This paper gives a method for estimating reserves uncertainty for oil and gas fields. The parametric method is a long-established statistical technique, yet has seldom been applied in the oil and gas industry. The power of the method lies in its simplicity, for this gives access to a ranking of uncertain variables in terms of importance in affecting reserves. Once the key uncertainties have been identified, attention can be focussed on appropriate contingency plans to reduce their impact. By planning for potential downsides and upsides in advance, project econonics become more robust. The technique is extended to production profile predictions.
The paper describes the statistics of the method, and then illustrates its application through a case example, the Forth Field, which lies in the northern North Sea and is due for development approval in the first half of 1993.