Calculation of Productivity of a Gas-Condensate Well: Application of Skin With RateDependent Pseudopressure

摘要

The most crucial region affecting well productivity is thernperforated region. An accurate determination of perforationrnperformance, required in the optimum design and wellrnproductivity estimation, could be made by fine gridrnsimulation, but it would be costly with many technicalrnlimitations. The alternative practical approach is the use of arnskin factor in open hole calculations resulting in the same flowrnperformance as that of the perforated well. However most ofrnthe skin calculations done today are based on single-phasernflow conditions.rnIn this work, we have developed a method to determinernthe effect of perforation on gas condensate well productivityrnby defining a skin factor to be used in the pseudo pressurernapplication. The main problem is that pseudo pressure in suchrnsystems is a function of velocity and the conventional skinrnfactor, which is calculated for a perforated well, cannot bernused directly in open hole calculations. This is due to the factrnthat the gas and condensate relative permeability (krnkr) canrnincrease significantly by increasing the flow rate, contrary tornthe common understanding. This effect, known as positiverncoupling, complicates the flow of gas and condensate near thernwellbore even further when it competes with inertial losses atrnhigher velocities typical of those around perforation tips.rn) The above complications, which require information onrnvelocity-location in the perforation region, have been tackledrnby proposing new techniques with an emphasis on theirrnpracticality. Sensitivity studies, comparing the results ofrndeveloped methods with those using finite element methods,rnindicated the reliability of the proposed techniques. Thernmethods can be used to estimate variations of skin due to longtermrncondensate banking and the need for any intervention andrnremedial action.