## 3 Results  
Figure 3 shows that the presence of graphene nanoplatelet and nanosilver gave an insignificant effect on the density of water-based mud (mud weight). Density of the blank sample is 9.00 ppg (i.e., pounds per gallon). This is a common density used during the first stage of a drilling operation [19]. A key feature of mud density measurement is to reflect the ability of the mud to carry drilled cuttings as the suspending mud has an associated buoyancy effect on the cuttings. In the presence of graphene nanoplatelet and nanosilver at 0.1 g, 0.5 g and 1.0 g, the density increment is less than 0.50 ppg. In a drilling operation, mud density is designed slightly higher than formation pressure to ensure maximum penetration rate [19]. Too high mud weight will cause loss circulation of formation, stuck of drill pipe, decrease on penetration rate and formation damage. While insufficient of mud weight (too low) will cause well collapse or instability of the well due to formation pressure higher than the hydrostatic pressure provided by mud column. Ultimately, selecting mud density during the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Material** & **Function** & **Quantity (g)** \\ \hline Fresh Water & Base & 287.22 \\ Prehydrated Gel & Additive-viscosityifier & 22.56 \\ Soda Ash & Additive-hardness control agent & 0.20 \\ Potassium chloride & Additive-ion exchange agent & 39.13 \\ Caustic Soda & Additive-pH control & 0.70 \\ Hydrozan® & Additive-viscosityifier & 1.50 \\ Hydro star NF® & Additive-fluid loss agent & 141.49 \\ Barite & Additive-weighing agent & 3.50 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Formulation of water-based mud. formulation stage is a key factor to realizing an effective drilling operation and remain economical. In general, the presence of graphene nanoplatelet and nanosilver gave an ambiguous effect on the mud weight due to the negligible dimension of its particle size. Mathematically, mud weight is calculated by the sum of weights over the sum of volumes. Since the weight of the added nanoparticle is negligible, the mud weight measurement will not be affected. Plastic viscosity (PV) is defined as a resistance of fluid to flow [4]. It is characterized as a major aspect of the stream resistance of the liquid created by mechanical friction within the fluid. PV represents a viscosity of drilling mud. Figure 4a shows the viscosity of water-based muds with and without the presence of the nanoparticles. Significant increment due to the presence of a graphene nanoplatelet and nanosilver as shown in Figure 4a is reflected in Figure 4b, in terms of percentage. Figure 4b shows that, with only 0.1 g of either the graphene nanoplatelet or the nanosilver, the increment of PV is up to 21.4% and 28.5%, respectively. At 0.5 g, the increment is tripled for graphene nanoplatelet and doubled for nanosilver. While at 1.0 g, both nanoparticles increased the mud viscosity to more than 50%. The statistical correlations for the mud viscosity in the presence of nanoparticle (NP) are (i) PV = \(-0.3417\) NP\({}^{3}\) + \(2.475\)NP\({}^{2}\)\(-\) 1.0333 NP + 12.9 (for graphene nanoplatelet) and PV = 3 NP + 11 (for nanosilver) with both of the correlations having R\({}^{2}\) = 1. The presence of nanoparticles in the drilling mud formulation contributed to (i) high solid content, and (ii) high stability of waterborne particles. This is the reason why the PV measurement was observed to be increased without the formation of additional attractive force. The Dejaguin-Landau-Verwey-Overbeek (DLVO) theory is a basis for theoretical calculations explaining the nanoparticles behavior in a solution. According to the DLVO theory, the stability of particles is determined by the net electrostatic surface interactions of the particles and their Van der Waals forces. The net electrostatic surface interaction between the nanosilver particles is further investigated by measuring the yield point (YP) values. Figure 3: Density measurement of water-based muds with 5% error bar.