Fracking fluid is roughly 99.5% water and sand by volume. The remaining 0.49% is a mix of chemical additives, each serving a specific function like reducing friction, killing bacteria, or preventing mineral buildup inside the well. That tiny percentage sounds negligible, but a single well can use anywhere from 1.5 million to 16 million gallons of fluid, meaning even half a percent translates to thousands of gallons of chemicals pumped underground.
The Three Main Components
Water makes up about 90% of fracking fluid by volume. Sand and similar granular materials account for another 9.5%. Chemical additives fill in the final fraction of a percent. For a typical well using 3 million gallons of fluid, that breakdown means roughly 2.7 million gallons of water, 285,000 gallons worth of sand, and around 14,700 gallons of chemical additives.
The water is pumped at extremely high pressure to crack open rock formations deep underground. Once those fractures open, the sand grains rush in and lodge themselves in the cracks, propping them open so oil or gas can flow out. This is why the sand is called “proppant.” Without it, the rock would simply close back up once the pressure stopped.
What the Sand Actually Looks Like
Most proppant is natural silica sand, though operators also use ceramic beads and resin-coated sand depending on conditions underground. The grains range from about 0.1 millimeters to 2.4 millimeters in diameter. Common size grades in the industry are labeled by mesh (20/40, 40/70, and so on), with each number corresponding to a specific grain size range.
A single well typically receives 2.5 to 4 million pounds of proppant. In shallower or lower-pressure formations, plain silica sand works fine. Deeper wells with higher pressures need stronger materials like ceramic proppants, which resist crushing. Some wells use blends: 30% ceramic mixed with 70% silica sand, for example. Wells using higher proportions of ceramic proppant tend to produce more oil and gas over their lifetime, which is why operators balance cost against performance when choosing their mix.
Chemical Additives and What They Do
Each chemical in fracking fluid has a specific job. The mix changes depending on the geology of the well site, the depth, and the type of rock being fractured. Here are the main categories:
- Friction reducers: The most common additive in modern “slickwater” fracturing. These are typically polyacrylamide-based polymers added at concentrations of 0.05% to 0.2%. They make water slippery so it can be pumped at high speed with less resistance, cutting the energy needed to push fluid thousands of feet underground.
- Acids: Hydrochloric acid, usually at 5% to 15% concentration, is pumped early to dissolve minerals and clean out cement from the wellbore, helping open initial pathways before the main fracturing begins.
- Biocides: Chemicals like glutaraldehyde kill bacteria in the fluid. Bacteria aren’t just a contamination concern; certain species produce hydrogen sulfide gas, which is toxic and corrosive.
- Scale inhibitors: Minerals in the rock and water can form hard deposits (scale) that clog the well. Inhibitors based on acrylic acid or phosphate compounds prevent this buildup, especially in high-temperature formations.
- Clay stabilizers: Shale contains clay minerals that swell when they contact water, which can choke off the very fractures the operator just created. Potassium chloride and similar salts keep clays from expanding.
- Surfactants: These reduce the surface tension of the fluid, helping it flow back out of the well after the job is done. Methanol and isopropanol are common choices.
- Crosslinkers and gelling agents: In some formations, operators need thicker fluid to carry heavier proppant loads. Borate salts and other crosslinking chemicals increase the fluid’s viscosity and elasticity.
- Breakers: Once fractures are propped open, the thickened fluid needs to thin out and flow back to the surface. Chemical breakers reduce viscosity at a controlled rate so the proppant stays in place while the fluid drains away.
How the Recipe Changes by Location
There is no single fracking fluid formula. The composition shifts based on the geological characteristics of each site, the chemistry of the local water supply, and the specific rock formation being targeted. A well in the Permian Basin of West Texas faces different temperatures, pressures, and mineral content than one in the Marcellus Shale of Pennsylvania. Operators adjust the type and concentration of each additive accordingly. A formation with high clay content needs more clay stabilizer. A deeper, hotter well might require different scale inhibitors or higher-strength proppants. This variability is one reason it’s difficult to make blanket statements about what “fracking fluid” contains.
What Comes Back Up
After fracturing, a portion of the fluid flows back to the surface. This “flowback water” contains the original chemical additives plus whatever it picked up from the rock formation thousands of feet below. The result is often highly saline water loaded with dissolved solids.
The dominant components in flowback are chloride, sodium, calcium, and potassium, which account for the extreme saltiness. Barium, strontium, lithium, bromide, and iron are also consistently found at elevated levels. Some samples contain trace amounts of lead, chromium, nickel, and other heavy metals, though typically at very low concentrations. Arsenic, mercury, and uranium were not detected in flowback samples from at least one multi-sample study. The composition of flowback water changes over time as well: fluid returning in the first few days looks different from fluid that comes back weeks later, because longer contact with the rock dissolves more minerals.
Disclosure and Transparency
In most U.S. states, operators are required to report the chemicals they use to FracFocus, a publicly accessible online registry. In New Mexico, for example, operators must file a complete disclosure within 45 days of completing a hydraulic fracturing job. The disclosures follow standardized forms and include the chemical components of each additive product.
There is a significant caveat. Companies can withhold specific ingredient information if they classify it as a trade secret or proprietary business information. This exemption is written into many state regulations. So while the broad categories of chemicals are publicly available, the exact formulations of certain products remain confidential. This trade-secret exception has been a persistent point of criticism from environmental groups and communities near drilling sites who want full transparency about what’s being pumped into the ground beneath them.