Co-injection case with M_ref,x = 500, K_ref,x = 100 mD, K_z/K_x = 0.1 and L_z = 10 m. Comparison of (a) NAPL recovery factor (RF, produced NAPL volume over initial NAPL volume in place, OOIP) and (b) produced surfactant concentration (C_f) and cumulative mass (M_f) time evolution as a function of V_DP for chemicals-free injection (“nofoam”), foam with constant M_ref,x (“ref”, dashed lines) and scaled M_ref,x (“mod”, solid lines). Relative variations are either in relation to a chemicals-free twin injection (“/ nofoam”) or a constant M_ref,x case (“/ foam”).