Changes

The diagenetic history of a carbonate reservoir can be complex, involving various phases of cementation, dissolution, compaction, and mineral transformation.<ref name=TW1990>Tucker, M. E., and V. P. Wright, 1990, Carbonate sedimentology: London, Blackwell, 496 p.</ref> Early oil migration can inhibit further diagenesis and preserve porosity in carbonate reservoirs.<ref>Neilson, J. E., N. H. Oxtoby, M. D. Simmons, I. R. Simpson, and N. K. Fortunatova, 1998, The relationship between petroleum emplacement and carbonate reservoir quality: Examples from Abu Dhabi and the Amu Darya Basin: Marine and Petroleum Geology, v. 15, p. 57–72.</ref>

The diagenetic history of a carbonate reservoir can be complex, involving various phases of cementation, dissolution, compaction, and mineral transformation.<ref name=TW1990>Tucker, M. E., and V. P. Wright, 1990, Carbonate sedimentology: London, Blackwell, 496 p.</ref> Early oil migration can inhibit further diagenesis and preserve porosity in carbonate reservoirs.<ref>Neilson, J. E., N. H. Oxtoby, M. D. Simmons, I. R. Simpson, and N. K. Fortunatova, 1998, The relationship between petroleum emplacement and carbonate reservoir quality: Examples from Abu Dhabi and the Amu Darya Basin: Marine and Petroleum Geology, v. 15, p. 57–72.</ref>

Dolomitization is the process by which calcium carbonate is altered to the magnesium-rich carbonate mineral dolomite. It has been estimated that about 80% of the reserves in the carbonates of the United States are in dolomite with 20% in limestone (North, 1985). Dolomitization materially affects the pore distribution of carbonate sediments. Dolomitization can act to eliminate heterogeneities in minor lithofacies that would otherwise form barriers or extensive baffles. Muddy carbonates can be transformed into porous dolomites with good intercrystalline connectivity. Dolomites tend to show higher porosities at increased depths of burial by comparison to limestones.<ref name=Ehrenberg2006 />

Dolomitization is the process by which calcium carbonate is altered to the magnesium-rich carbonate mineral dolomite. It has been estimated that about 80% of the reserves in the carbonates of the United States are in dolomite with 20% in limestone.<ref>North, F. K., 1985, Petroleum geology: Boston, Allen and Unwin, 619 p.</ref> Dolomitization materially affects the pore distribution of carbonate sediments. Dolomitization can act to eliminate heterogeneities in minor lithofacies that would otherwise form barriers or extensive baffles. Muddy carbonates can be transformed into porous dolomites with good intercrystalline connectivity. Dolomites tend to show higher porosities at increased depths of burial by comparison to limestones.<ref name=Ehrenberg2006 />

The process of dolomitization requires a large source of magnesium ions and a fluid transport path for the magnesium to move through the pore space. Several mechanisms have been proposed to explain dolomitization (Machel, 2004). For instance, in the reflux model of dolomitization, dolomite can form where hypersaline conditions exist in peritidal, lagoonal, and restricted basinal environments. Intense evaporation in the tropical heat will result in brine concentrations. The precipitation of gypsum and anhydrite removes calcium from the saline fluids, leaving a magnesium-rich residual brine. The dense, concentrated brine solution will subsequently filter down, reacting with the underlying sediments to form dolomite (Adams and Rhodes, 1960).

The process of dolomitization requires a large source of magnesium ions and a fluid transport path for the magnesium to move through the pore space. Several mechanisms have been proposed to explain dolomitization.<ref>Machel, H. G., 2004, Concepts and models of dolomitization: A critical reappraisal, in C. J. R. Braithwaite, G. Rizzi, and G. Darke, eds., The geometry and petrogenesis of dolomite reservoirs: Geological Society (London) Special Publication 235, p. 7–63.</ref> For instance, in the reflux model of dolomitization, dolomite can form where hypersaline conditions exist in peritidal, lagoonal, and restricted basinal environments. Intense evaporation in the tropical heat will result in brine concentrations. The precipitation of gypsum and anhydrite removes calcium from the saline fluids, leaving a magnesium-rich residual brine. The dense, concentrated brine solution will subsequently filter down, reacting with the underlying sediments to form dolomite.<ref>Adams, J. E., and M. L. Rhodes, 1960, [http://archives.datapages.com/data/bulletns/1957-60/data/pg/0044/0012/1900/1912.htm Dolomitization by seepage refluxion]: AAPG Bulletin, v. 44, p. 1912–1920.</ref>

==Rock types in carbonates==

==Rock types in carbonates==