# Fracturing Fluids and Their Application in the Republic of Croatia
## 5 Fracturing Fluids--Composition and Additives
### Classification of Fracturing Fluids
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Base Fluid** & **Fluid Type** & **Composition** & **Used for** \\ \hline \multirow{4}{*}{Acid} & linear gel & acid, guar or HPG & short fractures, carbonate formations \\ \cline{2-4}  & crosslinked gel & acid, crosslinker, guar or HPG & long and wide fractures, carbonate formations, \\ \cline{2-4}  & emulsion & acid, oil, emulsifier & moderate length fractures, carbonate formations \\ \cline{2-4}  & The application of acid fracturing is confined to carbonate reservoirs and is never used to stimulate sandstone, shale, or coal-seam reservoirs. \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Acid-based fracturing fluids. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Base Fluid** & **Fluid Type** & **Composition** & **Used for** \\ \hline \multirow{4}{*}{Alcohol} & methanol and water mixture or & \multirow{2}{*}{
\begin{tabular}{c} low permeability reservoirs with high clay \\ content, low formation pressure \\ \end{tabular} } \\  & 100\% methanol & \\ \cline{2-3}  & \multicolumn{2}{c}{Advantages} \\ \cline{2-3}  & Water usage is very reduced or completely eliminated. Methanol is not persistent in the environment (it \\ \cline{2-3}  & biodegrades readily and quickly under both anaerobic and aerobic conditions and photo-degrades relatively \\ \cline{2-3}  & quickly). It has excellent fluid properties: a high solubility in water, low surface tension and high vapor pressure. \\ \cline{2-3}  & It is a very good fluid for water-sensitive formations. \\ \hline \multicolumn{3}{c}{Disadvantages} \\ \cline{2-3}  & Methanol is a dangerous substance to handle because it has a low flash point—hence is easier to ignite—a large \\ \cline{2-3}  & range of explosive limits, high vapor density and invisibility of the flame. \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Alcohol-based fracturing fluids. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Base Fluid** & **Fluid Type** & **Composition** & **Used for** \\ \hline \multirow{4}{*}{Foam} & water-based & water, foamer, N\({}_{2}\) or CO\({}_{2}\) & low pressure formations \\ \cline{2-3}  & acid-based & acid, foamer, N\({}_{2}\) & low pressure, carbonate formations \\ \cline{2-3}  & alcohol-based & methanol, defoamer, N\({}_{2}\) & low pressure, water-sensitive formations \\ \cline{2-3}  & CO\({}_{2}\)-based & liquid CO\({}_{2}\) + N\({}_{2}\) & low pressure formations \\ \cline{2-3}  & \multicolumn{2}{c}{Advantages} \\ \cline{2-3}  & Water usage is reduced (or completely eliminated in the case of CO\({}_{2}\)-based foams). There is a reduced amount of \\ \cline{2-3}  & chemical additives. There is a reduction in formation damage. There is a better cleanup of the residual fluid. \\ \cline{2-3}  & Disadvantages \\ \hline \multicolumn{3}{c}{There is a low proppant concentration in fluid, hence decreased fracture conductivity. There are higher costs. The foams have a difficult rheological characterization, i.e., flow behavior is difficult to predict. A higher surface pumping pressure is required.} \\ \hline \end{tabular}
\end{table} 
Table 8: Foam-based fracturing fluids.