What is Frac Sand?
Frac sand is a specific type of crystalline silica sand. The specific type of silica sand used in hydraulic fracturing is very round and extremely durable. The sand is mixed with water and a small amount of chemicals, including biocides to kill microbes and surfactants to reduce surface tension, and pumped at high pressure into wells. The pressure creates cracks in the rock, the liquid flows in and the sand remains, propping the cracks open and allowing the hydrocarbons to flow to the surface. The roundness of the sand increases the permeability and allows higher flow rates, and the strength of the sand increases the resistance to being crushed, and keeps those cracks open.
Proppant is the general term for the additive that props open the cracks in the shale rock, and includes sand, resin coated sand, and manufactured ceramic spheres.
Types of Proppant
Frac sand production was traditionally produced in the northern Midwest states of Wisconsin and Minnesota and then shipped by rail and truck to the major oil basins. This sand is widely known as northern white.
As hydraulic fracturing in the U.S. took off, demand for the sand exploded as well, both from the number of wells drilled and completed and from the amount of sand used per foot of well length.
As demand for frac sand increased, the price exploded. The booming market and nationwide demand created an opportunity for local sand producers. Sand mines popped up across the U.S. much closer to the producing areas. These are often referred to as in-basin or regional sand. With transportation costs significantly lower for the locally sourced sand, many buyers switched a proportion of the sand they pump to include the sand from these in-basin mines.
The “mesh size” of sand is the diameter of grains. The most commonly used meshed sizes are 20-40, 30-50, 40-70, and 70-140 (usually known as 100 mesh).
Each well design uses a slightly different blend of sand mesh size, but the two most common are 40/70 and 100 mesh.
The crush strength of sand and other proppants varies by each mine or manufacturing process. It is measured in psi, typically labeled in thousands. For example “6k” means 6,000 psi. Different well designs and specific geologies of the different basins require different crush values.
Frac Sand Production
With the explosion of US tight shale oil production, the number of wells drilled and completed as well as the horizontal length of those wells increased substantially, thus greatly expanding use and demand for proppant.