Tar-Sands Drilling-Waste Management: A Clean Solution

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 112368, "Tar Sands Drilling Waste Management: A Clean Solution," by C. Nilsen, SPE, K. McCosh, SPE, and M. Kapila, SPE, M-I SWACO, originally prepared for the 2008 IADC/SPE Drilling Conference, Orlando, Florida, 4-6 March. The paper has not been peer reviewed. The full-length paper presents novel technology for treatment of tar-sands drilling waste generated from steam-assisted gravity drainage (SAGD) and other tar-sands drilling operations. The continuous treatment process is based on hot-water addition, mixing, and separation techniques to reduce the viscosity and specific gravity of the bitumen to separate it from the sand. Treatment of cuttings with light to heavy bitumen contamination has shown this treatment method to be a simple and effective means of producing clean sand and recovering the bitumen component. Introduction Tar sands are sandstone formations saturated with bitumen or heavy oil. The sandstone is thought to remain water-wet in the formation and can be unconsolidated, with the sand grains held together mainly by the bitumen. Alternatively, the sandstone can be consolidated, with silica or carbonate cement holding the sand together and bitumen filling the remaining voids. The bitumen deposits were formed in the geological past from crude oil that migrated to the surface of the Earth. Weathering and chemical and biological processes resulted in loss of the light fractions, leaving behind the very-viscous, solid or semisolid heavy fractions. Typically, bitumen has a density greater than 960 kg/m3. Over the millennia, weather and geologic action covered the semisolid bitumen with layers of soil, and today, most bitumen and heavy-oil production comes from deposits buried more than 400 m below the surface of the Earth. Bitumen deposits are found in more than 70 countries worldwide, but 75% occur in Canada and Venezuela. In Canada, most of the oil sands are located in three major areas in northern Alberta, which hold at least 175 billion bbl of recoverable bitumen. Where the heavy oil is thin it can be pumped out of the sands with progressing-cavity pumps (PCPs). To increase recovery, cold heavy-oil production with sand also is used in which sand is encouraged to enter the well by aggressive perforation and swabbing strategies. Removal of the sand with the heavy oil increases the formation permeability, expands the high-permeability zone as sand is produced, and prevents plugging of the near-wellbore region by asphaltenes or fines.