## 2 Materials and Methods
### Methods  
The laboratory rig is a modified Auto Flood Reservoir Conditions Coreflooding System (AFS-300). The modification was made in the part of the liquid receiving chamber at the exit from the core holder. Such parts as a sleeve, a chamber, and a cover were manufactured for this study. The sleeve is installed in the core holder and pressed against the rock  
Figure 4: A microphotograph depicts the crude oil containing paraffin matter. The image was taken on an Axio Imager light microscope with an M2M tripod at 200\(\times\) magnification. Figure 3: Crude reservoir oil sample before experiments. sample. The sleeve is hollow and allows fluid to filter out of the rock plug into the chamber. The chamber is a hollow, conical part that is connected to the sleeve. The chamber has two nozzles, such as the upper one for the outlet of the filtered liquid to the back pressure regulator and then to the flow meter, and the lower one for emptying the chamber. The chamber is filled with the liquid coming from the plug. The chamber has a sealing cap at the end. An emitter of elastic waves is screwed onto the cap. The experimental method is as follows: First, the liquid filtered through the rock sample passes through the sample into the chamber. Then, due to the relatively large volume of 600 mL, to save time for the experiment, the chamber is manually replenished with the same liquid (crude oil). Next, at least three pore volumes are filtered, and a trend is set for a decrease in the permeability of the rock due to blocking the pore space of the sample by paraffins and asphaltenes. Then, to observe the effect of the nonlinear load during filtering, the actuator of elastic waves (nonlinear load) is activated. As a result of the reciprocating motion of the actuator elements, a nonlinear load of a given frequency is created on the chamber cap. Cap vibrations are transmitted through the fluid filling the cone chamber through the sleeve to the end of the rock sample, after which the vibrations (elastic waves) further propagate through the matrix and fluid into the pore channels (the effect of a solid and liquid piston) [37]. The activation of nonlinear loads leads to a change in the permeability of the rock plug. The modernized design of the rig simulates the inflow of fluid from the formation into the well, in which the actuator for elastic waves is installed, which sends nonlinear loads to the near-wellbore formation zone towards the filtering oil. Improvements are shown in Figure 5. The principle of operation of the Langevin emitter is based on the ability of the material (crystals) of a piezoceramic element to change its dimensions in an electric field (also known as the inverse piezoelectric effect and similarly used as in the experiments by [38]). The actuator is characterized by one dominant frequency, at which it produces the maximum amplitude of reciprocating motion (enters into a resonance state). Therefore, the cap is made in such a way that it allows the actuator to be changed to study the filtration at different frequencies of a nonlinear load. The nonlinear signal is modulated on a Rigol DG1022 oscillator. Due to the low amplitude of the signal from the generator, a custom-built amplifier is used, which increases the signal amplitude to the maximum possible at the resonant frequency. The control of the frequency and amplitude of the signal received after the amplifier and coming to the actuator is carried out using the Hantek6204 BD oscilloscope and a workstation. In the experiments, the rock sample is in a state of all-round compression. With the help of a rubber cuff, an overburden stress is created in the core holder, simulating the rock pressure of 1000 psi (or 6.9 MPa). With the help of pumps supplying liquid to the ample inlet, a pore pressure of 100-150 psi (or 0.7-1.0 MPa) is created, while the back pressure regulator maintains pressure at the sample outlet.