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The Pinedale anticline is a large natural gas field in the Greater Green River Basin of Wyoming, located north of the giant Jonah field. Gas production is from overpressured fluvial channel sandstones of the Upper Cretaceous Mesaverde and Lance formations and the lower Tertiary “unnamed Tertiary” formation. To date, most studies have focused on the regional geology and potential hydrocarbon economics. This chapter discusses an integrated approach for reservoir modeling to reduce uncertainty in this tight-gas field development.

In this study, fluvial facies were defined using wireline logs. Object-based modeling was used to integrate well-log facies, object dimension, channel sinuosity, and orientation in building the three-dimensional facies model. The facies model was then used to guide petrophysical property modeling. Dependencies between rock properties were modeled using a geostatistical method. The final model honors the fluvial depositional characteristics and dependencies between the rock properties and was used for better uncertainty management in reservoir simulation and performance forecasting.

The Pinedale anticline (PDA) is located in the northwestern Greater Green River Basin in southwestern Wyoming (Figure 1A). Although the Jonah field, located just south of Pinedale in the same basin, has been extensively studied (Dubois et al., 2004; Robinson and Shanley, 2004; Apaydin et al., 2005), few studies have been published on Pinedale. Hydrocarbon analysis at the basin scale is limited to traditional geologic descriptions, including structural geology, stratigraphy, core description, and petrophysics (Law, 2002). Because the interwell facies and petrophysical property heterogeneities on the PDA significantly impact volumetrics assessment, drainage, new well placement, and depletion strategy, developing accurate models of the subsurface heterogeneities was very important.

To achieve optimal hydrocarbon depletion, an integrated study on small-scale heterogeneities was required. Reservoir modeling was conducted because it could incorporate uncertainty analyses on rock properties, including geologic facies, pore space, fluid saturation, and permeability. An area of 1.5 mi2 (3.9 km2) was selected in the southern part of Pinedale for detailed reservoir study and to determine well drainage areas, new well placement, and production forecasting. To mitigate boundary effects for dynamic simulation, the geocellular model was enlarged to an area of more than 2 mi2 (>5 km2), located on the crest of the anticline. Twenty-three wells with a full suite of petrophysical logs were available in the enlarged modeling area (Figure 1B).

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