Calcite Dissolution in Geothermal Reservoirs Using Chelants

Abstract

Chemical stimulation was studied in the laboratory as an alternative to hydraulic stimulation for increasing well injectivity and near-wellbore permeability in geothermal reservoirs. Two chelants, EDTA and NTA, were investigated for use as mineral- dissolution agents. A laboratory reactor was designed and fabricated for simulating the dissolution of calcium carbonate using these and other dissolution agents under controlled conditions that simulate a geothermal reservoir. Preliminary experimental data indicate that both EDTA and NTA are effective dissolution agents and that dissolution capacity increases with temperature. A reactive transport model of the laboratory reactor was constructed using TOUGHREACT for the purpose of simulating the calcite-dissolution process. Initial results indicate that, as expected, dissolution rate is directly proportional to flow rate, but indirectly proportional to pH.