Alleviation of effective permeability reduction of gas-condensate due to condensate buildup near wellbore
When the reservoir pressure is decreased below dew point pressure of the gas near
the wellbore, gas-condensate wells start to decrease production because condensate is
separated from the gas around the wellbore causing a decrease in gas relative
permeability. This effect is more dramatic if the permeability of the reservoir is low. The
idea proposed for reducing this problem is to eliminate the irreducible water saturation
near the wellbore to leave more space for the gas to flow and therefore increase the
productivity of the well. In this research a simulation study was performed to determine
the range of permeabilities where the cylinder of condensate will seriously affect the
wellÂ?s productivity, and the distance the removal of water around the wellbore has to be
extended in order to have acceleration of production and an increase in the final reserves.
A compositional-radial reservoir was simulated with one well in the center of 109
grids. Three gas-condensate fluids with different heptanes plus compositions ( 4, 8 and 11
mole %), and two irreducible water saturations were used. The fitting of the Equation of
State (EOS) was performed using the method proposed by Aguilar and McCain. Several
simulations were performed with several permeabilities to determine the permeabilities
for which the productivity is not affected by the presence of the cylinder of condensate.
At constant permeability, various radii of a region of zero initial water saturation
around the wellbore were simulated and comparisons of the effects of removal of
irreducible water on productivity were made.
Reservoirs with permeabilities lower than 100 mD showed a reduction in the
ultimate reserves due to the cylinder of condensate. The optimal radius of water removal
depends on the fluid composition and the irreducible water saturation of the reservoir.
The expected increase in reserves due to water removal varies from 10 to 80 % for gas
production and from 4 to 30% for condensate production.
Advisor:Jr, William D McCain; Lee, John; Berg, Robert
School:Texas A&M University
School Location:USA - Texas
Source Type:Master's Thesis
Keywords:condensate permeability ring cylinder productivity
Date of Publication:12/01/2004