Abstract
Matrix acidizing stimulation treatment in a multi-layered reservoir may achieve a limited success because of poor acid diversion to layers of lower permeability. A foam is currently used to temporarily plug higher permeability layers, and divert more acid to the damaged layers.
A combination of new factors that optimize the foam design parameters were assembled into a simple equation. The equation is based on laboratory experiments conducted on Berea sandstone cores under low (100 psi) and high (3000 psi) average pressures. According to this equation the degree of acid diversion into the damaged, lower permeability layers in the field can be specified and controlled.
A few parameters control the success of the foaming-acidizing process., hence there are a few input parameters to the equation. During a field acidizing job, the optimum combination of these parameters can be found from the calculation of the Average Optimized Diversion Factor (AODF). The AODF indicates how successfully the acid is diverted to the lower permeabilitylayers during the foam and acid injections. Results from the laboratory experiments show that the Average Optimized Diversion Factor (AODF) indicates instantly, from the inlet pressure and the change in acid injection rate, if the damaged zone will be successfully stimulated.
In field applications, fast calculations of the AODF can predict the effective removal of the damaged zones with time, using the change in the acid injection rate, bottom hole inlet pressure, and the volume of the acid injected as input parameters. Increase of the AODF indicates that the removal of the damaged zone is progressing in the right direction.
