Methodology and Results for the Assessment of Oil and Gas resources, National Petroleum Reserve, Alaska

Abstract

Oil and gas resources in each of the 24 plays within the National Petroleum Reserve in Alaska (NPRA) were estimated using a play analysis. Assessors specified geologic attributes, risks, and number of prospects for each play. Some specifications established distributions, while others were given as single values. From this information, sizes of oil and gas accumulations were simulated using a Monte Carlo algorithm. The number of such accumulations considered in a given simulation run was obtained from the distribution of the number of prospects. Each prospect in each successful simulation run was risked. This process yielded size-frequency distributions and summary statistics for the various petroleum categories. Estimates of remaining resources from individual plays were then aggregated, and measures of uncertainty computed. Technically recoverable, undiscovered oil beneath the Federal part of NPRA likely ranges between 5.9 and 13.2 billion barrels, with a mean (expected) value of 9.3 billion barrels. Technically recoverable, undiscovered nonassociated natural gas for the same area likely ranges between 39.1 and 83.2 trillion cubic feet, with a mean (expected) value of 59.7 trillion cubic feet. Mean values of the corresponding associated dissolved gas and natural gas liquid are 10.3 trillion cubic feet and 1.4 billion barrels respectively. modified version of the methodology used in the U.S. Geological Survey's 1998 assessment of the 1002 Area of the Artic National Wildlife Refuge (ANWR) (Schuenemeyer, 1999). Improvements included modifications to the input form, fitting beta distributions to specified fractiles, and new petroleum engineering models. Minimum reservoir sizes for oil and for gas were established to facilitate estimation of the number of prospects. Approximate deposit size distributions were generated at the mean, median, and 5 th and 95 th levels of uncertainty. Play resources were allocated to Federal land based on estimated proportions of oil and gas resources. Estimates of remaining resources from individual plays were aggregated into distributions of remaining resources for the total NPRA land area and for a subset, the Federal land area. The aggregation procedures also were modified from those used in the 1002-ANWR assessment. This chapter begins with a discussion of the geologic and engineering input, which was specified by the assessors for each play and entered on the assessment form. Following this, the Monte Carlo simulation is presented. We conclude with a discussion of the aggregation procedure. After presentation of the methodology, results will be summarized for each play and for the aggregate total of oil and nonassociated gas and various derivatives. Detailed discussion of the results is presented elsewhere on this Web site. Definition of terms is given in the Glossary. SPECIFICATION OF THE INPUT Information used by the assessment algorithm consisted of statistical models with parameters and assessor-specified distributions and constants. An assessment form, which was a modified ve...

Economic analysis of the 2010 U.S. Geological Survey assessment of undiscovered oil and gas in the National Petroleum Reserve in Alaska

“…The geologic assessment method (Schuenemeyer, 2003) and results (Houseknecht and others, 2010) are briefly reviewed here. The commercial value of newly discovered oil and gas accumulations depends on the expected size, hydrocarbon type (oil or gas 4 ), depth, location, and reservoir attributes.…”

“…A play is a set of known or postulated oil and (or) gas accumulations sharing similar geologic, geographic, and temporal properties, such as source rock, migration patterns, timing, trapping mechanism, and hydrocarbon type (Baker and others, 1984). Originally, the geologists had defined 24 plays to be assessed Schuenemeyer, 2003). Across all plays, the uniform minimum accumulation size for oil accumulations assessed was set at 50 MMBO of oil in place, and the minimum accumulation size for natural gas accumulations assessed was 250 billion cubic feet (BCF) of recoverable nonassociated natural gas (Schuenemeyer, 2003).…”

“…Originally, the geologists had defined 24 plays to be assessed Schuenemeyer, 2003). Across all plays, the uniform minimum accumulation size for oil accumulations assessed was set at 50 MMBO of oil in place, and the minimum accumulation size for natural gas accumulations assessed was 250 billion cubic feet (BCF) of recoverable nonassociated natural gas (Schuenemeyer, 2003).…”

Aggregation of estimated numbers of undiscovered deposits: an R-script with an example from the Chu Sarysu Basin, Kazakhtan: Chapter B in <i>Global mineral resource assessment</i>

“…An aggregation code presented in this report combines undiscovered deposit estimates and reports the aggregated total, assuming independence, total dependence, and positive dependence based on user-defined subjective pairwise correlations between each assessed area. The approach is similar to aggregation methodology described by Schuenemeyer (2003Schuenemeyer ( , 2005.…”

“…Using Monte Carlo simulations, these undiscovered deposit estimates are combined with tonnage and grade models to derive a probability distribution describing amounts of commodities and rock that could be present in undiscovered deposits within a study area. In some situations, it is desirable to aggregate the assessment results from several study areas (Schuenemeyer, 2003(Schuenemeyer, , 2005. This report provides a script developed in open-source statistical software, R (R Development Core Team, 2010), that aggregates undiscovered deposit estimates of a given type, assuming independence, total dependence, or some degree of correlation among aggregated areas, given a user-specified correlation matrix.…”