What Are H.F. Fluids?

Water and sand make up 98 to 99.5 percent of the fluid used in hydraulic fracturing. Chemical additives are also used. The exact formulation varies depending on the well. 

Chemicals serve many functions in hydraulic fracturing, including limiting the growth of bacteria, to preventing corrosion of the well casing. Chemicals are necessary to ensure fracturing is successful.

The conditions of the specific well being fractured determine the number of chemical additives needed. A typical fracture treatment will use very low concentrations of between 3 and 12 additive chemicals, depending on the characteristics of the water and the shale formation being fractured. Each component serves a specific, engineered purpose. The predominant fluids currently being used for fracture treatments in the gas shale plays are water-based mixed with friction-reducing additives (called slickwater). 

Friction reducers allow fracturing fluids and sand, or other solid materials called proppants, to be pumped to the target zone at a higher rate and reduced pressure than if water alone were used. Other additives include: biocides to prevent microorganism growth and to reduce biofouling of the fractures; oxygen scavengers and other stabilizers to prevent corrosion of metal pipes; and acids that are used to remove drilling mud damage within the near-wellbore area.

Fluids are used to create fractures in the formation and to carry a propping agent (typically silica sand) which is deposited in the induced fractures to keep them from closing up. The chart below taken from Modern Shale Gas Development in the United States: A Primer demonstrates the volumetric percentages of additives that were used for a nine-stage hydraulic fracturing treatment of a Fayetteville Shale horizontal well.