ESTIMATION OF ULTIMATE RECOVERY FOR UK OIL-FIELDS - THE RESULTS OF THE DTI QUESTIONNAIRE AND A HISTORICAL-ANALYSIS

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