Pore-scale analysis of gas injection in gas-condensate reservoirs

TL;DR

This study uses a pore-network model to analyze the micro-scale effects of gas injection for mitigating condensate banking in gas-condensate reservoirs, identifying the most effective gases for flow improvement.

Contribution

It provides the first detailed pore-scale analysis of gas injection effects on condensate removal and flow enhancement in sandstone reservoirs.

Findings

C2 and CO2 are most effective for condensate removal.

C1 and N2 can impair gas flow, especially when mixed with produced fluids.

Gas injection improves flow by re-vaporizing condensate at the pore scale.

Abstract

Condensate banking around wellbores can significantly shorten the production from gas-condensate reservoirs. Different approaches to mitigate this issue have been proposed in the literature, among which gas injection comes out with promising results. With this method, pressure maintenance and condensate re-vaporization can be achieved, lessening the flow blockage caused by liquid dropout and accumulation in the porous medium. While gas injection in gas-condensate reservoirs has been largely investigated at the meso and macro scales, data regarding the method's efficiency at the micro-scale are scarce. Therefore, the effects of local changes in gas and condensate properties stemmed from the interaction between injected and reservoir fluids at the pore-scale are poorly understood. In order to evaluate how these changes affect the transport in porous media, a compositional pore-network model was used to reproduce gas injection in a sandstone sample following condensate accumulation. C1, C2, CO2, N2, and produced gas were tested as the candidates for condensate banking remediation at different pressure levels. After gas flooding, condensate saturation, heavy component recovery, and gas relative permeability were quantified to appraise the achieved gas flow improvement. The results indicated that C2 and CO2 were the most effective gases to clear the accumulated condensate and re-establish the gas flow. Conversely, C1 and N2, especially mixed with the produced fluids, displayed the least favorable results, and could even lead to gas flow impairment.