(256c) Modeling Uncertainty and Impact of Non-Darcy Flow Regimes on Unconventional Well Performance.

Tight nano-pores in unconventional reservoirs can cause deviations from Darcy’s law where permeability becomes a strong function of pore size and pore pressure. Many studies have been conducted to quantify and correct for nano-pore effects on laboratory permeability measurements to account for changing flow regimes from slip flow to Knudsen diffusion. Several studies have noted that corrections to Darcy flow effects may be also important when analyzing well production behavior. However, there are no studies or guidance available to suggest under what reservoir or well conditions the non-Darcy flow regimes become important for a well’s performance. This paper illustrates how one can easily model the impact of non-Darcy flow regimes using a commercial simulator.

As pore dimensions gets smaller, the interaction of gas molecules with the pore walls becomes increasingly dominant as compared to interactions between gas molecules. This increases gas mobility; hence, lab permeability measurements may not be representative of actual reservoir conditions where; slip flow and Knudsen diffusion is important. This workflow uses the predictions from generalized Non-Darcy flow correction models as a function of Knudsen number as input into a flow simulator. As a result, one can model impact of changing flow regimes from Darcy flow to Knudsen diffusion. A stochastic approach is then used to assess the impact of non-Darcy flow on unconventional wells through flow simulations accounting for uncertainties in pore sizes, reservoir properties and well constraints.

This workflow provides guidance and risk assessment for the significance of gas slippage and Knudsen diffusion in production behavior and recovery of unconventional wells. The developed workflow was tested on both synthetic and real field datasets where the results showed that Non-Darcy flow regimes may have significant impact under certain reservoir conditions. This is a novel stochastic approach for the integration of data from pore level to reservoir scale to assess the impact of nano-pore effects on unconventional well performance. Importantly, it does not require that the simulator code be modified and can be performed using existing commercial simulator functionalities.