Effect of Acoustic Stimulation on Aqueous Phase Trapping in Low-Permeability Sandstones

Formation damage from aqueous phase trapping in low-permeability sandstones can be removed using mutual solvents, blends of alcohols and mutual solvents, and surfactants. These treatments modify the interfacial tension of the trapped fluids or the wettability of the formation. However, treatments intended to remove a certain type of damage may cause other types of formation damage due to incompatibility with the rock and formation fluids. High-frequency acoustic waves have been used in industrial applications to clean up and remove contaminants. Important studies have been conducted to extend the use of acoustic waves for wellbore stimulation. This technical paper presents a laboratory investigation to determine the effects of ultrasonic (UT) treatment on interfacial tension and wettability alteration during invasion of fracturing fluids treated with surfactants in low-permeability sandstones. An experimental program consisting of a series of spontaneous imbibition experiments was conducted to measure the spontaneous imbibition potential of sandstone rock cores treated with surfactants in the presence of UT energy. Spontaneous imbibition tests were conducted in two steps. In the first, spontaneous imbibition tests were conducted on untreated low-permeability sandstone core samples in the presence of UT radiation. In the second step, spontaneous imbibition tests were conducted on cores flooded with surfactant while exposing the core to UT radiation from an acoustic horn. In each series experiments, the power output was changed to monitor the effect of acoustic power on wettability alteration. Results obtained from the experiments showed that acoustic stimulation improves imbibition of water in both water wet and intermediate wet cores. Wettability alteration is attributed to enhancement of capillary forces in water wet cores. For cores treated with water repelling surfactants, improvement in imbibition is attributed to detachment of surfactant molecules from the pore walls due to acoustic streaming of sonic waves. This research was originally intended to investigate removal of trapped water from fluid injection of low-permeability sandstones by acoustic stimulation. However, the obtained results show that it is possible to improve the recovery of trapped hydrocarbon in low-permeability sandstones under the influence of acoustic stimulation.