Abstract: A Novel Microbial Survey Method for the Detection of Near Surface Hydrocarbon Microseepage

AUSNAUGH, JAMES M.

Detection of near surface soil alteration anomalies has been used for many years as a hydrocarbon exploration tool. The alteration effects, when reduced to the lowest common denominator, are attributed to hydrocarbon microseepage and the presence of bacteria. Various microbial surveying methods have been proposed and are being used today. These include the detection of ethane, propane, or butane consuming bacteria. Microbial populations increase over areas of active hydrocarbon microseepage, often forming an apical anomaly. Areas of high hydrocarbon flux, such as faults or fractures, yield a dramatic contrast relative to areas of minimal hydrocarbon seepage.

The proposed microbial method, which varies from others which rely on specific hydrocarbon consuming bacteria, uses non-specific aerobic bacteria that are ubiquitous in the near surface environment. As with other microbial methods, the bacteria population increases over the hydrocarbon seepage area. Bacteria counts are determined through a color change in the nutrient media. Light, or white, indicates the absence of bacteria while dark red indicates a significant number of microbes are present. Cultures are detected within 48 to 72 hours after exposure to the soil sample. Numeric values are assigned to each sample via image analysis of the exposed culture media. Due to ease of sampling, minimal analytical setup, and rapid detection, microbial surveys are an attractive alternative to other indirect near surface hydrocarbon detection methods.

AAPG Search and Discovery Article #90939©1997 AAPG Eastern Section and TSOP, Lexington, Kentucky