Using Rock Physics to Improve Qp Quantification in Seismic Data

Abstract:

Our goal is to accurately estimate attenuation from seismic data using model regularization in the seismic inversion workflow. One way to achieve this goal is by finding an analytical relation linking V_p to Q_p. We derive such an approximate closed-form equation by establishing that the key parameter affecting V_p in clean partially saturated gas sand is porosity, while the two key parameters affecting Q_p are porosity and water saturation. We find a simple equation that relates the dry-rock compressional modulus M_Dry to that of the mineral frame and porosity by using just one adjustable coefficient. Then we use a theoretical model relating Q_p at partial saturation to M_Dry, porosity, and water saturation. Finally, by using these two relations, we find a closed-form transform between Q_p and V_p at fixed water saturation. This relation is tested on well data from a clean clastic gas reservoir. Next we create a 2D synthetic gas reservoir section populated with Q_p and V_p and generate respective synthetic seismograms. The goal now is to invert this synthetic seismic section for Q_p. If we use standard seismic inversion based solely on seismic data, the inverted attenuation model has low resolution, incorrect position, and is distorted. However, adding our relation between velocity and attenuation, we obtain an attenuation model very close to the original section. This method is tested on a 2D real seismic data from GOM. The resulting Q_p model matches the geological shape of an absorption body interpreted from seismic section. By using this Q_p model in seismic migration, we make the seismic events below the high-absorption layer clearly visible, with improved frequency content and coherency of the events.