Thermodynamic Fluid Characterization in a Compositional Reservoir Model: A Field Gas Injection Study

In order to create an integrated simulation model, it is essential to have a fluid characterization based on revision and validation of the available laboratory data. These include PVT studies, production data, RFT logs, etc. In case of EOR process modeling, it is necessary to also consider the special fluid tests (swelling test and displacement measures on cores) which permit the evaluation of the injected gas effect on the original fluid properties in the reservoir, particularly at the saturation pressure.

The thermodynamic study based on the available experimental PVT data, taken from three appraisal wells of a carbonate oil field is presented. The fluid system flowing throughout two reservoir levels is characterized by means of equations of state finalised to a full 3D gas injection reservoir study. The objective is optimizing the field production strategies considering the injection of natural gas.

Overview of all the experimental data shows a good agreement among the tests performed on samples belonging to the same level. In this study two equations of state (three parameters Peng-Robinson equation) have been calibrated for the two levels. The simulated PVT parameters by the tuned EOS for the two levels are in good agreement with the already measured experimental data. In addition, the swelling test simulation shows a fair match within limits of cubic EOS.

The slim tube experiments performed by laboratory to state the miscibility/immiscibility condition of the reservoir oil with respect to the gas extracted at the separators are also simulated. Consequently the sensitivity of the miscibility conditions to possible variations of the composition of the injected gas is investigated.