Joint Estimation of Porosity and Saturation Using Stochastic Rock Physics Modeling

Porosity and saturation are fundamental sedimentary properties that affect both seismic wave propagation and appraisal development and production of an oil field. Traditionally, these parameters have been estimated from seismic impedances and velocities using Biot-Gassman theory and/or or porosity-velocity relationships. However, when using theory to relate surface seismic attributes to reservoir saturation, the porosity estimation problem and its affect on the unsaturated sedimentary properties should be addressed. Similarly, the problem of porosity estimation is also affected by the hydrocarbon saturation at the target. Because bulk modulus and density are affected by both porosity and saturation of the sediment, and because the shear modulus is affected by the sediment porosities, estimating hydrocarbon saturation and reservoir porosity from seismic data is a joint estimation problem. Moreover, the uncertainties associated with saturation estimation are related to the uncertainties we have in the porosity, and vice versa. In this paper, we present a methodology for joint porositysaturation estimation. We show how porosities and saturations can be jointly estimated using stochastic rock physics modeling and Bayesian estimation framework. We study the interdependencies of this reservoir property estimation problem within a given lithology unit.