* December WCS last at $32/bbl under WTI
* Synthetic for December at $6.85 under WTI
* Prices drop as Enbridge apportions pipeline space
CALGARY, Alberta, Nov 15 (Reuters) - Canadian cash crude prices weakened again on Thursday as Enbridge Inc unexpectedly limited shipments on two of its major oil export lines to the United States.
Western Canada Select heavy blend for December delivery last traded at $32.00 per barrel under the West Texas Intermediate benchmark, compared with the Wednesday settlement price of $30 per barrel under WTI, according to Shorcan Energy Brokers.
December light synthetic crude from the oil sands, which settled on Wednesday at $6 per barrel under WTI, was last seen at $6.85 below the benchmark.
Enbridge apportioned its 796,000 barrel per day Line 4, which takes crude from Edmonton, Alberta, to Superior, Wisconsin, and the 450,000 bpd Line 67, which runs from Hardisty, Alberta, to Superior, by 18 percent for the remainder of the month.
Canadian crude differentials had already widened after TransCanada Corp declared force majeure on some shipments on its 590,000 bpd Keystone pipeline as weekend power outages in Manitoba cut capacity on the line for three days, backing up crude supplies in Alberta.
"Prices fall when you can't get barrels into the system," a market source said.
Maintenance at some U.S. refineries has also cut demand for Canadian crude and widened differentials, which were at half current levels in mid-October.
BP Plc earlier this month shut a crude unit at its 337,000 bpd Whiting, Indiana, refinery, as it completes the final stage of a $4 billion project to increase the amount of Canadian heavy crudes it can process.
As well, Phillips 66 has been carrying out maintenance on its 362,000 bpd Wood River, Illinois, refinery, further limiting the need for Canadian crude. Sources said on Thursday that the work is complete and the affected units are beginning to be restarted.