An equivalent single phase approach to production data analysis in gas condensate reservoirs

In gas condensate reservoirs (GCR) operating below dewpoint pressure, two-phase conditions introduce non-linearities into the diffusivity equation, rendering conventional single-phase production data analysis unreliable. Recent studies, presented in a companion paper published in 2018, demonstrated the application of an equivalent single phase approach to improve the quality of GCR production data analysis using “Blasingame” type curves. That study analysed production data from radial GCR simulation models with fluid maximum liquid dropout ranging from 1% to 42%. The pressure-saturation/k_r data for the computation of equivalent-phase pseudovariables was determined using an approach based on two-phase steady-state (SS) theory. For saturated reservoirs, less consistent improvements in permeability, skin and drainage area estimates were obtained – an observation attributed to unrepresentative pressure-saturation/k_r data. This current study builds on the earlier work, by examining alternative sources of pressure-saturation data for use in the analysis of saturated GCR cases. PVT liquid-saturation curves and sufficiently representative pressure-saturation responses from the near-wellbore region of numerical simulations are considered. The results suggest that pressure-saturation data representative of the response in the near-wellbore region during transient flow is adequate for the two-phase analysis of long term production data using type curves. The results further highlight reservoir and well operating conditions under which each source of pressure-saturation data is most suitable for use with the equivalent-phase approach. A new time-based adjustment is also introduced to improve the quality of the equivalent-phase type curve analysis for cases in which the entire reservoir becomes saturated prior to stable boundary dominated flow (BDF) conditions. Finally, results are presented which show that our equivalent-phase approach can be successfully combined with other conventional production data analysis tools, e.g. type curves for hydraulically fractured wells, and straight-line techniques used in the analysis of BDF data, all of which were originally developed for analysing single phase systems.