Changes

[[file:predicting-reservoir-system-quality-and-performance_fig9-72.png|thumb|300px|{{figure number|3}}Recent limestones from the intertidal-supratidal zone that show petrographic aspects of vadose precipitation zone cements. Copyright: Purser;<ref name=Purser_1978>Purser, B. H., 1978, Early diagenesis and the preservation of porosity in Jurassic limestones: Journal of Petroleum Geology, v. 1, no. 2, p. 83-94</ref> courtesy Journal of Petroleum Geology.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-72.png|thumb|300px|{{figure number|3}}Recent limestones from the intertidal-supratidal zone that show petrographic aspects of vadose precipitation zone cements. Copyright: Purser;<ref name=Purser_1978>Purser, B. H., 1978, Early diagenesis and the preservation of porosity in Jurassic limestones: Journal of Petroleum Geology, v. 1, no. 2, p. 83-94</ref> courtesy Journal of Petroleum Geology.]]

The vadose precipitation zone begins where water in the vadose zone becomes saturated with CaCO₃. Slight temperature increases or CO₂ degassing causes calcite to precipitate. Cementation is generally minor and reflects pore-water distribution. Meniscus cement precipitates where water clings between grains in a meniscus manner. Pendulous or microstalactitic cement precipitates where water droplets form underneath grains. Cement tends to be very fine equant calcite crystals. If magnesium is present in pore water, then calcite precipitation may be inhibited and aragonite or even dolomite may precipitate.<ref name=ch09r35 />

The vadose precipitation zone begins where water in the vadose zone becomes saturated with CaCO₃. Slight temperature increases or CO₂ degassing causes calcite to precipitate. Cementation is generally minor and reflects pore-water distribution. Meniscus cement precipitates where water clings between grains in a meniscus manner. Pendulous or microstalactitic cement precipitates where water droplets form underneath grains. Cement tends to be very fine equant calcite crystals. If magnesium is present in pore water, then calcite precipitation may be inhibited and aragonite or even [[dolomite]] may precipitate.<ref name=ch09r35 />

The sketches in [[:file:predicting-reservoir-system-quality-and-performance_fig9-72.png|Figure 3]] illustrate recent limestones from the intertidal-supratidal zone. They show petrographic aspects of vadose precipitation zone cements.

The sketches in [[:file:predicting-reservoir-system-quality-and-performance_fig9-72.png|Figure 3]] illustrate recent limestones from the intertidal-supratidal zone. They show petrographic aspects of vadose precipitation zone cements.

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting reservoir system quality and performance]]

[[Category:Predicting reservoir system quality and performance]]