The Research And Application Of AVO Forward Response In Shale Gas Reservoir

This paper is mainly about the comprehensive study of the response characteris-tics of AVO forward in shale reservoirs.Taking the shale layers of Longmaxi-Wufeng Formation in Jiaoshiba as the research object, We selected parameters for model combining with the seismic data, well logging and drilling data, and analyzedthe response characteristics of AVO forward for the target formation considering the formation anisotropy.This paper studied the theoretical model and analyzed the effects of the thickness, wavelet frequency, Poisson’s ratio and anisotropic parameters on the response charac-teristics of AVO forward. Secondly, according to characteristics of shale layers of Wufeng-Longmaxi formation,such as little ups and downs, no fault,and stable transverse variation, we classified the anisotropy into formation anisotropy and realized forward modeling of horizontal transverse isotropic (VTI) medium model through Matlab and analysized its response characteristics,on the assumption that the shale is horizontal layer.The main achievements of the paper are as follows:(1) The AVO characteristics of shale bottom interface are consistent in JY1, JY2 and JY3 with different frequency wavelet AVO, Nearly zero reflection is positive. Wit h the increasing of incident angle, the reflection amplitude reduce slowly;when incident angle is bigger than 40 degree, reflection amplitude increases sharply.AVO intercept is positive, gradient is negative, fourth quadrant of the AVO crossplot;The AVO curves of shale top interface have big change ranges in JY1, JY2 and JY3, the gradient intercept statistics are shown in table 4-2:JY1 and JY2 have consistent gradient and intercept in different frequency; The forward result of JY3 in 70Hz do not agree with the forward results in lower frequency.(2) The AVO forward results of four interface in JY1, JY2 and JY3 show that the AVO characteristic of the actual prestack gathers do not match the AVO characteristic extracted from AVO forward modling gather which come to a conclution that Seismic prestack gathers is not suitable for AVO attributes inversion, using seismic prestacktongshi inversion for reservoir description and prediction.(3) The information of shale gas reservoir internal geted from the brittle forword is more abundant and good for more detailed division horizon.(4) From the paragraph of amplitude changing with incidence angle in JYl,we can see that the amplitude is positive and gradually increase with the increase of incident angle,when the layer is 2m,6m or 10m, P is positive, G is positive; when the layer is between 10m to 14m, polarity reversal occurred;When the layer is more thick than 14m,the amplitude is negative, P is negtive, G is negtive;AVO response change from quadrant I into the II quadrant.