In order to reveal in middle fault depression belt of Hailer-Tamtsag Basin buried hill oil and gas migration and accumulation characteristics, we summarize controlling effect of fault on oil and gas migration and accumulation of buried hill, which by analysing genetic mechanism of buried hills based on fault systems formation and evolution. Research shows that three types of fault system in Hailer-Tamtsag Basin: early stretched fault system(Type I), early stretched middle tensile shearing fault system(Type I-II), early stretched middle tensile shearing reverse late fault system(Type I-II-III). Type I-II and I-II-III are stretching by NW tensional stress in Nantun group ,which afford tectonic framework for syngenesis buried hill and epigenetic buried hill. Type I make buried hills complicated .It is also favorable to ancient geomorphological buried hill in the fault less affected zones. Although they formed cracks dense zone easier, Type I-II and I-II-III fault system damage the reservoir which is not conducive to " hydrocarbon-supplying window " formation; Type I fault system have less promotion on the development of the buried hill reservoir, while it is conducive to hydrocarbon accumulation as the block boundary in buried hill hydrocarbon. Fault formed source rocks two kinds for hydrocarbon mode: unidirectional and bidirectional, which formed two reservoir-forming pattern: Unidirectional transportation hydrocarbon of weathering crust or hydrocarbon of fracture damage zones and bidirectional transportation hydrocarbon of weathering crust or hydrocarbon of fracture damage zones.

U.S.A., There is a variety of salt domes with complex shapes in our work area. As high-velocity geologic units, subsurface salt domes bring about a series of problems for seismic data processing in time domain and interpretation in the seismic exploration. For example, false images of subsalt structure, abnormal stack velocity field, and difficult time-depth conversion of structural mapping, are all caused by complex wave-fields from irregular salt domes.Pre-stack depth migration is designed for imaging complex structures with strong velocity variations, especially horizontal variation. Complex salt domes are high velocity anomalous zones, which introduce strong velocity variation in horizontal and vertical directions. Consequently, depth migration should be effective in identifying subsalt structural traps. Our applications indicate that pre-stack depth migration produces reasonable seismic images for salt dome flanks surrounding sediments and underlying formations. As an illustration, we present a case study in this paper.This paper first analyzes the geological settings in our work area; then designs target-oriented multi-step modeling principle to establish the model above salt dome, the model of salt dome body, the model of the flanks and the bottom of salt dome, and the model beneath salt dome, which are constrained by the information of geology, logs and drilling information; next, different pre-stack depth migration methods are applied in this work area data, including Krichhoff pre-stack depth migration, one-way equation pre-stack depth migration and RTM; after that, demonstrates the successful imaging of subsalt carbonate rocks and the true shape of the underlying structures through the 3D pre-stack depth migration; finally, shows some results of pre-stack reservoir prediction. The results have proven that 3D pre-stack depth migration is an effective tool for subsalt oil and gas reservoir identification and evaluation; firstly, high-precision imaging of complex salt bodies, salt dome flanks and subsalt strata has been achieved with pre-stack depth migration; secondly, the structural map from pre-stack depth migration shows reliable geological structures in detail; thirdly, subsalt carbonate reservoir prediction and characterization have been successfully carried out with RAP pre-stack depth migration data; finally, well log constrained pre-stack multi-parameter inversion, such as neutron gamma, natural gamma and flouid factor, is a good approach to predict reservoir.

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