A study of the water injection phase of the Little Knife CO2 minitest has been completed using a three-dimensional, three-phase black oil simulator. The study was designed to investigate the water injection requirements for re-pressurization and the effects of the injection on the reservoir. An accurate reservoir characterization was necessary to accomplish this goal. It is believed that by including a detailed description of reservoir properties and production history, a good reservoir characterization was obtained. Using the resultant reservoir model, several prediction cases were run to simulate the effects of various injection plans on the minitest area. These cases included two injection start up dates and two different future production performance schedules. The following conclusions are drawn, based upon the results of this study: (1) the pressure in the minitest area will be raised above the calculated minimum CO/sub 2/ miscibility pressure of 3400 psig, if water injection is begun on either October 1, 1980 or September 1, 1980; (2) a water injection rate of 1150 STB/D, for fifteen (15) days, will adequately repressure the pilot area if the above dates are observed; (3) the current rate of reservoir fluid withdrawal will not adversely affect the pilot area if the aforementioned injection plan is utilized; (4) water injection in the pilot area will not strongly affect the average reservoir pressure in the D-zone of the Little Knife field. 28 figures, 11 tables.