Due to decreasing development of new conventional reservoirs the research in new unconventional sources and the increase in recovery of existing or already abandoned wells has become an important target for the future. The latter is done with different well treatments, where acidizing and flushing with solvent are the standard procedures to improve the flow behavior of plugged or polluted wells. Thereby the pollution originates from associated substance in the crude oil which form in many cases precipitations, alsphaltenes, scale and paraffins. However, the treatments with acids and solvents show several negative concomitant effects like degradation of crude oil or the need of neutralization which introduced the search for alternative treatment methods. One of them are well treatments with ultrasonic waves which is the topic of this master thesis. Ultrasonic treatments are performed by inserting an ultrasonic resonator into the well and producing ultrasonic waves for a certain time. This can lead to considerably improvements in flow rate. Nevertheless, the process of cleaning is very complex and even at elevated hydrostatic pressure and temperature not a well known topic. Therefore the company Progress Ultrasonic AG in cooperation with the chair of Petroleum and Geothermal Energy Recovery want to build a simulator for the laboratory, to test the behavior of ultrasonic treatments on well, perforations and the near wellbore area. Furthermore, the design of the "sonotrode" and the quality management should be improved. For this purpose two drafts have been made. The first one fitted the initial requirements, but those changed during the hole development process. Testing the attenuation through three completions under hydrostatic pressure, elevated temperature and saturated in different fluids were the main focus of the first draft. The second one offered additionally the possibility to test above atmospheric pressure. Laboratory tests in a water bath with the ultrasonic resonator at atmospheric pressure showed that casing shields the formation from the ultrasonic waves and nearly no waves traveled trough it except for the perforations. Additional tests for aquifer cleaning from the university of Mainz indicated, that the effects of cleaning change with increasing hydrostatic pressure. Cavitation, which is responsible for cleaning at atmospheric pressure, becomes negligible small above 5 bar hydrostatic pressure. Out of that a final simulator was designed, focusing on the study of the cleaning processes at elevated pressures and temperatures. In this simulator the ultrasonic device can be tested in different fluids with or without a casing. It is a sealed cylindrical pipe where the fluid can be pumped into it via a connection at the bottom. Since there will be test runs with borehole fluids, the simulator is standing in a box, to avoid a spill in in case of a leakage.