Numerical simulation of In-situ combustion and the effects of change in parameters on reservoir efficiency

In-situ combustion is a high-risk thermal recovery which usually is used for heavy oil and extra-heavy oil reservoirs. This method of EOR can be done as forward and reverse which latter has been found economically unattractive and difficult to apply. In forward combustion, dry and wet can be used. This paper focused on dry combustion. A sensitivity analysis with a compositional simulator has been done. Effect of porosity of reservoir, permeability of reservoir, anisotropy ratio, initial temperature and target total molar rate was analysed on different key parameters. Water cut, oil recovery factor, gas oil ratio, total water production, well productivity index and reaction’s rate in the reservoir during combustion simulated for 600 days. It found that when permeability increased from 500 millidarcy to 1000, 3000 and 5000 millidarcy, GOR curve changed rapidly before first 90 days and shift to the lower values. Moreover, water cut decreased slightly and oil production increased from 15285 STB to 15768, 16648 and 18280 STB respectively. Furthermore, oil recovery factor and water production increased. Decreasing in porosity from 0.38 in BASE case to 0.30, 0.25 and 0.20 resulted in decreasing oil recovery factor, oil production from 15285 STB to 12180 STB, 10392 STB and 8709 STB respectively, water production and GOR. Increasing initial reservoir temperature from 200 °F to 250 °F resulted in increasing oil recovery factor from 0.85 to 0.95. In addition, it causes water start to produce sooner. Anisotropy ratio does not have any special effect on reactions, but changing initial temperature resulted in a considerable change in reactions. It proved that target total molar rate has a great effect on the oil production. In the BASE case, total molar rate of oxygen was 300 lbmol/day at 200F at 70psi and recovery factor was 0.85. By changing oxygen molar rate to 250, 100 and 70 lbmol/day at 200F at 70psi recovery factor changed to 0.95, 0.56 and 0.39 respectively. It concluded that optimum molar rate was 250 lbmol/day between these values.