A method includes installing a measurement device on the injection wellhead, injecting a fluid into the injection well at a plurality of injection rates using a computer processor, measuring an injection bottom hole pressure at each injection rate to determine a plurality of injection bottom hole pressures using the computer processor, determining a relationship between the plurality of injection rates and the plurality of injection bottom hole pressures using the computer processor, and determining an injectivity index of the injection well using the relationship and the computer processor.