Fracturing fluid
- Also known as
- frac fluid, slickwater, frac surfactant
Fracturing fluid is the fluid pumped into a well during hydraulic fracturing to crack the rock and carry proppant into the fractures. It is mostly water, with small amounts of additives such as friction reducers, surfactants, biocides and scale inhibitors.
What is fracturing fluid?
Fracturing fluid does two jobs in hydraulic fracturing. First, pumped at high rate and pressure, it cracks the rock. Second, it carries proppant, usually sand, into the fractures to hold them open. After the treatment, part of it returns to the surface as flowback.
Types of fracturing fluid
- Slickwater: water with a friction reducer, pumped at high rates. It is the most common fluid in shale wells.
- Linear gels: water thickened with a polymer such as guar, which carries proppant better.
- Crosslinked gels: gels whose polymer chains are linked, typically with borate or zirconium compounds, to create a much thicker fluid for carrying more or larger proppant.
- Hybrid designs that combine slickwater and gel stages.
- Energized and foam fluids that include nitrogen or carbon dioxide, used where less water is desirable.
Common additives
Water and proppant typically make up well over 99 percent of a slickwater fracturing fluid. The additives, used in small amounts, include:
| Additive | Purpose |
|---|---|
| Friction reducer | Lowers pumping pressure so fluid can be pumped at high rates |
| Surfactant | Lowers interfacial tension, improves fluid recovery, prevents emulsions |
| Biocide | Controls bacteria that cause souring, corrosion and plugging |
| Scale inhibitor | Prevents mineral scale |
| Clay control | Reduces swelling and migration of clays |
| Breaker | Degrades gels after the treatment so they flow back |
| Iron control and acid | Clean up near the wellbore and keep iron in solution |
In the United States, operators disclose the chemicals used in individual wells through the FracFocus registry.
The role of surfactants
In tight rock, fracturing fluid that enters the rock around the fractures can be held there by capillary pressure, creating a water block. Surfactants in the fluid lower interfacial tension and can shift rock wettability, so more fluid flows back and oil and gas can reach the fractures. Some surfactants also prevent emulsions between the fluid and the reservoir oil. These additives are often called frac surfactants.
Frequently asked questions
Slickwater is fracturing fluid made of water with a friction reducer, and usually other additives, that allows very high pumping rates. It is the most common fluid for shale wells.
To lower interfacial tension and alter rock wettability so that less fluid is trapped in the rock, flowback improves, and emulsions are avoided.
Sources
- fracturing fluid; slickwater, SLB Energy Glossary
- What chemicals are used, FracFocus Chemical Disclosure Registry
- Hydraulic fracturing water cycle, U.S. Environmental Protection Agency