MODELING GAS-CONDENSATE WELL DELIVERABILITY

This paper gives an accurate method for modeling the deliverability of gas-condensate wells. Well deliverability is calculated with a modifi ed form of the Evinger-Muskat(1) pseudopressure (originally proposed f or solution-gas-drive oil wells). The producing gas/oil ratio (GOR) is needed to calculate pseudopressure, together with pressure/volume/tem perature (PVT) properties (black-oil or compositional), and gas/oil re lative permeabilities. The proposed method is successfully tested for radial, vertically fractured, and horizontal wells. Using the proposed deliverability model, we show that fine-grid single-well simulations can be reproduced almost exactly with a simple rate equation that uses pseudopressure. The key is knowing the producing GOR accurately. The effect of near-wellbore damage, vertical fracture, or flow improvement caused by horizontal well trajectory is readily incorporated into the rate equation as a constant skin term. The effect of gas/oil relative permeability is studied. We show that well deliverability impairment resulting from near-wellbore condensate ''blockage'' is dependent only on relative permeabilities within the range defined by 1 < k(rg)/k(ro ) < 50. Usually this represents gas and oil relative permeabilities ra nging from 0.05 to 0.3. Gas relative permeabilities at low oil saturat ions (k(rg) > 0.3) affect deliverability only for richer gas condensat es. A key observation and conclusion from this study is that critical oil saturation has no direct effect on well deliverability. We also sh ow that interfacial tension (IFT) dependence of relative permeability has little or no effect on gas-condensate well performance (e.g., leng th of plateau production). The most important application of this stud y is to provide a simple method for calculating bottomhole flowing pre ssure (BHFP) in coarse-grid models. We show that the proposed pseudopr essure method is readily calculated for each well grid cell on the bas is of only grid-cell pressure and saturation (i.e., producing GOR). Lo cal grid refinement near wells is not necessary, and relatively large well grid cells can be used and still provide an accurate description of well deliverability.