Abstract
This paper outlines a methodology for constructing equation of state (EOS) descriptions and source rock fluid composition correlations to describe the fluid properties of entire unconventional plays, such as the Eagle Ford shale play and the Permian Basin's Delaware Basin Wolfcamp formation. This methodology is tailored to match the quality of the available data in each play.
Sufficient reservoir fluid samples (either recombined companion surface separator samples or downhole fluid samples) with full pressure-volume-temperature (PVT) laboratory studies are required to span the range of fluids found in each play. These data provide the basis for tuning EOS parameters for C7+ pseudo-components and binary interaction parameters.
Source rock fluid composition varies with thermal maturity of the reservoir. The most direct measure of thermal maturity is C7+ mole weight (MW) determined for fluid samples; however, in areas with unstable production, such as slugging or cycling wells, a three-month-average producing condensate/gas ratio (CGR) is utilized as the basis for correlating the composition. The resulting tuned EOS models and source rock fluid composition correlations provide fluid descriptions for forecasting models, well models, artificial lift design tools, and facility models. When combined with proprietary maps of source rock thermal maturity measures, the models discussed here can be utilized to estimate fluid properties for undrilled acreage.
