Porosity LAMBDAs
Density and sonic porosity. The sonic pair is Raymer-Hunt-Gardner and the compaction-corrected Wyllie time average.
3 lambdas
PO.PP.Porosity.FromDensity
Porosity from the density log in a clean formation. The bulk density sits between the matrix density and the fluid density, and the fraction of the way across is the porosity. φ = (ρma − ρb) / (ρma − ρf). All three densities share one unit, g/cm³ on a density log. Shale and gas corrections are not in this equation.
PO.PP.Porosity.FromSonic.RHG
Sonic porosity from the Raymer-Hunt-Gardner field transform. It does not use a fluid transit time. An empirical constant, about 0.67 in sand and about 0.60 in carbonate, scales the fractional increase of transit time over the matrix. φ = C (Δt − Δtma) / Δt. Transit times share one unit, µs/ft on a sonic log. C is an input because the published range is 0.624 to 0.70, not a single lithology switch.
PO.PP.Porosity.FromSonic.Wyllie
Sonic porosity from the Wyllie time-average equation, divided by the compaction factor for an uncompacted sand. The time average overstates porosity when the adjacent shale is slower than 100 µs/ft. Dividing by Δtsh/100 brings it back. φ = ((Δt − Δtma) / (Δtf − Δtma)) / (Δtsh / 100). When the shale transit time is 100 µs/ft the divisor is 1 and the result is the compacted Wyllie porosity. Transit times are µs/ft.