PORE-THROAT MORPHOLOGY IN THE UPPER JURASSIC SMACKOVER FORMATION OF ALABAMA

A new parameter called ''a'' is calculated from capillary-pressure dat a. ''a'' = (m - 1)/2, where m is the slope of a line segment on a log- log plot of the difference between maximum cumulative intrusion volume and cumulative intrusion volume versus capillary pressure. ''a'' has been previously interpreted as a measure of pore-throat shape: ''a'' h as the value 1 for sheetlike pore throats, 2 for cylindrical pore thro ats, and 3 for equant pore throats. An alternative, and more likely, i nterpretation is that ''a'' measures pore-throat surface roughness. Th is inference is based on the observations that (1) ''a'' is calculated by a method analogous to that of fractal dimension, and fractal dimen sion is commonly interpreted as a roughness measure, (2) most ''a'' va lues in Smackover reservoir rocks from Alabama are low (< 1) and most pore throats in these strata are smooth, and (3) pore throats in sampl es of Smackover reservoir rocks with ''a'' values near 2 are not cylin drical. ''a'' is independent of ps permeability. If ''a'' is correctly interpreted as a measure of pore-throat roughness, then it probably a ffects liquid permeability and could influence producibility of oil an d gas-condensate.