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.
Organic acids, as reported to FracFocus, represent a diverse group of organic compounds characterized primarily by the presence of one or more carboxyl (-COOH) groups, though some also contain other acidic functional groups, such as sulfonic (-SO₃H) groups.1
This broad category is further divided into several subgroups based on structural variations and additional functional groups, which influence their chemical properties and applications:
- Carboxylic acids (76 reported chemicals)
- Polycarboxylic acids (27 reported chemicals)
- Alpha-hydroxy / thio and alpha-keto carboxylic acids (17 reported chemicals)
- Fatty acids (8 reported chemicals)
- Amino acids (5 reported chemicals)
From 2014 to 2024, FracFocus recorded 247,000 entries for organic acids, representing a total reported mass of 417 million pounds.
Organic acids and their derivatives serve diverse functions in hydraulic fracturing, including iron control, corrosion inhibition, pH control, scale control, acidizing, friction reduction, crosslinking, and biocidal activity. These functions highlight the multifaceted role of organic acids and their derivatives, which contribute to fluid stability, wellbore integrity, and the overall efficiency of the fracturing process.
Subclass: carboxylic acids¶
Number of reported materials: 76
The “carboxylic acids” subgroup within FracFocus’s Organic Acids category comprises compounds characterized by the presence of a carboxyl functional group (-COOH) bonded to either an alkyl or aryl moiety. This subgroup does not include carboxylic acids that fall into more specific classifications, such as fatty acids, amino acids, or polycarboxylic acids.
Commonly reported compounds include simple aliphatic carboxylic acids, such as Acetic acid (64-19-7) and Formic acid (64-18-6), along with their corresponding salts, such as Ammonium acetate (631-61-8).
This subgroup also includes functional derivatives, such as Acetic anhydride (108-24-7), a reactive dehydration product of acetic acid, and Ammonium acrylate (10604-69-0), the ammonium salt of the unsaturated carboxylic acid acrylic acid.
These carboxylic acids contribute to multiple functions in hydraulic fracturing fluid systems, including pH adjustment, iron control, and potentially other roles depending on their concentration and chemical interactions.
Most common carboxylic acids:
| Material | Name | Records and mass |
|---|---|---|
64-19-7 | Acetic acid | 59,100 records — 138,000,000 pounds |
64-18-6 | Formic acid | 17,300 records — 18,300,000 pounds |
631-61-8 | Ammonium acetate | 10,100 records — 71,900,000 pounds |
108-24-7 | Acetic anhydride | 8,630 records — 29,000,000 pounds |
10604-69-0 | Ammonium acrylate | 7,540 records — 2,660,000 pounds |
Subclass: polycarboxylic acids¶
Number of reported materials: 27
The “polycarboxylic acids” subgroup within the Organic Acids category reported to FracFocus includes compounds containing two or more carboxyl (-COOH) functional groups, which enhance their ability to interact with metal ions and influence solubility. Due to the presence of multiple carboxyl groups, these compounds function as chelating agents, forming stable complexes with metal ions such as calcium, magnesium, and iron.
Prominent examples include:
- Citric acid (77-92-9), a naturally occurring tricarboxylic acid with strong metal-binding properties.
- Various salts of ethylenediaminetetraacetic acid (EDTA), including:
- Ethylenediaminetetraacetic acid tetrasodium salt (64-02-8)
- Trisodium ethylenediaminetetraacetate (150-38-9)
- Ethylenediaminetetraacetic acid, disodium salt (139-33-3)
- Glycine, N,N-bis(carboxymethyl)-, trisodium salt (5064-31-3), commonly known as trisodium nitrilotriacetate (NTA), another effective chelating agent.
In hydraulic fracturing, polycarboxylic acids and their salts play a critical role in:
Enhancing fluid stability, ensuring that metal-induced gel degradation or unwanted precipitates do not interfere with the fracturing process.
Scale control, by preventing the precipitation of mineral deposits such as calcium carbonate or barium sulfate.
Metal ion management, particularly iron control, by stabilizing dissolved iron and preventing its oxidation or precipitation, which could otherwise impact fluid performance.
Most common polycarboxylic acids:
| Material | Name | Records and mass |
|---|---|---|
77-92-9 | Citric acid | 46,600 records — 60,800,000 pounds |
64-02-8 | Ethylenediaminetetraacetic acid tetrasodium salt | 12,600 records — 12,300,000 pounds |
5064-31-3 | Glycine, N,N-bis(carboxymethyl)-, trisodium salt | 9,930 records — 2,460,000 pounds |
139-33-3 | Ethylenediaminetetraacetic acid, disodium salt | 3,580 records — 109,000 pounds |
150-38-9 | Trisodium ethylenediaminetetraacetate | 3,570 records — 106,000 pounds |
Subclass: alpha-hydroxy / thio, alpha-keto carboxylic acids¶
Number of reported materials: 17
The “alpha-hydroxy / thio, alpha-keto carboxylic acids” subgroup within FracFocus’s Organic Acids category consists of carboxylic acids in which a hydroxyl (-OH), thiol (-SH), or carbonyl (=O) functional group is located at the alpha position (adjacent to the carboxyl carbon). This structural feature significantly influences their chemical reactivity, particularly in chelation and redox processes.
Frequently reported examples include:
- Glycolic acid (79-14-1) and its salt, Glycolic acid sodium salt (2836-32-0), both known for their mild acidity and chelating properties.
- Lactic acid derivatives, such as:
- Sodium DL-lactate (72-17-3), a buffering agent and pH stabilizer.
- D-Lactic acid (10326-41-7), a naturally occurring stereoisomer.
- Sodium erythorbate (6381-77-7), a stereoisomer of sodium ascorbate with antioxidant properties.
The presence of an alpha-hydroxy or alpha-keto functional group enhances their reactivity, particularly in metal chelation and redox reactions. As a result, these compounds contribute to:
- pH control, by acting as buffering agents.
- Iron control, by complexing with dissolved iron and preventing precipitation.
- Mild acidizing, helping to dissolve scale or mineral deposits within the wellbore.
Their dual functionality—combining acidic and hydroxyl (or carbonyl) groups—allows them to serve as both chelating agents and mild acids, making them versatile additives in fracturing fluid formulations.
Most common alpha-hydroxy / thio, alpha-keto carboxylic acids:
| Material | Name | Records and mass |
|---|---|---|
2836-32-0 | Glycolic acid sodium salt | 10,400 records — 7,370,000 pounds |
6381-77-7 | Sodium erythorbate | 8,870 records — 7,580,000 pounds |
79-14-1 | Glycolic acid | 1,450 records — 528,000 pounds |
72-17-3 | Sodium DL-lactate | 934 records — 1,110,000 pounds |
10326-41-7 | D-Lactic acid | 896 records — 742 pounds |
Subclass: fatty acids¶
Number of reported materials: 8
The “fatty acids” subgroup within Organic Acids category consists of long-chain aliphatic carboxylic acids, typically derived from natural sources, such as plants or animals. These compounds can be either saturated or unsaturated.
Commonly reported examples in this subgroup include:
- “Fatty acids, tall-oil” (61790-12-3), a mixture of fatty acids obtained as a byproduct from wood pulp processing.
- “Fatty acids, tall oil, reaction products with acetophenone, formaldehyde, and thiourea” (68188-40-9), a modified derivative with specific functional groups.
- Individual fatty acids, such as Oleic acid (112-80-1) and its salt, Potassium oleate (143-18-0).
Some entries, such as Pine oils (8002-09-3), are complex mixtures derived from natural sources and are not composed solely of fatty acids.
In hydraulic fracturing, these fatty acids, along with other fatty acid-containing chemicals, contribute to:
- Potentially influencing emulsion stability.
- Modifying interfacial properties,
- Reducing surface tension,
- Acting as surfactants, and
- Potentially influencing emulsion stability.
Most common fatty acids:
| Material | Name | Records and mass |
|---|---|---|
| 61790-12-3 | Fatty acids, tall-oil | 13,100 records — 5,280,000 pounds |
| 68188-40-9 | Fatty acids, tall oil, reaction products with acetophenone, formaldehyde and thiourea | 2,710 records — 838,000 pounds |
143-18-0 | Potassium oleate | 2,330 records — 36,500 pounds |
112-80-1 | Oleic acid | 2,110 records — 28,800 pounds |
| 8002-09-3 | Pine oils | 1,130 records — 124,000 pounds |
Subclass: amino acids¶
Number of reported materials: 5
The “amino acids” subgroup within Organic Acids category consists of molecules containing both a carboxyl (-COOH) group and an amino (-NH2) group. While amino acids are traditionally associated with biological systems, they also have industrial applications in various formulations. Throughout FracFocus, materials in this subgroup are infrequently reported.
Commonly reported compounds in this subgroup include:
- L-Glutamic acid (56-86-0), a naturally occurring amino acid.
- 4-Aminobenzoic acid (150-13-0), an aromatic amino acid.
Also listed are derivatives and modified compounds, such as:
- [(Carboxymethyl)amino]acetate (17593-73-6),
- Glycine, N,N-bis(carboxymethyl)-, ammonium salt (1:3) (32685-17-9), and
- Glycine, N-(2-((carboxymethyl)amino)ethyl)-N-(2-hydroxyethyl)-, disodium salt (62099-15-4).
The presence of multiple functional groups in these compounds suggests potential applications in:
- Chelation,
- pH buffering, and
- As building blocks for more complex additives used in hydraulic fracturing fluids.
Reported amino acids
| Material | Name | Records and mass |
|---|---|---|
17593-73-6 | [(Carboxymethyl)amino]acetate | 843 records — 2,440 pounds |
56-86-0 | L-Glutamic acid | 59 records — 598,000 pounds |
62099-15-4 | Glycine, N-(2-((carboxymethyl)amino)ethyl)-N-(2-hydroxyethyl)-, disodium salt | 17 records — 29 pounds |
32685-17-9 | Glycine, N,N-bis(carboxymethyl)-, ammonium salt (1:3) | 6 records — 332 pounds |
150-13-0 | 4-Aminobenzoic acid | 1 records — 216 pounds |
- All molecular structure images courtesy of the US EPA, except where noted. ↩︎