The upper Cretaceous Niobrara formation is widely known to be a highly commercial hydrocarbon producer, principally in Colorado and Wyoming.
Today, an intriguing program is afoot to assess the hydrocarbon potential of the Niobrara in south-central South Dakota.
Even though the formation is not ordinarily produced in this region, shows of natural gas are not unusual there. Some wells, in fact, are said to have produced gas for individual farms for as long as 20 years.
The current assessment program was initiated in 2012, when the American Indian Higher Education Consortium funded a cooperative education program between the Sinte Gleska University on the Rosebud Sioux Reservation in South Dakota and the South Dakota School of Mines and Technology (SDSM&T).
The aim was to involve Native American students in the energy resource evaluation process to provide educational opportunities that might result in energy exploration and production careers, according to AAPG member Daniel Soeder, research geologist at the U.S. Department of Energy’s National Energy Technology Laboratory (NETL) in Morgantown, W.Va.
“Potential benefits to the Sicangu Lakota Oyate from the development of such a resource could include more jobs, economic development and an affordable energy source,” Soeder said.
“The NETL has contributed in-kind geological and geochemical analyses and expertise to the project,” he noted.
He explained that the objectives were to characterize the Niobrara in South Dakota in terms of stratigraphy, composition, depositional environments, reservoir properties, regional trends, structural features, potential productive horizons and areas.
Less Can Be More
The strategy, overall, was designed to use geological data and models to determine gas-in-place and EUR.
Soeder noted that there were no public drill cores available for study in the proximity of the reservation.
Not to worry.
The project participants undertook a trend analysis using Niobrara drill cores from Nebraska, Wyoming and western South Dakota, which were sampled at the USGS core library in Denver.
“The regional samples indicated that the Niobrara contains organic matter content as high as 6 percent, derived from Type II kerogen, and thermal maturity in the biogenic gas window,” Soeder said.
“Porosity in the carbonate units may hold significant quantities of shallow gas,” he added.
Meanwhile, the Department of Environment and Natural Resources Geological Survey in South Dakota is acquiring a new core from a well relatively close to the reservation. This might provide additional information given its proximal location.
Whatever the final conclusions of the study, the shallow depth of the Niobrara at Rosebud negates the possibility of production of the large volumes of gas desired by the commercial energy companies.
Less can be more, in some situations.
“The relatively inexpensive drilling costs and modest expected production may provide the tribe with a secure and economical energy supply,” Soeder said, “suggesting a smaller-scale approach for unconventional gas development that could be applied elsewhere.”