The Study Of Sedimentary Facies And Geological Imodel Of Tongbomiao And Nantun Formation In Tanan Depression, Mongolia

The Tamtsag basin extending along northeast into China， locates at the eastof Mongolia， which is divided into six sub-basins. The South TamtsagDepression， which lied in the south of Tamtsag basin， is a small fault depressionextending from northeast to southwest. The study area was further divided into fivesub-tectonic units: the eastern steep slope belt， the eastern depression belt， thecentral uplift belt， the western depression belt and the western gentle slope belt.The study targets are Tongbomiao and Nantun formations in Lower Cretaceous.Tongbomiao formation was divided into five pay zones which include108layers. It mainly deposited fan delta and sometimes deposited alluvial fan in thebottom. The favorable areas concentrated in Block T19-34， Block T19-3andBlock T19-30. The effective sandbody types in Tongbomiao formation wereunderwater distributary channel and mouth bar. Pay zones TI and TII were themain developing targets. Nantun formation was divided into four pay zones whichinclude41layers. It mainly deposited turbidite fan and lake sedimentary system.The favorable areas concentrated in Block T19-19， Block T19-78and BlockT19-69. The effective sandbody type in Nantun formation was turbidite sandstone.Pay zones NI and NIV were the main developing targets.Pore structure and physical characteristics showed that the pore structure ofpay zone TI was medium to fine， the average value of porosity and permeabilitywere13.2%and6.1md， the pore structure of pay zone TII was medium to bad，the average value of porosity and permeability were12.7%and1md， the porestructure of pay zone NI was fine， the average value of porosity and permeabilitywere15.4%and13.8md， the pore structure of pay zone NII was medium to bad，the average value of porosity and permeability were14%and1.5md. Thedistributing rules of porosity and permeability followed the distributing rules offavorable sandstone.The type of oil reservoirs was mainly controlled by tectonic in Tongbomiaoformation. They most developed in the western gentle slope belt and central upliftbelt. The type of oil reservoirs was mainly controlled by sandstone in Nantunformation. Separated by Block T19-19， they most developed in the north part. Combined the study above， based on the geology models of different block，this paper analyzed the developing effect and impact factors from tectonicfeatures， sedimentary types， physical characteristics， and oil reservoir types.Finally， considering different areas， we proposed different solutions for thefuture exploitation.