Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/581365
13 AGGREGATES MANAGER October 2015 MINE MANAGEMENT with substances, like resin, to change its physical and chemical properties. No matter the type, proppant is designed to remain in place over the life of a well. The ideal proppant is fl owable to allow it to move deep into the fi ssures and strong enough to keep the fi ssures propped open without fracturing the grain. Proppant is often specifi ed by its strength, known as crush resistance or crush strength. It is measured in pounds per square inch (psi), with a higher psi indicating its ability to perform at greater pressure. Since proppant is used in large quantities, typically between 1,000 and 6,000 tons per well, proppant must also be economically feasible and transportable without impacting product quality. About 92 percent of proppant used in the United States today is frac sand. Frac sand is naturally occurring silica sand that has been tested and found to meet certain physical and chemical parameters that allow for the optimal conductivity of oil and gas. Silica sands, or sands that are monocrystalline quartz with a silica content of 99 percent or greater, are pre- ferred because they are chemically inert and do not interact with other chemicals used in the fracking fl uid. Frac sand quality Frac sand is subjected to quality test protocols recognized by the American Petroleum Institute (API) and the International Organization for Standardization (ISO) using methods API RP 19C and ISO 13503-2. Both the shape and strength of the sand grains predict the ability of the material to allow conductivity of oil and gas. Tested qualities include particle distribution, grain roundness and sphericity, turbidity, specifi c gravity, acid solubility, and crush resistance. Crush resistance, also called crush stress level, or K-value, measures the ability of the proppant to resist breaking down under pressure. Frac sand products Frac sand is sold in graded sizes, much like aggregates. The sand grains are sieved on woven wire mesh screens and blended to meet specifi cations. Products are named by their size relative to the top and bottom mesh numbers which relates to maximum and minimum grain diameter. The coarsest standard product for frac sand is 20/40. This means that 90 percent of the proppant product is small enough to pass through the 20 mesh screen (an opening of 0.85 mm) and large enough to be retained on the 40 mesh screen (0.425 mm). Each product allows for a distribution of grain sizes within the range. Other standard proppant sizes are 30/50, 40/70, and 50/140 also known as "100 mesh." Frac sands typically exhibit crush strengths as high as 8,000 psi for the 20/40 and 30/50 products and 10,000 to 13,000 psi for the 40/70 and 100 mesh products. Proppant products are typically specifi ed based on the particular appli- cation in the oil fi eld or gas fi eld, which are dependent on a number of features including depth, pressure, and tempera- ture of the well. Generally, shallower wells and softer source rocks can accept lower crush-resistant products. They can be as low as 2,000 to 4,000 psi for the larger 20/40 and 30/50 proppants, while 4,000 to 6,000 psi is typically specifi ed for the fi ner 40/70 and 100 mesh sizes. Deeper wells and high temperature wells often require the proppant to exhibit crush resistance of 6,500 to greater than 14,000 psi. Frac sand sources, mining, and production Silica sands that are suitable as frac sand are found in several regions across the United States. Frac sand mine locations are also established based on the ability to transport mate- rial economically to the oil and gas fi elds. Location is critical because the cost to transport frac sand is usually the highest contributor to total cost. © 2015 Proppant Today, LLC