Reserach On Prediction Methods Of Thin Bed Thickness

Thin beds are widespread in China.With the development of fossil energy exploration in China,thin sandstone and thin coal beds have attracted more and more attention.Thin beds have become an important part of lithologic reservoir research.For thin beds,quantitative thickness prediction is the basis of attribute analysis of thin beds.It is very important to understand the thickness change in industrial mining.Based on the energy spectrum formula of thin bed reflection coefficient,the inversion method of thin layer thickness,the thin layer top-bottom interface reflection coefficient and the elastic parameters of PP waves are derived in this paper.The research of thin layer thickness prediction has progressed and improved from time domain to frequency domain and from special model to general model.Previous studies have provided guiding conclusions for thin-bed thickness prediction.However,the seismic field has not yet provided a general and effective solution widely used in practical production.Thin-bed thickness prediction is still a difficult problem.It is necessary to continue to explore the quantitative prediction formula of thin-bed thickness.It has been proved that the energy spectrum of reflection coefficient of thin layer under vertical incidence is a function of reflection coefficient of top-bottom interface,time thickness and frequency of thin layer.On this basis,the formulas for calculating the time thickness of the thin layer,the reflection coefficient at the top and bottom of the thin layer and the elastic parameters of longitudinal wave are given by calculating the first and third derivatives of the reflection coefficient spectrum to the frequency.Compared with the existing thickness prediction methods,this method has high accuracy in thickness prediction,and is not affected by the absolute value or relative value of the reflection coefficient of the top-bottom interface.It is suitable for any thin layer that meets the assumption of weak impedance difference.On the basis of calculating the thickness of the thin layer,the method of calculating the reflection coefficient of the top and bottom interface of the thin layer is given according to the energy spectrum formula of the reflection coefficient of the thin layer.When the reflection coefficient of the top and bottom interface is known,the elastic parameters of the thin layer can be quantitatively solved and analyzed by replacing the unknown number with the empirical formula.Calculation of theoretical model shows that the elastic parameters of thin layer can be inverted analytically by this method,and the error can be controlled within 10%.The prediction results of actual data in Hangjin Banner show that the thickness prediction method in this paper can accurately predict the thickness of thin layer,the reflection coefficient of the top and bottom interface and the PP waves elastic parameters of thin layer.For the actual data of Huainan coalfield,this paper uses threedimensional combined well-seismic prediction method,time-domain thin-bed thickness prediction method and thickness prediction method based on thin-bed reflection coefficient spectrum to carry out inversion research.The results show that the accuracy of three-dimensional combined well-seismic prediction method is better than that of time-domain thin-bed thickness prediction method and energy spectrumbased thickness inversion method.The error of thickness inversion method based on reflection coefficient spectrum of thin bed deduced in this paper is large.The main reason is reflection coefficient calculated is inaccurate.