U.S. Geological Survey Open-File Report 03-041
Version 1.0

Figures
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Figure 1.  General location map of the North Slope of Alaska showing the location of NPRA, related oil and gas fields, and selected geologic provinces.

Figure 2.  Stratigraphic chart showing major reservoir rock units within and adjacent to NPRA. 

Figure 3.  The hydrocarbon composition, shown as gas dryness, C₁/C₂₊, plotted as a function of depth for the three major stratigraphic sequences on the North Slope.  A: Brookian reservoirs (green), B:  Beaufortian reservoirs (blue), C:  Ellesmerian reservoirs (red). 

Figure 4.  The hydrocarbon composition, shown as gas dryness, C₁/C₂₊, plotted as a function of depth for known oil and gas fields (A) and all samples including fields and individual wells outside of known accumulations (B).  Color coding as in Figure 3.

Figure 5.  The CO₂ content of North Slope gases as a function of depth, stratigraphic sequence, and the occurrence of samples within known fields (A) and all samples including non-field wells (B).

Figure 6.  The N₂ content of North Slope gases as a function of depth, stratigraphic sequence, and the occurrence of samples within known fields or in non-field wells. 

Figure 7.  Carbon isotopic composition of methane as a function of depth with samples color coded for stratigraphic sequence of the reservoir.

Figure 8.  Carbon isotopic composition of methane as a function of hydrocarbon gas composition, shown as gas dryness, C₁/C₂₊. 

Figure 9.  The carbon and hydrogen isotopic composition of methane with fields labeled according to Schoell (Schoell, 1983 .

Figure 10.  The natural gas plot (Chung, Gormly, and Squires, 1988) showing the carbon isotopic composition of individual hydrocarbons as a function of the carbon number (C_n) of the hydrocarbon.  Gases from Walakpa, Wolf Creek, and Umiat fields and one laboratory generated gas from the Hue Shale (see Figure 10E) are shown in 10A. Figure 10B shows gases from the South Barrow and East Barrow fields.  Gases from the greater Prudhoe Bay area are shown in figure 10C.  Additional gases from the greater Prudhoe Bay area and the adjacent fields on the western edge of the greater Kuparuk River field (Masterson, 2001) are shown in 10D.  Gases generated in the laboratory during hydrous pyrolysis of North Slope source rocks are shown in Figure 10E.  See text for discussion.

Figure 11.  Carbon dioxide concentration as a function of the carbon isotopic composition of CO₂ with samples distinguished by stratigraphic sequence of the reservoir.

Figure 12.  Carbon dioxide concentration as a function of the difference in carbon isotopic composition of ethane (C₂) and propane (C₃).  Arrows indicate different paths for gases altered by microbial oxidation of ethane and propane.