Document ID: OSHA-2010-0034-1538
Agency: osha
Document Type: Supporting & Related Material
Title: 
Posted Date: 2013-06-11T04:00Z

October 3, 2012 Phone Call with Eric Esswein, NIOSH Senior Industrial Hygienist                (303 236-5946 eje1@cdc.gov)
   1. Layout of a hydraulic fracturing site
      * Water tanks are set up around the perimeter of the site, which are typically filled using water trucks.
      * Water tanks pump water into the hydration unit, which is approximately 20 feet from the blender.
      * The sand movers, end of sand belts, and conveyor belts are adjacent to the blender.
      * Most sites have multiple sand movers (approximately 3).
            o Blender hoppers have the capacity to accept sand from multiple sand movers.
      * A conveyor belt is used as a stand-alone intermediate belt that connects multiple sand movers to one blender hopper. 
            o The ends of the sand belts come out of the end of each sand mover and place sand on the conveyor blet, which is moved to the blender hopper, which is where the water, chemicals, and sand are mixed together.
            o If there is only one sand mover on site, the ends of the sand belts can move sand directly to the blender hopper without using a conveyor belt.
      * The chemicals can be stores in totes on flatbeds or in chemical trucks, which also contain metering equipment.
            o Chemical trucks are connected to the blender with 10-20 ft hoses. 
      * Once the sand, water, and chemicals are mixed together in the blender, the mix is pumped to the high pressure manifold before being pumped into a well under pressure during well completion.
            o High pressure manifolds receive energy from pump trucks that have 2,000 HP diesel engines in the truck beds.
      * Sites set up takes approximately two days.
            o Sites do not consider the direction of prevailing winds in site set up.
          
   2. General movement of sand through a hydraulic fracturing site
      * Sand, or other proppants, are brought onto hydraulic fracturing sites using sand trucks.
      * Sand trucks fill sand movers through pneumatic filling hoses that connect to fill ports on the sides of sand movers.  
      * Sand movers transfer sand to blender hopper either using an intermediate conveyor belt, or directly from the end of the sand belt on the sand mover. 
      * In the blender hopper, the sand is mixed with water and chemicals, as mentioned previously.
         
   3. How sand use in hydraulic fracturing has changed in the past five to ten years
      * Hydraulic fracturing companies are using much more sand now than 5-10 years ago, and the sand used is much finer, both of which result in dustier sites.
      * Drillers use somewhere between 190,000 and 300,000 lbs of sand for each zone (areas in the horizontal section of the well in which the casing is perforated and the shale is hydraulically fractured).
            o Previously, drillers used approximately 50,000 lbs of sand per zone.
      * The increase in sand use can be attributed to multiple factors:
            o Laterals (horizontal portions of the well) are much longer than before.
            o There are many more zones per lateral than before, each requiring sand.
            o Laterals can have up to 40 zones, though the average is 14. 
      * Hydraulic fracturing sites previously only needed one sand mover, but now use multiple sand movers, due to the increased need for sand.
         
   4. Wireline Crew
      * Main job is to lower and retrieve things into the well bore (especially the perforator gun, which blows holes in the well casing, allowing hydraulic fracturing to occur).
      * Crew members are doing other things on site while hydraulic fracturing is occurring (such as building the next perforator gun).
      * They use a derrick and a wireline truck with a big spool of cable to lower and retrieve tools.
            o Crews sometimes go "fishing" for tools stuck in the well.
      * Hydraulic fracturing does not occur while wireline crews work in the well bore.
            o During hydraulic fracturing, well is under 7,000-9,000 psi water pressure. 

   5. Frequency of hydraulic fracturing
   * The drilling process takes longer than the hydraulic fracturing process.
   * Crews can hydraulically fracture 2-3 zones per day. Each zone is fractured separately.
   * Hydraulic fracturing crews are on a site for 7 to 10 days on average, though a well with many laterals and many zones per lateral could take much longer. 
         o "Frack Teams" include 5-8 people, who travel as a unit.
         o These teams include chemical truck drivers, hydration unit operators, sand mover operators, blender operators, and conveyor belt tenders, among others. 
   * This is complicated by the fact that many companies are starting to drill multiple wells (approximately 4) per well pad, to decrease the footprint of each well pad. 
   * A couple zones might be re-hydraulically fractured 10-20 years after a well originally starts producing, which is when the well may start producing less natural gas. 
         o Re-hydraulic fracturing teams can "re-fracture" 2 wells per day, and the process involves similar respirable silica exposure risks as the original fracturing process.

   6. Potential controls for respirable silica
   * During refilling of sand movers there were up to 1,000 CFM coming out of the thief hatches on the tops of the sand movers. 
   * NIOSH has developed the "NIOSH mini-bag house retrofit assembly" as a potential control.
         o This involves bag houses attached to the thief hatches on sand movers using transition flanges.
         o The proof of concept has been done on site. The bags did not blow off, static pressure was measured, and some leaks occurred but the sources are known.
         o NIOSH does not yet know how long the bags will last (how many cycles).
         o It is not a complex concept and uses standard industrial ventilation. 
         o This control will likely be commercially available in the future and NIOSH is developing a patent for this control.
            
   7. Barriers to obvious controls
   *   Black Cat proppant, which is a ceramic proppant that is only 1 percent silica, is 3-10 times as expensive as sand and is not always appropriate.
         o It is used where there is very high formation pressure, since it has higher compressibility than sand, which will be crushed by the pressure, closing the pathways for the gas to travel.
   * The sand cannot be transferred as a slurry. Companies cannot add moisture to the sand, because it needs to be free-flowing in order to be transferred with the existing transport mechanisms.
         o One company that NIOSH is working with has had some success with misters that create a very fine mist, which knocks dust out the air without wetting the sand. 
         o Eric is not sure what the operating parameters are in terms of acceptable moisture levels for sand. 
   * It is not-feasible to enclose conveyor belts, though companies have been open to the possibility of enclosing the conveyor belts under the sand movers.
         o Eric mentioned the idea of making the walls on either side of the conveyor belt deeper, which might, in effect, enclose the sand in the conveyor belt. 
   * Eric was not familiar with the belt speeds involved.
   * Sand ports on the sides of sand movers were often left open.
         o Sometimes the cover was stolen, since it's made of brass.
         o Most operators now demand that the side ports be kept closed.

   8. Additional educational materials
   * Eric mentioned that the Petroleum Extension Service (PETEX) is a good resource for educational materials about the hydraulic fracturing process: http://www.utexas.edu/ce/petex/
   * OSHA's Oil and Gas Safety Conference will also be a good educational opportunity: http://www.oshasafetyconference.org/Events/ugm/Osha2012/default.aspx.