Foothills Decompression/Recompression Facilities - A Unique Approach to Pipeline Expansion

Foothills Pipe Lines Ltd. ("Foothills") is the Canadian sponsor of the Alaska Natural Gas Transportation System (ANGTS), a pipeline project selected in Canada and the United States as the means for transporting Alaskan gas reserves to the lower 48 United States. In the early 1980's, the existing Eastern Leg and Western Leg Prebuild portions of the ANGTS were constructed and placed into operation for delivery of Canadian gas to U.S. markets. The Eastern Leg Prebuild in Canada extends approximately 396 miles from the point of bifurcation of the proposed ANGTS mainline near Caroline, Alberta to a point on the Canada/U.S. border near Monchy, Saskatchewan, where it interconnects with the Northern Border Pipeline Company pipeline system. Foothills is currently proceeding with expansion of its Eastern Leg Prebuild to accommodate increased Canadian gas exports. Because of the nature of the existing system configuration and operation, system design to accommodate the expansion faced unusual circumstances, and accordingly a unique solution was required. The existing Foothills pipeline, although designed for a maximum operating pressure of 1260 psig, is currently integrated operationally with the lower pressure NOVA Corporation of Alberta ("NOVA") pipeline system in Alberta, with both pipelines being constrained to deliver gas volumes to existing extraction plants at Empress, Alberta near the Alberta/Saskatchewan border at a fied inlet pressure of approximately 610 psig. The Foothills system, thus constrained in pressure at the Alberta/Saskatchewan border, nevertheless must transport gas the remaining distance to Monchy, Saskatchewan for delivery to Northern Border at maximum 1260 psig currently, and 1435 psig in the expansion case. Several expansion system designs were examined, including the unique scenario wherein Decompression/Recompression facilities at the Empress Extraction Plants would be required. Based on extensive engineering analysis including offline pipeline transient simulations to evaluate potential operational problems, it was concluded that the optimum manner of Foothills' system expansion entailed the raising of the operating pressure in the Foothills pipeline at Empress to nominal 1000 psig and the construction of the Decompression/Recompression facilities for purposes of maintaining gas stripping capabilities. Foothills is currently proceeding with design and construction of these Facilities.