Marcio Carvalho | Searcharxiv

arXiv2021

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

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.

physics.flu-dyn↗

arXiv2020

Compositional Pore-Network Modeling of Gas-Condensate Flow

Liquid dropout and retention in gas-condensate reservoirs, specially in the near wellbore region, obstruct gas flowing paths and impact negatively the produced fluid volume and composition. Yet, condensate banking forecasting is commonly inaccurate, as experiments seldom reproduce reservoir extreme conditions and complex fluid composition, while most pore-scale models oversimplify the physics of phase transitions between gas and condensate. To address this gap, a fully implicit isothermal compositional pore-network model for gas and condensate flow is presented. The proposed pore-networks consist of 3D structures of pores connected by constricted circular capillaries. Hydraulic conductances are calculated for the capillaries, which can exhibit single-phase flow or two-phase annular flow, according to local gas and liquid saturations, or be blocked by a liquid bridge, when capillary forces overcome viscous forces. A PT-flash based on the Peng-Robinson EoS is performed at control volumes defined for the pores at each time step, updating the phases properties. Flow analyses were carried based on coreflooding experiments reported in the literature, with matching fluid composition and flow conditions, and approximated pore-space geometry. Predicted and measured relative permeability curves showed good quantitative agreement, for two values of interfacial tension and three values of gas flow velocity.

physics.flu-dyn↗