Viren Kumar's dissertation
by
Viren Kumar, PhD
University of Texas at Austin, 2006
Supervisors: Gary A. Pope and Mukul M. Sharma
Well productivity in gas condensate reservoirs is reduced by condensate banking when the bottom hole flowing pressure
drops below the dewpoint pressure. Several methods have been proposed to restore gas production rates after a decline
due to condensate blocking. Gas injection, hydraulic fracturing, horizontal wells and methanol injection have been tried
with limited success. These methods of well stimulation either offer only temporary productivity restoration or are
applicable only in some situations. Wettability alteration of the rock in the near well bore region is an economic and
efficient method for the enhancement of gas-well deliverability. Altering the wettability of porous media from strongly
water-wet or oil-wet to intermediate-wet decreases the residual liquid saturations and results in an increase in the
relative permeability to gas. Such treatments also increase the mobility and recovery of condensate from the reservoir.
This study validates the above hypothesis and provides a simple and cost-efficient solution to the condensate blocking
problem.
Screening studies were carried out to identify the chemicals based on structure, solubility and reactivity at reservoir
temperature and pressure. Experiments were performed to evaluate these chemicals to improve gas and condensate relative
permeabilities. The improvement in relative permeability after chemical treatment was quantified by performing high
pressure and high temperature coreflood experiments in Berea sandstone, Texas Cream limestone and reservoir cores using
synthetic gas mixtures at reservoir conditions. Experiments were done at high flow rates and for long time periods to
evaluate the durability of the treatment.
Single well simulation studies were conducted to demonstrate the performance of the chemical treatment in the field. The
experimental relative permeability data was modeled using a trapping number dependent relative permeability model and
incorporated in the simulations. Effect of connate water saturation, drawdown pressure, skin, treatment radius and the
timing of the treatment during the life of the reservoir were investigated using a compositional simulator.
Spectroscopic studies using a scanning electron microscope, neutron magnetic resonance and time of flight-secondary ion
mass spectroscopy were used to determine the structural and reactive chemistry of the chemicals used and to evaluate the
extent of treatment on the rock surface. The study allows us to postulate and partly verify a detailed mechanism of
interaction between the rock surface and the chemical.
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