It has been over 75 years since German and Russian scientists first identified anomalous methane seeps above gas fields in the mid-1930's. In the United States a few years later, Rosaire and Horvitz extracted hydrocarbon gases from soil samples over oil and gas deposits. Leo Horvitz, a pioneer in the field of near-surface geochemical prospecting for oil and gas, presented his final paper titled “Hydrocarbon Geochemical Exploration after Fifty Years” at the Symposium on Unconventional Methods in Exploration for Petroleum held by the Institute for Earth and Man, Southern Methodist University in 1985. At the same symposium Leigh Price discussed the now abundant evidence and compared the many theories that attempted to explain vertical migration concluding with a now generally agreed upon gravity driven micro-bubble theory. This theory best explained the near vertical outline of most anomaly patterns found over petroleum deposits and the vertical migration “chimney” seen by both chemical and geophysical methods. Klusman modeled these migration mechanisms and calculated the rate of accent of gases which further confirmed the vertical nature of micro-seepage. Higher resolution geophysical data has confirmed the presence of the migration paths to the surface. Two AAPG Hedberg Research Conferences have been held presenting many of the theories, methods and debates on the topic. While some of the theories and techniques were controversial in the first half of the 20th century, vertical migration and micro-seepage is now widely accepted and many geochemical and remote sensing exploration methods are applied by the exploration industry to confirm the presence of hydrocarbon charged reservoirs. Instrument sensitivity has gained several orders of magnitude improving direct detection of micro-seeps in the near surface and now includes airborne methods. Complex hydrocarbon mixtures can now be differentiated, and numerous co-migrating elements can also be detected in the near-surface. Indirect methods identify many complex alteration, red-ox, electrical, magnetic and biological affects that result from the migrating hydrocarbons. The ability to detect most compounds at background levels has now introduced the requirement of sophisticated multivariate statistical analysis to distinguish background from anomalous conditions. The current methodologies used today will along with their advantages and disadvantages will be discussed along with anticipated future developments.
AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014