Pore-size distribution in sandstones
Journal Article
·
· AAPG Bulletin (American Association of Petroleum Geologists); (United States)
OSTI ID:5865693
Pore size in reservoir rocks is measured either directly in thin sections under a petrographic microscope or by injecting mercury under pressure into the rock sample. The frequency distribution for nominal pore-size data shows a log-normal pattern similar to that for grain size in sedimentary rocks. Therefore, the same transformed size unit (phi = -log[sub 2] X) traditionally used for grain size can be used for pore-size measurement. A routine was created which measured the entry mercury capillary pressure (Pc[sub atm]), converted this pressure to pore size in millimeters (X[sub mm] = 0.007/Pc[sub atm]), transformed the size values into phi units, and displayed the data as a pore-size frequency distribution. For clean, well-sorted sandstones, the distribution tend to a bell-shaped normal curve. Sandstones free from gravel and clay tend to show bimodal pore-size distributions as the grain-size sorting gets poorer. In fine to medium sandstones, a pore-size mode of 5-6 phi is associated with intergranular voids. Authigenic kaolin develops a pore-size mode around 8 phi. Quartz cement tends to obliterate small pores. Carbonate cement does not show preference for pore size, blocking eventually all the pore space. Clay sandstones have a pore-size mode of 11-12 phi. Pores smaller than 2 [mu]m (phi > 9) are considered to be micropores; they provide a large available surface and, accordingly, a high irreducible water saturation. 7 refs., 1 fig., 2 tabs.
- OSTI ID:
- 5865693
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (United States), Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Vol. 77:6; ISSN 0149-1423; ISSN AABUD2
- Country of Publication:
- United States
- Language:
- English
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