Abstract
Naturally occurring radioactive materials (NORM), has been observed in conjunction with natural gas production operations in certain Antrim gas wells in northern Michigan. Chemical analyses on field derived water samples from Antrim wells were compared with geologic and engineering Parameters using geologic and completion data in an attempt to determine the source and mechanisms associated with these observations.
The sources of the scale are unknown and potentially hazardous if radioactive levels exceed OSHA Standards. Mitigation measures could be costly and jeopardize the economic viability of the play.
NORM Antrim gas production facilities tested were found to be associated with barium sulfate scale which formed in central separators as well as in individual wells. Low levels of barium were found in waters from most wells, while sulfate was found in only some wells. Two models were developed based on the results of this study. One model assumes that sulfate is migrating from other formations. The other model assumes that the cause of the problems may be due to the mixing of waters and chemical reaction with oxygen, carbon dioxide, and/or bacteria either contained in the Antrim gas or migration from the Antrim outcrop a few miles north of the producing fields. The oxygen and bacteria, contained in the fresh water, may be reacting with pyrite to cause the formation of sulfate. Sulfate in tum is reacting with the naturally occurring barium and radionuclides to form the barium sulfate scale that is being observed in the field. However, from a Chemistry mass balance view, additional oxygen is required than can be supported by fluid migration alone. Other sources of oxygen would have to be introduced.
