## 2 Research Methods for Reservoir Fluid PVT High-Pressure Physical Property Analysis
### Prediction and Analysis of Formation Crude Oil Viscosity  
#### 2.3.1 Correlation Analysis of High-Pressure Physical Property Parameters  
When conducting the high-pressure physical property analysis of reservoir fluid PVT, the interconnections among the high-pressure physical property parameters are of great significance for grasping and forecasting the behaviors of oil and gas reservoirs. By employing Pearson correlation analysis, the linear associations between these parameters can be measured precisely. Take the bubble point pressure and the saturation pressure as  
\begin{table}
\begin{tabular}{c c c} \hline
**Serial Number** & **Parameter Name** & **Description** \\ \hline
1 & Bubble Point Pressure & The pressure at which the gas phase begins to form in the hydrocarbon mixture, which is an important parameter for evaluating the properties of reservoir fluids. \\ \hline
2 & Volume Factor & Represents the ratio of the volume of the underground fluid to the volume under standard surface conditions at a specific temperature and pressure. \\ \hline
3 & Crude Oil Viscosity & A physical quantity that describes the flow resistance of crude oil and has an important impact on oil field development and pipeline transportation. \\ \hline
4 & Dissolved Gas–Oil Ratio (GOR) & Represents the volume of dissolved natural gas in a unit volume of formation crude oil, reflecting the saturation of the oil and gas reservoir. \\ \hline
5 & Compressibility & A physical quantity that describes the sensitivity of fluid volume to pressure changes and plays an important role in reservoir dynamic prediction. \\ \hline
6 & Crude Oil Density & Represents the mass of a unit volume of crude oil and has a direct impact on fluid properties, reservoir physical properties, and productivity prediction. \\ \hline
7 & Saturation Pressure & The pressure at which the hydrocarbon mixture in the oil and gas reservoir reaches a saturated state, which is a key parameter for fluid phase behavior analysis. \\ \hline \end{tabular}
\end{table}
Table 1: High-pressure physical property parameters of reservoir fluid PVT.  
an example. Generally speaking, there exists a positive correlation between them. That is to say, when the pressure goes up, both the bubble point pressure and the saturation pressure will rise accordingly.  
As for the volume factor and the crude oil density, there might be a negative correlation. The reason is that when the crude oil density becomes larger, for the same mass of crude oil, the space it occupies will be smaller, and thus the volume factor will be lower. Moreover, there could also be a specific correlation between the crude oil viscosity and the dissolved gas-oil ratio. When the dissolved gas-oil ratio increases, it may cause the crude oil viscosity to decrease. This is because the dissolved gas will form tiny bubbles within the crude oil, which can contribute to reducing the flow resistance.  
The compressibility, which reflects how sensitive the fluid volume is to pressure changes, may also have a certain functional relationship with the bubble point pressure and the saturation pressure.  
To deeply analyze the correlations between these parameters, a correlation matrix between the parameters can be constructed, and the correlation strengths between each parameter can be visually displayed through visualization methods (such as a heat map). This analysis not only helps in understanding the physical properties of reservoir fluids, but also provides an important basis for reservoir evaluation and dynamic analysis. In practical applications, combined with advanced data analysis methods such as graph convolutional networks, the accuracy and practicability of parameter correlation analysis can be further improved.