New technique for calculation of well deliverability in gas condensate reservoirs

Abstract

Well deliverability is an important issue in forecasting the performance of many gas condensate reservoirs. Condensate accumulations near the wellbore may cause a significant reduction in the well productivity, even in the case of very lean fluids. Generally, the well deliverability is affected by two pressure-drop sources due to depletion and condensate buildup. Recently rapid spreadsheet tools have been developed to evaluate the well performance using material balance equation for depletion and two-phase pseudo pressure integral for well inflow performance. Most of them account for the effects of negative inertia and positive coupling in the calculation of gas relative permeabilities. This paper introduces a new method for calculation of well productivity in gas condensate reservoirs. This method uses the concept of two-phase pseudo pressure integral without any need to estimate the radius of two-phase region. In this approach the average reservoir pressure is calculated by using a general material balance equation. The only data required for implementing this method is PVT data, relative permeability curves and a table of well flowing pressure versus time. The new technique can be encoded on a spreadsheet in order to forecast the gas condensate well performance very rapidly. To validate the proposed approach we have used several single-well fine grid compositional simulations of a hypothetical reservoir model over a typical range of gas condensate reservoir parameters. We have shown that there is a reasonable agreement between the result of fine grid simulation and the prediction from the proposed approach.