The Trap Identification And Description Of Nantun Formation In The Southern Part Of Ulson

Southern Ulson sag mainly include unan secondary depression, and bayantala structural belt. With the influence of wuxi fault, the unan secondary depression presents a typical basket of half graben rift, and the bayantala region is the typical strike-slip and pull-apart structure. As traps are the place where oil and gas gather, the research of Nantun formation which is the main oil layer is very important to the exploration and development.In this study, according to the basic theory of sequence stratigraphy, combined with the logging characteristics, the Nantun Formation is divided into two third-order sequences and eight four-order sequences. Taking the synthetic seismogram as bridges, the comparison tracking and interpretation of nine reflective layers are finished, which are T22、T22-1、T22-2、T23、T23-1、T23-2、T23-3、T23-4 and T3. Taking them as a basis the structural maps of the 9 reflection layers are also compiled. Based on the structural map, combined with the related theory of structural geology, the traps identification of Nantun formation are complicated on the structural map of the top and the bottom of the third-order formation. The traps distribution and regional tectonic characteristics of Nantun group are also summarized. The identification of lithologic traps mainly based on the seismic attributes’ s analysis, the seismic spectral decomposition technology, the post stack seismic inversion technology and the sedimentary research. First with the sedimentary facies’ s analysis, determine the regional depositional background and the sedimentary model of sandstone at that time the second member of the Natun formation deposited, and then with the analysis of the seismic attribute and the seismic frequency of sandstone type prediction, a general concept of the sand body distribution patterns in the plane. Finally applied geophysics inversio n identification of each four-order sequence of sandstone distribution determine the shape and the spatial distribution of the sand stone, and the contact relationship between sandstone and mudstone, looking for sandstone pinchout, lithologic trap, lithologic trap identification and description, summarizes the characteristics of lithologic traps.The research shows that all the fault in this area can be divided into two categories: the early fault and the late fault. The early fault usually control the sediment of this area, and the strikes of the early faults are mainly NS. The late fault’s strikes are NWW, and they appeared when the Nantun formation deposited. The traps in Nantun formatin are faulted block traps and faulted nose traps. The fourth- order sequences esedimentary facies of the second member of the Nantun Formation are mainly fan delta and lacustrine facies deposition ring, among which lakefacies is the most important phase. Combined with the sedimentary background, the seismic attribute analysis technology, the seismic spectral decomposition technique, and the post stack seismic inversion technique, the lithologic trap types of the second member of the Nantun formation are mainly the stratigraphic up-dip annihilation trap.Finally combined with the analysis of the strata, reservoir and the cap of the second member of the Nantun formation in the southern Ulson basin, using the result of the structural traps and lithologic traps identification work, the area of the oil’s accumulation is found in the second member of the Nantun formation, and this area can provide useful information in the next exploration and development.