Disposal of drilling wastes in Permafrost Prudhoe Bay, Alaska

Since the late 1960's, drilling wastes, mostly muds and cuttings, have been generated as a result of developing Alaska's North Slope oil fields. These materials have been stored in above-ground reserve pits formed by constructing gravel berms on the tundra next to the gravel drill pad at each drill site. The tundra and underlying permafrost, which is about 550 m thick at Prudhoe Bay, served as a pit floor. For several years, North Slope operators have been evaluating and testing various methods for permanent disposal of these wastes. In early 1992, ARCO Alaska, Inc. evaluated burying the wastes in permafrost by conducting two pilot projects in winter. One project tested the procedures of excavating a drill site's wastes; the other involved placing these wastes into a large excavation where they would remain permanently frozen. This paper describes the disposal facility portion of the two projects. The East Sag Regional Disposal Facility was constructed near Drill Site 16. An ice road and ice pads were constructed to provide site access, material stockpile areas, and tundra protection. A mass excavation, about 107 m x 158 m x 12 m deep; was made using explosives and heavy equipment, then filled with about 180,000 m of drilling wastes from DS 3 and capped with clean material mounded above the surrounding tundra. Instrumentation was installed to measure the facility's performance. The East Sag project was successful and demonstrated that drilling waste disposal in permafrost is feasible. The data obtained will be useful for a full-scale project.