Pay probability cube generated from the lithology prediction workflow.
Seismic reservoir characterization service delineates productive zones
Challenge
Accurately define productive areas within an existing field
Solution
Employed a combination of prestack simultaneous inversion and seismic lithology classification to provide a more detailed delineation of the reservoir facies
Results
Reduced recovery uncertainty and better targeted reservoir sweet spots
Seismic attenuation skewed results
In one field, the operator was unable to distinguish individual reservoirs because of seismic attenuation effects. As a result, several production wells that were drilled based on surface seismic images were underperforming. Some vertically stacked reservoir sands could not be interpreted, and it was difficult to determine which sand units would be more productive based on porosity, hydrocarbon content, and lateral sand body connectivity.
The Schlumberger Reservoir Seismic Services group performed accurate seismic reservoir characterization. Although the input seismic data was of high resolution, the seismic gathers required optimization for the inversion process. The geology in the area caused attenuation of the seismic amplitudes, creating a shadow effect in the deeper portion of the seismic sections. This limited the accurate identification and delineation of production zones. Therefore, the measuring and removal of seismic attenuation was critical. Another step was to flatten the seismic events across offsets and still further improve the signal/noise ratio while maintaining the known AVO character of the reservoir.
The proposed solution included prestack simultaneous inversion (created using the ISIS suite of simultaneous inversion technology) that computed acoustic impedance and Poisson’s ratio. The inputs to the inversion are the results of the edited and analyzed well logs, angle stacks generated from the seismic data optimization, wavelets estimated for each of the seven angle stacks, and a low-frequency model generated from the well logs and constrained by the horizons and seismic processing velocities.
Locating more productive areas
A rock physics–based lithology prediction workflow integrated the well logs, seismic inversion, provide an estimate of the most probable lithology and by defining the most probable lithology class of the prospect and were used to populate and lithology-dependent probability distribution function was upscaled to seismic resolution and then used to generate optimal porosity and saturation estimates. The client integrated the improved seismic data with reservoir characterization to locate more productive areas in the field. These data may also be used as a basis for reservoir volumetrics analysis and may be updated as the reservoir depletes over time.
Client saved time and reduced recovery uncertainty
Recovery uncertainty was reduced through the use of high-fidelity seismic measurements that were consistently calibrated with other oilfield measurements. Increased resolution of the seismic data enabled the client to see individual reservoir units. Drilling risk was decreased through improved delineation of hydrocarbon-bearing sands. Armed with this information, the client was able to avoid drilling poorly producing wells.
