When frac fluid cracks open a rock formation, the fractures want to slam shut again the moment pumping stops and the pressure drops. Proppant is what prevents that. It is a granular material suspended in the frac fluid and carried into the new fractures; when the pressure is released, the grains physically prop the fractures open, preserving the flow channels that make the well produce.
A granular material — frac sand, resin-coated sand or manufactured ceramic — pumped into hydraulic fractures to hold them open against the closing stress of the surrounding rock.
Types of proppant
Three main families of proppant are used, trading cost against strength and quality:
- Silica frac sand is the most common and the cheapest proppant. It is naturally occurring high-purity quartz sand, sized and screened for fracturing. The vast majority of treatments use it.
- Resin-coated sand is frac sand coated with a resin that improves crush resistance and helps keep grains from flowing back into the wellbore.
- Ceramic proppant is manufactured for higher strength and more uniform, round grains. It performs best in deep, high-stress formations but costs significantly more than sand.
Silica frac sand is by far the most widely used proppant because it is the cheapest and abundantly available. Resin-coated sand and ceramic are reserved for wells where higher crush strength or grain uniformity justifies the added cost.
Mesh size and how proppant is specified
Proppant is specified by mesh size, which describes the grain diameter using the U.S. sieve system. A designation such as 40/70 means the grains pass through a 40-mesh screen but are retained on a 70-mesh screen — in other words, a defined size range. Larger grains (lower mesh numbers) create more conductive fractures but are harder to place; finer grains travel farther into the fracture network.
Beyond size, engineers care about grain sphericity and roundness, crush resistance and purity. Rounder, more uniform grains pack together to leave open pore space for flow, and stronger grains resist being crushed under the closure stress of deep formations. The right proppant choice balances those properties against cost for the specific reservoir being stimulated.
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Frequently asked
Proppant is the general term for any material that props fractures open. Frac sand is the most common type of proppant. All frac sand is proppant, but proppant also includes resin-coated sand and ceramic.
It is a size range. The grains pass through a 40-mesh sieve but are caught by a 70-mesh sieve, so the proppant falls within that band of diameters. Mesh numbers go up as grains get finer.
Ceramic is stronger and more uniform than sand, so it resists crushing in deep, high-stress formations and keeps fractures more conductive. The trade-off is that ceramic costs considerably more than frac sand.