| The Lunan area is located in the central part of the TARNAN uplift tectonic zone,and its Triassic clastic reservoirs have good paleotectonic development background and high-quality reservoir-cover combination type,which is an important oil and gas producing area in the Tarim Basin.With the deepening of oil and gas development,the main oil section of the Triassic in Lunan area has entered the stage of high water content and low rate of oil recovery.It is urgent to carry out an in-depth study on the stratigraphic sequence and sedimentary micro-phase of the main oil formation,to identify the spreading and evolution of sedimentary micro-phase in the stratigraphic framework,and to provide support for new stratigraphic lithological traps and remaining oil tapping in the area.This study takes the Triassic stratigraphy in the central platform area of Lunan low relief as the research object,guided by the theories of stratigraphic stratigraphy,seismic sedimentology and sedimentology,based on core observation,combined with data processing and analysis of drilling,logging and 3D seismic data,and carried out indepth research on the Triassic sedimentary phases in the central platform area of Lunan,with a view to providing some theoretical guidance for oil and gas exploration in the area.The following results have been achieved:The triassic system in the central platform area of Lunan can be identified as the key sequence interface within the triassic system,according to which the triassic system is divided into five tertiary sequences,named SQ1,SQ2,SQ3,SQ4 and SQ5 from bottom to top.comparative analysis shows that,except for SQ1,which is seriously denuded in the northern part of the study area,the rest of the sequences are developed in the whole area,among which SQ2,SQ3 and SQ4 sequences are the most developed triassic sand bodies.SQ2,SQ3 and SQ4 are the most developed Triassic sands.In the central platform area of Lunan,there are obvious differences in the longitudinal depositional characteristics of the Triassic,and five most common forms can be identified on the logging curves,including medium-high amplitude box-shaped,bellshaped,funnel-shaped,finger-shaped,and low amplitude linear,etc.The first four forms mainly reflect the deposition of sand bodies,and low amplitude linear is more common in the lower part of SQ3 and SQ4 sequences.Three sedimentary phases,including braided river delta,normal delta and lake,are mainly developed in the Triassic SQ2-SQ4 in the study area,and three subphases and eight microphases can be further identified.Among them,the braided river delta sediments are the coarsest in grain size and are dominated by conglomeratic sandstones and medium-coarse sandstones,which are mostly boxshaped and bell-shaped on the logging curves,and obvious foregrowth heterogeneous reflection structures can be seen on the seismic profiles.Normal deltaic sediments are dominated by fine sandstones,medium sandstones and mudstones,and medium-weak continuous wedge-shaped disordered reflection structures can be seen on the seismic profiles.The lake phase is mainly developed with shallow lacustrine mud,and the lithology is dominated by gray and dark gray mudstone and muddy siltstone,with a low amplitude dentate linear feature on the logging curve and a strong amplitude mat-like parallel-subparallel reflection structure on the seismic profile.Based on various data such as quartz content,composition maturity and sand-toground ratio,the comprehensive analysis indicates that the Triassic system in the study area was deposited by multiple sources,and the main sources come from the north and southeast of the study area,and a secondary source exists in the south of the study area.The study area has a braided river delta-lake-normal delta deposition system,and the overall deposition process is a lacustrine recession. |
