# Experimental Study on Fluid Dissipation Effects in Core Samples by NMR Measurement
## 4 Experimental Results  
### Fluid Dissipation Rate  
During NMR measurements at various dissipation time points, the mass of the core samples is recorded using an electronic balance. As dissipation time increases, the weight of both core samples exhibits a downward trend, initially decreasing rapidly before gradually stabilizing (as illustrated in Figure 2). Notably, during the initial 100 h (as indicated by the dotted line in Figure 2), the weight of the cores significantly decreases as dissipation time increases. Subsequently, the change in core weight becomes significantly smaller and gradually stabilizes.  
To eliminate the discrepancies in initial weight and volume of the cores, the decline in core weight over time is calculated and normalized based on sample volume, yielding the dissipation rate of fluid per unit volume of the core, as illustrated in Figure 3.  
The unit volume dissipation rate reflects the rate of fluid dissipation. The curve in Figure 3 is divided into three stages: The first stage occurs within the initial two hours, as indicated by the first dotted line in Figure 3, during which the dissipation value per unit volume of the core fluid is maximized. This phenomenon is attributed to the fluid remaining on the core surface, which rapidly disperses into the air due to the large contact area. The second stage occurs from 2 to approximately 64 h of dissipation, as indicated by the second dotted line in Figure 3, during which the dissipation rate is relatively stable and  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & **Volume (mL)** & **Dry Weight (g)** & \begin{tabular}{c} **Helium** \\ **Porosity (\%)** \\ \end{tabular} & \begin{tabular}{c} **Helium** \\ **Permeability (mD)** \\ \end{tabular} & \
\begin{tabular}{c} **NMR Porosity** \\ **(\%)** \\ \end{tabular} &
\begin{tabular}{c} **Oil Viscosity** \\ **(mPas)** \\ \end{tabular} \\ \hline A & 21.371 & 47.239 & 15.661 & 18.724 & 15.656 & 42 \\ B & 20.954 & 47.656 & 13.341 & 34.972 & 13.313 & 240 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Basic parameters of experimental samples.  
rapid. This stage likely involves the more easily dissipated fluid within the core rapidly escaping into the air through seepage channels. The third stage, referred to as the stable stage, occurs after 96 h, during which the fluid dissipation rate gradually decreases to a relatively stable low-value region. This stage represents the dispersal phase of movable oil, characterized by high oil viscosity and a significantly reduced dispersal rate. In the context of NMR core measurement technology, the second stage is the central focus of this research, characterized by a time distribution spanning from 2 to 96 h. This period corresponds to the interval during which the core is extracted from the wellbore and subsequently processed for measurement or further experimental analysis. During this critical phase, fluid changes within the core are most pronounced and exert the greatest influence on measurement results. These changes directly affect the accuracy and reliability of experimental data, making it essential to analyze the dissipation behavior of fluids during this stage comprehensively.  
Figure 3: The rate of fluid change in sample A and sample B.  
Figure 2: Mass change rate of sample A and sample B. Light blue and Green line represents the second stage of sample’s dispersion.