Miscible Carbon Dioxide flood imaging - Analysis of 4D seismic wavelet transform spectral composites

Subtlety of 4D seismic anomalies, in carbonates, call upon using high-resolution seismic, which require very demanding tighter cross-equalization standards. We present a non-equalization approach utilizing wavelet transform (WT) spectral components of time-frequency-amplitude analysis of 4D seismic data for both, imaging EOR/sequestration Carbon Dioxide flood in a thin (3-5 m thick) Upper Pennsylvanian oomoldic carbonate reservoir in central Kansas-USA, and for helping to identify fluid-flow controls. Pore space in these reservoirs is the result of 1) shallow water ooid grainstonc shoals deposited as complex, lenticular ooid shoals combined with 2) meteoric and deeper burial diagenesis that resulted in cements occluding original pore space and dissolving existing ooids to create oomolds. Low temporal resolution, as a result of decomposing into specific frequency components, resulted in vertical smearing of the 4D-anomaly related to CO2-injection. This vertical smearing of 4D-signature is, in a qualitative sense, advantageous as it causes expansion in the anomaly temporal span for thin reservoirs where a 4D-effect is subtle and temporally limited. Six seismic volumes from a baseline and two monitor surveys. Four volumes with dominant frequency of 40, 50, 60 Hz. and 70 Hz from each survey, were extracted using a Morlet wavelet basis for WT decomposition. We utilize the higher-frequency attenuating nature of CO2-invaded areas as an indicator for outlining CO2-favored facies trends using WT spectral ratios composites. The outlined CO2-swept area is highly correlated to a trend of higher attenuation of the higher frequencies. The manner in which spectral composites are formed in this study minimizes the need for cross-equalization due to the fact that each composite is constituted from the same survey. Several CO2-favored facies trends were identified and correlated with other gcoinformation.