Comparison of Acidizing and Ultrasonic Waves, and Their Synergetic Effect for the Mitigation of Inorganic Plugs

The oil and gas industry is plagued by inevitable formation damaged in the wellbore proximity during entire life of the well. Therefore, it is indispensable to ameliorate the damaged permeability by either using conventional applied techniques or ultrasonic-assisted stimulation method. The latter is characterized by efficient, simple and convenient, and environmentally secure method. Due to these distinguished characteristics, the demand of this physical Enhanced Oil Recovery (EOR) technique increased in petroleum industry. In this study, ultrasonic waves and hydrochloric acid (HCl) were used separately as well as in combination to recover the lost productivity caused by calcium carbonate (CaCO3) inorganic plugs in low permeability sandstone core samples. Results showed that permeability recovery increased with irradiation time up to 100 min; however, it decreased with further irradiation. This deviation could be due to particles bridge formation at later stage. In addition, optimum frequency and power of ultrasonic waves (20 kHz and 1000 W) significantly recovered the damaged permeability. Although maximum frequency (25 kHz) could not achieve maximum permeability, but higher power was quite effective. The damaged permeability recoveries of HCl and ultrasonic waves were 44.5% and 37.6% respectively, but the permeability recovery was escalated to 61.5% when HCl and ultrasonic techniques were applied together. Inorganic plugs using ultrasonic waves could chiefly be caused by cavitation, acoustic streaming, and heat generation in three different ways, such as cavitation, boundary friction and transformation upon hitting the medium.