Research On The Fine Logging Velocity Structure By Using The Second Difference Of The Seismic Traveltimes

Velocity inversion using traveltimes of seismic wave is a direct method to obtain average formation velocity and formation velocity in seismic exploration,and is also considered as one of the most reliable sources of formation velocity data.In seismic logging,data processing of seismic data is always a key problem.The accuracy of first break pickup and the reliability of inversion method are directly related to the accuracy of inversion results of velocity structure of underground formation.However,due to the complexity of underground strata,the transmission path and traveltimes curve of seismic wave after passing through multi-layered media become extremely complex,and the method of picking up first break and inversion also has some shortcomings in calculation accuracy.Therefore,there are still some difficulties in seismic data interpretation.How to improve the accuracy of data processing methods and thus improve the accuracy of inversion results has attracted wide attention of geophysicists.In order to solve the above problems,the forward simulation of seismic logging is carried out based on the study of seismic wave propagation law in layered media.Based on the analysis of the characteristics of seismic traveltimes curve,it is found that the jump point of second difference of seismic travelstimes curve has a good correspondence with the location of stratum interface.On this basis,a layered inversion method is proposed.The layered inversion method is verified by the theoretical traveltimes data obtained from the above forward simulation.Then the main calculation methods of interval velocity are introduced.By establishing homogeneous layered medium models,the traveltimes curves of each model are inverted under different offset conditions.The obtained interval velocity profiles are compared with the theoretical models,and the advantages and limitations of each method are discussed.The results show that the inversion results of the layered inversion method are more accurate and reliable than those of the conventional method.At the same time,the sawtooth fluctuation caused by the external interference of seismic data is eliminated,and the velocity curve of the inversion is more intuitive and clear.Finally,the first arrivals of some well logs in tiger cave area of Weng'an County,Guizhou Province is picked up,and the traveltimes data is inverted by layered inversion method.The interval velocity profile coincides with the actual borehole data,which proves the reliability of the method.The inversion results show that the method is accurate,fast and reliable,and can provide an effective reference scheme for the subsequent logging data processing work.