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Carbonate reservoirs are usually diffcult to map and identify in seismic sections due to their complex structure , lithology and diagenetic frabrics . The Midland Basin , located in the Permian Basin of West Texas , is an excellent example of these complex carbonate structures . In order to obtain a better characterization and imaging of the carbonate buildups , an acoustic impedance inversion is proposed here . The resolution of the acoustic impedance is the same as the input seismic data , which is greatly improved with the addition of the low frequency content extracted from well data . From the broadband volume , high resolution maps of acoustic impedance distributions were obtained , and therefore the locations of carbonate buildups were easily determined . A correlation between acoustic impedance and porosity extracted from well data shows that areas with high acoustic impedance were correlated with low porosity values , whereas high porosities were located in areas of low acoustic impedance . Theoretical analyses were performed using the time -average equation and the Gassmann equation . These theoretical models helped to understand how porosity distributions affect acoustic impedance . Both equations predicted a decrease in acoustic impedance as porosity increases . Inversion results showed that average porosity values are 5 % [plus or minus] 5 % , typical for densely cemented rocks . Previous studies done in the study area indicate that grains are moderately to well -sorted . This suggests that time -average approximation will overestimate porosity values and the Gassmann approach better predicts the measured data . A comparison between measured data and the Gassmann equation suggests that rocks with low porosities (less than 5 % ) tend to have high acoustic impedance values . On the other hand , rocks with higher porosities (5 % to 10 % ) have lower acoustic impedance values . The inversion performed on well data also shows that the fluid bulk modulus for currently producing wells is lower than in non -productive wells , (wells with low production rates for brine and hydrocarbons ) , which is consistent with pore fluids containing a larger concentration of oil . The acoustic impedance inversion was demonstrated to be a robust technique for mapping complex structures and estimating porosities as well . However , it is not capable of differentiating different types of carbonate buildups and their origin . |
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