Effect of rock physics parameters in the Simandoux model on inverted reservoir rock and fluid properties

摘要

Estimation of reservoir rock and fluid properties is highly dependent on the parameters used in the rock physics models. Determining water saturation is very important to estimate hydrocarbon reserves and is often computed using Archie's equation. Any uncertainty associated with the parameters in the Archie model as well as resistivity of clay in shaly sand formations may cause errors in the estimation of petrophysical parameters. It is very important to evaluate the relative impact of these parameters on reservoir rock and fluid properties. In this work, a series of sensitivity tests were carried out in order to investigate which of the formation water resistivity R_w, cementation exponent m, tortuosity factor a and resistivity of clay R_(clay) has the biggest impact on the porosity, water saturation and clay content derived from a petrophysical inversion, as well as how much they affect them. We vary the rock physics parameters and use joint inversion of seismic impedances and resistivity for estimating porosity, water saturation and volume of clay. The results were compared with a base case and show that brine resistivity and cementation exponent have the biggest impact on inverted rock and fluid properties, and that for the same fractional changes in rock physics parameters, water saturation is the most affected by uncertainties in brine resistivity. Although this sensitivity analysis was applied to a water-bearing well log data located in the Barents Sea, it can be extended to wells with hydrocarbons to understand the effect of uncertainties in saturation exponent on inverted petrophysical properties.