Architectural Heterogeneity Of The Clastic Carrier Beds Of The Cretaceous Qingshuihe Formation In Wu'erhe Area

This thesis carry out analyses of the unmanned aerial vehicle-based model,sedimentary charcteristics,magnetic susceptibility,and elemental content of Qingshuihe Formation outcrop in the Wu'erhe outcrop area.Detailed methology includes lithofacies classification,sedimentary facies interpretation,stratigraphic surface recognization,interlayer identification,and sandstone architecture illustration.Two sedimentary facies are interpreted in the study,as braided river and braided river delta,which carrier beds are recognized and models are established.Strata of the Qingshuihe Formation in the outcrop and subsurface have high similarity.Therefore,outcrop-based model can be applied to the ones in the subsurface.Finally,hydrocarbon migration pathways and favorable carrier beds and controlling factors are predicted by aforementioned analyses.The Qingshuihe Formation in the Wu'erhe outcrop area consists of pebbly sandstone,medium-grained sandstone,fine-grained sandstone,siltstone,and mudstone.The sedimentary structures of outcrop include trough cross bedding,tabular cross bedding,plane bedding,parallel lamination,and erosional surface.According to the sedimentary structures and lithology,five types of facies are classified as tabular cross bedded medium-grained sandstone with interbedded oil and gas beds(Sp),trough cross bedded fine-grained sandtone with oil(St),yellow-brown plane bedded fine-grained sandstone with oil spots(Sh),gray-white calcareous fine-grained sandstone(Sc),and brown parallel laminated mudstone(M).Five vertical relationships of these facies are recognized,which are M-Sp-Sc(St),Sp-Sc-St(thick layer)-St(thick layer)-M,St(thick layer)-St(thin layer)-Sc(M),M-Sh-M-Sh-M,Sh(St)-M-Sp(St),corresponding to the mid-channel bar,river channel,channel margin,inter distributary area,and overbank sedimentary facies,respectively.Five orders of stratigraphic surfaces are identified in the outcrop in order to illustrate the architectural heterogeneity of the carrier beds.Further,five types of interlayers are interpreted based on the surface analyses.The five types of interlayers are lenticular muddy interlayer,regional muddy interlayes,continuous calcareous interlayer at channel margin,discontinuous calcareous interlayer at channel margin,and discontinuous interlayer within the channel.Three types of sandstone vertical superimposition are identified,as fully connected sandstone bed,semi-connected sandstone bed,and unconnected sandstone bed.Porosity and asphalt content within the carrier beds are largely controlled by architectural heterogeneity.Heterogeneity model is constructed on the basis of combined analyses of porosity,asphalt content,sedimentary facies,sandstone distribution through using unmanned aerial vehicle.Fifth-order stratigraphic surface controls the regional muddy interlayer.Fourth-order surface controls the calcareous interlayer at the channel margin.Third-and second-order surfaces control the lenticular muddy interlayer and the discontinuous calcareous interlayer within the channel.For the subsurface strata,the straigraphic boundries of the three members of Qingshuihe Formation are recognized.The second member of Qingshuihe Formation can be subdivided into three intervals.Favorable carrier beds distribute in the eastern and western parts of the study area based on the interlay under the control of third-and fourth-order surfaces,sedimentary facies.The main controlling factors of heterogeneity in the east part are faults,sedimentary facies,and interlayers,and the west are interlayer and sedimentary facies.