东营凹陷沙三段古水介质盐度特征及其控制因素

Salinity characteristics of paleo-aqueous medium and their controlling factors in the third Member of the Shahejie Formation,Dongying Sag

东营凹陷沙三段浊积岩油藏是重要的油气增储领域,由于沉积期水体富灰特征明显,严重影响地球物理预测精度及储层的品质,因此恢复古水介质盐度、研究古盐度分布、寻找淡水稀释区显得尤为重要。综合利用微量元素、黏土矿物、碳-氧同位素等多种测试数据,探索了不同恢复方法之间的量化联系,并建立了一套综合表征方法,用于量化恢复研究区的古盐度并剖析其纵、横向展布规律。在此基础上,进一步探索了控制古盐度展布规律的成因机制。研究表明:高盐区主要分布于坨-胜断裂区、草北地区、中央背斜带及斜坡带地区,低盐区主要分布于淡水物源注入区及深洼区;古盐度展布受控于古气候旋回、古物源性质和深部卤水上涌,其中,古气候旋回控制了纵向水体盐度旋回,古物源性质及供应量控制了物源通道附近的平面水体差异,沙四段深部卤水上涌造成了局部高盐度水体;前三角洲附近的淡水影响区和洼陷中心的淡水稀释区的浊积岩储层品质更高且灰质泥岩的影响更小,因此是重力流砂体下步勘探的有利方向。

The turbidite reservoir in the third Member of the Shahejie Formation is an important field for oil and gas accumulation in the Dongying Sag.The obvious carbonate-rich characteristics of the water during the sedimentation period seriously affect the accuracy of geophysical prediction and the quality of the reservoir.Therefore,it is particularly important to carry out studies on salinity reconstruction of the paleo-aqueous medium in the study area.The authors integrated multiple test data of trace elements,clay minerals,carbon and oxygen isotopes,etc.to explore the quantitative links between different reconstruction methods and establish a set of comprehensive characterization methods to quantitatively reconstruct the vertical and horizontal differences of paleosalinity in the study area.On this basis,the authors further explore the mechanisms controlling the distribution pattern of paleosalinity.The study showed that the high salinity areas were mainly distributed in the Tuo-Sheng fault zone,the north slope of the Caoqiao area,the central anticline zone and the slope zone,while the low salinity areas were mainly distributed in the recharge area of freshwater and the deep depressions.The paleoclimate cycle controls the longitudinal water salinity cycle and the nature and supply of the source input control the difference in the plane water body near the source channel.The local high-salinity water body were caused by the upwelling of deep brine from the fourth Member of the Shahejie Formation.The results indicate that the next direction of turbidite exploration should target the freshwater-affected areas around the paleo-delta and the freshwater dilution areas around the sag center.