Changes

===Facies determinations===

===Facies determinations===

Since most tight gas reservoirs in North America are of detrital origin (shale, siltstone, and sandstone), primary processes of deposition, inferred from the examination of sedimentary characteristics in core, can have a strong impact on preserved porosity and permeability trends. An example of a sedimentological description and environmental interpretation of cored facies from a tight gas reservoir is shown in Figure 1.

[[file:evaluating-tight-gas-reservoirs_fig1.png|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 <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: Studies in Geology Series 24, p. 271–295.</ref>.)]]

[[file:evaluating-tight-gas-reservoirs_fig1.png|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 <ref name=pt06r93>Moslow, T. F., Tillman, R. W., 1986, Sedimentary facies and reservoir characteristics of Frontier Formation sandstones, southwestern Wyoming, ''in'' Spencer, C. W., Mast, R. F., eds., Low Permeability Sandstone Reservoirs: Studies in Geology Series 24, p. 271–295.</ref>.)]]

Since most tight gas reservoirs in North America are of detrital origin (shale, siltstone, and sandstone), primary processes of deposition, inferred from the examination of sedimentary characteristics in core, can have a strong impact on preserved porosity and permeability trends. An example of a sedimentological description and environmental interpretation of cored facies from a tight gas reservoir is shown in [[:file:evaluating-tight-gas-reservoirs_fig1.png|Figure 1]].

===Core to log correlations===

===Core to log correlations===