黄骅坳陷乌马营潜山属于持续深埋型潜山,地层水矿化度整体较高,地层封闭条件较好,而二叠系下石盒子组地层水具有异常低的矿化度特征.通过测试现今地层水的氘氧同位素值,分析流体包裹体岩相、均一温度与古盐度特征,揭示二叠系地层水淡化成因及其油气地质意义.结果表明:乌马营潜山现今地层水的氘氧同位素分布远离大气降水曲线,表明受现今大气降水影响较弱,烃类包裹体均一温度峰值主要分布在130～150℃范围内,以晚期成藏为主,部分包裹体地层水古盐度初始值小于5，,成藏期有明显降低现象,表明地层水经历了淡化过程.在晚白垩世末期,地层水淡化主要受下渗大气水淋滤作用影响.之后由于地层持续深埋,大气水下渗影响逐渐减弱.在沙河街组至明化镇组沉积时期,石炭系—二叠系煤系地层压实排水,排出的低矿化度地层水进入相邻的二叠系砂岩储层,导致储层地层水进一步淡化.地层水淡化促进次生孔隙的生成,改善储层物性,同时在局部形成碳酸盐胶结物,增强了储层非均质性.地层水淡化过程与油气运移充注同步进行,地层水流动方向指示了油气的运聚方向.

The formation water salinity of Wumaying buried hill, a continuous deep buried hill in the southern part of Huanghua Depression, is generally high, indicating that the formation is well sealed. It is worth noting that the formation water of the Permian Lower Shihezi Formation is of NaHCO3 water type, with the characteristics of low salinity（＜8.0 g/L）, low Cl- concentration, and high HCO3- concentration, which are obvious different with Well WG1 in nearby Wangguantun buried hill. By testing the hydrogen and oxygen compositions of the present formation water, analyzing the lithofacies, homogeneous temperature and paleo-salinity of fluid inclusions, the origin of Permian formation water and its petroleum geological significance are revealed. The results show that: (1) The distribution of hydrogen and oxygen isotope compositions is far from the curve of atmospheric precipitation, indicating that it is weakly influenced by the present atmospheric precipitation. (2) The peak value of homogenization temperature of hydrocarbon inclusions is mainly distributed in the range of 130-150℃, indicating that it is mainly formed in the late stage of reservoir formation. (3) The initial values of paleo-salinity of formation water in some inclusions are less than 5，, and there is a significant decrease in the accumulation period, indicating that the formation water has undergone a desalination process. (4) At the end of the Late Cretaceous, formation water desalination was mainly influenced by infiltration of atmospheric water. After that, the impact of atmospheric water infiltration gradually weakened due to the continuous deep burying of strata. During the sedimentary period from Shahejie Formation to Minghuazhen Formation, the Carboniferous-Permian coal measures strata were compacted and drained, and the drained low salinity formation water entered the adjacent Permian sandstone reservoir, which led to further desalination of the reservoir formation water. (5) Formation water desalination promotes the formation of secondary pores, improves the physical properties of the reservoir, and forms carbonate cement locally, which enhances reservoir heterogeneity. The desalination process of formation water is synchronized with the migration and filling of oil and gas, and the flow direction of formation water indicates the direction of migration and accumulation of oil and gas.