Natural gas has been turning up in North Dakota water wells for generations, and for the last four years geologists there have been studying its occurrence in observation water wells with the possibility in mind that it could be a viable commercial resource.
"It's been fairly well documented in a lot of the older survey publications and historical records that a lot of folks in North Dakota, especially around the turn of the century, had documented gas in their water wells....Just from drilling and pumping their well, they noticed they had nuisance gas," geologist Fred Anderson of the North Dakota Geological Survey (NDGS) told NGI's Shale Daily.
In fact, in years past North Dakotans used to capture some of the gas from their water wells and use it for heating, Anderson said.
"That kind of gave us the idea, 'Hey, this occurred in the past and really not many folks had taken necessarily a hard look at it. Could it be occurring now?' So we decided to kind of take existing field equipment that we knew works for testing for natural gas and other organics and put it to use in the field and see if we couldn't find something by scanning the observation well network throughout North Dakota."
The researchers found gas -- 905 occurrences in observation wells in 52 of North Dakota's 53 counties -- but where it's coming from has yet to be determined.
"As a result of this project, several significant shallow gas occurrences were discovered across the state," Anderson wrote in the January NDGS newsletter. "Gas was detected in both the oil- and coal-producing counties in the west as well as the eastern counties where fossil fuel resources are sparse or absent altogether. The geologic and hydrologic information collected from these shallow gas occurrences is providing insights and clues into the origins of natural gas in these areas. To date, the NDGS has published 75 maps and reports that were derived from the information generated from this project. Several more publications are forthcoming as we continue to investigate North Dakota's potential for shallow natural gas."
One possibility is that the gas is migrating from the shallow shale bedrock. Another is that the gas is occurring within the aquifer itself.
"In some of the aquifer sediments in North Dakota we have what are called detrital lignites, or detrital coal, and that can serve as a substrate for methanogens, or the bacteria that can produce shallow biogenic gas," Anderson said. "That's the kind of natural condition that we've observed throughout primarily eastern north Dakota and throughout the state. But the geology is complex enough in North Dakota that we think there's a variety of things going on that could be responsible for sourcing, so we're still trying to determine what those geologic conditions might be."
NDGS recently completed the first statewide reconnaissance of potential shallow gas occurrences in ground-water wells. The report, "Shallow Gas Field Screening in North Dakota: Field Data Report (2009 & 2010) for Selected Counties," is available from the NDGS website.
Anderson said NDGS has asked the North Dakota legislature a "nominal" amount of funding to cover the project's next steps, which include trying to determine the origin of the gas. The geologist said he would like to begin the work this summer and have some answers from it in about a year.