Production data analysis using type curves in gas condensate reservoirs - Impact of degree of undersaturation

Limited available literature on production data analysis (PDA) use modern decline type curves developed for single-phase analysis to analyse gas condensate reservoirs data without properly accounting for multiphase conditions. This could result in highly erroneous reservoir and well productivity parameter estimates. In this study, production data generated from fine-grid 1-dimensional compositional reservoir simulation models, with various degrees of undersaturation (initial pressures ranging from 5500 psia to 12000 psia), and wells operating at bottomhole pressures below dew-point, were analysed with Blasingame type curves, using the single-phase technique as well as a two-phase method introduced by our team, which is based on an equivalent-phase concept. The results demonstrate that at high degrees of undersaturation, where stabilised boundary dominated flow (BDF) is established before the entire reservoir becomes two-phase, single-phase analysis can produce relatively reliable parameter estimates. However the proposed two-phase method produced more reliable parameter estimates because of more confident type curve matches obtained particularly during boundary dominated flow. At low degrees of undersaturation, where the entire drainage volume becomes two-phase prior to the establishment of stabilised BDF, two-phase methods are shown to be absolutely necessary for obtaining the required quality of analysis and parameter estimates.