Changes

[[file:evaluating-tight-gas-reservoirs_fig2.png|thumb|{{figure number|2}}The depositional dip-oriented cross section through the Frontier Formation, Moxa arch area, Wyoming, showing facies relationships and inferred geometries. (Modified from Moslow and Tillman.<ref name=pt06r93 />)]]

[[file:evaluating-tight-gas-reservoirs_fig2.png|thumb|{{figure number|2}}The depositional dip-oriented cross section through the Frontier Formation, Moxa arch area, Wyoming, showing facies relationships and inferred geometries. (Modified from Moslow and Tillman.<ref name=pt06r93 />)]]

Documenting characteristic log signatures for reservoir facies can provide a valuable tool for constructing regional cross sections, determining facies relationships, and extrapolating reservoir geometries in areas of minimal or nonexistent core control (see [[Quick-look lithology from logs]]). Commonly, the gamma ray log provides the most distinctive log signature for individual facies ([[:file:evaluating-tight-gas-reservoirs_fig1.png|Figure 1]]). For low permeability gas reservoirs, crossover of the compensated neutron-formation density logs is the most reliable well log for indicating gas-saturated and porous intervals and for determining which intervals in the reservoir should be perforated and/or stimulated by hydraulic fracturing.

Documenting characteristic log signatures for reservoir facies can provide a valuable tool for constructing regional cross sections, determining facies relationships, and extrapolating reservoir geometries in areas of minimal or nonexistent core control (see [[Quick-look lithology from logs]]). Commonly, the [[Basic open hole tools#Gamma ray|gamma ray]] log provides the most distinctive log signature for individual facies ([[:file:evaluating-tight-gas-reservoirs_fig1.png|Figure 1]]). For low permeability gas reservoirs, crossover of the compensated neutron-formation density logs is the most reliable well log for indicating gas-saturated and porous intervals and for determining which intervals in the reservoir should be perforated and/or stimulated by hydraulic fracturing.

===Stratigraphic cross sections===

===Stratigraphic cross sections===