Post Stack And Pre Stack Seismic Inversion Attributes Based On Resolution And SNR Enhancement For Improved Reservoir Characterization

Seismic data typically has a limited frequency bandwidth due to the filtering of the lowfrequency data and attenuation of the high frequencies.Much pre-stack information that holds importance in reservoir characterization is lost after stacking the seismic data.An improved reservoir characterization,therefore,requires enhancement of the seismic data resolution as well as the signal-to-noise ratio(SNR)of pre-stack gathers.This dissertation aims to compare the influence of resolution and SNR enhancements on seismic inversion for improved reservoir efficient characterization.The methodology adopted for this purpose is petrophysical analysis,crossplotting technique,posts stack model-based inversion,prestack simultaneous inversion,Lambda-rho mu-rho(LMR)seismic inversion,and porosity slice estimation.Determination of the reservoir target zone is crucial for reservoir characterization,two prospect zones named Zone 1 and Zone 2 have been marked using petro-physical analysis.To differentiate the sandstone from shale and gas sands from brine sands,the crossplot between Density(RHOB)versus Neutron porosity(NPHI),P-impedance(Zp)versus effective porosity(PHIE),Resistivity versus effective porosity(PHIE),and primary wave velocity to shear wave velocity(Vp/Vs ratio)versus P impedance have been employed,which successfully depicts the presence of gas sand at target horizons.The seismic inversion comparative study has taken place based on resolution-enhanced and high signal-to-noise ratio data for post-stack and pre-stack data,respectively.Post-stack model-based seismic inversion gives P impedance(Zp)inverted volume.The study declared that when the seismic resolution is improved,but the SNR is reduced,the resolution-enhancement data has little effect on the inversion results because the underground imaging of the data volume is better before the resolution enhancement.Simultaneous inversion has been performed on the pre-stack seismic data resulting in the extraction of multiple volumes,namely,P impedance(Zp),density(ρ),shear impedance(Zs),and Vp/Vs ratio.By comparing,we found that data with improved SNR gives better lateral continuity and resolution.Both post-stack and pre-stack inversion results of the target reservoir show low impedance layer strata indicating the presence of hydrocarbon(gas sand)at desired depths.Further LMR technique is employed to check the response in the subsurface.The low value of lambda rho and the high value of mu rho also confirm the presence of gas sands.By comparing the post-stack(original data)with pre-stack data(high SNR),better results for pre-stack in the form of better lateral continuity and good well correlation.Lastly,the porosity slice versus P impedance slice for post-stack data(original data)and pre-stack data sets(high SNR)have been generated,it also gives more prominent and extended continuity results for the pre-stack data set and showed favorable sites for future well drilling.