Research On Reservoir Prediction Of Thin Sand-Shale Interbeded Layers,in Yong-Lian,Gaoyou Sag.subei Basin

Thin sand-shale interbed is one of the important oil and gas reservoirs in the east category.With the deepening of exploration,the research objects transfer gradually from structural reservoirs to lithologic reservoirs,identification and characterization of effective reservoirs and its hydrocarbon potential is more and more important.However,the reservoir thickness of single layer is usually smaller than tuning thickness.Limited by the resolution of seismic data,it is difficult to identify this kind of reservoirs form conventional seismic data.This paper discusses the geophysical identification method for thin sand-shale interbeded reservoir,take the application in Yong-Lian,Gaoyou Sag,Subei basinas for example.Based on logging data,we use seismic forward modeling and rock physics analysis to determine difficult prediction points in this area,test the appropriate technology,carry out lithology identification and favorable reservoir prediction gradually.Through forward modeling,we find that,porosity has the biggest influence on reservoir's density and velocity,the second influence is clay content,the minimum is fluid saturation.The AVO of favorable reservoir is type I.AVO attributes can reflect the boundary and inner heterogeneity of the reservoir,and also can favor prediction of the distribution of beneficial reservoirs.When reservoir thickness is less than 50 m,the amplitude of the seismic reflection is positively correlated with the thickness of the sand layer.We derived the regression relation between P-wave and S-wave velocity and porosity as well as clay content.If regression coefficient is high,we can calculate porosity of the reservoirs.Compaction correction is introduced into post stack seismic inversion,so that the normalization of P-wave impedance and the interpretation scale of sand and clay are unified,and the vertical resolving power of wave impedance is improved to a certain extent.Based on prestack seismic inversion,using elastic parameter crossplot analysis and Bayes discriminate statistics,we predict the favorable reservoir distribution,prediction results agree well with the geological information and well logging data in the study area.Beginning from the study of reservoir reflection characteristics,this paper establishes a set of methods for integrated seismic prediction of complex and subtle reservoirs through comprehensive application of prestack and post-stack reservoir prediction techniques.The method provides technical support for the reservoir description in Yong'an-Lianmeng Zhuang area.