Pinedale Anticline and Jonah Fields, Sublette County, Wyoming: A Geologic Discussion and Comparison
Dean P. DuBois, 2014. "Pinedale Anticline and Jonah Fields, Sublette County, Wyoming: A Geologic Discussion and Comparison", Pinedale Field: Case Study of a Giant Tight Gas Sandstone Reservoir, Mark W. Longman, Stephen R. Kneller, Thomas S. Meyer, Mark A. Chapin
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The Pinedale anticline and Jonah field in the northwest part of the greater Green River Basin produce natural gas and gas condensate from a thick succession of Upper Cretaceous and earliest Tertiary strata in the Lance Pool. Both producing areas are simple structural traps made more complex by the interbedded nature of the reservoir sandstones and sealing mudstones. In neither area is there a distinct top seal. The unusual pressure gradient exhibited by these two areas indicates that the mudstones intercalated with the reservoir sandstones are partially sealing and that there are sealing beds distributed vertically throughout the reservoir complex. Leakoff has been complete near the top of Lance Pool and is progressively less so deeper below the top of the Lance Pool.
The Pinedale anticline is a classic anticlinal structure formed by thrusting along the Pinedale thrust fault on the southwest flank and folding above the thrust. Jonah field is delineated by two main sub-vertical bounding faults and several internal faults that subdivide the field into smaller compartments. In both areas, high pressure occurs in the structural closure and is coincident with increased gas saturation and a subtle increase in porosity relative to outlying areas. Despite the low fraction of porous pay sands to gross interval, the great thickness of the Lance Pool combined with significant overpressure has resulted in world class accumulations of gas in place. Low permeability in both fields has driven development drilling to a high density (close spacing) to facilitate recovery of a significant portion of the high concentration of gas in place.
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Improved geologic insights combined with advances in technology and innovative thinking, mainly since the laste 1990s, have driven Pinedale field’s development and unlocked a giant natural gas resource in stacked low-permeability fluvial sandstones. Understanding this field can provide a model for developing similar tight sandstone reservoirs around the world. This memoir contains 15 well-illustrated, peer reviewed chapters that describe the history of field development, the deposition and diagenesis of the reservoir rocks, geophysical characteristics of the field, special core analysis techniques used to better quantify the reservoir, petrophysical characteristics and interpretations of the reservoir, the types and abundance of natural fractures, and fluid production characteristics in the field. Finally, static and dynamic models for the field are presented in an attempt to integrate all the pieces of this giant geologic puzzle.