Independent Oil & Gas (IOG), a company working to develop its Skipper oil discovery in the UK sector of the North Sea, has shared mixed results of its first operated appraisal well there.
The appraisal well was completed and, IOG says, it achieved its primary objective of retrieving oil samples from the Skipper reservoir in order to optimize the Skipper field development plan.
However, while the drilling of the appraisal well proved oil, the first sample results indicate that the oil is approximately 11° API and has a significantly higher viscosity than expected, IOG said.
Crude oil with high viscosity (typically above 10 cp), and high specific gravity is considered heavy. The API classifies heavy oil as crudes with a gravity below 22.3° API. In addition to high viscosity and high specific gravity, heavy oils typically have low hydrogen-to-carbon ratios, high asphaltene, sulfur, nitrogen, and heavy-metal content, as well as higher acid numbers , and might be difficult to extract.
This means IOG now needs to do more testing of samples and review its Skipper development options, which could take months to complete.
“These measurements do not align with our observations and therefore the remaining samples need to be reviewed and tested. Next steps will then be Reservoir modeling to consider potential development options. Determining commerciality may therefore take several months.”
Mark Routh, CEO of IOG said: “The analysis of the oil retrieved from the appraisal well indicates that Skipper is a heavy oil discovery with similar gravity to other nearby heavy oil fields. We have observed that the oil moves in the reservoir and is mobile at surface at ambient conditions.
“The initial oil analysis results are incompatible with our observations, therefore we are now reviewing our strategy to establish the commerciality of Skipper. In addition, we have an increased oil in place, higher observed reservoir permeabilities and an increased reservoir height from the crest to the oil water contact.”
As for the increased resources Routh is mentioning, following the appraisal results, management’s estimate of the most likely oil in place has increased from 136.5 million barrels (“MMBbls”) in the 2013 Competent Persons Report to 142.6 MMBbls.
Recovery factor estimates will be revised during the full field reservoir simulation studies which will now begin.