Use of Plays and Field Size Distributions in Minerals Management Service's Assessment of Undiscovered Domestic Petroleum Resources

Gary L. Lore, William C. Pecora

The Minerals Management Service (MMS) and the U.S. Geological Survey (USGS) are preparing to publish a joint assessment of the nation's petroleum resources. The MMS is responsible for the assessment of offshore resources of the outer continental shelf (OCS) and exclusive economic zone (EEZ) as part of the MMS leasing mission. A study of the resource assessment methodology of the MMS by the National Academy of Sciences recommended that the size of the smallest field assessed be specified when resource estimates are reported. For the joint MMS/USGS assessment, MMS will estimate an undiscovered resource base above a minimum field size of 1 million BOE for all OCS/EEZ areas. Estimates are also being prepared for undiscovered, economically recoverable resources which employ va ious minimum field size cutoffs as a function of price/cost relationships, economic projections, and other factors. Both types of estimates use the updated PRESTO III computer-based model to simulate repeated drilling programs of prospect distributions (plays) mapped using proprietary seismic data. Hypothetical, speculative, and stratigraphic-type plays are also modeled using input prospect or field size distributions.

To estimate fields as small as 1 million BOE for the undiscovered resource base estimate, prospect size distributions are sampled by PRESTO III using a Monte Carlo process. Extrapolations of smaller fields are made from each of the field size distributions which resulted from a single simulated drilling program or Monte Carlo trial. A linear regression of field ranks vs. log barrels of oil equivalent has proven to be the most appropriate extrapolation technique within the precision of the input variables of the model and the variety of shapes of field size distributions which are generated by thousands of Monte Carlo trials.

New Department of the Interior resources estimates of the OCS/EEZ are presented for the federal portions offshore the Alaska, Pacific, Gulf of Mexico, and Atlantic regions. The estimates reflect significant changes in economic conditions and new geological data.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.