Study on the phase behaviour of condensate gas in nanostructure media

Condensate dropout near the wellbore region in gas condensate reservoirs is the main reason for low well deliverability. Here, the gas and condensate phase behaviour in this region was investigated to find the conditions for better deliverability. Firstly, micro-computerised tomography (CT) experiments were carried out on a condensate gas system in four sandstone rock core samples. However, due to limitations of the experimental technique, the phase characteristics of the condensate gas could not be fully described in nanostructure pore scale. Therefore, an improved Peng–Robinson equation of state incorporating capillary force was used to simulate the flash phase behaviour of condensate gas and the constant volume depletion experiment in a single pore. Then, based on a pore network model generated using a random fractal method, a modified model was developed to investigate fluid distribution in a gas condensate system at the nanostructure pore scale. A new method was developed that applies a flash calculation in all throats in the network to estimate the amount of accumulated condensate in the corners of the throats. Finally, the phase behaviour of condensate gas in different types of porous media was studied in parallel capillary bundle and three-dimensional network models. The experimental phenomena observed in the CT experiments were explained by the characteristic simulation study. The results of this study provide theoretical support for phase behaviour predictions in condensate gas reservoirs.