CALGARY -- TransCanada Corp. is investing $2.4 billion to expand its NGTL natural gas system in Western Canada as growing production in the region has filled existing capacity and battered prices.

The company said Thursday that the decision to expand NGTL comes after it recently completed an oversubscribed open season, with shippers committing to one billion cubic feet per day of expansion capacity for an average of almost 29 years.

"The successful open season shows strong industry support to significantly expand transmission capacity out of the basin and improve market connectivity for Canadian natural gas production," said company chief executive Russ Girling in a statement.

The NGTL system is a dense web of pipeline that covers much of Alberta and runs into northeastern B.C., acting as a gathering system for producers in some of the richest natural gas basins on the continent.

Producers in the region have, however, been victims of their own success in unlocking the shale gas in areas like the Montney and Deep Basin, as pipeline constraints and lack of demand in some markets have hit prices that have even strayed into negative territory.

"If you imagine Alberta today as a sink and the tap's on, right now the sink is filling up faster than it can drain," said Brook Papau, managing director of RS Energy Group.

Traditional export routes to California and the U.S. Midwest, as well as using the gas in province, are full-up, said Papau, leaving producers to look to Eastern Canada to find better prices.

TransCanada said its investment in the NGTL system will help link more production to its Mainline system that runs to Ontario and which still has significant untapped capacity.

The expansion program will include approximately 375 kilometres of large diameter pipeline, compression facilities, meter stations and other associated facilities.

The company has already alleviated some pressure in the region after reaching long-term fixed price agreements last year with shippers on its Mainline, and said Thursday it continues to look at the potential of further expanding natural gas shipping on the pipeline.

"We continue to work diligently with industry to facilitate economic access for their natural gas to key export markets, including access to Eastern Canada and the U.S. Northeast through TransCanada's Canadian Mainline and downstream systems," said Girling.

TransCanada would have to invest some capital to restore the extra capacity in the Mainline, but another open season on the pipeline would be well-received, said energy analyst Ed Kallio, principal at Eau Claire Energy Advisory, Inc.

"I have no doubt that if they do an open season it will be very highly subscribed."

Producers have been scrambling to find alternatives after West Coast liquefied natural gas projects have failed to emerge, said Kallio, while producers haven't cut back on production because the shale formations are also yielding valuable liquids used to dilute thick bitumen.

"Those high value liquids are driving activity, and the natural gas comes along with it."

TransCanada said it expects to file a project description with the National Energy Board by the second quarter of this year to start the review process and hopes to begin construction on the NGTL expansion in 2019.

The Calgary-based company reported net income attributable to shareholders of $861 million or 98 cents per share in the fourth-quarter of 2017, compared to a loss of $358 million or 43 cents per share in the same period a year earlier.

Fourth-quarter earnings were boosted by a number of one-time items, including an $804 million recovery of deferred income taxes as a result of U.S. tax reform.

The company said it continues to make progress on its Keystone XL pipeline project after announcing sufficient shipper support in January but has still held back on officially sanctioning the project.

TransCanada has said it is however working on construction preparation as well as new landowner agreements in Nebraska and general permitting