## 3 Results and Discussion
### Characterization of the Salled Water-Based Fluid Formulations
As shown in Table 6, some palygorskite aqueous drilling fluid formulations presented filtrate volumes lower than or close to those obtained in this work. However, it is worth highlighting that the filtrate volumes of these formulations were, for the most part, obtained in an API filter press and, therefore, under less severe test conditions than those used in this study, which do not represent the field conditions of the petroleum wells to be abandoned. Even so, it is clear that the most efficient filtration control is obtained with palygorskite fluids whose formulation contains a significant number of additives, such as that proposed by [PERSON] et al. [41], who obtained an HPHT filtrate volume of 11 mL, a value practically equal to the minimum obtained in this work, which was 11.2 mL. However, the formulation proposed by the authors demands a higher cost and complexity in preparation when compared to the one proposed in this study. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Author** & **Formulation** & **Test Method** & **Summary of Results** \\ \hline [PERSON] et al. [39] & 400 mL of fresh water + 4\% of salt + 6.4\% of & & \\   [PERSON] et al. [39] & palygorskite + Variable content of PAC or & API filtrate volume * & FV\({}_{\text{API}}\) between 26.2 and 163.8 mL \\  & Xanthomonas Compestris Polymer & & \\ \hline [PERSON] et al. [17] & Water + palygorskite + Hydroxypropylamine + PAC & & \\   [PERSON] et al. [17] & + NaCl + cationic Polymer + triazine + MgO + calcium & API filtrate volume * & FV\({}_{\text{API}}\) between 3.9 and 6.0 mL \\  & carbonate + lubricant & & \\ \hline  & water + 1.5 wt\% composite bentonite + 1.5 wt\% & & \\  & palygorskite + 3 wt\% KCl + 3 wt\% Nano-SiO2-1 + & & \\  & 0.4 wt\% MMH-1 (Mixture of metal hydroxides) + & & \\  & 2 wt\% DFD (modified starch) + 0.3 wt\% LV-CMC + & & FV\({}_{\text{API}}\) = 7.2 mL (room \\ [PERSON] et al. [40] & 0.3 wt\% LV-PAC + 0.05 wt\% FC-1 (fluorecarbon & API filtrate volume * & temperature) \\  & surfactant) + 0.01 wt\% PTFE & & FVAPI = 6.8 mL (after \\  & (polytetrafluoroethylene) + 0.1 wt\% OS-1 (silicone & & aging for 16 h at 120 \({}^{\circ}\)C) \\  & surfactant) + 3 wt\% polymeric alcohol + & & \\  & 0.1 wt\% NaOH & & \\ \hline  & 2.5\% base mud + 0.4\% NaOH+ 0.1\% ZDP-1 (polymer & & \\  & anti-salt calcium and temperature resistance) + 8\% & & \\  & SMP-3 (resin filter loss reducer) + 2\% SPNH (lignite & & \\  & filter loss reducer) + 3\% ZDF-1+ 2 \% ZDGF (blocking) + & & HPHT filtrate & \\  & 30\% NaCl + 0.3\% CaO + 1.5\% CaCO\({}_{3}\) (2800 mesh) + & & volume & \\  & 4\% white oil + 0.4\% Span-80 + barite + 1.5\% SF260 & & \\  & (viscosity reducer) & & \\ \hline \hline \end{tabular}  
* * Filtration carried out at room temperature, with a pressure of 100 psi.  
\end{table} 
Table 6: Performance of palygorskite drilling fluids regarding filtrate control. Regarding the type and number of additives in the formulation, only the fluid developed by [PERSON] et al. [39] presents greater similarity with the formulation proposed in this work. However, its performance is inferior in terms of filtration control, so the minimum filtrate volume value (26.2 mL) is considerably higher than the filtrate volumes of the seven fluids formulated based on the factorial design carried out in this work. Thus, it highlights that the interaction between the additives used in the formulations proposed in this work, in appropriate proportions, ensured promising filtration control, especially for formulations with a higher PAC LV content (8 g), that is, F3 and F4, which may present themselves as suitable alternatives as barrier elements for well abandonment. Table 7 presents the values of the readings obtained from the viscometer for the speeds of 600, 300, 200, 100, 6, and 3 rpm and the values of the apparent viscosity (\(\upmu_{\text{a}}\)), plastic viscosity (\(\upmu_{\text{p}}\)), and yield point (YP) of each formulation.