COMPREHENSIVE MODELLING
OF GAS CONDENSATE RELATIVE PERMEABILITY AND ITS INFLUENCE ON FIELD PERFORMANCE
The productivity of
most gas condensate wells is reduced significantly due to condensate banking
when the bottom hole pressure falls below the dew
point. The liquid drop-out in these very high rate gas
wells may lead to low recovery problems. The most important parameter for
determining condensate well productivity is the effective gas permeability in
the near wellbore region, where very high velocities can occur. An
understanding of the characteristics of the high-velocity gas-condensate flow
and relative permeability data is necessary for accurate forecast of well
productivity. In order to tackle this goal, a series of two-phase drainage
relative permeability measurements on a moderate permeability North Marmara –1 gas well carbonate core plug sample, using a simple
synthetic binary retrograde condensate fluid sample were conducted under
reservoir conditions which corresponded to near miscible conditions. As a fluid
system, the model of methanol/n-hexane system was used
as a binary model that exhibits a critical point at ambient conditions. The
interfacial tension by means of temperature and the flow rate were varied in the laboratory measurements. The laboratory
experiments were repeated for the same conditions of
interfacial tension and flow rate at immobile water saturation to observe the
influence of brine saturation in gas condensate systems. The laboratory
experiment results show a clear trend from the immiscible relative permeability
to miscible relative permeability lines with decreasing interfacial tension and
increasing velocity. So that, if the interfacial tension is high and the flow
velocity is low, the relative permeability functions clearly curved, whereas
the relative permeability curves straighten as a linear at lower values of the
interfacial tension and higher values of the flow velocity. The presence of the
immobile brine saturation in the porous medium shows the same shape of behavior
for relative permeability curves with a small difference that is the initial
wetting phase saturations in the relative permeability curve shifts to the left
in the presence of immobile water saturation. A simple new mathematical model is developed to compute the gas and condensate relative permeabilities as a function of the three-parameter. It is
called as condensate number; NK so that the new model
is more sensitivity to temperature that represents implicitly the effect of
interfacial tension. The new model generated the results were in good agreement
with the literature data and the laboratory test results. Additionally, the end point relative permeability data and residual
saturations satisfactorily correlate with literature data. The proposed model
has fairly good fitness results for the condensate
relative permeability curves compared to that of gas case. This model, with
typical parameters for gas condensates, can be used to
describe the relative permeability behavior and to run a compositional
simulation study of a single well to better understand the productivity of the
field.
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