Changes

High-frequency upward-shoaling cycles commonly comprise individual hydraulic or flow units within carbonate reservoirs.<ref>Kerans, C., F. J. Lucia, and R. K. Senger, 1994, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0078/0002/0150/0181.htm Integrated characterization of carbonate ramp reservoirs using Permian San Andres Formation outcrop analogs]: AAPG Bulletin, v. 78, no. 2, p. 181–216.</ref> Porosity variation in carbonate reservoirs occurs at the scale of high-frequency cycles.<ref>Ehrenberg, S. N., 2004, [http://archives.datapages.com/data/bulletns/2004/12dec/1653/1653.HTM Factors controlling porosity in Upper Carboniferous-Lower Permian carbonate strata of the Barents Sea]: AAPG Bulletin, v. 88, no. 12, p. 1653–1676.</ref> Larger scale trends in porosity variation can also occur at the systems tract or sequence level.<ref name=Ehrenberg2006>Ehrenberg, S. N., G. P. Eberli, M. Keramati, and S. A. Moallemi, 2006, [http://archives.datapages.com/data/bulletns/2006/01jan/0091/0091.HTM Porosity-permeability relationships in interlayered limestone-dolostone reservoirs]: AAPG Bulletin, v. 90, no. 1, p. 91–114.</ref>

High-frequency upward-shoaling cycles commonly comprise individual hydraulic or flow units within carbonate reservoirs.<ref>Kerans, C., F. J. Lucia, and R. K. Senger, 1994, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0078/0002/0150/0181.htm Integrated characterization of carbonate ramp reservoirs using Permian San Andres Formation outcrop analogs]: AAPG Bulletin, v. 78, no. 2, p. 181–216.</ref> Porosity variation in carbonate reservoirs occurs at the scale of high-frequency cycles.<ref>Ehrenberg, S. N., 2004, [http://archives.datapages.com/data/bulletns/2004/12dec/1653/1653.HTM Factors controlling porosity in Upper Carboniferous-Lower Permian carbonate strata of the Barents Sea]: AAPG Bulletin, v. 88, no. 12, p. 1653–1676.</ref> Larger scale trends in porosity variation can also occur at the systems tract or sequence level.<ref name=Ehrenberg2006>Ehrenberg, S. N., G. P. Eberli, M. Keramati, and S. A. Moallemi, 2006, [http://archives.datapages.com/data/bulletns/2006/01jan/0091/0091.HTM Porosity-permeability relationships in interlayered limestone-dolostone reservoirs]: AAPG Bulletin, v. 90, no. 1, p. 91–114.</ref>

The measurement of carbonate body dimensions is a topic that gets less attention than is the case for siliciclastic reservoirs. A recent exception is Qi et al. (2007), where geometric data for ooid shoal, tidal flat, and eolian carbonate macroforms were used for constructing a 3-D reservoir model for the Big Bow and Sand Arroyo Creek fields in Kansas. The model has four zones with the ooid grainstone lithofacies showing the highest porosities and permeabilities. These form large linear shoals associated with structural highs. The model can be used to make predictions as a result of the simple zonation, large macroforms, and a reasonable correspondence between facies and rock properties. Many carbonate reservoirs are more complex than this and rather more difficult to model.

The measurement of carbonate body dimensions is a topic that gets less attention than is the case for siliciclastic reservoirs. A recent exception is Qi et al.,<ref>Qi, L., T. R. Carr, and R. H. Goldstein, 2007, [http://archives.datapages.com/data/bulletns/2007/01jan/BLTN05167/BLTN05167.HTM Geostatistical three-dimensional modeling of oolite shoals, St. Louis Limestone, southwest Kansas]: AAPG Bulletin, v. 91, no. 1, p. 69–96.</ref> where geometric data for ooid shoal, tidal flat, and eolian carbonate macroforms were used for constructing a 3-D reservoir model for the Big Bow and Sand Arroyo Creek fields in Kansas. The model has four zones with the ooid grainstone lithofacies showing the highest porosities and permeabilities. These form large linear shoals associated with structural highs. The model can be used to make predictions as a result of the simple zonation, large macroforms, and a reasonable correspondence between facies and rock properties. Many carbonate reservoirs are more complex than this and rather more difficult to model.

There may be several reasons why there is not so much measured data available for carbonate body dimensions compared to siliciclastics. Many carbonate reservoirs are characterized by rock types instead of lithofacies. Here, a combination of lithofacies and diagenesis acts as a control on rock properties. Thus, it is not always possible to make a predictive rock property model of a carbonate reservoir that is allied to the lithofacies model as in the example above.

There may be several reasons why there is not so much measured data available for carbonate body dimensions compared to siliciclastics. Many carbonate reservoirs are characterized by rock types instead of lithofacies. Here, a combination of lithofacies and diagenesis acts as a control on rock properties. Thus, it is not always possible to make a predictive rock property model of a carbonate reservoir that is allied to the lithofacies model as in the example above.

The choice of reservoir analogs can be problematic. Carbonate environments have changed substantially over geological time by comparison to siliciclastic environments; for example, the type of organism responsible for building reefs has varied throughout the geological record. For this reason, it is advisable to select an outcrop analog that was deposited at roughly the same time as the carbonate reservoir interval under investigation (Markello et al., 2006).

The choice of reservoir analogs can be problematic. Carbonate environments have changed substantially over geological time by comparison to siliciclastic environments; for example, the type of organism responsible for building reefs has varied throughout the geological record. For this reason, it is advisable to select an outcrop analog that was deposited at roughly the same time as the carbonate reservoir interval under investigation.<ref>Markello, J. R., R. Koepnick, and L. E. Waite, 2006, The carbonate analogs through time (CATT) hypothesis—A systematic and predictive look at Phanerozoic carbonate reservoirs: AAPG Search and Discovery Article 40185, 5 p.</ref>

==Importance of diagenesis==

==Importance of diagenesis==