Analysis of condensate banking dynamics in a gas condensate reservoir under different injection schemes

Abstract

If the reservoir pressure falls below the dewpoint pressure when producing a gas condensate reservoir, liquid dropout takes place in the reservoir. Liquid builds up in the near wellbore area causing what is known as a "condensate banking". This condensate banking significantly affects the well productivity since the gas relative permeability decreases. The formation of the condensate region near the wellbore can be prevented or delayed by gas injection since this reduces the loss of condensate by maintaining pressure and by vaporizing the liquid hydrocarbon phase into the injected gas. Water injection can also be an excellent alternative to maintain the reservoir pressure above the dewpoint pressure. We performed compositional simulation of a gas condensate reservoir under natural depletion, and injection of methane, injection of carbon dioxide, produced gas recycling and water injection. To monitor the condensate banking dynamics near the wellbore area, such as oil saturation and compositional changes, we incorporated a radial local grid refinement in our global Cartesian grid for the producer well. Results showed that carbon dioxide and water injection are the scenarios where the best final condensate recovery is achieved, although downstream separation is required when injecting carbon dioxide, and water injectivity is highly affected by heterogeneities. However, produced gas recycling is a good alternative if the delay in gas sales does not produce uneconomical consequences. Methane injection reported the lowest incremental condensate recovery because of the dramatic elevation of the saturation pressure. As a consequence the reservoir pressure was below the dewpoint pressure for a longer period of time. Also a partial and total vaporization of the condensate saturation near the wellbore area was observed when carbon dioxide, methane and produced gas were injected. Finally, since GOR is directly affected by the condensate production a generalized mathematical expression to predict GOR based on field variables such as gas production rate, gas injection rate, total hydrocarbon production, and original hydrocarbon in place, when injecting different gases was obtained.