Heavy-Oil Well Testing With an ESP, Offshore UK
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 148833, ’Methodologies, Solutions, and Lessons Learned From Heavy- Oil Well Testing With an ESP, Offshore UK in the Bentley Field, Block 9/3b,’ by Barny Brennan, SPE, Charles Lucas-Clements, and Steve Kew, SPE, Xcite Energy Resources; Yakov Shumakov, Lawrence Camilleri, SPE, Obinna Akuanyionwu, SPE, and Ahmet Tunoglu, SPE, Schlumberger; and Steve Hayhurst, SPE, and John Simpson, ADTI, prepared for the 2011 Canadian Unconventional Resources Conference, Calgary, 15-17 November. The paper has not been peer reviewed.
Production from heavy-oil fields in the UK continental shelf (UKCS) has become possible over the past 10 years. Despite substantial reserves in the UKCS of crudes with gravitiy of 20°API and lower, most of the activity has been exploration and appraisal drilling. The main reason for restricted activity has been high uncertainty of reservoir and fluid properties. A method was developed to find the most-suitable technology for testing these heavy-oil wells by use of an electrical submersible pump (ESP).
Introduction
Most UKCS production has been light oil, 30°API and lighter. The UK Department of Trade and Industry estimates 9.2 billion bbl of heavy oil in place in the UKCS. Many of the UKCS heavy-oil fields were discovered in the 1970s, but were considered uneconomical. Although considerable quantities of these UKCS heavy-oil resources with gravity lower than 20°API exist, the uncertainties in reservoir and fluid properties have con-fined activities mostly to exploration and appraisal testing. Inherent operational complexities also limit the use of conventional appraisal well-testing techniques.
The Bentley field contains 10 to 12°API oil (620-cp in-situ oil viscosity) in the Dornoch sandstone reservoir. The Bentley fluid is much heavier and more viscous than crudes at any field currently producing in the North Sea. Discovered in 1977 in a water depth of 371 ft, the field is 100 miles east of the Shetland Islands on the edge of the heavy-oil belt in the northern North Sea. The average reservoir depth is 3,700 ft. Since discovery of the field, several well tests have been performed in attempts to produce Bentley crude to the surface. However, technical issues with downhole-equipment reliability and the application of traditional well-testing techniques in the heavy-oil formation yielded unsuccessful tests with no flow to surface. Vertical Well 9/3b-5 was drilled in 2007 and tested in January 2008, flowing the first Bentley crude to the surface. The results of the test provided vital reservoir information and lessons learned for future operation planning.
In 2010, the operator drilled a horizontal well into the upper Dornoch sand-stone to gather additional data through coring and logging. A short well-testing program was used to collect representative downhole pressure/volume/temperature (PVT) samples to validate flow at commercial rates. A drillstem-test (DST) string and new operational procedures based on the lessons learned from the previous well tests were used.