Study On Sedimentary Microfacies Characteristics And Quantitative Restoration Of Paleoenvironment Of E₁f₃¹ Formation In Gaoyou Sag,subei Basin

Gaoyou Sag is an important oil reservoir in Suibei Basin,where the third submember of the Paleogene Funing Formation?E₁f₃?in the sag is one of the main oil-producing layers.In this paper,the sedimentary microfacies and its spatial distribution characteristics in the upper part of E₁f₃?E₁f₃¹?was studied based on regional geology,cores,well logging and grain size analysis.Additionally,the paleo-sedimentary environment in special strata was quantitatively restored.By exploring the distribution patterns and control factors of multiple sand-mud interbeds,the deposition model of E₁f₃¹ was established,with the purpose of predicting potential reservoir and providing a reference for the subsequent exploration in the study area.The main research results are as follows:?1?Sedimentary microfacies determination in the study area:confirming the types of sedimentary microfacies in the study area.Through single-well sedimentary microfacies analysis,well-tie section analysis and sand body distribution analysis,the sedimentary system of E₁f₃¹,which was originally designated as the delta front,is recently redefined as the‘wave-dominated delta-beach and bar'sedimentary system.In addition,the beach and bar system,which was widely developed in the north-central part of Gaoyou Sag,could be subdivided into 3 microfacies:beach sand,normal sand bar,and storm back-flow sand bar.A scientific sedimentary microfacies classification standard for the beach and bar system was established.?2?Quantitative restoration of paleoenvironment in key strata:the paleowater depth,paleogeomorphology,paleowave conditions,paleowind direction,and paleowind force during the sedimentary period of E₁f₃¹were quantitatively restored.The paleowater depth of E₁f₃¹ is generally deeper in the south and west,shallower in the north and east.There are two slope break belts in the area where the water depth is around 8m and 14m,along their inshore side the normal sand bar extended as strips,and the storm back-flow sand bar was developed in thelow-lying land of the lake.The paleowind direction of E₁f₃¹ is SSW,with the paleowind force of grade 5-7,which is dominated by grade 6,and the average wind speed is 12.45m/s.The strong wind force is one of the most important factors forming the widely distributed beach bar sand bodies in the north central area of Gaoyou Sag.?3?Sedimentary model construction:Based on the study of sedimentary microfacies and the restoration of the paleoenvironment in key strata,the sedimentary model of the‘wave-controlled delta-beach and bar system'of E₁f₃¹was established.In addition,the genetic models of normal sand bar,storm back-flow sand bar and wave-storm recombination sand bar were established based on each genetic mechanism.According to the distribution regularities and genesis mechanism of beach and bar sand bodies,it could be concluded that the formation of beach and bar system in the study area was highly influenced by paleowind field,paleogeomorphology and paleoprovenance.