Keeping Dust Down On Proppant Use

March 01, 2016
Matthew Navea, Preferred Sands and Peter Rozowski, The Dow Chemical Co.

Hydraulic fracturing is one of the final steps in completing a well in preparation for production of oil and gas, a process requiring a mixture of water, proppant and chemicals to be pumped downhole at extremely high pressures. Silica sand proppant is a key ingredient that is currently in high demand because of its durability, and its shape and size are well suited to prop open fractures in shale formations.

Regulatory Parameters

Despite silica sand’s benefits as a proppant in hydraulic fracturing, it generates crystalline silica dust during handling and transport. When exposed to and inhaled by workers onsite, it is associated with the risk of developing silicosis, an incurable but preventable disease that causes lung damage. Workers with silicosis have an increased risk of serious conditions such as tuberculosis and lung cancer, and the most severe cases of silicosis can be fatal.

The U.S. Occupational Safety and Health Administration (OSHA) estimates that nearly two million workers in the U.S. are at risk of silica exposure, and more than 100,000 are in high-risk jobs.

OSHA enforces permissible exposure limits (PELs) to regulate the inhalation and exposure to respirable crystalline silica. The PELs for respirable crystalline silica in the general industry are calculated based on the percentage of silica (in this case quartz) found in a collected sample. For this article the OSHA PELs will be conservatively based on 100% quartz, and the calculated PELs will be equal to 0.1 mg/cu. m.

The administration is working to significantly update regulations, which has led to a new proposed rule that would reduce PELs for respirable crystalline silica by about 50%, a necessary industry improvement. In one of the final steps toward publishing this proposed rule, OSHA has submitted a final draft to the Office of Management and Budget for final review. OSHA has stated that it hopes to publish a final rule in first-half 2016.

In 2011 the National Institute for Occupational Safety and Health (NIOSH) found that, “worker exposure to wellsite workers (engaged in hydraulic fracturing) routinely exceeded occupational criteria, in some cases by 10 or more times.” Since 2011 there has been a dramatic increase in silica sand proppant consumption due to industry advancements in completion techniques. As a result, significantly more sand is used per well completion since 2011, increasing potential respirable crystalline silica exposure risk for all workers in the frack sand supply chain.

NIOSH has recognized several points of dust generation at the well site, including:

• Dust ejected from thief hatches (access ports) on top of the sand movers during refilling operations while the machines are running (hot loading);
• Dust ejected and pulsed through open side ports on the sand movers during refilling operations;
• Dust generated by onsite vehicle traffic;
• Dust released from the transfer belt under the sand movers;
• Dust created as sand drops into or is agitated in the blender hopper and on transfer belts; and
• Dust released from operations of transfer belts between the sand mover and the blender.

NIOSH has identified a variety of levels of control to address occupational hazards as described in the widely accepted method to reduce risk under its hierarchy of controls. Two controls, elimination (or physically removing the hazard) and substitution (replacing the hazard) of the proppant, are significantly effective at reducing the risk of respirable crystalline silica exposure.

These are difficult levels of control as the silica sand proppant is necessary to fracture the shale. Eliminating silica sand proppant from the hydraulic fracturing process is not currently feasible due to the requirements of the shale fracturing process. Effective and safe innovations in silica sand proppant technology are the future of the industry.

Dust Control Technology

In response to anticipated changes in regulations and as a way to improve worker safety at the well site, Preferred Sands and The Dow Chemical Co. joined forces to help reduce industry workers’ exposure to risk in energy production by creating a product that inhibits exposure to respirable crystalline silica.

The collaboration resulted in a breakthrough proppant technology called DustPRO, a silica dust control innovation that uses a proppant-coating technology for dusting at the source and throughout the product life cycle. The treated proppant technology is a cost-effective safety measure that is designed to inhibit exposure to respirable crystalline silica and has been found to meet silica exposure limits while maintaining downhole performance.

The advanced silica dust control technology treats sand using the Tersus/Preferred DC chemistry, a proprietary inert polymer that is sprayed onto sand prior to transport to the well site. The product was designed with the goal of very low incremental environmental impact. Product components were selected based on requirements of low toxicity, flammability and high biodegradability.

The proppant technology does not require any additional dust control equipment on site, thereby helping to eliminate bulky ventilation equipment, remove dozens of unsafe tripping hazards and allow safe access to all critical equipment.

Silica sand is coated with DustPRO prior to transport to the well site (source: Preferred Sands)

Field Tests

Since its introduction in early 2014, the technology has gone from bench tests and research to onsite implementation. From May 2014 to May 2015, more than 360 million pounds of the treated proppant was pumped downhole by 16 E&P companies and 11 oilfield service providers across all major shale basins in the U.S. and Canada.

During that time, third-party industrial hygienists monitored the technology’s performance. Researchers collected personal and area samples at 12 different well sites in Colorado, Louisiana, North Dakota, Texas, West Virginia and British Columbia. Each site varied in topography, geography, altitude and weather conditions, but results across the board were impressive.

During well completion activities, 140 personal breathing zone samples were taken, and 95% of the samples came in below OSHA’s current PELs of 0.1 mg/cu. m, and 86% were below OSHA’s proposed PELs of less than 0.05 mg/cu. m.

Though this statistically significant research is preliminary, there are indications that silica sand treated in this manner will be considered an effective substitution control to minimize exposure to crystalline silica dust at the well site and during all sand transfer points. Emerging dust control technologies are helping to advance safe domestic energy production and simultaneously reducing the dust level at the well site. The use of this proprietary technology leads to a safer work environment, improving morale of workers on location and mitigating perceived risk to neighbors and the surrounding community.

Shown are samples of DustPRO treated sand (left) vs. uncoated sand in water (source: Preferred Sands)

Source: E&P Magazine