# Fracturing Fluids and Their Application in the Republic of Croatia
## 5 Fracturing Fluids--Composition and Additives  
The two main functions of a fracturing fluid during hydraulic fracturing are the transfer of energy from the frac pumps to the formation, creating the fracture and the transport and suspending the proppant. Since the goal of hydraulic fracturing is to increase the production of hydrocarbon, a fracturing fluid must be compatible with the formation minerals, minimize proppant pack and surrounding formation damage and be easily recovered after hydraulic fracturing [19].  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline  & \multicolumn{2}{c}{**Water Analysis**} \\ \hline
**Parameter** & **Required Value** & **Range of Values for Water Used in Croatia** \\ \hline pH & \textless{}8 & 5.7–7.9 \\ \hline Iron (mg/L as Fe) & \textless{}10 & \textless{}0.005–9.64 \\ \hline Total Hardness (mg/L as Ca, Mg) & \textless{}500 & 42.3–443.35 \\ \hline Chloride (mg/L as Cl) & \textless{}1000 & 0.071–63 \\ \hline Sulfate (mg/L as \(\text{SO}_{4}\)) & \textless{}100 & 0.045–70 \\ \hline Salts (mg/L) & \textless{}1.5 & 0.1–104 \\ \hline Bicarbonate (mg/L as \(\text{CaCO}_{3}\)) & \textless{}600 & 13.7–634.6 \\ \hline Density (kg/dm\({}^{3}\)) & \textless{}1.005 & 0.9998–1.0009 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Water analysis [3].  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt}} \hline \hline
**Test** & **Description** \\ \hline Proppant conductivity & Short- and long-term proppant conductivity. \\ \hline Proppant UCS & Determines unconfined compressive strength (UCS) of proppant (for resin-coated proppants). \\ \hline Composite sieve analysis & Determines the gradation of a sample. Sieve sizes include applicable sizes through number 200 mesh. \\ \hline Sphericity and roundness & Characterizes the physical appearance of proppant. \\ \hline Crush resistance & The strength of proppant is determined by quantifying the amount of proppant crushed at a given stress. \\ \hline Turbidity & Determines the amount of suspended particles or fine matter present in fracture sand by measuring the optical scattering and absorption of light from particulate matter suspended in a wetting fluid. \\ \hline Bulk density & Describes the mass of proppant that fills a unit volume, including both proppant and porosity. \\ \hline Apparent density & Measured with a low viscosity fluid that wets the proppant particle surface. It takes into account the volume of pore space inaccessible to the fluid. \\ \hline Absolute density & Density of the proppant, excluding the inaccessible pores in the proppant and void spaces between the proppant itself. \\ \hline Acid solubility & Often used to indicate and quantify the presence of impurities in fracture sand. \\ \hline Simulated fracture window & A large-scale physical model consisting of two pieces of Plexiglas held 6.35 mm apart. This is used to visually observe fluid flow through a simulated 6.35 mm fracture. Useful for comparative testing between two fracture fluids. Properties such as proppant transport capabilities, for example, can be tested and qualitatively and quantitatively measured. The model is 0.91 m tall and 2.44 m long. \\ \hline \hline \end{tabular}
\end{table}
Table 3: Proppant analysis.