Extended Elastic Impedance Inversion in Tight Sand Reservoirs

Surface seismic data plays a pivotal role in delineating hydrocarbon reservoirs and understanding the target reservoir properties. It has proven to be a valuable tool to identify sweet spots and optimize drilling practices and placements for horizontal wells (Treadgold et al., 2011). Tight sand reservoirs have increasingly become a prime target for oil and gas industry. The unconventionally low porosities encountered in such reservoirs are often a challenge for surface seismic data due to the limitations in the seismic response. Hence, the delineation and characterization of the reservoir porosity is hindered when using the conventional poststack inversion methods. In 1999, Connolly introduced the idea of Elastic Impedance (EI) as a generalization of Acoustic Impedance (AI) with varying incidence angles. The work was then expanded to the Extended Elastic Impedance (EEI) for reservoir properties predictions (Whitcombe et al., 2000). EEI attributes have proven very valuable for unconventional targets to improve reservoir predictions accuracy where minimal seismic responses are detected from surface seismic data. Sorting through different angles to capture the optimal response for the desired property can enhance the prediction accuracy by a considerable margin. Elastic impedance is believed to be more beneficial in reservoir characterization overall, not only in predicting the reservoir properties, but also in mapping the reservoir extent as well as the top and bottom of target reservoirs. The ability to add additional information from the shear impedance to the estimated acoustic impedance provides valuable information to differentiate lithology and fluids (Ogagarue, 2016)