Research And Application Of Fracture Prediction Technology For Narrow Azimuth 3D Pre-stack Seismic Data

With the continuous deepening of oil and gas exploration,fracture predicti on technology is favored by the oil and gas researchers.Fracture prediction tec hnology can be divided into pre-stack and post-stack fracture prediction technol ogies.The theories of post-stack fracture prediction and pre-stack fracture predi ction based on wide azimuth seismic data have been developed rapidly and wi dely used.In order to save cost and adapt to the actual collection environment,seismic data of narrow azimuth are usually collected in actual oil and gas ex ploration.In view of the narrow azimuth seismic data,the conventional pre-sta ck fracture prediction method based on dividing azimuth angle is no longer ap plicable,because the ellipse fitting can not be achieved with the narrow azimut h data.At present,the technology of narrow azimuth pre-stack fracture predicti on is relatively immature and there is no complete technical system,so it is di fficult to predict fracture.Based on the narrow azimuth 3D pre-stack seismic data,we have found that the seismic waves have a certain AVO difference effect especially in the narrow azimuth when the seismic waves propagate in the fractured medium and the isotropic medium through theoretical analysis,the analysis AVO characteristic of fractured medium and the AVO characteristic verification of the study area typical model in this paper.For different fracture density,narrow azimuth angle of the AVO also has similar results.Therefore,it is feasible to predict fracture in narrow seismic data with the AVO of different media.Based on the theory,a narrow azimuth 3D pre-stack seismic fracture prediction technology and its realization flow are presented in this paper.The key techniques are as follows: firstly,this paper is being presented at a optimization processing technology of pre-stack gathers based on the combination of “noise suppression-flattening-removing”,which can be carried out appropriate increasing or reduction for quality of different gathers.Secondly,based on the rock physical analysis and the logging data statistics,the regional background model AVO is established and the actual seismic AVO(normalization)is fitted.The standard deviation of the AVO difference between each time point of each gather in the target layer is calculated,which is used as the fracture density indication parameter of the time point in this gather.The whole data value is obtained by cyclic computation,so the prediction of fracture density is achieved.For the fracture development direction prediction,the post-stack fracture prediction technique is chosen and the related method theory is introduced in this paper,because the narrow azimuth pre-stack fracture prediction method only reflects the fracture development density.The narrow azimuth pre-stack fracture prediction technique and the post-stack fracture prediction method are used to predict the fracture density and direction of the granite buried hill in a certain area of Bohai Sea.The prediction result is basically consistent with the actual drilling result in the research area,and the fractures' distribution and development area on plane coincide with the regional geological background.It is shown that the narrow azimuth 3D pre-stack fracture prediction method is effective and combines the post-stack prediction method to form a complete and comprehensive technique suitable for the fracture prediction of narrow azimuth pre-stack seismic data.