| Popis: |
The porosity of carbonates as compared to sandstones is vastly more complex with simple intergrain porosity dominates sandstones while carbonates commonly exhibit complex secondary pore systems that may evolve during burial. Initial porosity of carbonates is much greater than that seen in sandstones due to common intragranular porosity. Fractures, both natural and induced, are much more important in carbonates. Diagenesis is a major factor in the development of ultimate pore systems in carbonates. The geologically based Choquette–Pray carbonate porosity classification is the most commonly used scheme. Their 15 different pore types are based on fabric selectivity. A major feature of the classification is its recognition of the potential of porosity evolution through time and burial. Three porosity development zones are recognized: eogenetic, dealing with surface processes; mesogenetic, dealing with burial processes; and telogenetic, exhumed rocks dealing again with surface processes. This classification is best used during exploration, while other engineering-based classifications such as the one developed by Lucia should be used in reservoir characterization and as input for reservoir modeling. Examples of all 15 pore types are given. |
