Changes

===Stratigraphic cross sections===

===Stratigraphic cross sections===

Lateral variability in facies relationships, and thus reservoir continuity and heterogeneity, are best determined from the construction of stratigraphic cross sections (see [[Geological cross section]]s). An example of a cross section through part of a tight gas reservoir is shown in Figure 2. Facies interpretations are based on [[core description]]s and extrapolation of log signatures for each cored facies to adjacent uncored wells. Distributary channel sandstones form the reservoirs, and bay, marsh, and crevasse splay mudstones form the seal. The lack of production in the two wells to the east is attributed to the pinching out of these mudstone facies and substantiates its importance as a stratigraphic seal. Note the laterally discontinuous nature of individual reservoir sandstone beds as depicted in the cross section.

Lateral variability in facies relationships, and thus reservoir continuity and heterogeneity, are best determined from the construction of stratigraphic cross sections (see [[Geological cross sections]]). An example of a cross section through part of a tight gas reservoir is shown in Figure 2. Facies interpretations are based on [[core description]]s and extrapolation of log signatures for each cored facies to adjacent uncored wells. Distributary channel sandstones form the reservoirs, and bay, marsh, and crevasse splay mudstones form the seal. The lack of production in the two wells to the east is attributed to the pinching out of these mudstone facies and substantiates its importance as a stratigraphic seal. Note the laterally discontinuous nature of individual reservoir sandstone beds as depicted in the cross section.

[[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 <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 <ref name=pt06r93 />.)]]