松辽盆地油田地下水化学场的垂直分带性与平面分区性

VERTICAL ZONATION AND PLANAR DIVISION OF OILFIELD GROUNDWATER CHEMISTRY FIELDS IN THE SONGLIAO BASIN, CHINA

松辽盆地地下水动力场的形成与演化控制了地下水化学场的形成与分布,地下水化学分布特征又反映地下水动力场的演化结果。在地下水化学场的形成过程中,影响沉积盆地地下水化学性质的因素较多,这些因素对地下水化学性质的影响作用在垂向上具有阶段性,在平面上具有选择性。前者导致地下水化学性质的垂直分带性,从浅到深可以划分出:1)大气水下渗淡化带,2)近地表蒸发浓缩带,3)泥岩压实排水淡化带(C1)—压滤浓缩带(C2),4)粘土矿物脱水淡化带和5)渗滤浓缩带等5种水化学剖面单元类型。后者决定了地下水化学场的平面分区性:1)盆地边缘为大气水下渗淡化区,2)盆地中央为泥岩压实排水淡化区,3)越流区为过渡区,4)越流-蒸发区为浓缩区。在泥岩压实排水形成的离心流方向上,矿化度、Na+浓度、Cl-浓度和盐化系数升高,(CO32-+HCO3-)、SO42-浓度、钠氯系数(γNa+/γCl-)和脱硫系数(SO24-/SO24-+Cl-)降低。在大气水下渗向心流方向上,矿化度、离子浓度和钠氯系数、脱硫系数和盐化系数一致升高。

In the Songliao Basin, the formation and evolution of underground hydrodynamic fields controlled the formation and distribution of groundwater chemical fields, meanwhile, the chemical properties of groundwater reflected the evolutional outcome of hydrodynamic fields. There were many factors affecting the hydrochemical characteristics of groundwater in the forming process of groundwater chemical fields, and the affecting action of the factors also had characters of lengthways stages and planar selectivity, the former resulted in the vertical chemical zonation of groundwater, five units could be divided downwards on its profiles:freshening zone due to meteoric water leaching downwards (A), concentrating zone for evaporation near the ground surface (B), freshening zone due to mudstone compaction-released water (C_ 1)—concentrating zone due to compaction and infiltration (C_ 2), freshening zone for the clay mineral dehydration (D) and seeping—concentrating zone (E). The latter dominated the planar chemical division of groundwater, namely, 1)freshening area due to meteoric water, generally in the margin of the basin asymmetrically, 2)freshening area for the mudstone compaction-released water in the central part of the basin, 3)transitional in cross-formational area, and 4)concentrating area by cross-formational flow and evaporation. In the direction of centrifugal flow caused by mudstone compaction in the depression area, the degrees of mineralization, the concentrations of Na +、Cl - and salinity coefficient (SC) increased, while concentrations of (CO 2-_3+HCO-_3) and SO 2-_4, (γNa +/γCl -) coefficients and desulfuration coefficients (DSC) decreased, and all of them increased along with the gravity-induced centripetal flow.