Pore Geometry Controls on Porosity and Permeability in the Tirrawarra Sandstone Reservoir, Cooper Basin, South Australia

Mohammad R. Rezaee and Cedric M. Griffiths

Pore geometry is a major control on hydraulic conductivity in a porous medium. Pore geometry may be defined in terms of pore and pore throat size, pore diameter, and pore shape (pore surface area, pore perimeter). Petrographic image analysis, and mercury injection data were employed to group fluvio-deltaic Tirrawarra Sandstone samples in the Moorari and Fly Lake fields into eight classes. The classes are separated according to the relative proportions of different kinds of porosity (microporosity, and primary and secondary macroporosity), size of pore spaces, size of pore throats, and pore diameter. The reservoir quality increases from class eight to class one and the Classes have a predictable relationship to sedimentary environment.

Class one samples, associated with meander, aeolian or beach-barrier environments, have primary macroporosity with partial quartz cement. Pore throats mostly exceed 10 micron. Mean pore space area is about 6300 micron. Mean pore diameter and mean pore perimeter are respectively 66 and 275 micron. Class eight, on the other hand, associated with a braid-delta environment, is dominated by microporosity. Mean pore space area is about 436 micron. Mean pore diameter and mean pore perimeter are respectively 25 and 76 micron. In addition the pore throat distribution shows poor sorting with a pore throat ranging from 0.1 to 0.5 micron.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California