Changes

===Petrological and mineralogical assessment===

===Petrological and mineralogical assessment===

A petrological thin section, SEM, and X-ray diffraction analysis of core samples from each sedimentary facies is highly recommended in any geological evaluation of tight gas reservoirs (see [[Thin section analysis]] and [[SEM, XRD, CL, and XF methods]]). Analyses of several tight gas sandstones have attributed the low average permeabilities, and thus poor reservoir quality, to the presence of authigenic or detrital clays or cements.<ref name=pt06r82>Masters, J. A., 1984, Elm worth—Case Study of a Deep Basin Gas Field: AAPG Memoir 38, 316 p.</ref><ref name=pt06r133 /> Since the occurrence of these constituents can be quite variable within a depositional system and can be facies dependent, a broad range of porosities, permeabilities, and gas saturation values often exists in any reservoir (Figure 4). Identifying and mapping those units of greatest reservoir potential are key to a successful evaluation.

[[file:evaluating-tight-gas-reservoirs_fig4.png|thumb|{{figure number|4}}Correlation of sedimentary facies and lithologies to petrographic reservoir quality. Distribution of reservoir facies in the subsurface Is compiled from observations of cores, well logs, and cross sections. (From <ref name=pt06r93 />.)]]

[[file:evaluating-tight-gas-reservoirs_fig4.png|thumb|{{figure number|4}}Correlation of sedimentary facies and lithologies to petrographic reservoir quality. Distribution of reservoir facies in the subsurface Is compiled from observations of cores, well logs, and cross sections. (From <ref name=pt06r93 />.)]]

A petrological thin section, SEM, and X-ray diffraction analysis of core samples from each sedimentary facies is highly recommended in any geological evaluation of tight gas reservoirs (see [[Thin section analysis]] and [[SEM, XRD, CL, and XF methods]]). Analyses of several tight gas sandstones have attributed the low average permeabilities, and thus poor reservoir quality, to the presence of authigenic or detrital clays or cements.<ref name=pt06r82>Masters, J. A., 1984, Elm worth—Case Study of a Deep Basin Gas Field: [http://store.aapg.org/detail.aspx?id=67 AAPG Memoir 38], 316 p.</ref><ref name=pt06r133 /> Since the occurrence of these constituents can be quite variable within a depositional system and can be facies dependent, a broad range of porosities, permeabilities, and gas saturation values often exists in any reservoir ([:file:evaluating-tight-gas-reservoirs_fig4.png|Figure 4]]). Identifying and mapping those units of greatest reservoir potential are key to a successful evaluation.

The common association of clays with tight gas reservoirs makes them very sensitive to formation damage. Hydraulic fracturing is therefore the least destructive and most preferred well [[stimulation]] technique.

The common association of clays with tight gas reservoirs makes them very sensitive to formation damage. Hydraulic fracturing is therefore the least destructive and most preferred well [[stimulation]] technique.