Evaluation of Changes in Expected Ultimate Recovery for US Gulf of Mexico Oil and Gas Fields, 1975–2016

Abstract

Quantifying the change in field expected ultimate recovery across time is an old and complex topic fraught with ambiguity and misinterpretation. In this paper, changes in recovery estimates performed by the Bureau of Ocean Energy Management in the US Gulf of Mexico are evaluated based on 782 offshore fields that began producing after 1975 and ceased production before 2017. At the time of first production, field expected ultimate recovery estimates totaled 6.3 billion barrels oil equivalent (38.6 exajoules), but by the end of their life, the fields produced 8.5 billion barrels oil equivalent (52 exajoules), a 35% growth. On an individual field basis, however, median recovery estimates grew less than 2%. The purpose of this paper is to explain the differences in these two statistics and quantify how expected ultimate recovery is influenced by field age, discovery year, reserve category, peak ratio, product type, size, and water depth to understand better the contribution of individual factors in reserves evaluation. Consistent interpretation of reserves category is probably the most important factor in application. Field age and size are positively correlated with changes in expected ultimate recovery in both the shallow water and deepwater regions of the US Gulf of Mexico, pre- and post-1988 evaluation periods are a significant factor, and a development variable referred to as peak ratio exhibits a meaningful correspondence. The results of this analysis show that Bureau of Ocean Energy Management procedures for expected ultimate recovery estimation in the US Gulf of Mexico post-1988 are consistent with the application of probable reserves classifications; these highlight the need for a precise understanding of factor inputs in reserves growth studies.