The Study On Methods Of Layer Absorbing Parameters Extraction Based On Prestack Seismic Data

More and more research has been done on the lithologic and concealed hydrocarbon reservoir rather than structural hydrocarbon reservoir. Thus the study on the seismic wave attenuation in viscoelastic medium has becoming a hotspot in recent years. Especially in the prediction of concealed lithologic natural gas reservoir, absorption parameter was regarded as one of the most sensitive and reliable indicators. The study, evaluation and compensation for underground medium on the absorption of seismic waves, are of great significance for processing prestack seismic data, improving the seismic imaging precision, explaining AVO effect logically and inversing physical attributes of the medium correctly.Real underground medium is featured by its viscosity; therefore, the study of viscoelasticity medium theory, which is the characterization of the medium, is particularly important. In this thesis, the viscoelasticity medium theory is first discussed, then, detailed analysis and comparison of several models of viscoelasticity medium and obtained that the models of KF and SLS are most practical. Further studying on reflection and transmission in viscoelasticity medium, then, detailed analysis and comparison of illustration, which provide theoretical foundation for further work.The basic theory of viscoelasticity medium and forward modeling study provide sound basis for the study of the seismic wave attenuation. Reflectivity method, a numerical transformation method, is the most effective way to achieve full-wave field simulation in layered half-space medium and in which multiple reflections and converted wave in reflective layer groups are considered. This thesis starts with the basic theory of viscoelastic medium, establishes the basic principle of reflectivity method forward modeling, and makes horizontal layer models of different viscoelastic media, respectively carries out the forward modeling in elastic medium and viscoelastic medium and makes analysis and comparisons between them, and finally analyzes, from different angles, the impact of the layer viscosity on seismic wave propagation.Layer absorption parameter, as an effective technology for reservoirs forecast, in particular, for natural gas reservoirs forecast, has gotten more attention. The author first studies the theory and characteristics of wavelet transform, and analyzes several conventional methods of Q-value calculation, then puts forward the methods of earth layer absorption parameters extraction based on pre-stack data by using spectrum decomposition technology, by which in time-frequency domain we could adequately consider changes of seismic waves affected by earth layer absorption, making earth layer absorption parameters extraction more accurately and more applicable. Meanwhile, it will be better that the data is to made appropriate pre-processing to improve the noise ratio of signals data before the work, and the final course of return-to-zero is done to achieve absorption parameters at zero offset so as to realize the inherent attenuation study of layer media truly. In the end, all the methods mentioned above are tested and applied in model data and the natural gas reservoirs exploration of a certain oilfield in east China. The result shows that the methods of extracting attenuation parameters discussed in this thesis are feasible and effective.