Study and Application of Seismic Sedimentology in Paleogeomorphology Restoration

Abstract

In Ordos basin, dolomite reservoir of lower Paleozoic Ordovician has a good prospect for exploration. Pre-carboniferous karst landform had a great influence on gas accumulation and enrichment. And the high parts of paleogeomorphology are favorable places for gas. Therefore, restoration of pre-carboniferous paleogeomorphology and relationship between paleogeomorphology and gas reservoirs are of important guiding significance in the search for Ordovician weathered crust gas reservoirs. However, it is difficult to restore the paleogeomorphology precisely due to the comprehensive effects of late regional deposition, climate, base-level change and tectonic movement. Although there are many ways to restore paleogeomorphology, there are some fundamental problems. In this paper, the research ideas and technical methods of seismic sedimentology are introduced innovatively for the first time, and the pre-carboniferous palaeogeomorphological morphology is precisely implemented by the comprehensive application of ‘‘Impression’’ method and ‘‘Residual Thickness’’ method, and the relationship between palaeogeomorphological units and gas accumulation is analyzed. The application effect is fine. Firstly, the seismic response model of different palaeogeomorphic units was established by means of forward modeling. By impedance inversion, formation lithology cube can be obtained, and the seismic profile was transformed into a geological profile to provide a basis for interpretation of fine erosion surface and stratigraphic slices. Secondly, Make full advantage of seismic data with high horizontal resolution, the ‘‘double interface’’ flattening technology and stratigraphic slice technology are used to characterize the boundary of paleogeomorphic units; Then, base on the great impedance difference, seismic inversion can be done to interpret the top of Ordovician with the inverted impedance volumes, so as to further improve the prediction accuracy; Finally, ‘‘Impression’’ method and “residual thickness” method are combined together to identify the true erosion grooves and restore the pre-carboniferous paleogeomorphology accurately. The technologies in this paper are applied in the largest 3D seismic project in Southeast Sulige, which greatly improve the accuracy of paleogeomorphology characterization. The area of ancient buried platform is expanded compared with the previous achievements, and the coincidence rate of drilled wells is also improved, which guides the selection of well location and the development of gas field.KeywordsPaleogeomorphology restoration90° phase changeStratal slicing double-interface flattenImpedance inversion