The most crucial region affecting well productivity is the perforated region. An accurate determination of perforation performance, required in the optimum design and well productivity estimation, could be made by fine grid simulation, but it would be costly with many technical limitations. The alternative practical approach is the use of a skin factor in open hole calculations resulting in the same flow performance as that of the perforated well. However most of the skin calculations done today are based on single-phase flow conditions.
In this work, we have developed a method to determine the effect of perforation on gas condensate well productivity by defining a skin factor to be used in the pseudo pressure application. The main problem is that pseudo pressure in such systems is a function of velocity and the conventional skin factor, which is calculated for a perforated well, cannot be used directly in open hole calculations. This is due to the fact that the gas and condensate relative permeability (kr) can increase significantly by increasing the flow rate, contrary to the common understanding. This effect, known as positive coupling, complicates the flow of gas and condensate near the wellbore even further when it competes with inertial losses at higher velocities typical of those around perforation tips.
The above complications, which require information on velocity-location in the perforation region, have been tackled by proposing new techniques with an emphasis on their practicality. Sensitivity studies, comparing the results of developed methods with those using finite element methods, indicated the reliability of the proposed techniques. The methods can be used to estimate variations of skin due to long-term condensate banking and the need for any intervention and remedial action.