The Canadian Energy Research Institute says growth in oilsands production over the next 20 years is expected to be slower than previously forecast, despite falling project construction costs.

In an updated study, the Calgary-based think-tank says it expects total oilsands output to grow from about three million barrels per day in 2018 to between 4.1 million and 5.8 million bpd in 2039.

In its reference or base case, CERI predicts bitumen crude output will grow by an average of 80,000 bpd or just over two per cent per year over the next 20 years, down from last year's estimate of three per cent growth, to about 4.7 million bpd.

It calculates overall capital spending will average $16.5 billion per year but notes risk factors including the recent tendency of the industry to defer or cancel projects, further success in cutting costs, uncertainty about Alberta's 100-megatonne cap on sector greenhouse gas emissions and the unknown future of export oil pipelines.

CERI says the slower growth will result in the industry staying well within the emissions cap, reaching 94 megatonnes by 2039 — under last year's forecast, the cap would have been reached by 2030.

It says the cost of building a new steam-driven oilsands project has fallen by 11 per cent to $40.61 per barrel of production, while an expansion project's cost has fallen by six per cent to $27.60 per barrel.