Experimental investigation of ultrasonic treatment effectiveness on pore structure.

During the whole life of oil production, enhancing the efficiency and optimizing the production of wells always have been discussed. Formation damage is one of the most frequent reasons for oil wells productivity reduction. This phenomenon can be caused by different factors such as fine migration, drilling mud invasion, asphaltene precipitation, capillary blockage reservoir fluids, and inorganic precipitation. Acidizing and hydraulic fracturing are two conventional well treatment methods usually applied to overcome the formation damage. However, due to destructive side effects of these methods, new methods such as Ultrasonic technology have helped to overwhelm these challenges. The usefulness of this method has been previously proven experimentally and operationally, but the effect of this technology on the pore structure has not been completely explored yet. In this paper, the effect of the ultrasonic wave on the pore structure during well stimulation is investigated. For this purpose, five samples of carbonate and sandstone with different rock textures were investigated to determine the effect of ultrasonic waves on flow behavior and microscopic pore structure through absolute permeability test, scanning electron microscope (SEM) images and petrography. The results showed that ultrasonic waves may affect pore structure through; initiation of micro-fracture and/or detachment of rock particle. The micro-fracture initiation is expected to increase the permeability while the detached particle may reduce or increase permeability through the clogging or opening the pore throat. For example, it was observed that ultrasonic waves significantly increase the permeability of Oolitic carbonate samples, while the controversial changes were observed in sandstone samples.