Studies of United Kingdom Continental Shelf (UKCS) Fields after a Decade of Production—So Really How Good are We at Estimating Subsurface Uncertainty?

Smith, Peter, University of Trinidad, Trinidad and Tobago

In the mid-nineties several new oil fields were approved for development in the UKCS with BP as operator. Some of these fields Andrew, Harding, Foinaven and Schiehallion were approved following extensive uncertainty analysis due to the marginal oil field economics at the time, with the combination of low oil prices and relatively modest reserves. The essen­tial question this paper addresses is now after a decade, with all the fields in production, what lessons can be learned from those early uncertainty assessments? This retrospective analysis is essential if the process of assessing subsurface uncertainty is to be improved in the future.

The importance of subsurface uncertainty studies in making new field development investment decisions is nowadays hardly ever debated. However, the methodology of how to conduct such an uncertainty study is still not clearly understood or articulated. It is often overlooked that when examining the reserves or commercial value uncertainty of field devel­opments, two factors need to be assessed, namely, the impact of a change in a variable and the probability of that change. In this paper it is shown firstly by a simple statistical analogue and then by analysis of the subsurface uncertainty that insufficient care is taken in estimat­ing the probability of events, whilst spurious accuracy is used in calculating the impacts. In this paper, uncertainty studies conducted in the mid-nineties are re-examined on the basis of the actual outcomes, to see if this view is valid. Moreover a set of practical guidelines

based upon the decade of new knowledge about the subsurface is offered to help navigate through this area

It is concluded that the essential difficulty of assessing uncertainty in field development is the integration of different E&P technologies along with the softer technologies of social science. By evaluating the track record of the earlier predictions with the current view of the Subsurface Uncertainty of thee UKCS fields leads the author to recommend more model cases and simpler modeling tools for future studies, as well as, far more team debate of the probability of key variables.