Jacob Glen Walker's theses
by
Jacob Glen Walker, MSE
University of Texas at Austin, 2000
Supervisors: Gary A. Pope
Mukul M. Sharma
The main objective of this research was to experimentally investigate the
phase behavior, interfacial tension, and relative permeability of a gas-condensate
mixture including the effects of surfactants and alcohols intended to increase the gas
relative permeability. This research was motivated by the need to mitigate the
reduction in well productivity caused by condensate buildup below the dew point.
A study to screen surfactants for ultra-low interfacial tension is presented.
Both nonionic and anionic surfactants were studied. Low interfacial tension
microemulsions were formed with propane- and butane-brine mixtures at elevated
temperature. The surfactant combination of an alkyl propoxylated sulfate and an alkyl
ethoxylated sulfate was the most successful at forming microemulsions with high
solubilization ratios.
The properties of a gas-condensate mixture are discussed and the effect of low
molecular weight alcohols and brine on the phase behavior of this gas-condensate
mixture is given. A vapor-liquid-liquid region exists over much of the hydrocarbon-brine-methanol mixture concentration space, but at high overall concentrations of
methanol, a single-phase liquid forms. The effect of salt on the phase equilibria of
alcohol-water mixtures is also presented.
A novel approach for measuring high-pressure interfacial tension by using the
spinning drop method is presented. Fluorinated surfactants did not significantly
decrease the vapor-liquid interfacial tension of a methane-butane mixture. Interfacial
tensions measured for a gas-condensate mixture showed excellent agreement with
estimates using parachors. The effect of methanol was investigated for volatile
hydrocarbon-methanol mixtures and it was determined that methanol increased the
vapor-liquid interfacial tension.
Steady-state corefloods conducted with a gas-condensate mixture are analyzed
and discussed. These corefloods were conducted to study the effect of surfactants and
methanol on the gas relative permeability after condensate buildup. The surfactants
tested did not increase gas relative permeability in the presence of a condensate
phase. Methanol, however, increased the gas end-point relative permeability in the
presence of condensate banking and water blocking. This occurs because of the
miscible displacement of brine and condensate from the core.
Ambient condition steady-state coreflood experiments were conducted to
determine if methanol injection into reservoir cores saturated with highly saline
brines would adversely affect the permeability due to clay swelling, fines migration
and/or precipitation of salt. Methanol did not cause clay swelling or fines migration in
these sandstone cores. However, injecting methanol into cores saturated with highly
saline brines caused permeability reduction due to salt precipitation.
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