ABSTRACT: Play Analysis Approach to the Minnelusa Formation, Northeastern Powder River Basin, Wyoming

Logan MacMillan, John Schuyler

The Pennsylvanian Minnelusa Formation has been a target for oil and gas exploration since the mid-1950s and remains one of the more active plays in the Rocky Mountain region. A historical perspective of industry activity for over 30 years, with the development of key technological advancements, should provide a classic case study of the application of the modern Play Analysis to this exploration target. Through 1988, 191 Minnelusa fields are recognized by the Wyoming Oil and Gas Commission, and are included in this review.

The depositional system of eolian reservoirs, organic-rich black shales, and lateral seals from lateral facies changes and truncation constitutes the petroleum system. The current primary paradigms for Minnelusa exploration are used to define the producing fields into subsets: truncation, lateral facies change, structural closure, and spillpoint, for each of the three producing horizons: A, B, and C, in the productive fairway.

A heuristic method for estimation of the ultimate recovery by field is used to generate a field size distribution for each subset. A plot of the field sizes, by producing horizon, shows a log normal distribution for each subset, as expected, but with decidedly different characteristics for each.

A review of the discovery dates and field size provides a data set for analysis for a Minnelusa Discovery Model. Given a specific area, the Discovery Model may have application to additional fields to be discovered and their size--a key to exploration strategic planning. However, critical analysis raises specific questions as to the validity of a Discovery Model, and, consequently, the geologic input for such a model.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990