WATFORD CITY, ND (KDAL) - An oil field accident on Saturday in western North Dakota claimed the life of a Duluth man.  49 year old Mike Krajewski was working at a hydraulic fracturing site north of Watford City.  The early investigation shows that as a valve was being turned, a pipe disconnected and hit Krajewski in the head.  OSHA is expected to conduct a detailed investigation into the accident.