Fracking sand is a highly specialized material used in hydraulic fracturing, or “fracking,” a technique for extracting oil and natural gas from underground rock formations. This sand is distinct from common construction or beach sand because it possesses unique physical properties that allow it to perform a demanding mechanical job deep within the earth. It is a manufactured commodity, derived from natural sources, and engineered to meet stringent industrial specifications for strength and shape. The material’s primary purpose is to maintain the flow of hydrocarbons from the reservoir rock to the wellbore, necessary for economic recovery.
The Physical and Chemical Characteristics
Fracking sand is primarily composed of high-purity silica, specifically quartz, which gives the grains a hardness of 7 on the Mohs scale. This high silica content is necessary for the sand to withstand the immense pressures encountered thousands of feet below the surface. The sand grains must also exhibit a high degree of sphericity and roundness. This smooth, rounded shape minimizes the points of contact between grains, creating the maximum amount of void space for fluids to flow through the packed material.
A non-spherical or irregularly shaped sand, like common beach sand, would pack too tightly and crush more easily under pressure, severely limiting the well’s productivity. The most telling characteristic is the sand’s crush resistance, which is its ability to remain intact when squeezed by the closing pressure of the rock formation. Depending on the application, high-quality fracking sand can withstand compressive stresses ranging from approximately 6,000 to 14,000 pounds per square inch (psi). This strength is paramount because if the grains fracture, the resulting angular fragments can fill the open spaces and clog the flow path for oil and gas.
The sand is also carefully sorted for uniform grain size, which is measured in mesh size, with common specifications including 20/40, 30/50, or 40/70 mesh. A consistent size range further ensures that the sand packs together efficiently, creating interconnected channels that maintain high permeability. The uniformity and spherical nature of the grains work together to prevent a tight, impenetrable packing arrangement that would choke off the flow of hydrocarbons.
Function as a Proppant
Fracking sand’s function is to act as a proppant, which is an industry term for a material used to “prop” open the newly created fractures in the reservoir rock. During hydraulic fracturing, a mixture of water, chemicals, and the proppant is injected into a wellbore at high pressure. This fluid pressure exceeds the strength of the rock, causing it to crack and create a network of micro-fissures and fractures.
When the pumping pressure is lowered and the surrounding rock attempts to close the fractures, the sand remains behind to hold the fissure open. The packed sand provides a structural support system, preventing the rock from collapsing back onto itself. This supported space, known as the proppant pack, must maintain a high level of fracture conductivity, which is the measure of how easily oil and gas can flow through the packed sand to the wellbore.
The physical integrity of the sand is constantly challenged by the closure stress of the surrounding rock, which can range from 30 to 80 megapascals (MPa) in deep shale formations. If the proppant crushes or embeds into the rock formation, the fracture conductivity decreases dramatically. Therefore, the choice of proppant is a balance between its cost and its ability to resist crushing and maintain the open, high-conductivity pathway.
Geological Origin and Processing
The high-quality sand required for this application is sourced from specific geological formations that naturally contain the necessary quartz purity and grain structure. In the United States, a primary source is the Middle and Upper Ordovician St. Peter Sandstone formation, which is prominent across the Midwest, including Wisconsin, Illinois, and Minnesota. This ancient sandstone is highly prized for its nearly pure quartz composition and its already rounded, durable grains.
Another important source is the Jordan Sandstone, as well as the Hickory Sandstone Member in Texas, sometimes informally referred to as “Brady” sand. The rock formations that yield this sand are often relatively friable, meaning they are easily broken apart, which simplifies the initial mining and crushing process.
The raw material goes through a precise processing sequence to meet industry specifications. This typically involves washing to remove impurities like clay and iron oxides, drying for handling efficiency, and screening or sizing. The screening step separates the grains into specific mesh sizes (e.g., 40/70 mesh) required for different well conditions, ensuring the final product provides optimal uniformity and conductivity.