Fig. 5-1. Generation of gases with depth: C₂₊ represents hydrocarbons heavier than CH₄; N₂ is generated initially as NH₃.

Fig. 5-2. Genetic characterization of natural gases by compositional and isotopic variation: (a) formation of natural gas and petroleum in relation to maturity of organic matter; (b) relative concentration of C₂₊ hydrocarbons in relation to ¹³C in CH₄, with arrows indicating compositional changes due to shallow migration (Ms) and deep migration (Md) (reproduced with permission from Schoell, 1983a, 1983b). 

Fig. 5-3. Genetic characterization of natural gases by isotopic variation: (a) relative concentration of deuterium and ¹³C in CH₄; (b) relative concentration of ¹³C in CH₄ and in C₂H₅, with arrow Md indicating the result of mixing with isotopically-positive CH₄ from depth, and arrow Ms indicating the result of shallow mixing with isotopically-negative CH₄ of biogenic origin (reproduced with permission from Schoell, 1983a, 1983b).

Fig. 5-4. Experimental scheme for anaerobic decomposition of natural organic matter (from Kim and Douglas, 1972).

Fig. 5-5. Anaerobic microbial evolution of CH₄ upon decomposition of various organic substrates (reproduced with permission from Janezic, 1979)

Fig. 5-6. Geochemical methods of prospecting for petroleum and natural gas (reproduced with permission from Kartsev et al., 1959).

Fig. 5-7. Methane and total hydrocarbon gases in subsoil before and after an earthquake (reproduced with permission from Zorkin et al., 1977).

Fig. 5-8. Differentiation of methane (1) and heavy hydrocarbons (2) during migration from an artificial source (reproduced with permission from Sokolov, 1971 b).

Fig. 5-9. Arrival at a surface well of hydrocarbon gases following a subsurface coal-burn experiment at Rawlins, Wyoming (reproduced with permission from Jones and Thune, 1982).

Fig. 5-10. Changes in flux of propane concentration (dashed lines) with barometric pressure (solid line) and rainfall (shaded bars) at two surface sample sites over an underground propane storage reservoir.

Fig. 5-11. Propane concentrations and soil colour of augered samples along a traverse of sample sites over an underground propane storage reservoir.

Fig. 5-12. Relation of near-surface gases to deep faults and oil fields along a traverse in the San Joaquin Valley, California (reproduced with permission from Jones and Drozd, 1983).

Fig. 5-13. Relation of near-surface gases to proposed deep fault adjacent to Lost Hills oil field, San Joaquin Basin, California (reproduced with permission from Jones and Drozd, 1983).

Fig. 5-14. Variations in methane concentration in air above a petroleum reservoir (reproduced with permission  from Antropov et al., 1981).

Fig. 5-15. Variations in methane concentration in air as a result of seismic shock to the ground (reproduced with permission  from Antropov, 1981).

Fig. 5-16. Variations in methane concentration in air with crustal displacement in a seismically-active region (reproduced with permission  from Antropov et al., 1981).

Fig. 5-17. Typical mass spectra of gas and oil, R. Klusman personal communication.

Fig. 5-18.  Location of major basins in the USA (shaded) and surface geochemical surveys (black dots) carried out by Gulf Research and Development Company.

Fig. 5-19.  Soil gas sampling procedure used by Gulf Research and Development Company.

Fig. 5-20.  a) Frequency distribution of the sum of methane homologs in 3,500 samples from different types of reservoirs (reproduced with permission from Nikonov, 1971); b) Location of gas, oil, and condensate surveys.  Frequency distributions of hydrocarbons in soil gas over different basins: c) methane content (%C₁); d) methane:ethane ratio (C₁/C₂); e) propane:methane ratio (1000 x C₃/C₁); d) Pixler ratio diagram, Pixler (1969); f) Soil gas plotted on Pixler diagram; g) Reservoir gas analysis plotted on Pixler diagram, Verbanac, et al., (1982).

Fig. 5-21. Percent-methane in soil gas over the Sacramento and San Joaquin Basins, California.

Fig. 5-22. Well locations from USGS open file report offshore Louisiana (reproduced with permission from Rice, 1980).

Fig. 5-23.  Compositional crossplots of Rice's reservoir gas analysis.  The underlying color code was chosen to distinguish oil, oil-condensate, gas condensate and gas within Rice's Gulf of Mexico production data.

Fig. 5-24. Crossplots of the compositions of dissolved gases anomalies from offshore Louisiana reservoirs and sniffer surveys: a) Rice well gases; b) Typical marine sniffer gases anomalies; c) marine sniffer gases from a gas area; d) marine sniffer gases from an oil area.

Fig. 5-25. Stainless steel disaggregation mill used in headspace analysis

Fig. 5-26. Scheme for lithological classification of samples prior to interpretation of gases released by acid extraction (reproduced with permission from Poll, 1975).

Fig. 5-27. Comparative fluorescence spectra of nine crude oils of different gravity (reproduced with permission from Purvis et al., 1977)

Fig. 5-28. Fluorograms of reservoir hydrocarbons and corresponding hydrocarbons extracted from sediments in the Gulf of Mexico.  (Reproduced with permission from J. Brooks, GERG).

Fig. 5-29. Relation between fracture intensity and gas leakage: (a) plan showing lineament, fractures and gas sample sites;  (b) distribution of fracture intersections with distance from lineament; (c) distribution of anomalous gas sample sites with distance from lineament (reproduced with permission from Richers et al., 1986).

Fig. 5-30. Cross-section through the Lost River oil field, West Virginia, and profile of propane in soil gas (reproduced with permission from Matthews et al., 1984).

Fig. 5-31. Spatial distribution of soil gas hydrocarbons over Filo Morado oil field, Argentina; dot size indicates ethane concentration; dot color indicates C₁/C₂ ratio, green (oil), yellow (intermediate), and red (gas).

Fig. 5-32. Spatial distribution of soil gas hydrocarbons at Loma de La Lata oil and gas field, Argentina; dot size indicates ethane concentration; dot color indicates C₁/C₂ ratio, green (oil), yellow (intermediate),  and red (gas).

Fig. 5-33.  a) High Island Geochemical Sniffer Track Map for 1988 Sniffer Survey; b) Marine Compositional Crossplot for 1988 Sniffer Anomalies.

Fig. 5-34.  Profile of dissolved hydrocarbon data from High Island sniffer survey;  a) East-West Line A-B; b) South-North Line C-D; c) North-South-North Line E-F; d) Marine Compositional Crossplot for 1988 Sniffer Anomalies.

Fig. 5-35.  a) Methane Contour Map of Regional 1984 Soil Gas  Data, Railroad Valley, Nye County, Nevada; b) Propane Contour Map of Regional 1984 Soil Gas Data, Railroad Valley, Nye County, Nevada.

Fig.5-36.  Geological/Geochemical Seep Model Illustrating Possible Migration Pathways for Railroad Valley, Nevada.

Fig. 5-37. Ethane Color Compositional Dot Map for Regional 1984 Railroad Valley Soil Gas Data, Pixler Ratio Composition in inset.

Fig. 5-38.  Mapped Photolinears, Currant Detail Area, Jones et al. (1985).

Fig. 5-39. a) Methane Contour Map of 1985 Currant Detail, Soil Gas Data, Railroad Valley, Nye County, Nevada; b) Propane Contour Map of 1985 Currant Detail, Soil Gas Data, Railroad Valley, Nye County, Nevada.

Fig. 5-40. a) Ethane compositional dot map for 1985 Currant Detail, Railroad Valley, Nevada; b) Pixler-type diagram characterisation of anomalous soil gas hydrocarbons associated with known oil fields in Railroad Valley, Nevada; c) Methane/Ethane Scatter Plot for 1985 Currant Detail Soil Gas Data, Railroad Valley, Nye County, Nevada

Fig. 5-41. Comparison of Propane Contour Maps for a) 1984 and b) 1985 Soil Gas Data, Currant Detail Area Railroad Valley, Nye County, Nevada, Illustrating Importance of Sample Spacing.

Fig. 5-42.  Comparison of a) 1984 and b)1985 Ethane Color Dot Maps, Illustrating Repeatability of Soil Gas Compositional Data.

Fig. 5-43. Clear Creek, Ryckman Creek, and Whitney Canyon-Carter Creek Fields.

Fig. 5-44.  Composite cell map in which the Monte Carlo simulations have been applied to methane, ethane, and propane anomalies, highlighting the regions where all three of these gases are above their respective medians.