Hydraulic fracturing
- Also known as
- fracking, frac, fracturing, hydrofracturing
Hydraulic fracturing is a well stimulation technique in which fluid is pumped into rock at pressures high enough to crack it, and sand or another proppant is carried into the cracks to hold them open, creating pathways for oil and gas to flow to the well.
What is hydraulic fracturing?
Hydraulic fracturing, often called fracking or fracing, is a way of making a well produce more by creating fractures in the rock around it. A fluid is pumped down the well faster than the rock can absorb it, until the pressure exceeds the strength of the rock and it cracks. The fluid carries a granular material called proppant, usually sand, into the fractures. When pumping stops and pressure falls, the proppant holds the fractures open, leaving conductive channels through which oil and gas can flow to the well.
The technique was first used commercially in 1949. Combined with horizontal drilling, it is what made production from shale and other tight rock economic, and it transformed U.S. oil and gas output from the late 2000s onward.
How a fracturing job works
- Well preparation. The well is drilled, often with a long horizontal section running through the target formation, and cased.
- Stages. The horizontal section is divided into many stages, each isolated and treated in turn. A modern shale well may have dozens.
- Perforating. Holes are made in the casing to connect the well to the rock.
- Pumping. Fracturing fluid is pumped at high pressure to create fractures, followed by fluid carrying proppant.
- Flowback. After all stages are treated, the well is opened and part of the injected fluid returns to the surface before production begins.
What is in fracturing fluid
Most unconventional wells use slickwater: water with a small amount of friction reducer so it can be pumped at high rates. Water and proppant typically make up well over 99 percent of the fluid. The remaining additives can include friction reducers, surfactants, biocides, scale inhibitors, clay stabilizers, and, in gel-based fluids, gelling agents and crosslinkers. In the United States, operators disclose chemicals used in individual wells through the FracFocus registry.
Why fluid-rock interaction matters
Fracturing creates fracture surface area, but production also depends on how well oil and gas flow from the rock into those fractures. Shale pores are extremely small, so capillary pressure can hold treatment water in the rock next to the fractures, creating a water block that restricts flow. Surfactants in the fracturing fluid are used to lower interfacial tension and shift rock wettability so that fluid is released, flowback improves, and hydrocarbons can reach the fractures. Operators judge the results by early production, water cut and, over time, estimated ultimate recovery.
Hydraulic fracturing at Locus
Locus’s SUSTAIN is a biosurfactant frac surfactant added to fracturing fluid, which Locus describes as reducing interfacial tension and capillary pressure to improve cleanup and reservoir contact in shale wells.
Frequently asked questions
Drilling creates the wellbore. Hydraulic fracturing is a separate completion step, carried out after drilling, that cracks the rock around the wellbore to improve flow into it.
It lowers interfacial tension between the fluid and the oil and can alter rock wettability, so less fluid is trapped in the rock and more flows back, improving the flow of oil and gas into the fractures.
Treating a single stage takes hours. A multistage horizontal well can take days to a few weeks to complete, depending on the number of stages and the operation’s design.
Sources
- hydraulic fracturing, SLB Energy Glossary
- The Process of Unconventional Natural Gas Production; hydraulic fracturing resources, U.S. Environmental Protection Agency
- What chemicals are used, FracFocus Chemical Disclosure Registry