TO INVESTIGATE THE USE OF AIR INJECTION TO IMPROVE OIL RECOVERY FROM LIGHT OIL RESERVOIRS

Abstract

Air injection into light oil reservoirs is now a proven field technique, because of the unlimited availability and low access cost of the injectant. One of the key of a successful air injection project is the evaluation of the process by carrying out representative laboratory studies. In this research, experimental set up has been developed to understand air injection process for improving oil recovery for depleted light oil reservoirs and the parameters on the basis of different petrophysics and fluid sample properties. In order to provide reliable experimental data, pressure and temperature experiments (up to 11032 KPa and 600 °C), at non-Isothermal conditions ramp of 5 o C/ min., were performed with unconsolidated cores (sand pack) and reservoir oils, at representative conditions of the air injection process into light oil reservoirs. The effects of porous media type, gas flux, heat input, water saturation and total pressure on the rates of the in- situ oxidation reaction were measured. When air is injected, the oxygen contained in the air (mainly of 79 % N 2 and 21% O 2 ) reacts with the hydrocarbons in place, by oxidation reaction. The produced combustion gases consisting of CO 2 , CO, O 2 and N 2 depend on the temperature conditions and the nature of the crude oil. The generation of a high temperature oxidation zone is preferable for its higher oxygen uptake potential, it’s more efficient carbon oxides generation and the creation of an oil bank downstream of the thermal front, both of the latter factors contribute to the improvement of the recovery. In both cases, the important point to assess is the oxygen consumption to prevent oxygen arrival at the producers and to sustain the combustion front. This is one of the main objectives of the air injection experiments. By continuous analysis of the produced gases from the reactor, at linearly increased temperature rate, it was found that combustion of crude oil in porous media follows a complex series of reactions. These reactions can be divided into three sequences :( 1) low temperature oxidation, (2) fuel deposition, and (3) fuel combustion. A model is proposed to analyze and differentiate among these reactions. The method developed is reasonably fast and can be used to measure the oxidation and deposition of fuel for a given crude oil and porous medium.The major conclusions are: 1. 100 percent utilization of oxygen was observed. 2. Significant oil recovery was achieved about 85 percent of original oil in place (OOIP). 3. The generation of flue gases by oxidation process was very efficient in terms of carbon oxides with an average percentage of gas composition of 10 % CO 2 and 4 % of CO and balance unreacted oxygen. 4. The H/C ratio for the deposited fuel decreases when temperature increases. 5. Increasing the injection pressure of system decreases the m-ratio [(CO/ (CO+CO 2 )] Expressions were obtained for low temperature oxidation rate of oil, the fuel deposition rate and the burning rate of fuel as a function of fuel concentration The relative reaction rate of carbon oxidation was used. The activation energy of each reaction was different for most of the runs. A significant effect of the heat input on activation energy was observed, a lower heat input producing larger activation energy. The effect of total pressure up to 11032 KPa indicated kinetic control with 21 % Oxygen partial pressure. This research will contribute to the overall understanding of air injection process and enable to be made of the most appropriate technique for a given reservoir. Use of less expensive method in tertiary phase will encourage the producers for additional recovery in this area.