Predicting formation factor and resistivity index in simple sandstones

The electrical conductivity of a porous medium is strongly dependent upon the geometry of its pore system. A network model for electrical conductivity is presented that captures the geometry of an accurately characterized sphere pack. The model can be applied to sandstones by simulating the results of diagenetic mechanisms such as compaction and quartz cementation in the sphere pack. Model predictions of formation factor and resistivity index match measurements for uncemented bead packs, for fused bead packs and for clean sandstones. The predictions involve no adjustable parameters and do not depend upon measurements of other properties. The predictive ability of this approach provides physical insight and practical benefits, such as reducing uncertainty in estimates of hydrocarbons in place in unconsolidated and consolidated sandstone reservoirs.