Abstract

The UK Department of Trade & Industry (DTI) recently sent out a questionnaire (see Appendix) to North Sea operating oil companies to survey the different methods used in the estimation of ultimate hydrocarbon recovery and production forecasting. The feedback revealed significant differences in approach between operators in estimation methods and also a wide range of perceptions of the value and accuracy of ultimate recovery and production forecasts. This paper reports the findings of the survey and also takes a historical look at how accurate ultimate recovery estimates have actually been for UK Continental Shelf oil fields developed over the last decade. Historical reserves estimates have been rather inaccurate, with many fields exhibiting changes in estimated ultimate recovery over a ten-year period of over 50%. These inaccuracies have had a severe effect on facilities requirements for many large North Sea fields. The fields studied have required an average of 60-80% more wells than anticipated at the time of Development Plan submission and up to 400% average increase in platform water handling capacities has been necessary. Average field lifetimes have been over a decade longer than originally expected. Accommodating unexpected changes of this magnitude within existing offshore facilities has proven a very expensive exercise and we therefore suggest there is a need for a more unified approach by the industry to ultimate reserves estimation.

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