Aggregates Manager Digital Magazine
Issue link: https://read.dmtmag.com/i/107584
OPERAT 1 H Geology is key Best Practices for Frac Sand ydraulic fracturing, or fracking, is the means of generating fractures in rock by injecting fluid and a proppant, such as sand, under pressure, to release oil or natural gas. The purpose of the proppant is to keep the fissure open in the rock. And with a recent boom in both oil and natural gas well drilling, there is an increased demand for natural and manmade proppants — including ceramic beads, resin-coated silica sand, and natural silica sand. Of the three, natural silica sand that meets proper specifications can be the most cost-effective choice. According to Chris Kelley, Aggregates Division manager for McLanahan Corp., frac sand specifications are set by the American Petroleum Institute (API). "In general, what makes for a good frac sand is a high silica content sand that is spherical and rounded, and capable of withstanding extremely high pressures without breaking apart," he says. Kelley explains that new deposits are examined in order to determine their economic viability as frac sand deposits. There are a number of tests required, including the following: • Sieve analysis, • Sphericity and roundness, • Crush resistance, • Solubility, and • Turbidity. Many of these tests determine if the sand has the ideal geological characteristics. But in addition, he says, "The sieve analysis allows process engineers AGGREGATES MANAGER to provide complete mass balances for the process, ensuring that cyclones, pumps, dewatering screens, sumps, pipes, sizing screens, conveyors, dryers, sizing screens, and all other equipment are capable of handling the range of feeds expected to be fed to the plant." When Fred Weber, Inc. was approached in 2007 by a group interested in processing frac sand from the St. Peter's Sandstone deposit within the company's Festus, Mo., limestone quarry, the producer investigated the section of silica sand to see if its characteristics met the criteria. Tom Greco, vice president of operations for Mississippi Sand, LLC, said Fred Weber had previously sold nominal volumes of this silica sand as an additive for the cement industry. "Once it was determined that the silica sand met the criteria for frac sand, Fred Weber and this group teamed up and became partners. The plant was constructed in 2008 and sold its first ton of frac sand in July of that year," Greco says. Since April 2012, Mississippi Sand is now independent of Fred Weber, Inc. from an ownership perspective, although the two companies still have a valuable working relationship. Greco explains that the frac sand plant is located within the 550-acre Fred Weber quarry, which continues to produce limestone. The quarry company mines the sandstone feed for the frac sand plant. "Having the frac sand plant in the quarry is similar to having an asphalt plant within a quarry — which the Fred Weber quarry also has onsite," he says. Frac sand is emerging as specialty sand with characteristics that completely set it apart from traditional construction and masonry sand. In a nutshell, what makes for good frac sand is a high-silicacontent (98 percent or more) sand that is spherical, of consistent size, and capable of withstanding extremely high pressures without breaking apart. Tests for new deposits include sieve analysis, sphericity and roundness, crush resistance, solubility, and turbidity. 4 Dry, saleable product The frac sand product must have less than 1 percent moisture, so the material enters a dryer. Prior to this, producers may choose to use a dewatering screen (which provides a stackable/conveyable product with a moisture content of 10 to 15 percent). Vacuum belts are another option that can provide moisture contents in the range of 4 to 6 percent. Lower moisture content will reduce BTU requirements in the drying process. They are often used if the wet plant discharge directly feeds the dryer from a surge bin.