| Popis: |
West Sak is a heavy oil accumulation within the Kuparuk River Unit on the North Slope of Alaska. It is a Cretaceous, shallow marine sandstone. It contains 7–9 billion barrels of oil in place with an oil gravity that ranges from 10–22 degrees API. Initial oil production began in 1997 at approximately 3,000 BOPD and has increased to over 16,000 BOPD in March 2005. Development plans are in place to achieve a rate of over 40,000 BOPD by 2007. This paper describes the evolving development plan for the West Sak field, with emphasis on the technical advances that have resulted in large-scale commercial development. Early West Sak development consisted of stimulated vertical wells on a 40-acre waterflood pattern with typical production rates of 150-250 BOPD. Utilizing the evolution in horizontal and multi-lateral drilling technology, the development plan has progressed to extended reach multi-lateral injectors and producers with horizontal and undulating slotted liner completions is excess of 8000 feet per lateral. Peak rates of over 5000 BOPD and sustained rates of over 1500 BOPD have been achieved. With the higher reservoir throughput rates, the distance between wells has increased, reducing well count and improving the development cost per barrel. Significant changes have also been made to the completion design and production strategy. These include changing from sand exclusion to sand management, adding intervention capabilities with multi-lateral completion equipment, optimizing the drill-in-fluid, and adding a backup gas lift system to the standard electrical submersible pump (ESP) completions. Finally, the enhanced recovery process has evolved from waterflood to a viscosity reducing water-alternating-gas (VRWAG) process, improving expected recovery by 2-3 percent of OOIP. Application of new technology and optimized development decisions have reduced development cost by approximately 25% in terms of $/BOE and unlocked value in a major resource. |
