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Rock Physics Modeling of Salt Plugged Carbonate Reservoir Rocks — Winnipegosis Formation, North Dakota


Winnipegosis is a Devonian-Mississippian aged formation that conformably overlies the Ashern Formation and is dominantly a limestone in the Williston Basin, North Dakota. This formation has produced commercial quantity of hydrocarbons in specific regions in the state. The majority of the production from the Winnipegosis comes from the pinnacle reefs where the pores of the reservoir rock have not been plugged with salt mineral. Salt plugging of the prolific carbonate reservoirs is known to be the reason for failure for many wells in the salt diapir as the main cap rock. The main objective of this study was to perform an integrated petrophysics and rock physics workflow to improve reservoir characterization. We applied different fluid replacement models along with the solid-fluid substitution in order to distinguish between the salt-plugged and potential reservoirs in the Winnipegosis Formation in ND. To understand the sensitivity of elastic rock properties to the pore fluid type in the reservoir, three different fluid replacement models (FRM) were applied to the well data including the Hashin-Shrikman, Barryman-Milton and modified or extended Gassman theory. The results are showing that all of the FRM methods can well predict the changes in the reservoir when the fluid saturation is altered and solid-fluid replacement is occurred. It was found that the modified Gassman model can better predict the changes in the shear wave velocity for the wells which the salt has plugged the pore spaces with a good match with the measured well log and field data.