# Influence of Stress Anisotropy on Petrophysical Parameters of Deep and Ultradeep Tight Sandstone
## 3 Materials and Methods
### Experimental Equipment and Experimental Samples  
To study the influence of water saturation on sonic and electrical parameters, the rock sample No. 3-11-8-1 was selected, and different water saturation levels for the experimental group were set as 0%, 50%, 64%, 78% and 100%. The confining pressure and axial pressure remained unchanged, at 60 MPa and 78 MPa, respectively (Figure 4). It is important to note that this experiment was repeated many times for the given samples to conduct the rock physical parameter tests under different conditions. The following experiments were the same, and there was no further elaboration. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Analysis of the Factors** & **Clay Content/\%** & **Water Saturation/\%** &
\begin{tabular}{c} **Confining** \\ **Pressure/MPa** \\ \end{tabular} & **Axial Pressure/MPa** \\ \hline \multirow{8}{*}{Water saturation} & 24.2 & 0 & 60 & 78 \\  & 24.2 & 20 & 60 & 78 \\  & 24.2 & 40 & 60 & 78 \\  & 24.2 & 60 & 60 & 78 \\  & 24.2 & 80 & 60 & 78 \\  & 24.2 & 100 & 60 & 78 \\ \hline \multirow{2}{*}{Horizontal maximum principal stress or horizontal minimum principal stress, buried depth} & 20.1 & 100 & 52 & 57.2 \\  & 20.1 & 100 & 56 & 67.2 \\  & 20.1 & 100 & 60 & 78 \\ \hline \multirow{2}{*}{Horizontal maximum principal stress or horizontal minimum principal stress, buried depth} & 16.9 & 100 & 44.6 & 58 \\  & 16.9 & 100 & 52.3 & 68 \\  & 16.9 & 100 & 60 & 78 \\ \hline \multirow{2}{*}{Confining pressure} & 13.7 & 100 & 50 & 78 \\  & 13.7 & 100 & 60 & 78 \\  & 13.7 & 100 & 70 & 78 \\  & 13.7 & 100 & 80 & 78 \\ \hline \multirow{2}{*}{Axial pressure, stress ratio} & 8.4 & 100 & 60 & 66 \\  & 8.4 & 100 & 60 & 72 \\ \cline{1-1}  & 8.4 & 100 & 60 & 78 \\ \cline{1-1}  & 8.4 & 100 & 60 & 84 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The experimental scheme. Figure 3: The stress ratio distribution frequency. To study the influence of the stress ratio on the sonic and electrical parameters, the rock physical parameters of core No. 1-2-1 were tested. First of all, in this paper, the stress ratio, which is an important parameter reflecting the anisotropy of in situ stress, was defined as the ratio of axial pressure to confining pressure. Four experimental groups were set: (1) confining pressure of 52 MPa, axial pressure of 57.2 MPa, and stress ratio of 1.1; (2) confining pressure of 56 MPa, axial pressure of 67.2 MPa, and stress ratio of 1.2; (3) confining pressure of 60 MPa, axial pressure of 78 MPa, and stress ratio of 1.3; (4) confining pressure of 64 MPa, axial pressure of 89.6 MPa, and stress ratio of 1.4. The specific test scheme is shown in Table 2.  
To study the influence of the burial depth and confining pressure on the sonic and resistivity parameters, two types of experiments were set up. The specific experimental scheme is as follows:  
(1) Rock physics experiments under the same stress ratio and different confining pressures  
Four groups of rock physical parameters were tested for rock sample No. 1-2-2. The experimental conditions were as follows: (1) confining pressure of 44.6 MPa, axial pressure of 58 MPa, and stress ratio of 1.3; (2) confining pressure of 52.3 MPa, axial pressure of 68 MPa, and stress ratio of 1.3; (3) confining pressure of 60 MPa, axial pressure of 78 MPa, and stress ratio of 1.3; (4) confining pressure of 67.7 MPa, axial pressure of 88 MPa, and stress ratio of 1.3 (Table 3). To analyze the influence of the P-wave velocity, S-wave velocity, S-wave velocity ratio and resistivity on the confining pressure, the P-wave velocity, S-wave velocity ratio and resistivity were tested under confining pressures of 44.6 MPa, 52.3 MPa, 60 MPa and 67.7 MPa, respectively, and the stress ratio remained unchanged. The curves of P-wave velocity and confining pressure, S-wave velocity and confining pressure, P-S wave velocity ratio and confining pressure, and resistivity and confining pressure were fitted.