Hydrocarbon Microseepage: A Significant but Underutilized Geologic Principle with Broad Applications for Petroleum Exploration and Production

It is well documented that mature source rocks and most oil and gas accumulations leak hydrocarbons,that this leakage (or microseepage)is widespread, predominantly vertical, and is dynamic. Hydrocarbon microseepage occurs in all petroleum basins, and forms the basis for most geochemical, microbiological, and non-seismic geophysical hydrocarbon detection methods.

The surface manifestations of hydrocarbon microseepage can take many forms including (1) anomalous hydrocarbon concentrations in soils, sediments, waters, and atmosphere;(2) microbiological anomalies;(3)mineralogic changes such as formation of calcite, pyrite, uranium, elemental sulfur, and magnetic iron oxides and sulfides; (4)bleaching of redbeds; (5) clay mineral changes; (6)acoustic anomalies;(7) radiation anomalies; (8) electrochemical changes;and(9 )biogeochemical changes and geobotanical anomalies.

Applications of hydrocarbon microseepage to petroleum exploration and production include (1) documenting that oil/gas has been generated in frontier basins; (2) high-grading leads and prospects on basis of likely hydrocarbon charge; (3) identifying presence of by-passed pay in old or abandoned fields;(4) monitoring hydrocarbon drainage due to production in producing fields or waterfloods; and (5) identifying sweet spots in unconventional resource plays.

Seismic data will continue to be unsurpassed for imaging trap and reservoir geometry, but in many geologic settings seismic yields no information about whether a trap is charged with hydrocarbons. A review of 2700 US and international exploration wells - all drilled after completion of microseepage surveys - documents that 82% of wells on prospects with a microseepage anomaly were completed as oil or gas discoveries; in contrast, only 11% of wells drilled on prospects with no associated seepage anomaly resulted in a discovery. When hydrocarbon microseepage data is properly acquired and interpreted, it can significantly reduce exploration risks and costs by improving success rates and shortening development time.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California