Microseepage of hydrocarbons can cause anomalies in surface geochemistry. When potential oil fields are surveyed, the shapes of these anomalies can be used to identify the location of the subsurface hydrocarbon source. Such geochemical anomalies only show the end point of a seepage route, which can be vertical in areas with simple geological features, allowing straightforward identification of the source. However, in more complex geologies seepages can traverse laterally to over 100km from the source, complicating the process of locating it and requiring extensive geological knowledge.

Geochem1

Over the last 5 years ANE have been conducting geochemical surveys of our Namibian concession. We employed Geofrontiers, a Texas based geochemical exploration company to collect and analyse soil samples. Using acid extraction techniques, the presence of C1 (natural gas) through to C4 (liquefied petroleum gas) hydrocarbons were investigated. Their report found significant concentrations of these paraffins in a number of regions of the concession, up to 100 times the background concentration.

Geochem2

In a second round of tests, the ratios of methane to ethane and propane were examined in samples with particularly high concentrations. The ratios indicate that the hydrocarbons were produced by a thermogenic process (high temperatures at great depths) rather than through the biogenic processes which can create them at the surface. In addition, these ratios indicate that light crude is the most likely source from which the paraffins migrated to the surface.