Facies Proportion Curves Establish a Stratigraphic Framework for the Lance Formation, Jonah Field, Wyoming

Luneau, Barbara¹, Dean DuBois², Debra Nishida^2 
1 Schlumberger, Greenwood Village, CO
² Encana Oil and Gas, USA, Denver, CO

The Lance Formation and overlying Unnamed Tertiary section comprise the principal producing interval in Jonah Field. These formations represent more than 3000 feet of highly heterogeneous fluvial channel, crevasse splay, and floodplain deposits. As a result, field-wide, correlative stratigraphic surfaces are limited. Individual sand packages may appear to correlate locally but change or disappear across short distances. The lack of internal stratigraphy becomes a challenge to performing finer-scale comparative analysis across the field.

As part of a reservoir modeling and simulation effort in the field, statistical vertical facies proportion curves have been generated during geocellular model construction. These curves function as input to facies model construction. They also serve as a guide for establishing pseudo-correlations within the field. Comparison of the vertical facies proportion curves for different subareas within the field reveals similar variations of sand and non-sand facies. This variation is most likely reflecting large-scale fluctuations in sediment supply or accommodation that cannot be distinguished at an individual well scale.

Facies proportion analysis has proved to be a useful tool to analyze areal changes in stratigraphic packages within the field. The curves can be used like logs to establish pseudo-correlations along surfaces of significant depositional change providing a framework for comparative analysis of producing horizons and potential connectivity in the reservoir.