Controlling Effect Of Micro-paleogeomorphy On Beach-bar Formation And Its Restoration

The beach-bar,as a new important oil and gas reservoir in China,is now an important target for exploration.However,its depositional mechanism controlled by various factors has not been fully modeled,and the control mechanism of paleogeomorphy is unclear,either.Besides,there is no effective method to restore micro-paleogeomorphy where beach-bars developed.To solve these problems,in this paper,based on the relationship between micro-paleogeomorphy and beach-bars,beach-bar sand bodiesin the upper fourthmember of the Eocene Shahejie Formation(Es4s)in south Boxing Sag,Dongying Depression are taken to study.The quantitativeclassification scheme of beach-bars sedimentary environment under different slope is put forward,and the quantitative geological models of beach-bars are established.Besides,a quantitative technology for restoring the micro-paleogeomorphy where beach-barsdeveloped is put forward innovatively based on the restoration of macro-paleogeomorphy.The quantitativeclassification scheme of beach-bars sedimentary environment is put forward.Considering the significant control action of lakeshore slope(geomorphy)for lakeshore hydrodynamic zones synthesizing wave and water depth,a quantitative classification scheme of hydrodynamic zone under the background of gentle gradient slope(less than 1/20)and high gradient slope(more than 1/20)is establishedbased on modern coastal dynamic theory,theoreticalanalysis and mathematic model.The quantitative geological models of beach-bars are established.The beach-bar formation mechanisms in different hydrodynamic zones are analyzed quantitatively by the analysis of wave characteristic,water environment and sand movement.At the same time,the ideal location and scale of the beach bar in different hydrodynamic zones are quantified.The beach-bar types under different slope in Qinghai lake are recognized and the database of paleogeomorphy-sand bodies are established based on the beach-bar quantitative model.Macro-paleogeomorphy before the deposition of beach-bars is restored.Through using single well and seismic data,the standard stratum and its paleo-sedimentary thicknessafter compaction correction arecalibrated and restored.And then,by sequence stratigraphy and impression method,the macro-paleogeomorphy of Es4 s base is restored as a slope zone with a higher distribution in the south than the north.A quantitative technology for restoring the micro-paleogeomorphy where beach barsdeveloped is put forward innovatively.Imitating craniofacial restoration method,taking the paleogeomorphy-sand bodies of Qinghai lake as a reference,the micro-paleogeomorphy where beach bar developed in the study area is restored.Finally,the micro-paleogeomorphy of study area is restored by synthesizing the macro-paleogeomorphy.And after matching it with the distribution of beach-bar facies,it is obtained that under a macro background of lakeshore slope,beach-bars are usually formed at the relative high macro-paleogeomorphic part of Boxing faultterrace zone in the study area.