in-situ remediation
Hydraulic fracturing for enhanced in-situ remediation of contaminated soii
and groundwater
The development of industry in
North America has resulted in the
water, or the drawing of vapours from the soils using conventional vertical recovery
the fracturing fluid to revert to that of water after a preset time period, typically 18 to 24
construction and operation of a
wells, is neither effective nor economic.
hours. This causes the fluid to flow back
multitude of diverse industrial fa
Consequently, these sites have typically been remediated by relocating the problem through the "dig, haul and dump" approach. The permeability, and hence the effec
from the fracture into the injection well, leaving the sand to permanently prop open
cilities across the continent. Historically, these facilities have included steel mills,
coal gasification plants, wood preserving fa cilities, chemical plants, oil refineries and, today, include the latest high tech electron ics and manufacturing industries. Despite their substantial benefits to mankind above
tiveness of in situ remediation of fine
grained soils can be enhanced through the development of a network of induced hori zontal fractures in the soil. These induced
the ground, many have left a not so at
tractive legacy be
Surface Spills/ Tank Leakage
neath the surface - soil
pletely bio-degradable and environmentally friendly. Fracturing technologies have been devel oped in the United States by the University of Cincinnati (hydraulic fracturing) and the New Jersey Institute of Technology(pneu matic fracturing). Both of these tech
Facility
and groundwater con tamination.
the fracture. The fracture fluids are com
nologies involve multiple entries into
Groundwater
Sub-surface con
Tank
Level
a borehole with sev
Farm
ter table or a dissolved
eral different pieces ofequipment. Hence the fracturing proc ess using these tech nologies is time con suming and rela tively expensive.
phase in the groundwater. In situ
ates, an international
tamination may exist in many forms, such
vapours LNAPL
as immiscible fluids
(NAPLs) above and below the water table, vapours above the wa
Colder Associ
methods used to remediate sub-surface
contamination prima rily involve promoting Schematic of multi-phase remediation of contaminants using hydraulic fracturing. some form of fluid
(liquid or vapour) flow through the soil in which the contamination is located. This
flow is typically encouraged by the installa tion of pumping wells below the water ta ble, or the installation of soil vapour extrac tion wells above the water table. The ef fectiveness of these remediation methods is
controlled primarily by the permeability of the soil.
A major portion of the surface of North America is covered by fine grained soils.
fractures can be formed through the proc ess of either pneumatic or hydraulic frac turing. Fractures can be formed in soil using ei ther a gas (pneumatic fracturing) or a liq uid (hydraulic fracturing). Hydraulic frac turing has been used in the oil industry for many years as a method of enhancing the
production from oil wells. During the frac turing process, fluid is injected into an iso lated section of a borehole in the formation
A major portion of the surface of North America Is covered by fine grained soils, usually silts and clays, that were laid down beneath Ice sheets. In glacial lakes,
by rivers, or along estuaries and coasts.
firm ofconsulting en gineers, has devel oped a technology that enables fractures
to be initiated, propa
gated and propped with sand sequentially with increasing depth in a single excursion into the ground. The key to this technology is a piece of equipment called the "Fractool", for which a patent application is currently pending. The Fractool technol ogy has the potential to enable a site to be fractured more cost effectively than the other available fracturing technologies to date. The Fractool was developed in the
Calgary, Alberta office of Colder Associates as a result of large scale laboratory studies of hydraulic fracturing of oil sand. This work was subsequently extended to inves tigate the effectiveness of fracturing on the
permeability of clays. The Fractool frac turing technology has been demonstrated in the field at three clay test sites in Canada. The most extensive field trial to date was
usually silts and clays, that were laid down beneath ice sheets, in glacial lakes, by riv ers, or along estuaries and coasts. These soils are generally not very permeable to ei ther liquids or gases, and also contain natu ral vertical fractures through which the con taminants preferentially move. The in situ
containing a preformed notch. The pump ing rate of the fracturing fluid and its prop erties are designed to promote the growth
remediation of contaminated sites underlain
sand can be held in suspension in the fluid during the fracturing process. A breaker is also added that will cause the viscosity of
by these types of soils through the pumping of NAPLs and/or contaminated ground42
of horizontal fractures out from the well.
undertaken at a former service station site
in Regina, Saskatchewan, in late 1993. The site is underlain by a medium to high plastic glaciolacustrine clay, and the petro
The fracturing fluid comprises a starch based guar gum dissolved in water. A cross
leum hydrocarbon contamination is associ
linker is added to stiffen the fluid so that
clay above the water table. Three unfractured and eleven hydraulically fractured wells were installed at the
ated with natural vertical fractures in the
site. A total of eleven tonnes of sand were
Environmental Science & Engineering, November 1994