Acids |
To achieve greater injection ability or penetration and later to dissolve minerals and clays to reduce clogging, allowing gas to flow to the surface. |
Hydrochloric acid |
Biocides |
To prevent bacteria that can erode pipes and fittings and to break down gellants that serve to ensure that fluid viscosity and proppant transport are maintained. |
1-methyl-4-isothiazolin-3-one, bronopol, glutaraldehyde |
Breakers |
To allow the breakdown of gellants used to carry the proppant; these are added near the end of the hydraulic fracturing sequence to enhance flowback. |
Ammonium persulfate, magnesium peroxide |
Clay stabilizers |
To create a fluid barrier to prevent mobilization of clays, which can plug fractures. |
Tetramethyl ammonium chloride, sodium chloride |
Corrosion inhibitors |
To reduce the potential for rusting in pipes and casings. |
Ethoxylated octylphenol and nonylphenol, isopropanol |
Crosslinkers |
To thicken fluids, often with metallic salts, in order to increase viscosity and proppant transport. |
Ethylene glycol, sodium tetraborate decahydrate, petroleum distillate |
Defoamers |
To reduce foaming after it is no longer needed in order to lower surface tension and allow trapped gas to escape. |
2-ethylhexanol, oleic acid, oxalic acid |
Foamers |
To increase carrying capacity while transporting proppants and decreasing the overall volume of fluid needed. |
2-butoxyethanol, diethylene glycol |
Friction reducers |
To make water slick and minimize the friction created under high pressure and to increase the rate and efficiency of moving the hydraulic fracturing fluid. |
Acrylamide, ethylene glycol, petroleum distillate, methanol |
Gellants |
To increase viscosity and suspend sand during proppant transport. |
Propylene glycol, guar gum, ethylene glycol |
pH control |
To maintain the pH at various stages with buffers to ensure the maximum effectiveness of various additives. |
Sodium hydroxide, acetic acid |
Proppants |
To hold fissures open, allowing gas to flow out of the cracked formation; usually composed of sand and occasionally glass or ceramic beads. |
Styrene, crystalline silica, ceramic, graphite |
Scale inhibitors |
To prevent buildup of mineral scale that can block fluid and gas passage through the pipes. |
Acrylamide, sodium polycarboxylate |
Surfactants |
To decrease liquid surface tension and improve fluid passage through pipes in either direction. |
Naphthalene, 1,2,4-trimethylbenzene, ethanol, methanol, 2-butoxyethanol |
Categories and uses for commonly applied chemicals that are commonly used throughout the hydraulic fracturing process with specific examples provided for each category class. Adapted with permission from Colborn T et al. (2011). Reprinted by permission of Taylor & Francis LLC (http://www.tandfonline.com). |