SPECIAL SAND CRITICAL FOR SHALE OIL RECOVERY
Industrial mineral by Harold Hough
While the demand for many mined products is down, one of the hottest mined products is sand, fracking sand, that is. Fracking sand is used for hydraulic fracturing, which has been responsible for the boom in oil production in the US. And, is so critical that demand for this specialized sand has more than tripled in the last four years. In 2013, over 56 billion pounds of fracking sand was used to increase oil and natural gas production.
Fracking sand is not your ordinary sand. It has many unique characteristics that make it ideal for fracking. Fracking is the process of retrieving oil, natural gas, or natural gas liquids from naturally impermeable rock formations like shale. Hydraulic fracturing involves drilling a well into the rock, sealing the portion of the well in the petroleum-bearing zone, and pumping water under high pressure into that portion of the well. This water contains sand and a gel to suspend the sand in the water.
Large pumps at Earth's surface increase the water pressure in the sealed portion of the well until it is high enough to exceed the breaking point of the surrounding rocks. When their breaking point is reached they fracture suddenly and water rushes rapidly into the fractures, inflating them and extending them deeper into the rock. Billions of sand grains are carried deep into the fractures by this sudden rush of water. Two to five million pounds of fracking sand can be required to stimulate a single well.
When the high pressure pumps are turned off, the rock formation deflates. However, the sand that was pumped in holds open the fractures enough that oil and gas can pass out of the rock and into the well. The sand also acts as a filter that prevents formation cuttings from entering the well bore.
But, not all sand can be used in fracking. It has to be high purity silica since that is the only type of sand that can stand the high pressures of the deflating rock and resist chemical attacks in the harsh environment underground. The grains have to be spherical so it can be carried in the fluid without creating turbulence. And, the grains have to of a uniform size in order to meet the needs of the rock formation and to prevent clogging. Fortunately, there are certain specific sandstone formations that are ideal like the St. Peter Sandstone, Jordan Sandstone, Oil Creek Sandstone and Hickory Sandstone formations.
What makes these formations ideal is that they have undergone considerable weathering and erosion, which has washed other mineral grains away and left sand grains with spherical shapes. Unlike other sandstone formations, they haven’t undergone several tectonic upheavals that deform and crack the sand grains.
Fracking sand also requires considerable processing after mining. It needs to be washed to remove the undesirable fine particles, dried, and screened to separate the different grain sizes. The grain size can range from 0.1 millimeters to 2 millimeters, depending on the customer’s needs. Some sand undergoes additional processing in order to make a premium product for high pressure applications. Fairmont Minerals of Ohio is a leader in hydraulic fracturing sand due their resin technology. Their resin coated sand has helped the hydraulic fracturing industry by allowing 2-4 times more oil and gas movement compared to raw frac sand. Their products can withstand closure pressures of up to 10,000 psi.
Traditionally, most fracking sand came from formations in Texas and Wisconsin. In fact, Wisconsin fracking sand is so valuable that it has its own name, “Northern White,” which is 99 percent silica and has a compressive strength between 6,000 and 14,000 pounds per square inch. About 9,000 truckloads of Northern White leave Wisconsin each day for the oil fields. However, as demand has grown, sand mining companies are looking at exploiting other sandstone formations that were ignored in the past because the demand wasn’t there. Some of these new fracking sand mining areas are found close to the surface in Illinois, Indiana, Iowa, Kansas, Kentucky, Minnesota, Michigan, Missouri, and Nebraska. Since weight is an important consideration, the closer the sand is to the oil field, the more competitive it is. That means these Midwest States may be providing fracking sand for a long time to come.