# Fracturing Fluids and Their Application in the Republic of Croatia
## 7 High-Volume Hydraulic Fracturing of Shale Gas in Croatia  
The exploration and production of hydrocarbons, such as shale gas, requires the combined use of high-volume hydraulic fracturing and directional (especially horizontal) drilling. This hydraulic fracturing technique raises specific challenges, in particular for health and environment [31; 77; 78; 79; 80]. One of the main public and scientific concerns is the contamination of shallow groundwater aquifers with fugitive hydrocarbon gases and HF \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Well**} & \multicolumn{5}{c}{**Well Name**} \\ \cline{2-6}  & **W-1** & **W-2** & **W-3** & **W-4** \\ \hline Water-based gel, m\({}^{3}\) & 191.7 & 140.4 & 445.3 & 571.4 \\ \hline Proppant, kg & 30,000 & 21,000 & 151,000 & 150,000 \\ \hline Maximum frac pressure, bar & 373 & 390 & 510 & 588 \\ \hline Maximum slurry rate, m\({}^{3}\)/min & 3.5 & 3.5 & 4.0 & 4.0 \\ \hline FCD, dimensionless & 171 & 5149 & 147 & 17.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 16: Main hydraulic fracturing summary. FCD: fracture conductivity. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Well**} & \multicolumn{5}{c}{**Before HF**} & \multicolumn{5}{c}{**Post HF**} \\ \cline{2-9}  & **Qg (m\({}^{3}\)/d)** & **Qc (m\({}^{3}\)/d)** & **Qw (m\({}^{3}\)/d)** & **Pwh (bar)** & **Qg (m\({}^{3}\)/d)** & **Qc (m\({}^{3}\)/d)** & **Qw (m\({}^{3}\)/d)** & **Pwh (bar)** \\ \hline W-1 & 280,000 & 28 & 7 & 120 & 315,000 & 38 & 8 & 125 \\ \hline W-2 & 15,000 & 2 & 140 & 65 & 55,000 & 7 & 104 & 102 \\ \hline W-3 & 2400 & 1 & 1 & 31 & 28,000 & 17 & 22 & 45 \\ \hline W-4 & 1200 & 0 & 0 & 20 & 30,000 & 2 fluids that may migrate to shallow aquifers if hydraulically induced fractures intercept the vicinity of fault zones and leaky abandoned wells [34]. A framework for investigating HF impacts on shallow aquifer was established with the European Union framework which can be further used for other areas. The European Commission formulated initiatives that aimed to understand, prevent and mitigate the potential environmental impacts and risks of shale gas exploration and exploitation (e.g., Horizon 2020 program LCE-16-2014) [34]. According to the recommendations of the European Commission on minimum principles for the exploration and production of hydrocarbons (such as shale gas) using high-volume hydraulic fracturing [5; 81] member states have the right to determine the conditions for exploiting their energy resources, as long as they respect the need to preserve, protect and improve the quality of the environment. For the purpose of this recommendation, \"high-volume hydraulic fracturing\" means injecting 1000 m\({}^{3}\) or more of water per fracturing stage or 10,000 m\({}^{3}\) or more of water during the entire fracturing process into a well. This recommendation lays down the minimum principles needed to support member states who wish to carry out the exploration and production of hydrocarbons using high-volume hydraulic fracturing, while ensuring that the public health, climate and environment are safeguarded, resources are used efficiently, and the public is informed. Before high-volume hydraulic fracturing operations start, member states should ensure that: (a) the operator determines the environmental status (baseline) of the installation site and its surrounding surface and underground area potentially affected by the activities and (b) the baseline is appropriately described and reported to the competent authority before operations begin. A baseline should be determined for: (a) the quality and flow characteristics of surface and ground water; (b) water quality at drinking water abstraction points; (c) air quality; (d) soil conditions; (e) the presence of methane and other volatile organic compounds in water; (f) seismicity; (g) land use; (h) biodiversity; (i) status of infrastructure and buildings; (j) existing wells and abandoned structures. The above mentioned recommendation will be implemented in Croatian parliament in 2021.