Leveraging on Extended Elastic Impedance (EEI) Technology to Find More Hydrocarbon in a Matured Basin

Abstract The need for WRFM (well, reservoir, and facility management) with infill wells cannot be over-emphasized and has become essential for assets maturation and ullage utilization. EEI is the application of angle rotation in the conventional acoustic impedance under certain approximation. It essentially works by projecting intercept and gradient together with different angles which highlight different features. Extended Elastic Impedance (EEI) has proved to be a highly convenient framework for seismic AVO studies. EEI logs can be directly related to the petrophysical properties of interest, and seismic EEI reflectivity volumes can be obtained directly from the prestack data via linear projection in sin2 θ. In this project, we modelled the "chi" angles from the logs and applied the different chi angles to the prestack seismic dataset. This can be likened to a bandlimited seismic inversion product. The chi angles of the lithology indicators- Share Impedance (SI), MuRho and Density and the fluid indicators- Saturation, Fluid factor (FF) and LamdaRho were derived and applied on the seismic dataset for generating a 3D property distribution map. The input to the EEI inversion is the seismic angle sub-stacks of near (0-10deg), mid (10-20deg) and far (20-30deg) solving the AVA_2term Shuey AVO fitting function- intercept and gradient only. In some cases where the seismic S/N ratio in the ultra-far angle stack is high, it could be considered for the inversion and would give rise to the 3rd term- curvature, but in our case, it was considered noisy. To ensure stability of the inversion, the substacks were aligned both spectrally and on the waveforms and the seismic dataset was further post-processed. Amplitude maps generation and sculpting were done on the different EEI generated seismic volumes and the result provided insight in the lithology and fluid study at the reservoirs of interest. This has led to field life extension by several years more than design life and is helping to keep xxxkbpd-sized facility full via world class WRFM, infill drilling and growth projects. The EEI result helped in identified new leads and revalidated existing leads aiding well placement.