Changes

[[file:evaluating-tight-gas-reservoirs_fig1.png|left|thumb|{{figure number|1}}A cored sequence of tight gas reservoir facies and correlations to electric log responses of the Frontier Formation, Green River basin, Wyoming. Lithologies and sedimentary characteristics are summarized in this kind of description; facies and environments of deposition are shown on the right. (From Moslow and Tillman.<ref name=pt06r93>Moslow, T. F., Tillman, R. W., 1986, [http://archives.datapages.com/data/specpubs/resmi1/data/a066/a066/0001/0250/0271.htm Sedimentary facies and reservoir characteristics of Frontier Formation sandstones, southwestern Wyoming], ''in'' Spencer, C. W., Mast, R. F., eds., Low Permeability Sandstone Reservoirs: [http://archives.datapages.com/data/alt-browse/aapg-special-volumes/sg24.htm Studies in Geology Series 24], p. 271–295.</ref>)]]

[[file:evaluating-tight-gas-reservoirs_fig1.png|left|thumb|{{figure number|1}}A cored sequence of tight gas reservoir facies and correlations to electric log responses of the Frontier Formation, Green River basin, Wyoming. Lithologies and sedimentary characteristics are summarized in this kind of description; facies and environments of deposition are shown on the right. (From Moslow and Tillman.<ref name=pt06r93>Moslow, T. F., Tillman, R. W., 1986, [http://archives.datapages.com/data/specpubs/resmi1/data/a066/a066/0001/0250/0271.htm Sedimentary facies and reservoir characteristics of Frontier Formation sandstones, southwestern Wyoming], ''in'' Spencer, C. W., Mast, R. F., eds., Low Permeability Sandstone Reservoirs: [http://archives.datapages.com/data/alt-browse/aapg-special-volumes/sg24.htm Studies in Geology Series 24], p. 271–295.</ref>)]]

The extremely low permeability of tight gas reservoirs severely restricts the ability of gas to migrate appreciable distances. Consequently, the most important geological characteristic of this type of reservoir is the nature and distribution of [[porosity]] and permeability (Table 1). The most common reason for the minimal permeabilities is the occlusion of interstitial pore throats by detrital or authigenic clays or cement (see [[Rock-Water interactions: formation damage]]). Thus, a proper geological evaluation of tight gas reservoirs requires a multidisciplinary approach to assess the depositional and diagenetic controls on [[reservoir quality]] and heterogeneity.

The extremely low permeability of tight gas reservoirs severely restricts the ability of gas to migrate appreciable distances. Consequently, the most important geological characteristic of this type of reservoir is the nature and distribution of [[porosity]] and permeability (Table 1). The most common reason for the minimal permeabilities is the occlusion of interstitial pore throats by detrital or authigenic clays or cement (see [[Rock-water reaction: formation damage]]). Thus, a proper geological evaluation of tight gas reservoirs requires a multidisciplinary approach to assess the depositional and diagenetic controls on [[reservoir quality]] and heterogeneity.

===Facies determinations===

===Facies determinations===