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Approximately 80% of the hydrocarbon reserves in carbonate rocks in North America are found in rock that is essentially pure dolomite. In many reservoirs the field limits are determined by the distribution of dolomite, because the dolomitization process is conducive to the production of a favorable reservoir rock. The distribution of dolomite may be determined by (1) those rocks that were within the flow path of a dolomitizing fluid (water-controlled dolomitization) and (2) the susceptibility of a rock within the flow path of a dolomitizing fluid to dolomitization (rock-controlled dolomitization). The second factor may be controlled by permeability at the time of dolomitization, particle size, or solubility of the original particles. The identification of the cause of the location of an individual dolomite body is significant to understanding its size and distribution.
Paleozoic carbonate rocks containing abundant crinoids commonly illustrate the idea of rock-control dolomitization. The significant parameter appears to be the original fabric of the sediment and is related to the ratio of carbonate mud to carbonate sand-size grains. The hydrology of hypersaline brine on Bonaire in the Netherlands Antilles provides a model from the Holocene that illustrates water-controlled dolomitization. In this model, access to hypersaline brine determines whether a sediment or rock will have the opportunity for dolomitization.
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