Critical Parameters in Static and Dynamic Modeling of Tight Fluvial Sandstone Reservoirs

Barbara A. Luneau, Osman G. Apaydin, and Fabian Iwere
Schlumberger, Greenwood Village, CO

Within the stacked tight gas sandstone reservoirs of the Rocky Mountain Basins, complex depositional environments, heterogeneous and often low reservoir quality, and significant variation in important reservoir parameters contribute greatly to risk and increase costs associated with development. In an effort to characterize such reservoirs and maximize field deliverability, an integrated static and dynamic evaluation was performed in Jonah Field, Sublette County WY to select an appropriate geostatistical modeling method that best represents the production from a tight, stacked fluvial sandstone reservoir.

The geological scenarios incorporated variations of three widely used facies modeling algorithms: fluvial object, defined object, and sequential indicator simulation. The model constraints, including facies at wellbores, global facies proportion, vertical facies probability, and areal facies probability constructed from well data were held constant between the scenarios, and infill well locations were used to evaluate the static facies prediction. Reservoir dynamic models were used to rank individual scenario performance. Streamline simulation was used to evaluate sweep efficiency and connectivity. The results were evaluated qualitatively and quantitatively to select the appropriate modeling workflow for constructing the static and dynamic models of the field.

The highest ranked scenarios are characterized by maximum channel body width greater than 1700 ft, non-uniform length/width ratio with maximum greater than 2 and less than 4, and a modeling algorithm that allows for multidirectional lateral connectivity. Additional volumetric and incremental recovery sensitivities are evaluated using the results of infill drilling programs to identify likely ranges of channel facies fraction and dimensional parameters.