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

Abstract

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.

Keywords

• palaeosalinity recovery
• controlling factor
• turbidite reservoir
• paleo-aqueous medium
• the third member of shahejie formation, dongying sag