Porosity Distribution Estimation from Acoustic Impedance on Post-Salt Albian Carbonate, Offshore Brazil

Summary Carbonates reservoirs are very complex due to vertical and lateral facies variability caused by diagenetic effects, producing a very complex pore system with large range in porosity and elastic properties. This characteristic makes very difficult to establish a unique relationship between porosity and velocity or acoustic impedance, so it is necessary to get a detail facies classification and from then establishing the relationship between petrophysical and elastic properties for each facies. Based on this heterogeneity, we performed a reservoir characterization considering the different sedimentological environments and how this impact the elastic properties and porosity distribution on the reservoir on a post-salt Albian carbonate in Campos Basin, Brazil, divided on five main facies intervals: Muddy, Packstone, Grainstone, Dolomite and Cemented, where Packstone and Grainstone are the pay intervals, while Dolomite and Cemented are tight, and Muddy is an argillaceous level. Acoustic impedance shows a separation between reservoir and non-reservoir facies, and from this separation linear relationships were fitted between Acoustic Impedance and Total Porosity for each group of facies. Then, Acoustic Impedance from a post-stack acoustic inversion was transformed into Total Porosity, using the relationships. The results illustrate a porous upper reservoir and tight lower reservoir, and near field exploration opportunities.