What is Frac Sand?
Frac sand is a high-purity quartz sand with very round grains. It is very durable and provides a crush-resistant material used in the oil and gas industry for hydraulic fracturing (also called “fracking). Rock units composed of quartz grains that have gone through multiple cycles of weathering and erosion are potential sources of frac sand material. This evolution has removed most mineral grains other than quartz resulting in grains with very round shapes.
The demand for frac sand has risen dramatically in recent years as an increasing number of oil and natural gas wells use the hydraulic fracturing process. A single well using hydraulic fracturing can use a few thousand tons of frac sand. The surge of specialized drilling has created a billion dollar frac sand industry in just a few years.
How Frac Sand is Used
Some subsurface rock contains large amounts of oil, natural gas, or natural gas liquids that cannot flow freely to a well because the rock is impermeable to the degree that the fluids cannot flow through them. The fracking process presents a solution by creating fractures in the rock.
This is accomplished by drilling a well into the rock and sealing the portion of the well in the petroleum-bearing zone. Water treated with chemicals and thickeners to create a viscous gel is then pumped into that portion of the well using a high pressure process. The gel facilitates the water’s ability to carry grains of frac sand in a suspended state.
Large pumps at the surface increase water pressure in the sealed portion of the well until pressure is sufficient to fracture surrounding rocks. Water rushes rapidly through the fractures, making them larger and pushing them deeper into the rock. Because billions of sand grains are pushed deep into the fractures, it can take several thousand tons of frac sand to stimulate a single well.
Why Frac Sand Makes a Good Proppant
After the surface pumps are turned off, the fractures contract but do not close completely because they are propped open by billions of grains of frac sand. This occurs when there is sufficient sand remaining in the rock to resist the force of the closing fractures.
Frac sand is known as a “proppant” because it props the fractures open by forming a network of pore spaces that allow petroleum fluids to flow out of the rock and into the well. Although there are other types of proppants available, depending on the type of well, frac sand often delivers the highest performance.
Characteristics of High Quality Frac Sand
Proppants used in the petroleum industry must meet very demanding specifications. The typical characteristics of high quality frac sand include:
- high-purity silica sand
- a grain size that is perfectly matched to job requirements
- a round shape that allows it to be carried in hydraulic fracturing fluid with little turbulence
- durability to resist the crushing forces of closing fractures
Frac sand comes in various sizes. It can be as small as 0.1 millimeter in diameter to over 2 millimeters in diameter. Most frac sand used in the oil and gas industry is between 0.4 and 0.8 millimeters in size.