Crossplot Analysis for Viscosity Sensitive Elastic Attributes in Freeman Field, Niger Delta

Elastic properties were estimated using log data from wells in the Freeman field of Niger Delta. The goal was to investigate the existence of relationships between elastic attributes and reservoir fluid viscosity. The attributes considered include Acoustic impedance, Lambda-rho, VpVs ratio, Poisson ratio and Young modulus and they were estimated using rock physics models. Crossplots colour coded with the measured viscosity for three different reservoirs were analyzedto determine sensitivity of these elastic attributes to variations in reservoir fluid viscosity.The cross-plot of Lambda-rho versus Poisson ratio revealed that the reservoir with comparatively high viscosity clustered on lower Lambda-rho and higher poisson ratio while the reservoir with the lowest viscosity clustered around higher Lambda-rho and lower Poisson ratio. The cross-plots also revealed that the relatively high vicosity reservoir had higher velocity ratio but lower acoustic impedance and Young modulus while the reservoirs with lower viscosities plotted on higher acoustic impedance and Young modulus but lower Velocity ratio. The analyses showed that some elastic attributes have a level of sensitivity to fluid viscosity, a situation that may be exploited ininferring reservoir fluid viscosities directly from seismic data.