Changes

===Core to log correlations===

===Core to log correlations===

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.

Documenting characteristic log signatures for reservoir facies can provide a valuable tool for constructing regional [[cross section]]s, 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===