Experimental study of high-temperature foam for acid diversion

Foam treatments are used worldwide for acid diversion in matrix acid well stimulation. Many field treatments require foam effectiveness at elevated temperature in the presence of both acid and corrosion inhibitor.This study examines four surfactant formulations at room temperature, 104 °C (220 °F) and 204 °C (400 °F), with and without acid and corrosion inhibitor. The surfactants included amphoteric as well as nonionic foaming agents. The acid formulation was a mixture of chelating agent and HCl, with pH about 4. Formulations were tested at all three temperatures for foaming with N2 gas (80% quality) at back-pressure of 600 psi (4.1 MPa) in sandpacks and for bulk-foam stability in a pressure cell.Foam was created in most cases at 24 °C (75 °F) without acid or corrosion inhibitor. Creating foam with acid and corrosion inhibitor at 204 °C was more difficult, requiring higher injection rates and lower foam quality. Once formed, strong foam had higher mobility at elevated temperatures than at room temperature. Addition of corrosion inhibitor was more adverse to foaming than acid itself. At 204 °C foam propagation was slower, and steady-state pressure gradient was lower, than at 24 °C. The two steady-state strong-foam regimes reported elsewhere were present at 104 °C and in the presence of acid. Pressure gradient at 104 °C was lower in both high-quality and low-quality foam regimes.The bulk-foam stability results agree qualitatively with the sandpack results, but quantitative relationships between the two tests are hard to draw. These results also suggest that these surfactants may degrade over a period of time, for example, a couple of hours at 204 °C. Residence time in the heated sandpack therefore should be properly accounted for in design of experiments.These results are consistent with decreasing foam stability at higher temperature; adverse interactions between foaming surfactant and inhibitor; easier foam generation and propagation at higher velocity and lower foam quality; and greater difficulty in creating foam under conditions that reduce steady-state foam strength.These results can aid design of high-temperature foam-acid diversion treatments.