Table 3.

Summary of research publications related to US field tests.

Reference	Overview	Main Characteristics	Findings
Chang et al. [23]	First application of ultrasonic technology in offshore wells in Southeast Asia	Irradiation time 20 min/ft Frequency 20 kHz US power 1 kW	•Oil production increased by 30 % in well X after US treatment •Pressure communication between tubing and casing in well Y successful removal of wax clogging gas lift valves by US •Potential for stimulation of the tubing walls and gas lift valves if any plugging suspected
Abramov et al. [3]	Study of influence of ultrasound on fluid viscosity under reservoir conditions	US generator 9 kW Frequency 19 kHz Max. temperature 65 °C Exposure time 24 h	•Oil production increase by 0.4 tons/day •After 4 h treatment, viscosity reduction of 16 % was observed
Mullakaev et al. [65], [66]	Testing of US equipment in 27 wells in Samotlorsk field	Frequency 19 kHz Max. temperature 85 °C US power 2 kW	•Average increase in production rate by 75 % •Well productivity index increased by 40 % •Decrease in water cut by 8.2 %
Abramov et al. [2]	Study of a selective ultrasound technique for perforated regions in horizontal wells with high water cut	Oil density 940 kg/m3 Paraffin content 47 wt% Viscosity 6,800 mPa.s US generator 2–10 kW Frequency 13–26 kHz	•Oil production increased by 91 % •Water production decreased by 20 %
Mullakaev et al. [64], [67]	Testing of thermo-acoustic equipment in Samotlorsk field, Samara region and Utah, USA	Frequency 19 kHz Max. temperature 85 °C US power 2 kW	•Production increased by 75 % in Samotlorsk, 107 % in Samara region, and 4.45 ton/day for over 6 months in Green River Formation
Abramova et al. [5]	US treatment for enhanced oil recovery	Over 100 wells with different characteristics Frequency 13–26 kHz	•Success rates of 90 % •Oil production rate increased 40–100 % •Effects sustained for 3–5 months •Additional testing for efficiency without pump optimization effect confirmed US oil productivity enhancement and water cut reduction
Abramov et al. [4]	Application of ultrasonic enhancement on failing wells by stimulating the wells with an ultrasound source	Permeability 20 mD Porosity 15 % Frequency 18–27 kHz US power 10 kW	•Production rate increased by 50 % •For wells with high permeability and porosity, potential increase for up to 85 % •For wells with low permeability and porosity, recommended combined treatment with chemicals