There is an increasing hydrocarbon demand from a diminishing resource base in the North Sea. Technological advancements and government support coupled with activities in the UK Continental Shelf are enabling the development of untapped heavy oil resources. Heavy oil appraisal-well testing has always been a primary source of information for reservoir characterization, well deliverability, and evaluation of potential technologies for further application in field development.

Until recently, heavy oil well tests have been limited and deemed challenging because of the complexities associated with the nature of the heavy crude and lack of a proven well-test concept with a strong track record. Technical challenges in heavy oil well testing include designing the most appropriate ESP-DST string, maintaining fluid mobility through the surface test spread, achieving efficient separation for safe and environmentally friendly disposal, and obtaining accurate flow rate measurements. With recent technological developments, enhancements in the well test design, and appropriate equipment selection, a heavy oil well test has been engineered for success by bringing together multi-disciplinary teams and emphasizing the importance of proper job design and operational collaboration.

This paper describes the evolution of the practically proven heavy oil well-testing methodology applied in the Kraken heavy oil field with 15° API crude located in the UK Continental Shelf. A horizontal well was successfully tested in 2011 by using an innovative ESP-DST string, a dual-energy gamma ray venturi-type multiphase flow meter, a new burner system and realtime data monitoring. This paper also presents the lessons learned for obtaining high quality data to extract critical reservoir information with confidence through pressure transient analysis. This success paves the way for confident development drilling to commence on the Kraken field and also proves the heavy oil well testing concept for future applications in the North Sea heavy oil fields and elsewhere.

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