Single-Well Performance Predictions for Gas Condensate Reservoirs

Gas condensate wells, producing with a flowing bottom-hole pressure belowthe saturation pressure, suffer a more rapid decline in productivity than thatpredicted by the theory for dry gas wells. A compositional radial reservoirmodel has been developed and used to predict the productivity loss of three gascondensate wells. Introduction Production data for some gas condensate producing Production data for somegas condensate producing wells have shown that the productivity is severelycurtailed when the flowing bottom-hole pressure is less than the saturationpressure of the in-place fluid. It is generally accepted that this reduction isdue to accumulation of condensed liquid near the wellbore and, for lowproducing rates, accumulation of condensate within the tubing string or theannulus, or both, depending on the type of well completion. Liquid condensateaccumulation, hereafter referred to as condensate accumulation, is defined asthe condensed hydrocarbon liquid saturation within the formation in excess ofthe saturation given by the experimental volumetric depletion data. Kniazeffand Naville and Eilerts et al. each developed models for predicting thesaturations and pressures in the vicinity of a gas condensate pressures in thevicinity of a gas condensate producing well. The method used by Eilerts et al.producing well. The method used by Eilerts et al. requires data for the fluidsystem obtained from laboratory flow experiments in the porous media ofinterest. Both studies predicted high condensate saturations in the region ofthe well. O'Dell and Miller presented a simple method based on steady-stateflow concepts that can be used to estimate quickly the deliverability from thewell. Results obtained using this method indicate that predictions of producingrates will be pessimistic if the predictions of producing rates will bepessimistic if the average reservoir pressure is below the saturation pressureof the in-place fluid. pressure of the in-place fluid. Roebuck et al. developedthe first models that consider the flow of individual components and accountfor component mass transfer between phases as dictated by phase equilibriadata. One of these models was used to predict the performance of a producingwell in a reservoir containing a rich gas producing well in a reservoircontaining a rich gas condensate. The duration of the prediction was very short(0.25 day), so no definite conclusions could be inferred from the study. Theresults did show that condensate accumulated very rapidly adjacent to the wellas soon as the flowing bottom-hole pressure fell below the saturation pressure. The purpose of this paper is to describe the use of a modified version of theone-dimensional (1-D) radial model developed by Roebuck et al. to studylong-term single-well performance in three gas condensate reservoirs. This workwas done to (1) show the effect of condensate accumulation on wellproductivity, (2) evaluate the applicability of a productivity, (2) evaluatethe applicability of a steady-state method similar to that presented by O'Delland Miller, and (3) evaluate the effect of phase equilibria data and relativepermeability characteristics on predicted performance. predicted performance. Description of Model Roebuck et al. give detailed descriptions of 1-D linear, 1-D radial, and 2-Dcompositional models. Briefly, the models predict the flow of each hydrocarboncomponent* and the water phase as a function of time and space. JPT P. 860