A Mechanism Research In Complex Piedmont Zone Seismic Noise

Oil and gas resources are rich in western China piedmont belt, such as Kera-2, Dina-2 where large gas fields discovered, promoted the development of the oil and gas exploration in the piedmont zone. So the piedmont zone is one of the most important fields of oil and gas exploration. However, the complexity of the piedmont zone area, makes the piedmont zone seismic exploration has been an enormous problem in the Geophysics exploration. The low S /N ratio and the static correction, deduced to the low velocity layer, the existence of uneven geologic body and the surface with topography, are the most two problems.When seismic wave through the low velocity layer, the energy attenuation is very large, and generate a lot of interference wave. Low velocity layer always have complex structure, and different parts of the geological have different composition and structure,even in the same area the low velocity layer could also have big difference, so the impact mechanism of the low velocity layer to seismic wave field is more complicated. The complexity of the piedmont zone also reflect in the development of surface uneven geologic body, also is what we call the abnormal geologic body. The uneven geologic body have different size,different irregular shape and different vecolity between the surrounding rock, and randomly distributed in the surface formation, thus to produce a variety of interference wave as reflection, scattering and diffraction, seriously influenced the seismic wave field imaging.The ups and downs of terrain changes caused the spread of seismic wave near the surface present a complex phenomenon, and produced a variety of surface disturbance which covered the deep and inherently weak reflection.The complex terrain conditions bring severe challenges for the seismic data acquisition, data processing and explanation.To solve these problems, we must first know the propagation law of seismic wave field under irregular surface, it is the premise and foundation for seismic data acquisition and processing. The main research content is summarized as follows:1) All kinds of regular interference waves related to the low velocity layer;2) Seismic noises associated with the surface uneven geologic body;3) Seismic noises associated with the ups and downs of terrain changes.Based on the low velocity layer, the surface uneven geologic body and the ups and downs of terrain changes three different surface profile model is established in this paper, then numerical simulate the models by acoustic wave equation and elastic wave equation to forward modeling the seismic section, analyzing the wave field snapshot to figure out the special ray direction, the path of seismic wave field, the waveform characteristics and the spatial relationships, etc. After this, we could research the piedmont belt special formation mechanism in a system way, and study the theory and formation mechanisms of the seismic wave field in the piedmont zone, preliminary understanding the seismic wave propagation theory and formation mechanism of various complex surface conditions in the piedmont zone of,to provide theoretical foundation and basis for solving the problems in the piedmont zone seismic exploration.