Computation of Porosity Using Sand and Carbonate Rock Physics Models in an Iranian Oilfield

Abstract

In this case study, we have employed post stack inversion, guided by rock physics, to estimate reservoir porosity in an Iranian oil field. The reservoir, based on the lithology and porosity information can be divided into 8 zones and 19 subzones with lithologies comprised of shale, sand and carbonates. Among them, three zones above WOC are carbonate and sandstone. We use different rock physics model to estimate porosity from wire line and seismic data. The procedure uses stack and estimated wavelet to determine the elastic parameter: Pwave impedance. Different rock physics model were applied to relate acoustic impedance (AI) to porosity. This allowed performing rock physics analysis, not only on well log data, but also on seismic data (post stack inversion results). The poststack inversion of AI within the target zone was projected onto the template to generate porosity volume. One of the most important issues in carbonate rock physics is fracture distribution. Petrophysical analysis in carbonate sections of the reservoir shows that fracture distribution is limited and production is mostly from matrix porosity. Fractures in the carbonate zone are mostly joints with 0.5 mm opening and 15 cm in length, so the isotropic medium assumption can be made. The results show that Nur-Dvorkin (1996) model and Raymer-Greenberg-Castagna (1997) are appropriate for predicting porosity in sandstone and carbonate zone of the reservoir respectively and predict porosity up to 30% which shows good agreement with the porosity values measured from well log data.