# Influence of Stress Anisotropy on Petrophysical Parameters of Deep and Ultradeep Tight Sandstone
## 4 Results and Discussion  
### Influence of Water Saturation on Sonic and Electrical Parameters  
Rock sample No. 3-11-8-1 was tested, and the P-wave signal change waveform and S-wave signal change waveform of different water saturations were output (Figure 5a,b).  
\begin{table}
\begin{tabular}{c c c} \hline
**Confining Pressure (MPa)** & **Axial Pressure (MPa)** & **Stress Ratio** \\ \hline
50 & 78 & 1.56 \\ \hline
60 & 78 & 1.30 \\ \hline
70 & 78 & 1.11 \\ \hline
80 & 78 & 0.975 \\ \hline \end{tabular}
\end{table}
Table 4: The experimental scheme for sample No. 3-2-14-1.  
\begin{table}
\begin{tabular}{c c c} \hline
**Confining Pressure (MPa)** & **Axial Pressure (MPa)** & **Stress Ratio** \\ \hline
60 & 66 & 1.1 \\ \hline
60 & 72 & 1.2 \\ \hline
60 & 78 & 1.3 \\ \hline
60 & 84 & 1.4 \\ \hline \end{tabular}
\end{table}
Table 5: The experimental scheme for sample No. 3-10-5-1.  
Rock water saturation affects the size of rock physical parameters. The P-wave velocity, S-wave velocity and resistivity of rock samples with water saturations of 0%, 50%, 64%, 78%, and 100% were statistically analyzed and fitted to the curves. The experimental results show that (1) with increasing water saturation, the P-wave velocity changed in three stages. When the water saturation was 0-23%, the P-wave velocity increased with increasing water saturation, and the slope was large. When the water saturation was 23-78%, the P-wave velocity decreased with increasing water saturation. When the water saturation was between 78% and 100%, the P-wave velocity decreased with increasing water saturation (Figure 6a). (2) The S-wave velocity decreased linearly with increasing water saturation, and there was a negative correlation between the S-wave velocity and water saturation (Figure 6b). (3) When the water saturation was less than 70%, the resistivity decreased with increasing water saturation. When the water saturation was greater than 70%, the resistivity was basically unchanged with increasing water saturation (Figure 6c). In general, with the change in water saturation, the shear modulus will change, which will lead to changes in longitudinal and transverse wave velocity.  
The mineral composition of rock affects the scale of rock physical parameters. In the experiment, rock samples with different contents of feldspar, quartz and clay were set up to output the velocity ratio of each rock sample. The points of different feldspar contents and their corresponding ratios, different quartz contents and their corresponding ratios were cast and fitted to the curves. The experimental results show that (1) there was an approximately positive correlation between the velocity ratio of the P-S wave and feldspar content (Figure 7a), and (2) there was a positive correlation between the P-S wave velocity ratio and quartz content (Figure 7b). (3) The ratio of the P-S wave velocity was positively correlated with the clay content (Figure 7c). (4) The rocks in the study area are mainly quartz minerals. Quartz plays a major role in the influence of P-wave and S-wave velocity, followed by feldspar and clay.  
Figure 5: Waveform diagrams of P-wave (**a**) and S-wave (**b**) signal variation.  
Figure 6: Relationship curves between P-wave velocity, S-wave velocity, resistivity and water saturation.