A Computational Fluid Dynamics Approach to Predict Pressure Drop and Flow Behavior in the Near Wellbore Region of a Frac-Packed Gas Well

Abstract

Well completion plays a key role in reservoir production as it serves as a pathway that connects the hydrocarbon bearing rock with the wellbore, allowing formation fluids (e.g. oil, gas, water) to flow into the well and then up to production facilities on the surface. Frac-packing completion (F&P) is a well stimulation technique that vastly increases the fluid transport capability of the near wellbore region in comparison with the original formation capacity by filling fractures and perforation tunnels with high-permeability proppant, thus enabling higher production rates for the same pressure drop. Hence, it is of interest for the production engineer to have an accurate description of the actual and predicted production performance in terms of pressure drop and flowrate after the F&P completion process is done. However, in developing a mathematical model of this scenario two critical challenges should be faced: (a) as fluid flows at high flowrates it begins to deviate from linear behavior, i.e. Darcy’s law is no longer valid, (b) compressible fluid flow behavior in the near wellbore region cannot be intuitively predicted due to the geometrical complexity introduced by the well completion (e.g. perforation tunnels and fractures). Additionally, this kind of mathematical model must take into account the existence of three different domains: reservoir (porous, low permeability), completion region (porous, high permeability), and free flow region. In view of these complications, this study presents a computational approach to model and characterize the near wellbore region with F&P completion using computational fluid dynamics (CFD) modeling, combining a non-linear (non-Darcy or Forchheimer) real gas flow in porous media with a turbulence model for the free flow region. This study is classified into three parts: 1) verification case, 2) Darcy vs. non-Darcy flow, and 3) erosion analysis. All simulation cases are assumed to be isothermal, steady state gas flow. Streamlines are implemented to identify the possible kinds of flow regimes, or patterns, in the near wellbore region and it is shown that gas flow pattern can be high unpredictable. Turbulence production and erosional velocity limit are also analyzed. Finally, mathematical correlations for well completion performance of this particular case study are derived using data curve fitting. In conclusion, the CFD approach has proven to be a powerful yet flexible computational tool that can help the production and/or reservoir engineer to predict flow behavior as well as production performance for a gas producing well with F&P completion, while providing an insightful graphical description of pressure and velocity distribution in the near wellbore region.