With gas production from gas condensate reservoirs, the flowing bottomhole pressure of the production well decreases. When the flowing bottomhole pressure becomes less than the dew point pressure, condensate accumulates near the wellbore area and forms a condensate bank. This results in loss of productivity of both gas and condensate. This becomes more serious in intermediate permeability gas-condensate reservoirs where the condensate bank reduces both the gas permeability and the well productivity.
Several techniques have been used to mitigate this problem. These methods include: gas cycling, drilling horizontal wells, hydraulic fracturing, injection of super critical CO2, use of solvents and the use of wettability alteration chemicals. Gas cycling aims to keep the pressure of the reservoir above the dew point pressure to reduce the condensation phenomena. The limited volumes of gas that can be recycled in the reservoir can hinder the application of this method. In order for an ideal recycle, gas volume injected into the reservoir will be larger than the total gas that can be produced from such a reservoir. Other approaches are drilling horizontal wells and hydraulic fracturing where the pressure drop around the wellbore area is lowered to allow for a longer production time with only single phase gas flow to the wellbore. These approaches are costly as they require drilling rigs. Another technique is the use of solvents which shows good treatment outcomes, but the durability is a questionable issue in these treatments. Moreover, wettability alteration needs to be approached very carefully as to not cause permanent damages to the reservoir. It was reported in many studies the use of fluorinated polymers and surfactants dissolved in alcohol-based solvents for wettability alterations treatments.
Each method has its own advantages and disadvantages, and can be applied under certain conditions. The paper presents all of these methods along with their advantages and disadvantages, besides description of some of their field applications and case studies.