistry of an oil bearing sedimentary basin. The properties of underground water show variations in the vertical direction, giving rise to a vertical zonation with respect to underground water chemistry. Five zones could be divided downwards, including 1) the freshening zone due to meteoric water leaching (A); 2) the evaporation concentration zone near the surface (B); 3) the freshening zone due to stratum compaction released water(C\-1)—infiltration concentration zone during the mudstone compaction and water releasing (C\-2); 4) the freshening zone for clay mineral dehydration (D); and 5) the seepage concentration zone (E).\; The hydrodynamic fields in the Songliao Basin are obviously asymmetrical, with the characteristics of gravity induced centripetal flow recharged by meteoric water along the edge to the inner part of the basin mainly in its northern and eastern regions, centrifugal flow and cross formational flow in the center of the basin, as well as the cross formation flow evaporation discharge area in its southern area. Hydrodynamics controls the planar distribution of underground\|water chemical fields: 1) the freshening area due to penetrating meteoric water generally at the basin edges; 2) the freshening area for mudstone compaction released water at the center of the basin; 3) the cross formational area as the transitional area; and 4) the concentration area by cross formational flow and evaporation. The mineralization degree and the concentrations of Na\++ and Cl\+- and their salinity coefficients tend to increase, while the concentrations of (CO\+\{2-\}\-3+HCO\+-\-3) and SO\+\{2-\}\-4 and the metamorphism and desulfuration coefficients tend to decrease along the centrifugal flow direction caused by mudstone compaction in the depression area. But all of them tend to increase along the gravity induced centripetal flow direction.