The ester is injected at about 10,000 ppm concentration in the same water the well produces. Since the ester partition coefficient is measured in the laboratory before the test using produced water and test reservoir oil. For this example, the ester K value is 5. This means that the ester, ethyl acetate, is five times more soluble in the oil than it is in the water. As a test example we will illustrate a 1000 bbls SWCT test. The first 250 bbls will carry the ethyl acetate, into the reservoir. As soon as the ester enters the pore space containing residual oil, the ester partitions into the stationary oil according to the partition coefficient K. The black dots represent this ester. The light blue represents the injected water. Notice that the injected water separates from the ester tracer. This is because the ester progress slows down relative to the injected water. The ester spends considerable time in the stationary the oil phase. During this time, the ester is stationary. Since the ester is also in equilibrium with the moving water phase, the net result is a slower velocity for the ester than the water being injected.