1. How is hydraulic soil fracturing using the FRAC RITE™ process effective
for in situ remediation of contaminants in low permeability soil?
The FRAC RITE™ process creates highly conductive pathways (i.e. fractures)
containing sand that radiate from the borehole into surrounding contaminated soils.
These sand-filled fractures act as “highways” to accelerate the movement of
contaminants from low permeability soils (i.e. K < 10-6 m/s) through the permeable
sand towards the well bore.
The permeable sand fractures increase the “reach” of a fractured recovery well to a
greater mass of contaminants. The fractures effectively shorten the distance that
contaminants must travel before reaching a permeable pathway to the recovery well.
Since the sand inside the fractures keeps the fractures propped open, fracture
longevity and long term performance is ensured.
Soil hydraulic fracturing also allows the simultaneous injection of treatment
amendments (e.g. surfactants, nutrients, bio-amendments, slow release oxidizers, etc.)
during fracturing to further expedite the in situ remediation of contaminants.
2. What kind of performance enhancement can I expect from Fractured
Wells compared to conventional wells for in situ site remediation?
That depends on the soil type, soil fracturing intensity, nature and distribution of
contaminants, remediation methodology used, etc. Our experience from placing
hundreds of fractures for site remediation has shown that soil fracturing can:
" Increase Bulk Permeability in soils by up to three orders of magnitude
" Double the Radius of Influence of Fractured Recovery Wells
" Increase Contaminant Removal Rates by twentyfold
" Reduce Time required for Site Remediation by more than half
" Reduce number of Recovery Wells required by up to 75%.
Specific examples of Fractured Well performance used with various remediation
technologies can be found in the BENEFITS link.
3. What cost savings are obtainable using the FRAC RITE™ process of
hydraulic soil fracturing?
Cost is dependent on many factors including mobilization, scope of fracturing
required, incorporation of additional remedial amendments into the fracture slurry,
drilling conditions, need for subsurface fracture mapping, etc.
When conducting Remediation Life Cycle cost comparisons at sites remediated using
soil fracturing versus conventional methods, the cost savings have been in the order of
30% to 60% of the Total Cost of Remediation.
These cost savings are due primarily to faster clean-ups achieved, and significantly
fewer wells and related downhole equipment, infrastructure, monitoring, sampling,
etc. required for fracture-enhanced remediation.
At a former gas plant site in Alberta, Canada, the FRAC RITE™ process saved the
client $1.35 million in remediation costs compared to the best alternative remedial
options identified by their environmental consultant.
4. Can you fracture any type of soil? What about bedrock?
We use different downhole fracturing equipment and configurations depending on the
nature of the soil to be fractured. We can fracture most soils except coarse gravel,
cobbles and boulders, or fill soils containing obstructions such as construction rubble,
etc. Most bedrock can be fractured due to better borehole stability than typically
present in unconsolidated sediments. We have even fractured saturated municipal
landfill wastes for enhanced leachate and methane recovery.
5. How many fractures can you place in a typical working day?
We are usually able to create two to three fractured, vertical boreholes per day,
containing 3 to 6 fractures each, in a “typical” soil fracturing application (usually to
fracturing depths of less than 15 metres).
The time required for fracture placement depends on many factors including the depth
of drilling required, sand requirement per fracture, drilling conditions, addition of
treatment amendments, equipment access, weather conditions, extraordinary health
and safety precautions, etc.
6. Can I use fracturing to simultaneously inject treatment amendments to
facilitate in situ remediation?
Yes, we call the use of soil fracturing with simultaneous emplacement of treatment
amendments the BIO FRAC™ process. Many chemical and biological amendments
have been incorporated into our fracture slurry formulation and injected into
contaminated soils. This usually requires that we carry out bench scale laboratory
testing in order to determine the chemical compatibility and mixing ratios achievable
for field fracturing applications. Examples of incorporating treatment “additives” to
our fracture slurry on past projects include surfactants, nutrient solutions, zero valent
iron, polyglucosamines, and solid phase peroxides and permanganates, among others.
Treatment amendments can also be injected into the network of sand fractures any
time after fracturing for subsequent “re-inoculation” of contaminated sites.
7. Is it possible to fracture soils from horizontal boreholes?
Yes, Frac Rite™ has carried out the only known application of soil fracturing from a
horizontal well bore for enhanced in situ remediation in Canada. We use a variation of
our conventional fracturing tools to enable soil fracturing in horizontal well bores;
fracture slurry formulation procedures used are the same as for fracturing in vertical
boreholes.
8. Is there any way of determining where the fractures were placed in the
subsoils after fracturing?
Each individual fracture created in the subsurface can be mapped, if necessary, using
a geophysical technique called tiltmeter fracture mapping. This geophysical method
uses an array of surface sensors called “tiltmeters” which are positioned in a
concentric or grid pattern around the borehole to be fractured. The tiltmeters sense the
magnitude and direction of micro ground movements induced by each fracture placed
in the subsurface. Dataloggers record the micro ground movements and the data is
downloaded for processing using an inverse parameter geophysical model. The model
interprets the most likely geometric configuration and dimensions of each fracture
created in the subsurface soils. The fracture configuration data is subsequently fed to a
three dimensional computer graphics model which produces a three dimensional
colour image of the fracture network configuration at each fractured borehole.
9. I have sites across North America and elsewhere that I wish to consider
for soil fracturing. How do I know that they are candidate sites, and are
you able to service a wide geographic area?
We subject all potential candidate sites to an assessment process using our soil
fracturing SITE DATA CHECKLIST . This checklist allows prospective users to
quickly provide site-specific geotechnical and environmental data that is pertinent to
the assessment of their site for soil fracturing. It can be faxed or emailed back to us
for a timely assessment including an initial cost estimate, if required.
Because of our network of alliance partners, we are able to provide our soil fracturing
services across North America and elsewhere. Our personnel have conducted soil
fracturing operations in continental Europe, the USA, and Canada. Soil Fracture
networks have been designed for clients in North America, Europe, and Africa for
applications ranging for enhanced subsurface hydrocarbon recovery to construction
dewatering, landfill leachate recovery, and drainage enhancement for improved
geotechnical slope stability.
10. How does hydraulic soil fracturing differ from pneumatic soil fracturing,
and what are their relative advantages and disadvantages?
Hydraulic and Pneumatic fracturing are techniques used to artificially fracture soils
and thereby increase soil permeability. The main difference is in the penetrating fluids
used in each method. Hydraulic fracturing involves the use of a water-based, highly
viscous slurry containing sand to create a fracture and prop it open with sand.
Pneumatic fracturing involves the injection of compressed gas (usually air) to create a
fracture, which is initially self-propped but will tend to close over time.
Both hydraulic and pneumatic fracturing have similar costs and well installation
requirements, but hydraulic fracturing has one distinct advantage. Sand-propped
fractures are permanent and will not close off over time (Walden, 1997), thereby
providing fracture longevity and enduring permeability enhancement for in situ site
remediation. The need for keeping fractures propped is especially important in soils
that contain swelling clays or at excessive overburden pressures, conditions which
tend to close off unsupported fractures.
Pneumatic fracturing has been shown to successfully enhance permeability in rock
formations such as siltstones and shales (Kidd, 1996), and dry, brittle cemented soils,
which have some ability to “self prop” due to their consolidated nature. Applications
of pneumatic fracturing in unconsolidated sediments are generally not as effective
(Dockstader, 1994). Pneumatic fracturing trials conducted in Germany and sponsored
by the European Union Environmental Commission showed that unpropped fractures
created in sandy silts, at a depth of only two metres below the ground surface, clogged
and squeezed shut within two weeks of fracturing (Neemann and Burkant, 1994).
They concluded that re-fracturing of the soil would be necessary on a regular basis in
order to maintain the permeability enhancements obtained by pneumatic fracturing.
A summary of the advantages and disadvantages of hydraulic and pneumatic
fracturing is summarized in the table below:
| Hydraulic Soil Fracturing |
Pneumatic Soil Fracturing |
| Effective in soils and rock |
Primarily effective in rock |
| Long term permeability enhancement |
Short term permeability enhancement in
unconsolidated sediments |
| Specialized equipment and fluid
chemistry expertise required; more
logistics required |
Less equipment and expertise required;
not as much logistics involved; ongoing
O & M costs to maintain fracture network |
| Better control of fracture parameters due
to negligible leak-off of viscous sand
slurry |
Difficult to control/predict fracturing due
to high leak-off of air resulting in fracture
short circuiting to ground surface |
| Low leak-off prevents spreading of
subsurface contaminants | Injected air can potentially spread soil
vapour phase contaminants |
| Geophysical and visual mapping of
individual fractures is routine | Mapping and prediction of fractures
extremely difficult |
| Simultaneous injection of many treatment
amendments (e.g. surfactants, chemical
reagents, bio-amendments, nutrient
solutions, etc.) possible during fracturing
due to carrying capacity of viscous
fracture slurry. Subsequent injections of
treatment amendments possible into
subsurface fracture network without need
to remobilize equipment for refracturing | Limited injection of treatment
amendments during fracturing due to
poor carrying capacity and amendment
distribution (“packing off”) in fractures
when using air. Subsequent injections of
treatment amendments require
remobilization of fracturing equipment to
refracture soils |
| Fracture clogging by fines is minimized
because frac sand is designed to act as a
geotechnical filter while maintaining
enhanced permeability | Fractures are unsupported; migration of
fines quickly clogs fractures. |
| Greater range of adaptability with
remediation technologies (e.g. Dual
Phase Extraction, Bioremediation) | Not readily adaptable to many
remediation technologies. |
| Hydraulic fracturing technology proven
and in use since 1949 for enhancing
permeability and production in petroleum
industry, and since late 1980’s in
environmental industry. | Pneumatic fracturing developed in late
1980’s for application in environmental
industry. |
|
Let us assess your site for Soil Fracturing.
