# Fracturing Fluids and Their Application in the Republic of Croatia
## 5 Fracturing Fluids--Composition and Additives
### Fracturing Fluid Additives
A breaker reacts with the crosslinker and gel once in the formation, making it easier for the fluid to flow to the well. The reaction produces ammonia and sulfate salts which are returned to the surface in produced water. A **clay and shale stabilizer** locks down clays in the shale structure and prevents clay hydration. It reacts with clays in the formation through a Na-K ion exchange. The reaction results in NaCl which is returned in produced water. It also replaces binder salts such as CaCl2, helping to keep the formation intact as the CaCl2 dissolves. A **crosslinker** maintains the viscosity as the temperature increases by fluid crosslinking. It combines with the breaker in the formation to create salts that are returned to the surface in produced water. An **iron chelating agent (iron control) helps prevent the precipitation of metal oxides. It reacts with minerals in the formation to create salts, CO2 and water, all of which are returned to the surface in produced water. A **non-emulsifier** is used to break or separate emulsions (oil/water mixtures). It is generally returned to the surface with produced water, but in some formations may return in the produced natural gas. A **pH adjusting agent/buffer** regulates the pH value of the fracturing fluid and maintains the effectiveness of other additives, such as crosslinkers. It reacts with acidic agents in the fracturing fluid to maintain a neutral pH. The reaction results in mineral salts, water and CO2 which is returned to the surface in produced water. A **friction reducer** reduces the friction generated while the fluid is pumped down the tubing at high flow rates. **Gelling agents (viscosifers) are added to the fracturing fluid to increase the viscosity. This increases the fracture width so it can accept higher concentrations of a proppant, it reduces the fluid loss to improve fluid efficiency, improves proppant transport and reduces friction pressure. For conventional wide biwing fractures, the carrier fluid must be sufficiently viscous (normally 50 to 1000 mPa-s at nominal shear rates from 40-100 s\({}^{-1}\)) to transport higher proppant concentrations (120-1200 kg/m\({}^{3}\)). \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Fracturing Fluid Additives** & **Function** \\ \hline
**Additive** & **Typical products** & **Function** \\ \hline Scale inhibitor & ethylene glycol, methanol, ethylene & \\  & diamine tetraacetic acid (EDTA) & \\ \hline  & ethanol, naphthalene, & \\ Surfactant & methanol, isopropyl alcohol, & \\  & lauryl sulfate & \\ \hline Proppant & silica sand, resin-coated sand, & \\  & ceramic proppant & Keeps fractures open \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Cont. **Scale inhibitors** prevent scales in pipe (tubing) and formation. The product attaches to the formation. The majority of the product returns to the surface with produced water while any remnants react with microorganisms that break down and consume the product. A **surfactant** reduces the surface tension of the fracturing fluid in the formation and helps improve fluid recovery from the well after the hydraulic fracturing is completed. Some surfactants are made to react with the formation, and some are designed to return to the surface with produced water or with produced natural gas. A **propant** (propping agent) keeps fractures open, allowing for hydrocarbon production. It stays in formation embedded in fractures so it is used to \"prop\" the fracture open. After the injection of fracturing fluid, fractures start to close under the influence of geostatic pressure. The function of the proppant in a fluid is to prevent fracture closure and to maintain their stability during the production of hydrocarbons. Proppants should be strong, resistant to crushing and corrosion and available at low cost [49; 69]. If possible, they should have a low density because of their better transportation through a fluid from the surface to the reservoir.