Exploration for heavy oil, in an offshore setting carries special challenges and risks, especially during the well testing phase. Bringing the heavy oil to surface and then disposing of this oil efficiently without polluting the offshore environment is a challenge. Flow testing oil with APIs as low as 8 degrees would be challenging in itself; when this oil is also sour, the challenges are magnified many-fold, especially when considering the limited space on offshore drilling rigs.
Saudi Aramco has started a program aimed at exploration and evaluation of heavy oil reserves in the Arabian Gulf. The objective of testing this sour, heavy oil was to obtain reservoir fluid samples, get productivity data and characterize the reservoir. While attempting to dispose of the oil in an efficient manner, initial attempts to test this heavy oil were unsuccessful. Prematurely terminating these tests resulted in not obtaining all of the required test data.
A heavy oil team was formed in early 2008 to determine solutions to the inability to properly characterize the reservoir on heavy oil well tests. This multidisciplinary team of professionals held two workshops, where heavy oil experts from major service companies provided their global expertise. This information was then blended with local operational requirements to create a unique well testing design. This design has successfully been implemented in two wells (onshore and offshore).
The use of an Electric Submersible Pump (ESP) although common in production scenarios, was successfully implemented for the first time on a heavy oil drill stem test in Saudi Arabia.
This paper summarizes the problems associated with testing heavy oil, the options studied, the reasons for selection of the chosen test method, the downsides of the selected plan, the trial testing on land and the successful implementation of the final plan in an offshore environment. It is a summary of the planning process necessary to get a good heavy oil test in a sensitive offshore environment.