American Oil and Gas Reporter - August 2017 - 49

SpecialReport: Hydraulic Fracturing Technology
that it places in the ground and a crew can ill afford to suspend
operations while waiting on sand.
Last Mile Delivery Methods

The traditional last mile system is composed of pneumatic
trailers that deliver sand to the well site, where it is blown off
from the pressurized trailer into a "mountain mover" or "sand
king," a large storage trailer that typically consists of five
separate bins, each holding the contents of a trailer. The blowoff operation utilizes an air pump connecting to piping on the
bottom of the trailer, and literally blows the sand from the
trailer into the sand king. Typically, several sand kings are employed and dump onto a T-belt, which feeds into the blender.
This operation is noisy because of the high-pitched whine of
the blower pumps, dusty in the absence of additional dust
control measures, congested with truck positioning and time
consuming.
Because of the large number of sand trailers required to
"feed the beast" of a frac operation, and because a pumping
company cannot afford to prematurely run out of sand and terminate a frac or delay the next frac stage, there are generally a
dozen or so trucks lined up ready to blow off when their turn
comes. This leads to a traffic nuisance for nearby residents and
commuters and to stand-by or "demurrage" charges by the
trucking companies. In addition, this increases the congestion
and health, safety and environmental exposure on the frac site
as truckers back into position and prepare blow lines while
others pull off location after emptying.
The advantage of the legacy blow-off method is that there is
a lot of pneumatic equipment available, with around 500 U.S.
frac fleets utilizing this delivery method in 2014 featuring crew
members knowledgeable in how to use the system. Negatives
include the length of time necessary to unload a pneumatic
trailer, with the determining factor being air pump pressure.
As noted, the higher the air pressure, the faster the trailer
unloads. But frac sand can be damaged by air pressures exceeding
20 psi, and higher blow-off air pressures mean more silica dust,
which not only can damage the conductivity of the proppant
pack, but the respirable dust is harmful and must be captured.
Unfortunately, more respirable silica dust is generated with both
smaller proppant mesh sizes and at higher blower pressures.
It should be noted that new Occupational Safety & Health
Administration regulations take effect in July 2018 to limit onsite employee silica dust exposure to 50 micrograms a cubic
meter, eventually actionable at 25 micrograms. Figure 1 shows
500 micrograms of respirable silica dust, which is the equivalent
of the maximum exposure volume allowed under the new
OSHA regulations during a worker's shift.
A newer type of system consists of portable silos that are
erected temporarily at the well site ahead of the fracturing
process and allow anywhere from 2 million to 20 million
pounds of sand to be pre-stocked in the silos. As the job
progresses, the stored proppant is fed onto a belt or directly into
a frac blender. The system can be useful when time is available
to preload the silos to ensure a full load of sand is available
before the frac operation starts. The pre-stocked volume can be

FIGURE 1
500 Micrograms of Respirable Silica Dust
Courtesy of Aeris Dust Control

enough to support one-four days' worth of frac sand supply,
after which it must be replenished with the required daily consumption rate.
Typically, the silos are loaded using pneumatic trailers, with
the sand blown up into the silos to fill them. Unloading the
pneumatic trailers requires the same amount of time (45 minutes
a trailer on average), and generates the same amount of dust,
noise, onsite truck traffic congestion and trucking standby
charges.
Mobile Containers

The latest last mile technology involves mobile containers
that combine many of the portable silo's benefits, including
pre-stocking sand on location prior to an operation, but add a
significant new benefit: much faster unloading. The portable
containers are hauled to the well site on flatbed or drop-deck
trailers and are clipped onto the trailers with ISO quick clips
that can be locked or unlocked very quickly so that a load of
containerized sand, similar in volume to that of a pneumatic
trailer, can be unloaded by a forklift, replaced with empty containers, and sent on its way back to the transload facility for its
next load in fewer than than 10 minutes.
This speedier method for dropping off a load of sand
eliminates the necessity for trucks to line the road as they wait
to blow off (which translates to happier neighbors and commuters).
Furthermore, it shrinks pollution caused by idling trucks, opens
more space around the well site and trims costs associated with
AUGUST 2017 49

American Oil and Gas Reporter - August 2017

Table of Contents for the Digital Edition of American Oil and Gas Reporter - August 2017