Burial History Modeling of the Jonah Field Area, Sublette County, Wyoming: Evaluation of Hydrocarbon Charge Potential Using Risk Modeling

Coskey, Robert J. and  Jay E. Leonard
Platte River Associates, Inc, Boulder, CO

The hydrocarbon charge at Jonah field is the result of a complex series of temporal and spatial petroleum system events. Burial history and risk modeling were used to evaluate the generative capacity of each potential source rock within the Jonah Field / Pinedale Anticline area. The models were constrained by temperature, vitrinite and pyrolysis data were used to estimate the timing of generation/expulsion and focused on evaluating generative capacity of the Lance Formation as contrasted to estimated gas-in-place at Jonah. 

Although the models were data constrained, these data are generally sparse and many geologic uncertainties still exist. To manage uncertainty a stochastic approach was utilized. To test the trapping capacity of the reservoirs in the Jonah and Pinedale areas, charge elements of TOC, source area and migration efficiency as well as trap elements of reservoir area, reservoir gross thickness, seal efficiency, etc, were input as distributions rather than discrete values. The modeling results suggest that the potential source rocks in the Lance, upper Mesaverde and lower Mesaverde (Rock Springs) formations can provide the Jonah trap with approximately 2 to 4 tcf gas-in-place (P50). This gas volume is significantly less than current in-place estimates and suggests that hydrocarbons were generated from deeper sources such as the Hilliard Shale or Mowry Shale and/or have migrated from a larger fetch area.