Geomicrobial Prospecting for Microseepage in the Ramu Basin, Papua New Guinea

Ramsay Barret, James D. Tucker

Geomicrobial prospecting was employed to evaluate the hydrocarbon potential of the Banam anticline in the Ramu Basin, Papau New Guinea. The Banam anticline is a conspicuous surface antiform measuring over 8 × 25 km. The geomicrobial technology employed in this survey measures the populations of butane indicating microorganisms in the shallow soils. The light hydrocarbons needed for microbial activity have migrated upwards along macro/microseeps from subsurface hydrocarbon accumulations. Four separate traverses, totaling 55 kilometers, were geologically mapped and sampled for microbial analysis. Two parallel dip traverses 8 km apart were sampled over the entire width of the anticline. The results indicate both traverses exhibit microbial counts well above background o er the crest of the structure and are clearly correlative. The highest microbial counts occur on the surface expressions of parallel faults which can be mapped down the entire length of the anticline. A third line was designed to cross an area with numerous gas seeps of biogenic origin (defined as >98% methane and carbon isotope values of <-55). The microbial counts over this methane seep area registered no increases. This strongly suggests the elevated, butane indicating microbial populations over the Banam Anticline demonstrate the presence of thermogenicly derived, heavier hydrocarbons. The fourth regional traverse reflected background microbial counts with occasional anomalous peaks which are associated with mapped faults. Geomicrobial prospecting used in conjunction with geolo ical mapping has proved to be a useful lead tool in helping to evaluate the potential hydrocarbon accumulations in remote areas prior to seismic.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995