EXPLORATION FOR SHALLOW NATURAL GAS IN NORTH DAKOTA BY FID FIELD SCREENING OF GROUND-WATER WELLS

Exploration for natural gas occurrences in ground-water wells completed within unconsolidated Pleistocene glacial sediments and Cretaceous bedrock of the Fox Hills and Hell Creek Formations reveal numerous potential occurrences of shallow natural gas in North Dakota, possibly providing insight into areas of gas generation, migration, and accumulation in the shallow (<1,524 m) subsurface. More than 3,000 wells throughout North Dakota were tested during the 2006 - 2009 field seasons for the occurrence of methane using portable flame-ionization-detector (FID) instrumentation. Ground-water observation wells within Steele, Renville, Bottineau, Emmons, Kidder, Stutsman, Rolette, Towner, Ward, Barnes, Morton, LaMoure, Burleigh, McHenry, Pierce, Sheridan, Benson, and Logan counties, along with ground-water observation and stock-supply wells in Oliver, Mercer, Dunn, Billings, Stark, Slope, McLean, Traill, Griggs, Ransom, Richland and Sargent counties, have been field screened. Over 740 occurrences have been documented with FID responses ranging from 0.2 ppm to 50,000 ppm (5%), as methane in air. Preliminary assessments indicate that the majority of documented methane occurrences continue to be associated with the presence of lignite, either as detritus within the aquifer sedimentary matrix, or as stratiform beds within the monitored interval. These results suggest localized shallow methanogenesis along with potential migration and accumulation from underlying organic-laden Cretaceous sediments.