Alaskan Heavy Oil: First CHOPS at an Untapped Arctic Resource

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 133592, ’Alaskan Heavy Oil: First CHOPS at a Vast, Untapped Arctic Resource,’ by J.P. Young, SPE, W.L. Mathews, SPE, and E.J. Hulm, SPE, BP Exploration Alaska, originally prepared for the 2010 SPE Western Regional Meeting, Anaheim, California, 27-29 May. The paper has not been peer reviewed. Alaska’s North Slope is a world-class petroleum resource basin with two of the largest producing fields in North America, Prudhoe Bay and Kuparuk River unit. What is not widely known is the vast resource of heavy oil above these reservoirs. Although comparable in size to these fields, it remains untapped as a result of the complexity of producing heavy oil in an arctic environment. The keys to commercializing this heavy-oil resource are primarily technology and favorable economics. Introduction The total North Slope heavy-oil resource is defined by approximately 1,500 wells that penetrate the Ugnu sands for deeper targets and multiple high-quality 3D-seismic surveys. Resource size ranges from 18 to 27 billion bbl of oil in place, and the oil is found in multiple reservoir zones extending across the basin. Initial appraisal is focused on the 12 to 18 billion bbl within the Lower Ugnu (M-sand) reservoirs. The Ugnu structure is characterized by a normal-faulted monoclinal dip toward the northeast. The depth of the Ugnu pool varies from 4,500 ft in the east to 3,000 ft in the west. Multiple fault families are present, as indicated by 3D seismic. The faults tend to compartmentalize the Ugnu reservoirs by providing effective updip and lateral seals. Lower Ugnu oil quality improves to the east, corresponding to increased burial depth from west to east. The deeper, less-viscous oil in the east is believed to be suited to simple “cold”-production techniques that exploit solution-gas drive. The shallower, heavier oil in the west is believed to be suited to energy-intensive thermal techniques that heat the oil in situ. Reservoir-Performance Variability Excluding mechanical issues, most variation in well rates and recovery is likely to be associated with changes in key reservoir and fluid properties. The Lower Ugnu reservoir sands are highly unconsolidated, which limits the ability to acquire quality core samples and measure key reservoir parameters accurately. In addition, the sands were deposited as fluvial-deltaic channels, which are among the most heterogeneous reservoir types.