Analysis of Well-Completion Performance and Production Optimization of a Gas Well Using Computational Fluid Dynamics

Abstract

Summary This paper investigates the effects of high production rates on well performance for a casedhole gas well using two types of completion schemes: frac pack and gravel pack. We model fluid dynamics in the near-wellbore region, where the most dramatic changes in pressure and velocity are expected to occur, using computational fluid dynamics (CFD). The fluid-flow model is dependent on the Navier-Stokes equations augmented with the Forchheimer equation to study inertial and turbulence effects in regions where the velocity increases and decreases sharply over a relatively small length scale. Real-gas properties are incorporated into the momentum-balance equation using the Soave-Redlich-Kwong (SRK) equation of state (EOS) (SRK-EOS). The near-wellbore model is pressure-driven under steady-state and isothermal conditions. Well-performance curves are generated depending on simulation results for both completion schemes. Furthermore, we introduce the concept of rate-dependent pseudoskin factor to assess inertial and turbulence kinetic energy (TKE) losses under various pressure differential. Analysis of the simulation results suggests that the rate-dependent pseudoskin changes from negative at low gas-production rates to positive at medium-to-high gas-production rates. This is primarily because of the inertial and turbulence effects being triggered at a certain flow rate, which we define as the optimal operating point. We demonstrate that the gas-deliverability curve plotted along with the pseudoskin-factor curve allows us to estimate the optimal operating condition as the point where the rate-dependent pseudoskin is zero. An analytical model to estimate the optimal production rate is proposed as an extension to typical multirate tests.