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Reservoir Modeling 6000 Feet of Gross Fluvial Section, Pinedale Tight Gas Field, Wyoming

Chapin, Mark A.1; Diomampo, Gracel 1; Ugueto, Gustavo 1; Roach, Hampton 1; Fleming, Carolyn 1
1 Shell, Denver, CO.

The giant Pinedale gas field, Green River Basin, Wyoming produces from a 5000-6000 ft interval of the Upper Cretaceous and Lower Tertiary. The reservoir comprises discontinuous, lenticular fluvial sands intercalated with overbank sand, silt and mud. Typical porosities for the field are <12% with permeability in the micro-darcy range. A typical well may have 50 channel sand packages, bundled into 15-20 artificial frac stages and commingled. Modeling to date has focused on the interaction of complex fluvial sand geometry with artificial hydraulic fractures, increasing pore pressure with depth, and variable water saturation. Although natural fractures have been recognized, their demonstrable impact to production is localized.

Despite significant compaction and cementation, we can demonstrate good correspondence of core and log petrophysical properties to facies. Because of this, it is desirable to use facies to populate reservoir models. A multi-step approach was used to populate small (< one square mile) “sector” models of different parts of the field. Logs were used to determine facies via neural nets and petrophysical cutoffs. Facies were distributed via object modeling, then petrophysical properties were distributed within facies using sequential Gaussian simulation.

Gross channel ribbons and bars objects were placed first, guided by interpolated V-shale - a proxy for sand correlation. Detailed facies bodies were then distributed within those elements. Because net/gross, sand thickness, sand correlation, and overbank character change throughout the section, different zones were modeled using different body dimensions. Acceptable history matches were attained despite the architectural complexity using production data, bottom hole pressure, PLTs and distributed permanent pressure gauges.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009