Seepage features of high-velocity non-Darcy flow in highly productive reservoirs

Reservoir seepage characteristics are complex under high production rate conditions, especially in the near-wellbore region. The motion pattern of seepage changes due to its high flow velocity, leading to a nonlinear relationship between the pressure gradient and the kinematic velocity, as well as leading to the high-velocity non-Darcy flow characteristics of the fluid flow. Aimed at determining the non-Darcy flow-generating mechanism and the seepage law for reservoirs with high and extra high production rates, we performed steady 'pressure gradient-flow rate' core displacement experiments by displacing the typical cores with simulated oil and with the formed water. By analyzing the displacement experiments, we determined the basic rule and influencing factors of high and extra high production reservoirs. With the application of the dimensionless analysis method to analyze the experimental data, we investigated the value and variation range of the Reynolds number that determines whether a non-Darcy flow will occur. By introducing the Forchheimer equation, we established the calculation method of the non-Darcy coefficient and achieved an accurate characterization of the seepage law of high and extra high production reservoirs. Finally, by applying this method to the data from typical high production wells in West Africa, we found that the calculation results of the new model were in accordance with the measured values, which indicates that the new method and model presented in this study can be used for actual well test analysis and deliverability evaluation of high and extra high production reservoirs.