The first 250 bbls of water with ethyl acetate is followed with a 750 bbl water injection to push the ester bank away from the well about 15 to 20 feet. All the injection water is tagged with a material balance tracer such as iso-propyl alcohol (IPA). The K for IPA is near zero (0.01). The ester tracer stays together as a donut shaped bank and is continuously in equilibrium with both the oil and water phases. This injection usually is completed in one to two days.