Prediction of Capillary Fluid Interfaces during Gas or Water Coning in Vertical Wells

Gas and water coning cause oil production to be significantly reduced and costs associated with the production to be significantly increased. Simulation and experimental methods, coupled with simple analytical solutions or correlations, are typically used to identify the oil rate that minimizes coning and maximizes recovery. Current analytical solutions, however, assume negligible capillary pressure, which leads to segregated flow. This paper presents new analytical solutions that relax this assumption. The new coning solutions apply to vertical wells where in situ fluids are in vertical equilibrium. The development identifies the important dimensionless groups that control the effect of coning on oil recovery and illustrates how simultaneous two-phase flow affects capillary fluid levels in the formation. Dimensionless two-phase production windows are constructed to identify critical rates, the largest oil rate at which water (or gas) will not be produced.