Changes

[[file:evaluating-diagenetically-complex-reservoirs_fig1.png|thumb|300px|{{figure number|1}}Cross section in the Crane Field, Richland County, Montana, showing extreme irregularities in the development of porous dolomite zones in the Red River Formation below the C-anhydrite.<ref name=pt06r78 />]]

[[file:evaluating-diagenetically-complex-reservoirs_fig1.png|thumb|300px|{{figure number|1}}Cross section in the Crane Field, Richland County, Montana, showing extreme irregularities in the development of porous dolomite zones in the Red River Formation below the C-anhydrite.<ref name=pt06r78 />]]

Diagenetic alterations are defined here as all physical and chemical alterations that affect a sediment subsequent to deposition, including tectonically produced fractures and faults. Diagenetic alterations that have been observed to generate reservoir heterogeneities having a major influence on reservoir rock properties are shown in Table 1. In sandstone reservoirs, carbonate and anhydrite cementation, clay authigenesis, secondary porosity generation, and fracturing are the most commonly reported alterations. In carbonate reservoirs, the diagenetic components most often observed are gypsum/anhydrite cementation, dolomite replacement, secondary porosity generation, and stylolitization. A cross section from Longman<ref name=pt06r78>Longman, M. W., Fertal, T. G., Glennie, J. S., 1983, [http://archives.datapages.com/data/bulletns/1982-83/data/pg/0067/0005/0700/0744.htm Origin and geometry of Red River Dolomite reservoirs, western Williston basin]: AAPG Bulletin, v. 67, p. 744–771.</ref> illustrates the complexity of porosity development in one of the few well-documented examples of a diagenetically complex reservoir ([[:file:evaluating-diagenetically-complex-reservoirs_fig1.png|Figure 1]]).

Diagenetic alterations are defined here as all physical and chemical alterations that affect a sediment subsequent to deposition, including tectonically produced fractures and faults. Diagenetic alterations that have been observed to generate reservoir heterogeneities having a major influence on reservoir rock properties are shown in Table 1. In sandstone reservoirs, carbonate and anhydrite cementation, clay authigenesis, secondary porosity generation, and fracturing are the most commonly reported alterations. In carbonate reservoirs, the diagenetic components most often observed are gypsum/anhydrite cementation, dolomite replacement, secondary porosity generation, and stylolitization. A [[cross section]] from Longman<ref name=pt06r78>Longman, M. W., Fertal, T. G., Glennie, J. S., 1983, [http://archives.datapages.com/data/bulletns/1982-83/data/pg/0067/0005/0700/0744.htm Origin and geometry of Red River Dolomite reservoirs, western Williston basin]: AAPG Bulletin, v. 67, p. 744–771.</ref> illustrates the complexity of porosity development in one of the few well-documented examples of a diagenetically complex reservoir ([[:file:evaluating-diagenetically-complex-reservoirs_fig1.png|Figure 1]]).

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