Changes

In deserts, dune sediments aggrade laterally and vertically as large-scale sand blankets. These may be very thick (more than 300 m [1000 ft]), and cover hundreds of square kilometers.<ref name=Richardsonetal_1988a>Richardson, J. G., J. B. Sangree, and R. M. Sneider, 1988, Eolian dunes: Journal of Petroleum Technology, v. 40, no. 1, p. 11–12.</ref> Internally, dunes comprise thick, cross-bedded intervals of well-rounded, well-sorted sandstones. They are normally the most productive lithofacies in eolian reservoir systems. Flatter-lying eolian sand sheets may be found along the margins of dune systems.<ref name=Kocurekandnielson_1986>Kocurek, G., and J. Nielson, 1986, [http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3091.1986.tb00983.x/abstract Conditions favourable for the formation of warm-climate eolian sand sheets]: Sedimentology, v. 33, no. 6, p. 795–816.</ref>

In deserts, dune sediments aggrade laterally and vertically as large-scale sand blankets. These may be very thick (more than 300 m [1000 ft]), and cover hundreds of square kilometers.<ref name=Richardsonetal_1988a>Richardson, J. G., J. B. Sangree, and R. M. Sneider, 1988, Eolian dunes: Journal of Petroleum Technology, v. 40, no. 1, p. 11–12.</ref> Internally, dunes comprise thick, cross-bedded intervals of well-rounded, well-sorted sandstones. They are normally the most productive lithofacies in eolian reservoir systems. Flatter-lying eolian sand sheets may be found along the margins of dune systems.<ref name=Kocurekandnielson_1986>Kocurek, G., and J. Nielson, 1986, [http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3091.1986.tb00983.x/abstract Conditions favourable for the formation of warm-climate eolian sand sheets]: Sedimentology, v. 33, no. 6, p. 795–816.</ref>

Interdune and fluvial sediments generally show poorer reservoir characteristics by comparison to dune lithofacies. They are poorly sorted and are more likely to contain evaporite cements. Intercalated fine-grained sand and silt laminations together with diagenetic cementation tend to produce reservoir intervals with very poor vertical permeability. Nagtegaal<ref name=Nagtegaal_1979>Nagtegaal, P. J. C., 1979, [http://onlinelibrary.wiley.com/doi/10.1111/j.1747-5457.1979.tb00699.x/abstract Relationship of facies and reservoir quality in Rotliegends desert sandstones, southern North Sea region]: Journal of Petroleum Geology, v. 2, p. 145–158.</ref> used multivariate analysis to determine the factors controlling the porosity of eolian sediments from the Permian of the southern North Sea. He found that the main control on porosity is grain sorting, which varies from well sorted in dune sandstones to less well sorted in the other associated sediments. The relationship between original sedimentary texture and porosity has survived even after extensive diagenesis. The very poor permeability characteristics of interdune sediments are commonly reported. Lindquist<ref name=Lindquist_1983>Lindquist, S. J., 1983, [https://www.onepetro.org/journal-paper/SPE-10993-PA Nugget Formation reservoir characteristics affecting production in the overthrust belt of southwestern Wyoming]: Journal of Petroleum Technology, v. 35, no. 7, p. 1355–1365.</ref> found a contrast in permeability of four to five orders of magnitude between interdune and dune deposits in the Nugget Sandstone of southwestern Wyoming.

Interdune and fluvial sediments generally show poorer reservoir characteristics by comparison to dune lithofacies. They are poorly sorted and are more likely to contain evaporite cements. Intercalated fine-grained sand and silt laminations together with diagenetic cementation tend to produce reservoir intervals with very poor vertical permeability. Nagtegaal<ref name=Nagtegaal_1979>Nagtegaal, P. J. C., 1979, [http://onlinelibrary.wiley.com/doi/10.1111/j.1747-5457.1979.tb00699.x/abstract Relationship of facies and reservoir quality in Rotliegends desert sandstones, southern North Sea region]: Journal of Petroleum Geology, v. 2, p. 145–158.</ref> used multivariate analysis to determine the factors controlling the porosity of eolian sediments from the Permian of the southern North Sea. He found that the main control on porosity is grain sorting, which varies from well sorted in dune sandstones to less well sorted in the other associated sediments. The relationship between original sedimentary texture and porosity has survived even after extensive [[diagenesis]]. The very poor permeability characteristics of interdune sediments are commonly reported. Lindquist<ref name=Lindquist_1983>Lindquist, S. J., 1983, [https://www.onepetro.org/journal-paper/SPE-10993-PA Nugget Formation reservoir characteristics affecting production in the overthrust belt of southwestern Wyoming]: Journal of Petroleum Technology, v. 35, no. 7, p. 1355–1365.</ref> found a contrast in permeability of four to five orders of magnitude between interdune and dune deposits in the Nugget Sandstone of southwestern Wyoming.

==Geometry==

==Geometry==