A New Methodology To Assess the Conventionally Recoverable Undiscovered Petroleum Resource Base of OCS Lands
Authors: Pecora W.C. , Cooke L.W. 
Published: October 2008

ABSTRACT
The U.S. Minerals Management Service (MMS) for the first time has undertaken an assessment of undiscovered, conventionally recoverable petroleum resources that are not constrained by economic considerations. The new type of estimate is termed Undiscovered Resource Base (URB). It is calculated to realistically bracket the range of conventionally recoverable hydrocarbon volumes which probably remain to be discovered in the forseeable future on Federal Outer Continental Shelf (OCS) lands. The URB estimate is designed to be a geologic baseline assessment. It can be used to model a variety of unconventional recovery scenarios based on speculations as to future enhanced production technologies.

INTRODUCTION
Estimates of economically recoverable hydrocarbons, such as those previously published in Environmental Impact Statements, represent our hydrocarbon resource endowment with noncommercial hydrocarbon volumes removed from the totals. These types of estimates are appropriate in assessing areas proposed for leasing. They model economic constraints and incentives that would affect whether resources will be developed and produced as a result of Federal leasing of OCS lands.
Rapid changes in petroleum prices and production costs has emphasized the desirability of another category of estimates for long-term planning purposes. As a result, MMS has expanded its assessment of undiscovered, economically recoverable hydrocarbon resources to include accumulations in smaller or deeper geologic traps in high-cost regimes that would not be economic at current prices. The methodology to derive this estimate is termed DIST, referring to distributions of possible field sizes. The estimate of the URB more adequately portrays the conventionally recoverable longer-term potential of high-cost frontier areas and economically inaccessible mature productive areas.

DEFINITIONS
The term URB is defined as an unconfirmed quantity of naturally occurring oil and gas estimated to exist in accordance with regional geologic analyses that would be conventionally recoverable from oil and gas fields larger than 1 million oil equivalent barrels (MMBOE) regardless of current accessibility or economics. Accumulations less than this level in size may be included in those cases where recovery is economically viable (nearshore, Gulf of Mexico (GOM) Region). Confirmation of the existence and quantity of this volume depends upon the results of future drilling of prospects and plays modeled by the PRESTO computer-based model.
The URB definition is modified from one use1 by the National Petroleum Council in their assessment of Arctic resources. An assessment of the URB is responsive to recommendations 0f the National Academy of Sciences.

DEVELOPMENT OF METHODOLOGY
Currently available seismic and well log information, in conjunction with analog studies, provide sufficient control to adequately catalog large prospects for the PRESTO play inventory. The inventory is primarily a free byproduct from mapping eventually used in bid adequacy determination after a lease sale. Gaps in the inventory appear at the lower end of possible prospect and play sizes where imposed mapping or economic constraints have deleted smaller prospects or geologic outcomes. A methodology was needed to expand the PRESTO inventory to model hydrocarbon resources from fields smaller than the range of minimum accumulation sizes of prospects in the inventory.