sentences:  Few Canadian refineries can process more than small amounts of heavy oil, so production has traditionally gone to United States asphalt plants.This changed in the 1980s, however, with the announcement that construction would begin on two heavy oil upgraders.Like the plants at Syncrude, Suncor and Shell's Scotford facility near Edmonton, these refinery-like operations turn heavy oil and bitumen into lighter and lower-sulfur, more desirable crude.