# Fracturing Fluids and Their Application in the Republic of Croatia
## 6 Hydraulic Fracturing in Croatia
### Case Study
#### 6.2.1 Job Design and Fluid Composition  
HF service by using appropriate software identifies values of parameters specific to the reservoir and the well that are critical to the optimal fracture treatment design. Estimated or inaccurate values can result in premature screenout and reduced fracture penetration because of pad fluid depletion, unpropped fractures, damaged proppant pack conductivity, and increased treatment costs because of an excessive pad volume [75]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Well Name**} \\ \cline{2-5}  & **W-1** & **W-2** & **W-3** & **W-4** \\ \hline \multicolumn{5}{c}{**Geological data**} \\ \hline Depth, m & 2823 & 2776 & 4646 & 3410 \\ \hline Reservoir fluid & gas condensate & gas condensate & gas condensate & gas condensate \\ \hline Production intervals & 2529–2561 & 2739–2776 & 3782–3818.5 & 3298–3392 \\ depth, m & 2529–2561 & 2739–2776 & 3782–3818.5 & 3298–3392 \\ \hline Lithology & limestone & limestone & quartzite & siltstone \\ \hline Porosity, \% & 12–14 & 12–14 & 10 & 1–4 \\ \hline Permeability, 10\({}^{-3}\) μm\({}^{2}\) & 8.4 & 1.3 & 0.021 & 0.1 \\ \hline Reservoir pressure, bar & 255 & 255 & 332 & 480 \\ \hline Reservoir temperature, \({}^{\circ}\)C & 146 & 149 & 190 & 178 \\ \hline HF goals & \begin{tabular}{c} Enable production with \\ lower drawdown \\ \end{tabular} & \begin{tabular}{c} Remove skin and increase \\ productivity index \\ \end{tabular} & \
\begin{tabular}{c} Increase wellhead \\ pressure and enable gas \\ production \\ \end{tabular} &
\begin{tabular}{c} Remove skin and increase \\ productivity index \\ \end{tabular} \\ \hline \multicolumn{5}{c}{**Well design**} \\ \hline Well path & Vertical & Directional & Vertical \\ \hline Production casing dia, & 177.8 (7) & 177.8 (7) & 177.8 (7) & 177.8 (7) \\ \hline Liner dia, mm (inch) & 127 (5) & 144.3 (4.5) & - & - \\ \hline Open hole dia, mm (inch) & - & 95 (3.75) & - & - \\ \hline Tubing dia, mm (inch) & 88.9 (3.5) & 88.9 (3.5) & 73.02 (2.785) & 88.9 (3.5) \\ \hline \hline \end{tabular}
\end{table} 
Table 14: Geological and well design data for the selected wells. W-1–W-4: well 1–well 4. The fracturing fluid composition used for the hydraulic fracturing of the considered wells is presented in Table 15. The basic fracturing fluid additives used in all four cases were similar (gelling agent, crosslinker, surfactant, clay control additive, breaker, stabilizer) while other additives were added to adjust the desired composition for optimizing the hydraulic fracturing operation. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{5}{c}{**Fracturing Fluid Composition**} \\ \hline \multirow{2}{*}{**Additive, Unit**} & \multicolumn{4}{c}{**Wells**} \\ \cline{2-5}  & **W-1** & **W-2** & **W-3** & **W-4** \\ \cline{2-5}  & \multicolumn{4}{c}{**Total Quantity**} \\ \hline Proppant, kg & 30,000 & 21,000 & 151,500 & 150,000 \\ \hline Gelling Agent, kg & 1135 & 887 & 12,297 & 11,600 \\ \hline Crosslinker, l & 600 & 460 & 1750 & 1750 \\ \hline Surfactant, l & 260 & 250 & 510 & 708 \\ \hline Clay Control, l & 520 & 500 & 1020 & 1160 \\ \hline HT breaker, kg & 44.5 & 31.3 & 129 & 225 \\ \hline HT Encapsulated breaker, kg & 39 & 22 & 125 & 140 \\ \hline HT Stabilizer, kg & 49 & 53.5 & 285 & 450 \\ \hline Delay Agent, kg & 67 & - & - & - \\ \hline Stabilizer, l & 160 & 230 & - & - \\ \hline pH Buffer, kg & 99 & 71.7 & - & - \\ \hline LT friction reducer, kg & 48 & 48 & - & - \\ \hline MT friction reducer, kg & 460 & 222 & 127 & - \\ \hline HT friction reducer, kg & - & - & - & 127 \\ \hline Acetic Acid (10\%), kg & - & - & 434 & 1250 \\ \hline Dry Guar Polymer, kg & - & - & 100 & - \\ \hline HT-high temperature; MT-medium temperature; LT-low temperature. &  
\end{table} 
Table 15: Fracturing fluid composition. Figure 4: Locations of the wells in the northern part of Croatia.