PE/Uma Matrix Crossplot -- Representative Sample (WellStrat Pure Intervals)

PE, the photoelectric factor measured by the density tool (curve mnemonic PEF), is a strong, largely porosity-independent indicator of a rock's mineral composition. Uma is PE's zero-porosity matrix equivalent -- what the photoelectric response would read for a pure sample of that mineral with no pore space -- calculated here from PEF and bulk density using NPHI as an independent porosity estimate. The PE/Uma matrix crossplot provides a porosity-corrected companion to the PEF/RHOB crossplot method, using an independent well population and lithology label source. Lithology labels are sourced from the OGA/NSTA WellStrat database, restricted to a picked interval recorded as 100% single lithology. Up to 100 wellbores per lithology class are sampled (a capped, reproducible sample), each with the full PEF, RHOB, GR, DT, and NPHI curve set. Bulk density is similarly corrected to its matrix equivalent, DENSma -- what the density log would read for a pure sample of that mineral with no pore space, the same porosity correction applied to PE above.

U

-- the standard symbol for the volumetric photoelectric cross section (barns/electron x electron density, in barns/cc)

ma

-- the standard subscript for "matrix" (zero-porosity, pure-mineral value)

Uma

-- "U, matrix value"

DENSma

-- matrix density

PHIma

-- apparent matrix porosity -- what the neutron-porosity tool would read for a pure, zero-porosity sample of that mineral; not actually zero, because the tool's response is calibrated to limestone