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→Upward-shoaling cementation and compaction reservoir model
The upward-shoaling model is based on a depositional model of sediment aggrading to sea level. As the water shallows, the energy conditions increase, resulting in a vertically stacked sequence from mudstones and wackestones at the bottom to packestones and grainstones at the top ([[:file:carbonate-reservoir-models-facies-diagenesis-and-flow-characterization_fig3.png|Figure 3]]).
The upward-shoaling model is based on a depositional model of sediment aggrading to sea level. As the water shallows, the energy conditions increase, resulting in a vertically stacked sequence from mudstones and wackestones at the bottom to packestones and grainstones at the top ([[:file:carbonate-reservoir-models-facies-diagenesis-and-flow-characterization_fig3.png|Figure 3]]).
Cementation and compaction occur with burial, reducing the reservoir quality of the mud-supported mudstones and wackestones more than the grain-supported packestones and grainstones. The result is a vertical sequence of lower porosity and permeability mud-supported rocks at the base and higher porosity and permeability grain-supported rocks at the top. Consequently, the best quality flow unit occurs at the top of the sequence (see [[Flow Units for Reservoir Characterization]]). The permeable units are confined to the grainstone bars.
Cementation and compaction occur with burial, reducing the reservoir quality of the mud-supported mudstones and wackestones more than the grain-supported packestones and grainstones. The result is a vertical sequence of lower porosity and permeability mud-supported rocks at the base and higher porosity and permeability grain-supported rocks at the top. Consequently, the best quality flow unit occurs at the top of the sequence (see "[[Flow units for reservoir characterization]]"). The permeable units are confined to the grainstone bars.
If the grainstone bars are exposed to meteoric diagenesis, significant separate vug porosity can develop, causing a loss of permeability while retaining porosity. In the dolomite environment, grainstone bars are commonly cemented with anhydrite, and intercrystalline porosity in mud-supported sediments forms the permeable facies.
If the grainstone bars are exposed to meteoric diagenesis, significant separate vug porosity can develop, causing a loss of permeability while retaining porosity. In the dolomite environment, grainstone bars are commonly cemented with anhydrite, and intercrystalline porosity in mud-supported sediments forms the permeable facies.