Laboratory Measurements of Condensate Blocking and Treatment for Both Low and High Permeability Rocks

Coreflood experiments were conducted in Berea sandstone and Texas Cream limestone cores to quantify the loss in relative permeability caused by condensate accumulation. The in-situ condensate saturation was established dynamically by precise control of core inlet and outlet pressures. It is well known that retrograde condensate dropout can cause significant productivity loss in low permeability reservoirs. This paper shows that such losses can also occur in high permeability reservoirs. Gas relative permeability reductions of 91% to 97% were seen in 2-5 md limestone cores and 95% to 98% in 246-378 md sandstone cores. In light of the new data presented here, the common perception that condensate blocking around wells in high-permeability reservoirs is not significant should be re-examined. Our previous coreflood experiments showed that methanol treatments increased the gas relative permeability in low permeability carbonates, but we had not yet determined the required methanol treatment volumes as done in this study. Methanol displaces retrograde condensate and maintains improved gas relative permeability well into the post-treatment production period. Methanol also displaces water and this can also contribute to higher gas relative permeability in those cases when the initial water saturation is high enough to significantly add to the total liquid blocking of the gas. These results can be used to help reservoir engineers evaluate and treat gas-condensate wells with reduced productivity. Reservoir engineers should be especially careful to evaluate the damage done in such high-permeability reservoirs if the well's pressure drawdown is high enough to result in pressures below the dew point pressure.