* Three major lines face mid-month apportionment
* Enbridge blames series of operational issues
* WCS heavy quoted at $38 under WTI
CALGARY, Alberta, Jan 10 (Reuters) - Enbridge Inc has imposed mid-month rationing on three of its Canada-U.S. oil pipelines, exacerbating an already-tight export capacity situation that has led to deep discounts on Canadian heavy crude oil.
Enbridge, the largest transporter of Canadian oil, said it was forced to make the move after a series of operational issues across its system threatened to force large volumes scheduled to move this month to be held over into February, according to sources that have seen a company memo to shippers.
The 796,000 barrel per day Line 4, between Edmonton, Alberta, and Superior, Wisconsin; and 450,000 bpd Line 67, between Hardisty, Alberta, and Superior, are apportioned at 10 percent. Line 6A, which can carry 609,000 bpd between Superior and Griffith, Indiana, is apportioned at 16 percent.
Enbridge normally sets apportionment levels monthly. It will set new limits for February volumes based on shipper nominations following the close of this month's trading period.
The company blamed the mid-month pipeline rationing for the first two pipelines on power outages in Manitoba and an electrical equipment failure at Edmonton in late December, according to the sources.
Apportionment on 6A is due to unplanned outages on that line and the adjoining 6B, terminal problems where the two lines connect, as well as high inventory levels at Chicago.
Rising volumes of heavy crude and limited pipeline capacity to move it to major markets has pressured Canadian oil prices over the past two months, hitting the bottom lines of producers and even prompting the Alberta and Canadian governments to warn of the impact on the economy.
Western Canada Select heavy blend from February last sold for $38 a barrel under benchmark West Texas Intermediate, compared with $37.10 under WTI on Wednesday, according to Shorcan Energy Brokers.