Well-ties Based On Prestack Wavefields Simulation

Currently,the main target of petroleum exploration gradually turn to complex structural and lithologic reservoirs.The difficulty of exploration is increasing,which calls for fine seismic data interpretation.Well-ties with log synthetic seismogram is a bridge that links well logging and seismic,which is the basis of seismic data interpretation.Conventional synthetic seismogram is based on one-dimensional convolution model,but with the improvement of fine seismic interpretation,this method has exposed some shortcomings and problems and lead us to chase wrong layers.We have difficulty to understand underground structure through the "axis" on the seismic data.In order to get more precise synthetic seismogram calibration,this paper was studied from the following several aspects.Well logs were often affected by geological factors and produce abnormal values.Conventional well logging curves correction include environmental effect correction,getting rid of the exceptional points,logging depth correction and standardization of well logging curves,etc.In this paper,the variable window median filter was carried out for the well logging curve to remove noise and keep the real signal in the same time.The zonation of well logs is beneficial to balance the scale differences of the well logs and seismic and improve the speed of the modeling.For wavelet extraction,we analysed the relationship between the seismic wavelet frequency and synthetic seismograms through to the experiment of actual seismic data.we selected seismic traces with a higher signal to noise ratio to extract statistical wavelet.We extraced deterministic wavelet with well data and well seismic trace.According to the horizontal layered thin layer,we use the reflectivity method for modeling.Reflectivity method can only be applyed to horizontal layered media and it has a high precision of forward modeling method.The simulation precision is higher than the finite difference method and the ray method,including converted wave and multiples.P-wave and s-wave can be separated easily and computational efficiency is very high.Forward modeling was carried out by transmission matrix,we can simulate the effect of multiple wave and converted wave through controlling the transmission matrix.Not requiring uniform sampling,we can easily introduced formation absorption effect on seismic wave propagation.Normal time difference correction and stack were applied to the simulated common reflection point gather,the stack trace was used as synthetics seismogram to calibrate the seismic reflections for well-tie.Compared with the conventional synthetic seismogram,the variation of seismic reflection amplitude with the offset,internal multiple wave and converted wave were taken into account,which makes the synthetic seismogram very similar to seismic data on the forming mechanism.Our experiment simulated the influence of the multiples,converted wave and NMO.We analyzed the cause of the error for synthetic seismogram calibration essentially.The results show that the consistency of synthetic seismogram and well-nearby traces was improved especially for the thin layer and weak reflection,and the reliability of well-ties was senhanced by using the new method.