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Line 87: − 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 (Figure 3).+ − + − +
→Upward-shoaling cementation and compaction reservoir model
===Upward-shoaling cementation and compaction reservoir model===
===Upward-shoaling cementation and compaction reservoir model===
[[file:carbonate-reservoir-models-facies-diagenesis-and-flow-characterization_fig3.png|thumb|left|{{figure number|3}}Schematic diagrams of the upward-shoaling cementation and compaction reservoir model and the subtidat-supratidal dolomitlzation and sulfate emplacement reservoir model.]]
[[file:carbonate-reservoir-models-facies-diagenesis-and-flow-characterization_fig3.png|thumb|{{figure number|3}}Schematic diagrams of the upward-shoaling cementation and compaction reservoir model and the subtidat-supratidal dolomitlzation and sulfate emplacement 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]]).
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.