| Popis: |
This paper presents the results of an investigation on the application of the enzyme bovine carbonic anhydrase for reducing the permeability of a sandstone porous medium during CO2 flooding. This process provides a method for improving conformance of injected water and CO2 in an absolutely environmentally friendly manner. Carbonic anhydrase enzyme accelerates the hydration reaction of CO2 with water. Hence, in presence of carbon dioxide and divalent ions, such as calcium, this enzyme leads to rapid precipitation of calcium carbonate. The precipitation reaction causes reduction in the permeability of the flooded regions of the reservoir. Therefore, upon subsequent injection of CO2 and water, injected fluids would flow through the unswept parts of reservoir, improving the conformance of the injected CO2 and water. Experiments were carried out to investigate the effect of various enzyme concentrations, temperature and pH on the precipitation reaction. Enzyme concentrations at 2, 4 and 8 micro mole per litter were tested. Also, effect of temperature was studied by performing experiments at room temperature, 30 °C and 55 °C. A mathematical model was developed to predict the extent of precipitation of calcium carbonate. Subsequently, coreflood experiments, using Berea sandstone cores, were conducted and the degree of reduction in the permeability of the cores was measured. Also, in order to investigate the effect of injection scheme on permeability reduction, two different methods of injection were tested. For all sets of flow experiments, the permeability of the core was reduced to less than half of its initial value. |
