Pore systems

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Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Predicting the occurrence of oil and gas traps
Chapter Predicting reservoir system quality and performance
Author Dan J. Hartmann, Edward A. Beaumont
Link Web page
Store AAPG Store

Rocks can be classified on the basis of their pore geometry into four major pore categories that can be divided into ten subcategories. Extensive experience and laboratory analysis show that these pore type categories have a particular behavior when interacting with fluids that can be used to predict the behavior of reservoir systems over time.

Pore geometry is categorized as intergranular, intercrystalline, vuggy/moldic, or fracture. Pore throat sizes are categorized into mega-, macro-, meso-, and micro-pore types. Combining both pore geometry and pore type into a classification scheme is an effective method of describing pore systems. For example, a very fine-grained sandstone might be classified as having intergranular mesoporosity or a limestone as having vuggy macroporosity.

Table 1 describes a typical rock type for each pore type in the classification.

Table 1 Typical rock types by pore class
Pore geometry/pore type Archie Non-Archie
Intergranular/interparticle Intercrystalline Clay cemented Vuggy Fracture
Mega/macro Clean, coarse sandstone or carbonate grainstone
  • Coarsely crystalline carbonate
  • Quartz- or carbonate-cemented coarse sandstone
Chlorite- or illite-cemented (pore-lining) coarse sandstone Connected vugs or vugs in a crystalline matrix Fracture width >50µ
Meso Clean, coarse silt to very fine sandstone or carbonate grainstone
  • Very fine to medium crystalline carbonate
  • Quartz- or carbonate-cemented fine to medium sandstone
  • Chlorite- or illite cemented (pore-lining) fine to medium sandstone
  • Kaolinite-cemented (pore-filling) coarse sandstone
Poorly connected vugs or oomolds in a fine to medium crystalline matrix Fracture width 5-50µ
Micro Clean clay-size to fine siltstone or clay-size carbonate
  • Silt-size crystalline carbonate
  • Quartz- or carbonate-cemented silt to very fine sandstone
Sandstone with clay in pore throats Dispersed vugs in microcrystalline matrix Fracture width <5µ

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