Ultrasonic Removal of Near-Wellbore Damage Caused by Fines and Mud Solids

Abstract

Summary Laboratory experiments were conducted to investigate the feasibility of using ultrasonic energy to reduce formation damage caused by fines and mud solids. Cores were damaged with drilling muds in a dynamic filtration cell. Damage caused by fines migration was simulated with freshwater injection. The damaged cores were then treated with ultrasonic energy at various frequencies and intensities. The experiments were conducted with fully brine-saturated cores and cores partially saturated with decane. Permeability was monitored as a function of ultrasonic treatment time during backflow for three different sections of each core. Permeability increase, the depth of treatment, and the ultrasonic energy requirements were investigated for both sandstone and limestone cores. The results showed that permeability increased by a factor of three to seven after ultrasonic treatment for cores that were damaged by mud solids and fines migration. Treatment was successful for frequencies of approximately 20 to 80 kHz and acoustic intensities of approximately 20 to 250 W/m2. For these wavefield parameters, the effective depth of treatment for reducing fines damage was approximately 2.5 in. Damage caused by mud infiltration penetrated only the first 2.5 in. of the cores, and thus, ultrasonic treatment had no effect on deeper sections.