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Humble formula

1. n. [Formation Evaluation]
A particular relation between the formation factor (F) and porosity (phi) proposed by the Humble Oil Company. The original formula was expressed as F = 0.62 / phi2.15. A nearly equivalent form, with a simpler porosity exponent, is F = 0.81 / phi2. These formulae are considered most suitable for relatively high-porosity, sucrosic, or granular, rocks. See Winsauer WO, Shearin HM, Masson PH and Williams M: Resistivity of Brine-Saturated Sands in Relation to Pore Geometry, AAPG Bulletin 36 (1952): 253-277.