## 2 Methodology
### Slurry density  
Slurry density refers to the mass ratio of solid particles to liquid in the slurry, which significantly impacts shaft wall stability, drilling speed, and environmental protection [20]. Therefore, slurry density is a crucial parameter for evaluating slurry performance. In this experiment, a glass hydrometer was used to measure slurry density. After thoroughly mixing the slurry, it was poured into a 250 mL graduated cylinder. The hydrometer was then gently placed into the slurry, and the density was read from the scale where the hydrometer intersects the slurry surface [37]. The relationship between the CMC solution content, the bentonite content, and slurry density is shown in Figure 3a. It is observed that as bentonite content increases, the solid particles in the slurry increase significantly, leading to a considerable rise in slurry density. In contrast, changes in the CMC solution content have minimal effect on slurry density. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **Bentonite** & **CMC** & **Water** & \begin{tabular}{c} **Anhydroous** \\ **Sodium** \\ **Carbonate (g)** \\ \end{tabular} & \begin{tabular}{c} **Sodium** \\ **Tripolyphosphate** \\ **Solution (g)** \\ \end{tabular} & \begin{tabular}{c} **Density** \\ **(g/cm3)** \\ \end{tabular} & \
\begin{tabular}{c} **Apparent** \\ **Viscosity (cp)** \\ \end{tabular} &
\begin{tabular}{c} **Colloidal** \\ **Rate (\%)** \\ \end{tabular} \\ \hline N-T-1 & 30 & 20 & 550 & 1.0 & 1.0 & 1.025 & 8.57 & 97.0 \\ N-T-2 & 64 & 20 & 550 & 1.0 & 1.0 & 1.051 & 10.17 & 96.6 \\ N-T-3 & 101 & 20 & 550 & 1.0 & 1.0 & 1.081 & 15.12 & 96.0 \\ N-T-4 & 143 & 20 & 550 & 1.0 & 1.0 & 1.115 & 19.66 & 94.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Effect of variation of bentonite content on slurry properties. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**No. **} & **Bentonite** & **CMC** & **Water** & \begin{tabular}{c} **Anhydroous** \\ **Sodium** \\ **Carbonate (g)** \\ \end{tabular}  & \begin{tabular}{c} **Sodium** \\ **Carbonate (g)** \\ \end{tabular}  & \begin{tabular}{c} **Sodium** \\ **Tripolyphosphate** \\ **Solution (g)** \\ \end{tabular}  & \begin{tabular}{c} **Density** \\ **(g/cm3)** \\ \end{tabular}  & \ \begin{tabular}{c} **Apparent** \\ **Viscosity (cp)** \\ \end{tabular}  & \begin{tabular}{c} **Colloidal** \\ **Rate (\%)** \\ \end{tabular}  \\ \hline N-C-1 & 90.0 & 13 & 550 & 1.0 & 1.0 & 1.071 & 9.3 & 94.6 \\ N-C-2 & 90.0 & 20 & 550 & 1.0 & 1.0 & 1.071 & 12.0 & 96.4 \\ N-C-3 & 90.0 & 27 & 550 & 1.0 & 1.0 & 1.072 & 17.8 & 97.1 \\ N-C-4 & 90.0 & 34 & 550 & 1.0
2. Slurry viscosity  
Slurry viscosity refers to the ability of the slurry to resist flow when subjected to external forces and is a key indicator of the slurry's flow characteristics. Common methods for measuring slurry viscosity include rotational viscometers, Marsh funnels, and others. In this experiment, both a rotational viscometer and a Marsh funnel viscometer were used [37]. A 700 mL sample of slurry was placed into the Marsh funnel viscometer with the bottom valve closed. A slurry cup was positioned at the funnel's outlet, and the valve was opened while timing the flow of 500 mL of slurry into the cup to calculate the viscosity value. Additionally, the apparent viscosity of the slurry was measured using the rotational viscometer. The relationship between the CMC solution content, the bentonite content, and slurry viscosity is illustrated in Figure 3b. It was observed that as the contents of both the CMC solution and bentonite increased, slurry viscosity significantly rose. When both contents were at the same percentage, increasing the CMC solution content had a more pronounced effect on increasing slurry viscosity compared to bentonite. This is likely because bentonite has fewer particles that can form colloidal solutions, whereas the CMC solution is a high-viscosity colloid, offering a more effective thickening effect compared to bentonite. 3.