KOPASKA-MERKEL, DAVID C., Geological Survey of Alabama, Tuscaloosa, AL

ABSTRACT: Influence Of Pore-Throat Morphology On Permeability of A Carbonate Beach Deposit.

From capillary-pressure data one can estimate _a_ the power to which throat "radius" is raised in calculating throat volume. _A_ implies throat shape: _a_ = 1 for sheetlike throats; 2 for cylindrical throats; and 3 for equant throats. _A_ values << 1 are common, and may correspond to linear throats; modified sheetlike throats in which a constricted region makes the effective bottleneck nearly two dimensional. Linear throats should be common in dolostones dominated by intercrystalline or moldic pores (the latter because they are separated by intercrystalline pore systems in the "matrix").

A dolomitized carbonate shoreface deposit from the Jurassic Smackover Formation in Silas field, Choctaw county, Alabama, dominated by moldic and secondary intraparticle pores, was studied in order to estimate _a_ values and to relate _a_ to other petrophysical parameters: median throat size, 16th and 84th percentile throat sizes, mercury-recovery efficiency, porosity, and permeability. Factor Analysis identified 3 orthogonal factors accounting for 83% of the sample variance. Factor 1 (50% of variance) is a throat-size and permeability factor; factor 2 (19%) is a recovery efficiency and porosity factor; factor 3 (14%) is a throat shape factor. Throat shape is independent of other petrophysical variables, and permeability covaries primarily with the sizes of the larger throats. Samples coring high on factor 1 consist of massive ooid dolograinstone, dominated by molds and secondary intraparticle pores. Samples scoring high on factors 2 and 3 are diverse (massive and laminated coid dolograinstone, laminated coid pellet dolograinstone, and pellet dolograinstone); some include intercrystalline pores.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.