Summary The low viscosity and density of carbon dioxide (CO2) usually result in the poor sweep efficiency in CO2-flooding processes, especially in heterogeneous formations. Foam is a promising method to control the mobility and thus reduce the CO2 bypass because of the gravity override and heterogeneity of formations. A switchable surfactant, Ethomeen C12, has been reported as an effective CO2-foaming agent in a sandpack with low adsorption on pure-carbonate minerals. Here, the low mobility of Ethomeen C12/CO2 foam at high temperature (120 °C), high pressure (3,400 psi), and high salinity [22 wt% of total dissolved solids (TDS)] was demonstrated in Silurian dolomite cores and in a wide range of foam qualities. The influence of various parameters, including aqueous solubility, thermal and chemical stability, flow rate, foam quality, salinity, temperature, and minimum-pressure gradient (MPG), on CO2 foam was discussed. A local-equilibrium foam model, the dry-out foam model, was used to fit the experimental data for reservoir simulation.
A switchable cationic surfactant, e.g., tertiary amine surfactant Ethomeen C12, has been previously described as a surfactant that can be injected in high pressure CO2 for foam mobility control. C12 can dissolve in high pressure CO2 as a nonionic surfactant and equilibrate with brine as a cationic surfactant. Here we describe the adsorption characteristics of this surfactant in carbonate formation materials. The adsorption of this surfactant is sensitive to the equilibrium pH, the electrolyte composition of the brine, and the minerals in carbonate formation materials. Pure C12 is a nonionic surfactant. When it is mixed with brine, the solution has high pH and limited solubility. However, when the surfactant solution in brine is equilibrated with high pressure CO2, the pH is about 4, the surfactant switches to a cationic surfactant and becomes soluble. Thus the adsorption is also a function of pH. The adsorption of C12 on calcite at low pH is low, e.g., 0.5 mg/m 2. However, if the carbonate formation contains silica or clays, the adsorption is high, as is typical for cationic surfactants. The adsorption of C12 on silica decreases with increase in divalent (Ca 2+ and Mg 2+) and trivalent (Al 3+) cations. This is due to the competition for the negatively charged silica sites between the multivalent cations and the monovalent cationic surfactant. An additional effect of the presence of divalent cations in the brine is that it reduces the dissolution of calcite or dolomite in presence of high-pressure CO2. The dissolution of calcite and dolomite is harmful because of formation damage and increased alkalinity. The latter raises the pH and thus increases adsorption of C12 or even cause surfactant precipitation.
A switchable cationic surfactant, e.g., tertiary amine surfactant Ethomeen C12, has been previously described as a surfactant that can be injected in high pressure CO 2 for foam mobility control. C12 can dissolve in high pressure CO 2 as a nonionic surfactant and equilibrate with brine as a cationic surfactant. Here we describe the adsorption characteristics of this surfactant in carbonate formation materials. The adsorption of this surfactant is sensitive to the equilibrium pH, the electrolyte composition of the brine, and the minerals in carbonate formation materials.Pure C12 is a nonionic surfactant. When it is mixed with brine, the solution has high pH and limited solubility. However, when the surfactant solution in brine is equilibrated with high pressure CO 2 , the pH is about 4, the surfactant switches to a cationic surfactant and becomes soluble. Thus the adsorption is also a function of pH. The adsorption of C12 on calcite at low pH is low, e.g., 0.5 mg/m 2 . However, if the carbonate formation contains silica or clays, the adsorption is high, as is typical for cationic surfactants. The adsorption of C12 on silica decreases with increase in divalent (Ca 2+ and Mg 2+ ) and trivalent (Al 3+ ) cations. This is due to the competition for the negatively charged silica sites between the multivalent cations and the monovalent cationic surfactant. An additional effect of the presence of divalent cations in the brine is that it reduces the dissolution of calcite or dolomite in presence of high-pressure CO 2 . The dissolution of calcite and dolomite is harmful because of formation damage and increased alkalinity. The latter raises the pH and thus increases adsorption of C12 or even cause surfactant precipitation.
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