The Adjustment of EOS of Gas-condensate Mixture under the Condition of Input Data Shortage

Abstract

The article characterizes the key difficulties which emerge during the simulation of phase behaviors described using the model of “black oil” or fully functional compositional model with the help of the equation-of-state (EOS) in order to create valid continuously operating geological-technological 3D models of gas-condensate reservoirs. The input data for 3D filtration reservoir modeling, the development of which started in the 1960s, are the results of initial gas-condensate and thermodynamic studies. Hydrocarbon component composition of reservoir gas in the existing gas-condensate studies is given only to fraction C5+. Taking into account the peculiarities of initial thermodynamic research with the use of the differential condensation experiment and the absence of such type of experiment in the list of standard experiments in commercially-available PVT-simulators, there appeared a need to develop rational approaches and techniques for correct integration of existing geological-production data in PVT modeling. This article describes the methods for adjusting Peng-Robinson equation-of-state under the condition of input data shortage. Depending on initial data availability and quality, the authors have suggested two different methods. The first PVT-modeling method, which makes it possible to adjust the equation-of-state, is based on the data of component composition of gases and fractional composition of the stable condensate. In case the data of fractional composition of the stable condensate are not available, the authors suggest the second method that is the splitting of fraction C5+ following Whitson volumetric methodology. The suggested methods and two different approaches to EOS adjustment allow effective PVT-modeling using available geological and production data. Study results are presented as the graphical dependencies of comparison of potential hydrocarbons C5+content change in reservoir gas before and after configuring the equation-of-state, as well as the synthetic “liquid saturation” loss curve of the CVD experiment.