The Study Of Pre-stack Seismic Attributes Methods

With the development of oil and gas exploration direction changing from structural reservoirs to lithologic reservoir, the tight sandstone and shale reservoirs, the interpretation of seismic exploration is furtherly difficult. The interpretation is based on data acquisition and processing, so the higher quality of seismic data volume and new processing techniques must keep up with the pace of the Times. "2W1H" (wide azimuth, wide broadband and high density) exploration way and OVT-domain data processing method just meet the requirement.Seismic data acquired from wide azimuth seismic exploration are distributed more widely and have more uniform azimuth and offset range. Taking use of offset information can reflect the characteristics of the underground lithology and fluid. Using azimuth information can better analyze the difference of seismic wave travel time, velocity, amplitude, frequency and phase when it spreads in anisotropic medium, and can identify the anisotropic characteristics of strata. And then reflect the fault characteristics and fracture characteristics.When got the high quality seismic data, the matching high-end processing technology still need to preserve the included offset and azimuth information. OVT processing data technology newly developed is able to obtain a 5D (3D coordinate system, offset and azimuth) OVT gathers information, and provide good data basis for seismic data interpretation.Seismic attribute analysis method can be used to make full use of seismic data and found that the geological features of underground structure. This paper designs the prestack OVT gathers stack template and take partly azimuth Angle analysis, offset and offset-azimuth joint analysis method to study area as a whole or piecewise partition for OVT domain data processing of prestack seismic data. And flexibly extract prestack attributes with fully actual seismic data. In addition, on the basis of attribution exaction the azimuth anisotropy is analyzed due to the provided azimuth information. And the horizontal anisotropy of underground fracture medium has been studied. The fracture trend has been successfully predicted through a variety of properties variation characteristics. The prediction results conforms to the drilling data and make a comparative analysis between pre-stack and post-stack fracture prediction method.This paper relies on OVT-domain wide azimuth 5D prestack gathers, makes a brief overview on the OVT domain development, theory, process and advantages, puts forward gathers stack template selection methods, extracts and analyzes the prestack AVO attributes and other attributes for the OVT gathers, studies the underground high Angle fracture horizontal anisotropic medium model, predicts fracture by the ellipse fitting on the basis of attribute anisotropic analysis, then extracts prestack AVO attributes along the fracture main direction, eliminates the fracture anisotropy effect on the result of oil and gas prediction. Finally the following main conclusions are concluded:(1) Wide azimuth seismic exploration has obvious advantages than the conventional exploration. Wide azimuth, wide broadband and high density exploration has been heavily promoted popularization. Although involves the rapid increase of the cost, wide azimuth prestack data can get more info about azimuth and offset, can improve the imaging accuracy and better continuity, especially in complex geological structure area the light effect is much better.(2) Being relative to the conventional prestack gather, the OVT prestack gather also has obvious advantages. OVT-domain process technology can obtain all-azimuth and full offset information. In a OVT the offset and azimuth is roughly same. Such OVT gathers energy is more balanced, and is conducive to prestack fracture prediction considering the problem of anisotropy in wide azimuth.(3) The azimuth anisotropy of seismic attributes is the basis of fracture prediction in HTI medium. This article discusses the travel time, amplitude, AVO gradient and frequency four attributes fracture prediction methods. Because of the effect of complex structure and overlying strata in different area, the predict accuracy of every method may not be same. This needs comprehensive analysis and contrast to select the right properties prediction.(4) Eliminating fracture azimuth anisotropy contributes to AVO analysis and guide the oil gas distribution prediction. To eliminate the influence of the fracture is to conduct AVO analysis along the fracture main direction and predict oil and gas.