Theoretical and Methodological Features for Gas-condensate PVT Fluid Modelling with Limited Data

Abstract

Majority of gas-condensate reservoir discoveries in Dnieper-Donets Basin (Ukraine), is characterized by limited composition only up to C5+, phase behavior studied by non-equilibrium, so called differential condensation PVT experiment, combined with the uncertainty in condensate production allocation to individual wells, makes the direct application of the results in modern PVT modeling software not possible. The new method, based on the Engler distillation test (ASTM86) for definition of pseudo-components combined with synthetic creation of liquid saturation curve for CVD experiment, was proposed and successfully applied for different gas-condensate reservoirs in the area of study. The quality control (QC) of the PVT model is further performed by applying material-balance method on a single-cell simulation model for exported black-oil PVT formulation when needed. The method proved being useful for modeling of multiple gas-condensate reservoirs of Dnieper-Donets Basin with different potential condensate yields varying from 30 to 700 g/m3 and as an example presented for two reservoir fluids with 108 and 536 g/m3. Results of numerical simulation studies were within the engineering accuracy in comparison to historically observed values. The investigation showed that a representative fluid model can be create in the cases when no detailed fluid composition or required laboratory experiments are available. PVT model can be efficiently validated and QC-ed by performing material-balance type numeric simulation constructed with one cell. However, the proper fluid sampling and PVT cell laboratory experiments are still major requirements for precise reservoir fluid characterization and equation of state (EOS) modeling.