Background for this classification summary
- Visit the Classification Index to see other groups.
- The summary on this page follows the classification scheme of Elsner and Hoelzer, 2016. Quantitative Survey and Structural Classification of Hydraulic Fracturing Chemicals Reported in Unconventional Gas Production. Environmental Science and Technology. 3290-3314. DOI: 10.1021/acs.est.5b02818.
- Elsner and Hoelzer’s thorough and influential article provides a wealth of chemical context about fracking materials including health and environmental implications and suggestions for deeper analysis. However, the work was based partially on a early set of FracFocus (through 2013). Subsequent years have added new materials and millions more records. To extend their analysis to the rest of the FracFocus materials, we used Google’s Gemini to assist us in assigning classifications in line with EH’s methodology.
- Analysis from a FracFocus download, Jan 2025.
- Masses are not available for all records, so reported masses below are sums of only the available masses. See documentation.
- To provide useful technical information about these chemical groups, we use generative AI tools to assist with summaries (Google’s Gemini). These tools are prompted with details of the classification scheme (by Elsner and Hoelzer, 2016) and information about reported chemicals in the group. To limit inaccuracies, we feed the resulting output to competing models (OpenAI’s ChatGPT) to check for accuracy and ambiguity. In addition, we consulted Fink, Johannes, “Petroleum Engineer’s Guide to Oil Field Chemicals and Fluids” Third Edition. (2021) Gulf Professional Publishing. 1028pp.
- Functions reported here are summarized from the FracFocus field “Purpose.” There are limitations to this data: not all chemical records have a reported purpose (the “systems approach” explicitly excludes “Purpose” values from chemical records). Furthermore, “Purpose” typically describes the product, not individual chemicals within the product. The individual ingredient may serve a chemical role in the product that is different from the reported “purpose” (for example, synthetic polymers might be labeled “proppant”, but they are not primary proppants, but rather coatings for sand grains to enhance their performance.) In general, consider these “functions” as the larger purpose played by the product that contains the ingredient.
Synthetic polymers constitute a significant class of chemicals employed in hydraulic fracturing, as evidenced by the 153,000 records, totaling 1.94 billion pounds, reported to FracFocus between 2014 and 2024. These large molecules, formed by the polymerization of repeating structural units (monomers), are engineered to possess a wide range of properties that make them valuable components of fracking fluids and related products.1
FracFocus data reveals a diverse array of synthetic polymers utilized in hydraulic fracturing, which can be categorized into several subgroups:
- Acrylamides/acrylates (43 reported chemicals): Water-soluble polymers commonly used for their thickening and stabilizing properties.
- Phenol/formaldehyde/epoxy polymers (24 reported chemicals): Thermosetting polymers formed through condensation reactions, known for their strength and resistance to heat and chemicals.
- Other vinyl polymers (14 reported chemicals): A diverse group encompassing polymers derived from various vinyl monomers, each with unique properties and applications.
- Others (24 reported chemicals): A diverse category encompassing polymers that do not fall into the other specific subgroups.
- Silicones (11 reported chemicals): Polymers with a silicon-oxygen backbone, known for their thermal stability and hydrophobic properties.
- Halogenated polymers (4 reported chemicals): Polymers containing halogen atoms, which can impart flame resistance and other specialized properties.
While these polymers themselves may not directly serve the reported purposes, they are crucial components of fracking products that perform those functions. FracFocus data indicates that products containing synthetic polymers are commonly used as:
- Friction reducers: Reducing frictional pressure losses during pumping operations.
- Proppants: Keeping hydraulically induced fractures open to facilitate hydrocarbon flow.
- Corrosion inhibitors: Protecting wellbore infrastructure from the corrosive effects of fracking fluids.
- Scale control: Preventing the formation of mineral scales that can impede fluid flow.
- Biocides: Controlling microbial growth that can negatively impact fracking operations.
- Gelling agents: Modifying the viscosity of fracking fluids to enhance proppant transport.
- Diverters: Controlling fluid flow within the wellbore to ensure effective treatment of the target zone.
- Antifoam agents: Preventing the formation of foam, which can hinder fracking operations.
The extensive use of synthetic polymers in various fracking products highlights their importance in hydraulic fracturing operations.
Subclass: acrylamides/acrylates
Number of reported materials: 43
Acrylamide- and acrylate-based polymers are a class of water-soluble synthetic polymers widely used in hydraulic fracturing. They are typically formed through the polymerization of acrylamide and acrylic acid monomers, often with varying ratios and potential modifications to tailor their properties. Common examples reported to FracFocus include polyacrylamide (CASRN 9003-05-8), sodium polyacrylate (CASRN 9003-04-7), and various copolymers such as ammonium acrylate-acrylamide copolymer (CASRN 26100-47-0) and acrylamide-sodium acrylate copolymer (CASRN 25085-02-3). These polymers are valued for their ability to modify fluid viscosity, reduce friction, and stabilize suspensions, making them crucial in various fracking applications, including friction reduction, fluid loss control, and proppant transport.
Most common acrylamides/acrylates:
| Material | Name | Records and mass |
|---|---|---|
| 25987-30-8 | 2-Propenoic acid, polymer with 2-propenamide, sodium salt | 15,300 records — 278,000,000 pounds |
9003-05-8 | Polyacrylamide | 10,800 records — 485,000,000 pounds |
| 26100-47-0 | Ammonium acrylate-acrylamide copolymer | 8,660 records — 150,000,000 pounds |
9003-04-7 | Sodium polyacrylate | 4,530 records — 10,700,000 pounds |
| 25085-02-3 | Acrylamide-sodium acrylate copolymer | 3,120 records — 69,200,000 pounds |
Subclass: phenol /formaldehyde / epoxy polymers
Number of reported materials: 24
Phenol-formaldehyde and epoxy resins constitute a class of thermosetting polymers used in hydraulic fracturing, particularly in proppant coatings and cement additives. Phenol-formaldehyde resins, such as Bakelite (CASRN 9003-35-4), are synthesized through a condensation reaction between phenol and formaldehyde, forming a highly crosslinked network structure. Epoxy resins, which include compounds incorporating bisphenol A, nonylphenol, and oxirane monomers (e.g., CASRN 68123-18-2, 30846-35-6, 129828-31-5), cure through reactions between epoxide groups and hardeners. These polymers exhibit excellent thermal stability, chemical resistance, and mechanical strength, making them suitable for demanding downhole applications.
Most common phenol /formaldehyde / epoxy polymers:
| Material | Name | Records and mass |
|---|---|---|
| 9003-35-4 | Bakelite | 13,700 records — 514,000,000 pounds |
| 68123-18-2 | Phenol, 4,4′-(1-methylethylidene)bis-, polymer with 2-(chloromethyl)oxirane, 2-methyloxirane and oxirane | 1,920 records — 2,430,000 pounds |
| 72283-36-4 | Oxirane, 2-methyl-, polymer with oxirane, mono-(9Z)-9-octadecenoate, methyl ether | 1,330 records — 28,400 pounds |
| 30846-35-6 | Formaldehyde, polymer with 4-nonylphenol and oxirane | 870 records — 840,000 pounds |
| 129828-31-5 | 2-Propenoic acid, polymer with 4-(1,1-dimethylethyl)phenol, formaldehyde, 2,5-furandione, 2-methyloxirane, 4-nonylphenol and oxirane | 762 records — 2,730,000 pounds |
Subclass: “other vinyl polymers”
Number of reported materials: 14
The category of ‘other vinyl polymers’ includes a diverse group of synthetic polymers characterized by a backbone derived from carbon-carbon double bond-containing monomers. Some materials reported in FracFocus under this category include polybutene (CASRN 9003-29-6), a polyolefin used in lubricants and viscosity modifiers, and poly(oxy-1,2-ethanediyl), α-(carboxymethyl)-ω-[(9Z)-9-octadecen-1-yloxy]- (CASRN 57635-48-0), a copolymer of ethylene oxide and octadecenyl alcohol commonly used as a surfactant or scale inhibitor. These polymers contribute to hydraulic fracturing applications such as friction reduction, scale inhibition, and viscosity modification, owing to their unique molecular structures and functionalities.
Most common “other vinyl polymers”:
| Material | Name | Records and mass |
|---|---|---|
| 68648-89-5 | Benzene, ethenyl-, polymer with 2-methyl-1,3-butadiene, hydrogenated | 4,940 records — 8,960,000 pounds |
15220-87-8 | Propylene pentamer | 2,860 records — 14,000,000 pounds |
| 9003-29-6 | Polybutene | 1,170 records — 26,000,000 pounds |
57635-48-0 | Poly(oxy-1,2-ethanediyl), α-(carboxymethyl)-ω-[(9Z)-9-octadecen-1-yloxy]- (ACI) | 536 records — 1,070,000 pounds |
| 1252600-17-1 | Poly[oxy(methyl-1,2-ethanediyl)], .alpha.-(2-aminomethylethyl)-.omega.-(2-aminomethylethoxy)-, phosphonomethylated, sodium salts | 450 records — 896,000 pounds |
Subclass: “others”
Number of reported materials: 24
‘Others’ is a diverse subgroup within synthetic polymers, encompassing a wide range of materials with varied chemical structures and applications. Examples reported to FracFocus include thiourea-formaldehyde copolymers (CASRN 68527-49-1), which form chemically resistant resins; polydioxanone-based polymers (CASRN 9051-89-2), which may have niche applications in biodegradable fracturing additives; polyquaternium-42 (CASRN 31512-74-0), a cationic polymer used for fluid modification; polyaziridine copolymers (CASRN 52501-07-2), which serve as crosslinking agents; and polyterephthalic acid-ethylene glycol copolymers (CASRN 9016-88-0), which may be used in specialized coatings or proppant applications. Due to their diverse compositions, these polymers exhibit a variety of properties and fulfill specialized roles in hydraulic fracturing, including fluid stabilization, friction reduction, and crosslinking.
Most common “others”:
| Material | Name | Records and mass |
|---|---|---|
| 68527-49-1 | Thiourea, polymer with formaldehyde and 1-phenylethanone | 19,300 records — 6,970,000 pounds |
| 9051-89-2 | 1,​4-​Dioxane-​2,​5-​dione, 3,​6-​dimethyl-​, (3R,​6R)​-​, polymer with rel-​(3R,​6S)​-​3,​6-​dimethyl-​1,​4-​dioxane-​2,​5-​dione and (3S,​6S)​-​3,​6-​dimethyl-​1,​4-​dioxane-​2,​5-​dione | 10,900 records — 86,900,000 pounds |
31512-74-0 | Polyquaternium 42 | 5,520 records — 3,030,000 pounds |
| 52501-07-2 | Aziridine, polymer with methyloxirane and oxirane | 1,630 records — 1,740,000 pounds |
| 9016-88-0 | 1,4-Benzenedicarboxylic acid, polymer with 1,2-ethanediol and .alpha.-hydro-.omega.-hydroxypoly(oxy-1,2-ethanediyl) | 1,340 records — 17,400 pounds |
Subclass: silicones
Number of reported materials: 11
Silicones, also known as polysiloxanes, are a unique class of synthetic polymers characterized by a backbone of alternating silicon and oxygen atoms. This inorganic backbone provides high thermal stability, low surface tension, hydrophobicity, and chemical resistance. Common silicones reported to FracFocus include various polydimethylsiloxanes (PDMS) (CASRN 63148-62-9), which are used as lubricants and defoamers, and cyclic siloxanes like octamethylcyclotetrasiloxane (D4, CASRN 556-67-2) and decamethylcyclopentasiloxane (D5, CASRN 541-02-6), which may function as carriers or processing aids. These materials contribute to improved performance in hydraulic fracturing fluids by reducing friction, controlling foam, and enhancing fluid stability in demanding downhole conditions.
Most common silicones:
| Material | Name | Records and mass |
|---|---|---|
| 63148-62-9 | Siloxanes and Silicones, di-Me | 4,060 records — 3,870,000 pounds |
| 67762-90-7 | Siloxanes and Silicones, di-Me, reaction products with silica | 1,940 records — 533,000 pounds |
556-67-2 | Octamethylcyclotetrasiloxane | 771 records — 1,170 pounds |
| 68937-55-3 | Siloxanes and Silicones, di-Me, 3-hydroxypropyl Me, ethoxylated propoxylated | 763 records — 14,700 pounds |
541-02-6 | Decamethylcyclopentasiloxane | 759 records — 842 pounds |
Subclass: halogenated polymers
Number of reported materials: 4
Halogenated polymers used in hydraulic fracturing contain fluorine or chlorine within their structures, imparting chemical resistance, thermal stability, and barrier properties. Common examples reported to FracFocus include vinylidene chloride/methyl acrylate copolymer (CASRN 25038-72-6), which may function as a coating or fluid stabilizer; polytetrafluoroethylene (PTFE, CASRN 9002-84-0), a chemically resistant fluoropolymer likely used as a lubricant or friction-reducing additive; polyvinylidene chloride (PVDC, CASRN 9002-85-1), known for its barrier properties and potential coating applications; and a polymeric reaction product incorporating a triazine ring and halogenated piperidine groups (CASRN 70624-18-9), which may act as a chemical stabilizer. These materials contribute to improved performance in hydraulic fracturing by enhancing fluid stability, reducing friction, and providing chemical resistance.
Most common halogenated polymers:
| Material | Name | Records and mass |
|---|---|---|
| 25038-72-6 | Vinylidene chloride/methylacrylate copolymer | 5,080 records — 4,410,000 pounds |
9002-84-0 | Polytetrafluoroethylene | 3,940 records — 70,900 pounds |
9002-85-1 | Polyvinylidene chloride | 82 records — 31,200 pounds |
- All molecular structure images courtesy of the US EPA, except where noted. ↩︎