Evaluating Net Sand Thickness on Seismically Thin Reservoirs – An Integrated Approach Applied to Kadanwari Field

Rock properties of seismically thin reservoirs cannot be quantified correctly using either amplitude or impedance data because of tuning effects. An original approach developed at Eni combines forward modeling, tuning analysis and rock physics to deal with such limitations. Band-limited seismic resolution and tuning effects can be turned to the geophysicist’s advantage by using an appropriate workflow combined with an understanding of what reservoir properties can be safely extracted given a certain reservoir body’s spatial configuration. We have applied these concepts to the Kadanwari field (Pakistan), where gas-bearing reservoir sands are below seismic resolution. Rock physics modeling is used to relate rock to elastic properties; then forward modeling of various rock-property scenarios are used to understand the seismic response with decreasing thickness. Finally, tuning charts are built and used to quantify the target reservoir property (net thickness). The net thicknesses output by this workflow are compared with the results of cluster analysis techniques, and the internal consistency of net maps is checked against the sedimentologists' depositional model; they both proved positive, confirming once more the validity of the approach which has already been tested successfully on several other fields worldwide.