Changes

[[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 Moslow and Tillman.<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 Moslow and Tillman.<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.

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.