Methanol treatment in gas condensate reservoirs: A modeling and experimental study

• Core flood apparatus set up to study condensate blocking and chemical treatment in cores.
• Experimental tests to quantify the loss in relative permeability caused by condensate accumulation.
• Evaluation the use of methanol to restore the gas relative permeability in gas condensate reservoirs.
• Modeling and simulation of methanol treatment on condensate-blocked rocks using cubic-plus-association (CPA) equation of state.
• Solving differential equations by orthogonal collocation method, which is particularly attractive for solving nonlinear problems.

Well productivity in gas condensate reservoirs is reduced by condensate blockage when the bottom-hole pressure drops below dew point pressure. The present experimental study on limestone cores shows that the relative permeability of gas decreases due to liquid blockage; furthermore, methanol has proven effective in the removal of condensate and restoration of gas relative permeability. In this research, the decrease in gas relative permeability caused by condensate banking and the effect of methanol treatment on condensate-blocked rocks was simulated using the cubic-plus-association (CPA) equation of state. The CPA equation of state was applied to the modeling of two-phase flows through cores for methanol–hydrocarbon mixtures due to charge transfer and hydrogen bonding, both of which may strongly affect the thermodynamic properties of such mixtures. Differential equations were solved by means of the orthogonal collocation method, a method particularly attractive for solving nonlinear problems. The modeling results confirm the experimental results, and both methods indicate that significant productivity loss can occur in retrograde gas condensate reservoirs when the flowing bottom-hole pressure falls below dew point pressure. Moreover, the results show that methanol treatment can improve gas relative permeability by a factor of about 1.3–1.6. These results may help reservoir engineers and specialists to restore the lost productivity of gas condensate.