# Fracturing Fluids and Their Application in the Republic of Croatia
## 5 Fracturing Fluids--Composition and Additives
### Fracturing Fluid Additives  
Fracturing fluid composition (type and concentration of additives) depends on reservoir conditions (temperature and pressure) [20]. Additives help optimize the various parameters of the fracturing fluid and include crosslinkers, clay control agents, gel stabilizers, surfactants, foamers, gel breakers, fluid loss additives, friction reducers, scale inhibitors, biocides, and pH control additives [30; 68; 69]. They are added into fracturing fluids for three purposes [58]: easier fracture creation, proppant transport improvement and reservoir formation damage reduction. Additives which enhance fracture creation are: viscosifers, temperature stabilizers, pH control agents and fluid loss control additives. The reduction in reservoir formation damage is accomplished with: breakers, biocides, surfactants and clay control agents [70]. Additives and their functions are listed in Table 12. In Croatia, for all additives used to prepare fracturing fluid a Material Safety Data Sheet (MSDS) and/or Safety Data Sheet (In Croatian: Sigurnosno-tehnicki list--STL) must be provided. MSDSs and STLs must be filled out according to the amended Appendix II of REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) Regulation published by the European Commission as Regulation (EC) No. 453/2010 amending Regulation (EC) No. 1907/2006 [71]. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{4}{c}{**Fracturing Fluid Additives**} \\ \hline
**Additive** & **Typical products** & **Function** \\ \hline Water & fresh, salt or produced water & Base (carrier) fluid \\ \hline Acid & hydrochloride or acetic acid & Dissolves minerals \\ \hline Biocide & amides, aldehydes, quaternary amines, chlorine dioxide & Kills bacteria \\ \hline Breaker & calcium or magnesium & Causes gel degradation and reduces fluid viscosity \\ \hline Clay stabilizer & potassium chloride, sodium chloride, calcium chloride, polyamines & Prevents clay swelling \\ \hline Crosslinker & borate, titanium, zirconium, aluminum & Increases the molecular weight of the polymer by crosslinking the polymer backbone into a 3-D structure. Increases the base viscosity of the linear gel. Increases the elasticity and proppant transport capability of the fluid. \\ \hline Iron chelating agent & Citric acid, acetic acid, thioglycol acid, sodium & Keeps iron in solution \\  & erithorbate & \\ \hline pH adjusting agent/ & sodium hydroxide, sodium carbonate, potassium & \\ buffer & hydroxide, potassium carbonate, acetic & Controls the pH \\  & acid formic acid, magnesium oxide & \\ \hline Friction reducer & polyacrylic acid, polyacrylamide, ethylene glycol, methanol & Reduces the friction \\ \hline Gelling agent & guar and its derivatives (HPG, CMG, CMHPG), cellulose and its derivatives & Increases the viscosity \\  & (HEC, CMHEC), surfactants & \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Fracturing fluid additives. **Water (base carrier fluid) creates fracture geometry and suspends a proppant. One portion of the injected water remains in the reservoir formation while the remaining volume of water returns to the surface with natural formation water as \"produced water\". The actual volume of returned water varies from well to well. **  
An **acid** helps dissolve minerals and initiate cracks in rock. It reacts with minerals present in the formation to create salts, water and CO2. An acid/corrosion inhibitor protects the casing from corrosion. It bonds to metal pipe surfaces downhole. Any remaining product not bonded is broken down by micro-organisms and is consumed or returned in produced water. A **biocide** eliminates bacteria in the water and prevents bacterial activity that can cause corrosive by-products. It reacts with microorganisms that may be present in the fracturing fluid and formation. These microorganisms break down the product with a small amount of the product returning to the surface in produced water. A **breaker** allows a delayed breakdown of gel when required. In other words, it causes gel degradation.