West Sak Multi-Lateral Wells—Making North Slope Viscous Oil a Reality

By

M.R. Werner (Phillips Alaska, Inc.)

After cessation of a waterflood pilot in 1986, it was over ten years before development of the West Sak viscous oil resource in the Kuparuk River Unit (KRU) became reality. Development commenced in the eastern KRU at 1D pad in 1997 with conventional wells and frac and pack completions. In 2000, the first horizontal multi-lateral wells on the North Slope were drilled at 1D and demonstrated the potential forWest Sak rates of over 1000 BOPD. Multi-lateral based development was expanded to 1C pad in 2001. The next planned phase of development will return to 1J pad, the site of the original waterflood project.

TheWest Sak is a shallow marine sequence comprised of very fine-to- fine grained, storm-deposited sandstone beds. The D and B sands of the upper member average 30 and 20 feet thick, respectively, and are good targets for multi-lateral drilling. The lower West Sak A Sands consist of thinner interbedded sandstones and are a greater challenge for efficient development.

Shallow depth and structure are critical factors in West Sak rock and fluid properties. The sands are poorly consolidated, prompting concern for sand control methods. The West Sak is deeper in the eastern KRU and the higher reservoir temperature and improved viscosity of the biodegraded crude are more favorable for waterflood. Faulting is the primary control on distribution of hydrocarbons and the initial development area from 1C south to 1J appears to be a continuous accumulation with common oil-water contacts and similar oil quality.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.