Foothills: The Future for Exploration

The Calgary exploration industry is faced with the major challenge of finding new gas reserves and developing them in a cost effective and sustainable manner to meet growing consumer demand. Natural gas consumption in North America is expected to climb from the current 25 Tcf a year to 30 Tcf a year by 2010. With the current gas reserves in North America at 250 Tcf*, the implication is that all the gas consumed after 2010 will have to be discovered and brought on production in the next 10 years. At present the reserve replacement is declining at 7% a year in Canada and 17% a year in North America.

One of the focus areas for the exploration industry to find large gas reserves is the Foothills - the gas prone area of the Western Canadian Sedimentary Basin dominated by overthrust tectonics. This describes a style of deformation where the rocks have been horizontally compressed or “shortened” into fold and fault dominated structures where low angle thrust faults are common. It is the predominant style in an area of 100,000 square miles in Western Canada that lies between the 49th parallel in the south and the Arctic Ocean in the north. It covers parts of Alberta, British Columbia, Yukon and the western Northwest Territories. The southern half of the Foothills has 40 Tcf of gas, of which 23 Tcf is marketable reserves. A total of 13 Tcf of gas have been produced from this area in the last 50 years.

The Foothills provide the oil and gas exploration industry of Western Canada with a unique opportunity for several reasons. First, nowhere in the world is a complex tectonic domain with the potential for such large reserves so well documented in terms of geological, geophysical and engineering data. Second, the Foothills area lies adjacent to a very active area of conventional exploration and development. Third, the exploration industry in Western Canada is technically and financially sophisticated. Last, but by no means least, the southern half of the Foothills is already tied into the North American gas market.

One of the challenges for exploration and development in the Foothills lies in the amount of data that needs to be processed and interpreted to explore for and develop the natural gas reserves of the area. In this talk we explore the past and present development of the Foothills in light of three key elements: structural style, stratigraphic framework and history of exploration. The resulting model will provide a useful tool with which to understand the present activity and the future potential of the Foothills.

The Foothills Fields fall into five general categories. The first four play types are dominantly controlled by structure. The last play type is stratigraphic in nature:

• The First-Generation plays are typified by the Turner Valley Field thrust sheet, first drilled in 1913, well before the oil and gas industry in Western Canada had even fully embraced the concept of low angle thrust faults. It has provided 14Tcf of gas to the reserves in the Foothills.
• The Second-Generation plays are those like the Waterton Field duplex, discovered in 1957. By then seismic was a well-developed tool. Also, enough time had passed since the 1939 drilling of the Livingstone Thrust at Savanna that the concept of low angle thrust faults was well accepted by the oil and gas industry. This play type has contributed a further 10 Tcf of gas to this reserve base.
• The Third-Generation play type is a much more recent play type that developed in the 1970s and is best seen in the Sukunka Field in northeast British Columbia. This play is one dominated by folding. It has contributed 8 Tcf of gas to the Foothills reserve base.
• The Triangle Zone plays have a more complicated history. The first field is the Ricinus Cardium field drilled in 1968. But more recently the play got a fresh lease of life with the drilling of the Lovett River Cardium field in 1993. It appears to be a complex mixture of folding and faulting. This play type is responsible for about 4 Tcf of gas in the Foothills gas reserve.
• The Reef Plays are found both in the regional and on the thrust sheets in the Foothills and are typified by the Blackstone Field, which was discovered in the 1970s. They have contributed about 2 Tcf of gas to the reserves.

Driven by “$4.00 gas,” there has been a paradigm shift in the Western Canadian gas industry over the last six months. There is now intense pressure to find “quick” ways to shorten the exploration cycles in the Foothills. While technology is helping to achieve this goal there is still a significant lead-time required to develop these projects. Without a good technical understanding of Foothills, the exploration industry in Western Canada is in danger of missing an opportunity to develop these reserves in a cost effective and sustainable way.