Page 162 - Geochemical Remote Sensing of The Sub-Surface

Light hydrocarbons for petroleum and gas prospecting 13 9

Fig. 5-5. Anaerobic microbial evolution of CH4 upon decomposition of various organic substrates.

Another approach was that taken by Coleman (1979), who studied both the chemical
and isotopic composition of glacial till gases in Illinois. Coleman obtained the same
result, finding that C2-C4 gases are not present in the glacial till gases in Illinois.
Coleman also determined 14C age dates on the gases and showed that the biogenic
methane varied from about 10,000 years to as much as 40,000 years in age. This is
particularly significant since it suggests that no bacterial generation of C2-C4
hydrocarbons occurs, either initially in test tubes or even within the first 40,000 years in
glacial till.

TABLE 5-11

Generation of C1-C4 hydrocarbons in vitro (average concentrations, ppm)

36~ 25~
Gas Inoculate Control Inoculate Control
Methane 14,862.000 3.416 4,814.000 2.003
Propane 0.081 0.073 0.051 0.050
i-butane 0.022 0.022 0.014 0.009
n-butane 0.055 0.060 0.038 0.033
Ethylene 5.101 1.670 2.310 0.434
Propylene 0.086 0.089 0.057 0.045