Well Deliverability Predictions for a Low-Permeability Gas/Condensate Reservoir

Abstract

Abstract It is well known that the deliverability of gas condensate wells can be impaired by the formation of a condensate bank once the bottomhole pressure drops below the dew-point. There have been many excellent laboratory studies on gascondensate relative permeability that describe this phenomenon, but integrated laboratory-simulation-field studies that compare systematic predictions to field performance are few. This work presents a careful and comprehensive evaluation of deliverability of several wells in a low permeability gas condensate reservoir. This sandstone reservoir has permeability ~ 10 md, porosity ~ 10%, and condensate yield ~ 50 bbls/MMscf. Our approach consists of the following steps - (i) careful selection of core samples that cover the range of expected responses; (ii) design of fluid systems that mimic reservoir fluids, but at lower temperatures; (iii) appropriate relative permeability measurements krg = f(krg/kro, Nc) for a range of flow conditions; (iv) fitting this data to several different relative permeability models for use in reservoir simulators; (v) use of analytical spreadsheet tools to calculate deliverability; (vi) detailed single well compositional models with realistic geology and boundary conditions extracted from full field models, honoring complex producing rules and differential depletion; (vii) comparison of prediction to four wells, three vertical and one inclined. We have been able to reasonably predict the performance of these wells. The productivity reduction of the wells were found to be in the range of 80%, the majority of which occurred in the initial phases of production. Our ability to reasonably predict the performance has given us confidence that our approach, including measuring only the relevant portion of the relative permeability curves and using synthetic fluids, may be sufficient.