Reducing the Permeability of Sandstone Porous Media to Water and CO2: Applicationof Bovine Carbonic Anhydrase Enzyme

摘要

This paper presents the results of an investigation on theapplication of the enzyme bovine carbonic anhydrase forreducing the permeability of a sandstone porous mediumduring CO2 flooding. This process provides a method forimproving conformance of injected water and CO2 in anabsolutely environmentally friendly manner. Carbonicanhydrase enzyme accelerates the hydration reaction of CO2with water. Hence, in presence of carbon dioxide and divalentions, such as calcium, this enzyme leads to rapid precipitationof calcium carbonate. The precipitation reaction causesreduction in the permeability of the flooded regions of thereservoir. Therefore, upon subsequent injection of CO2 andwater, injected fluids would flow through the unswept parts ofreservoir, improving the conformance of the injected CO2 andwater.Experiments were carried out to investigate the effect ofvarious enzyme concentrations, temperature and pH on theprecipitation reaction. Enzyme concentrations at 2, 4 and 8micro mole per litter were tested. Also, effect of temperaturewas studied by performing experiments at room temperature,30 oC and 55 oC. A mathematical model was developed topredict the extent of precipitation of calcium carbonate.Subsequently, coreflood experiments, using Berea sandstonecores, were conducted and the degree of reduction in thepermeability of the cores was measured. Also, in order toinvestigate the effect of injection scheme on permeabilityreduction, two different methods of injection were tested. Forall sets of flow experiments, the permeability of the core wasreduced to less than half of its initial value.