Abstract: Fluid recognition in the south Ordos Basin using seismic data encounters two challenges:one is the tight reservoir,the physical properties of which are not clear,and thus the rock physical parameters that are sensitive to oil-bearing are unknown;the other is that the quality of seismic data is relatively poor,which can hardly satisfy the need of elastic parameter inversion.Hence,this study proposed methods and procedures that can overcome these challenges in rock physical modeling,seismic data processing and inversion.Regarding the complex mineralogy compositions of tight oil reservoirs in the South Ordos Basin,we proposed a way of constructing an anisotropic rock physical model.And on the basis of modeling and rock physical analysis,we identified that the ratio of Lame's coefficient and shear modulus are sensitive to oil-bearing in strata.Given the low signal-to-noise ratio in the south Ordos Basin,we introduced some solutions for certain key parts of data processing,including multi-scale static correction,amplitude consistency correction,angle gather correction,and simultaneous inversion of elastic parameters,and got reliable results for elastic parameter inversion.In combining the sensitivity parameters and results of elastic parameter inversion after rock physical analysis,we predicted the oil-bearing property of Chang 7 Member of certain exploration area in the south Ordos Basin,and the prediction matched well with the actual drilling results.The associated methods and region-specific solutions are efficient in practical application,and thus to certain extent,the technical difficulties in seismic fluid recognition for tight oil reservoirs in the South Ordos Basin with low signal-to-noise ratio are solved.

Key words: seismic inversion, rock physics, fluid recognition, tight oil, Yanchang Formation, Ordos Basin