Hydrofracturing
Introduction
Hydrofracturing is only used in bedrock
formations and is a water well development process that involves
injecting large volumes of water under high pressure through the
well into the bedrock formation immediately surrounding it. The
desired result of this well "stimulation" is to widen
existing fractures in the bedrock and/or extend them further into
the formation. By enlarging the network of water bearing fractures
supplying water to the well, it is hoped to realize an increase
in the water production . Hydrofracturing can be a cost effective
means of increasing the yield of newly drilled wells with insufficient
production rates or for existing older wells with production rates
that have progressively become lower due to mineralization of
existing bedrock fractures.
History
Originally developed for use in the oil
industry, hydrofracturing is a relatively new to the drinking
water well industry. Due to its more controllable process, hydrofracturing
is now the preferred method of many contractors for developing
bedrock. Compared to older methods of increasing well production
(blasting with dynamite or application of dry ice to capped wells),
hydrofracturing offers more benefits with less risk of well failure.
Process
After removing all piping and pumps from
the well, the procedure begins by lowering an inflatable hard
rubber packer into the wellbore. In the bedrock, the packer is
set a minimum of 20' below the end of the casing and 60' below
the surface of the ground to prevent the pressurized water from
breaking through the ground surface and to avoid surface water
and contaminants entering the well. After placement, the packer
is inflated thereby sealing off the section of the well below
and high pressure water is pumped through the packer into the
bedrock. Hydrofracturing procedures usually require between 500
and 2000 pounds per square inch (psi) pressure though in some
cases up to 3000 psi may be necessary to achieve adequate penetration
into the bedrock formation.
As the rock formation resists the flow
of the pressurized water, the pressure within the sealed-off section
of the well will rise. It is this focused pressure that can force
fissures in the bedrock to widen and elongate and wash out sediment
in the fractures. If the bedrock yields and the pressurized water
finds its way into these small cracks, the pressure will suddenly
drop off. This generally means that the bedrock is accepting water
and is ready to proceed to the next step.
Once the pressure has dropped off, water
is pumped into the formation at a rate of 25 to 60 gpm. Up to1200
gallons of water will be pumped into the formation in an effort
to remove mineral deposits and debris that can be forced into
the bedrock from the pressurizing procedure. Only clean, disinfected
water is used for injection due to the extreme pressures involved
and the potential for forcing contaminants into the aquifer.
Successful hydrofracturing procedures
are usually indicated by a sudden drop in the pressure combined
with increased flow of pumped water into the formation. Additionally,
a strong backflow of cloudy water when the pressure is released
represents success as that reflects the removal of the sand, rocks,
mineral deposits, and other debris that previously occupied the
newly-opened cracks and fissures. A complete hydrofracturing procedure
may require deflating and lowering the packer deeper into the
wellbore a number of times. At each stage, the entire pressurization
and injection process is repeated.
Considerations
Hydrofracturing can be applied to bedrock
wells only. A bedrock well is one that obtains its water by water
flow through cracks, fissures, and fractures in the rock intersected
by the wellbore. Water yield of a bedrock well depends on the
number of fractures encountered, their width, orientation, and
how well they are connected to other fractures in the rock formation.
As there can be risk of impacting an adjacent well, it is important
to identify the locations of any neighboring wells. This process
is not recommended if there are other wells within 100' feet of
the target well. Dave Jelinek Well Drilling, Inc.
is experienced with hydrofracturing and can advise you on whether
your well is a candidate for this procedure. Existing wells must
meet current code requirements for casing depth and thickness.
Yield Testing
When successful, hydrofracturing can
produce modest well yield increases. However, depending on the
original yield of the well, a modestly increased yield may represent
a significant increase if the original yield was very low. A typical
well yield rate after hydrofracturing is 1/2 to 5 gallons per
minute though occasionally large increases in well recovery rates
are realized. Due to geologic conditions, in some instances hydrofracturing
will not increase well yield.
Yield tests can be performed after a
hydrofracturing procedure to gauge the effectiveness of the process.
Test pumping is usually 20 hours or more depending on if the water
is clean.
Summary
Though there is no way to predict exactly
what the outcome will be, Jelinek Well Drilling,
Inc. has generally had success in our service area with
hydrofracturing and will recommend it to well owners that suffer
from inadequate water yield or from reduced well recovery due
to a gradual "tightening" of the bedrock aquifer through
the years. Please contact us to schedule a consultation regarding
your low-yield well.
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