Turbidity is the measure of suspended particles, such as clay or sand, in distilled water, and it is one of many testing methods performed for American Petroleum Institute’s (API) Recommended Practice 19C and the International Organization for Standardization’s (ISO) 13503-2 proppant testing standards. Current API and ISO standards require turbidity to be 250 Formazin Turbidity Units (FTUs) or less. In essence, a lower turbidity means the sand is cleaner and has less dirt and silt attached to each particle.
While sand is screened into different mesh sizes ranging from 20 to 100 depending on the shale application, what remains constant is the need for proppant with low turbidity. This is better quality sand that maximizes operations while also being safer for employees and the environment.
Proppant needs to go through a rigorous and strict quality control cleaning process before it is suitable to be sold to customers. The washing process cleans sand, removing silt and clay content to reduce FTUs. Sand for fracturing use is typically placed in demineralized water for 30 minutes and then shaken by a wrist action shaker for an additional 30 seconds. The sand sits in a beaker of water for five minutes and then the suspended-particle sample is tested by a turbidity meter or spectrometer for FTUs.
Silicosis, a lung condition caused by inhaling too much silica over a long period of time, is a major concern and focus in the sand industry. Symptoms of silicosis can appear after years of exposure to silica dust, and symptoms often worsen over time as the lungs continue to scar. Both the U.S. Occupational Safety and Health Administration (OSHA) and the U.S. Mine Safety and Health Administration (MSHA) regulate silica dust exposure. The U.S. National Institute for Occupational Safety and Health (NIOSH) also studies and helps with regulation for silica dust exposure.
In addition, the NIOSH recommends that those entering a trade industry who may have contact with silica dust should receive medical examinations at least every three years. OSHA has jurisdiction over the safety and health of workers, including workers involved in upstream oil and gas operations. MSHA has jurisdiction over mine sites that manufacture sand for oil and gas operations. Sand with lower turbidity produces less dust and is the safest option for workers.
High turbidity in sand directly correlates with high silica exposure during hydraulic fracturing operations. Service companies are required to put in engineering controls, such as a dust collection system, chemical dust suppressors or other systems, which add to the operating costs. The exposure to silica also affects the workers on site requiring mask filtration systems or limited work hours hindering operations, which also delays production and output.
There is a tremendous demand in the energy industry for sand as rig counts continue to increase. As sand providers work to fulfill the growing needs of their customers, it is important to stick to quality control processes, ensuring the best products with the lowest turbidity are provided.