| |
 |
 |
|
|
The genesis of GeoSierra's patents, specialized
equipment, and expertise for its "trenchless construction" of
deep PRBs was the discovery in 1992 that it was possible to induce and
control the direction (orientation pathway) of a vertical fracture in
certain soils. From this discovery the idea was conceived to perfect the
process of controlled vertical hydraulic fracturing with the objective
of then being able to apply the process as a key technology component
for installation of PRB walls in the subsurface. An extensive series of
hydraulic fracturing experiments in soils and weakly cemented sediments
was then completed by conducting over 250 tests in a variety of soil conditions.
These tests and experiments were excavated to verify the extent, orientation
and thickness of the resulting vertical hydraulic fractures. These experiments
proved the eariler discovery that by creating an artificial fracture at
the required azimuth in the soil, controlled vertical hydraulic fracturing
of the soil could be maintained and fracture coalescence between multiple
injections could be assured, thus providing the subsurface pathway for
the formation of an iron PRB wall. It was the discovery in 1992 that ultimately
led to the four patents being awarded to GeoSierra from 1999 through 2002
with respect to its proprietary technologies design and for installation
of iron PRBs. |
| |
 |
| |
 |
| |
 |
|
One of the forerunners of GeoSierra's
fracture technology was field demonstrated as a proof of concept
under contract to the U.S. Army Corps of Engineers at a site in
New Hampshire. These demonstration tests utilized the earliest form
of the fracture initiation device consisting of a driven flat-faced
probe with an inflatable packer mounted above the probe. The proof
of concept demonstrated, from the initiation and propagation of
twenty-three vertical hydraulic fractures, that fracture azimuth
could be controlled and maintained, fracture coalescence of multiple
injected fractures could be assured, and fracture thickness of up
to 9" could be accomplished. |
|
| |
|
| |
 |
| |
|
|
|
The first commercial fracture initiation
device developed by GeoSierra was a twelve (12) ft long tool, 6"
in diameter, that was inserted into a 6.25" diameter PVC casing
pre-drilled and grouted into the soil to the full depth of the required
fracture. The tool was a chain saw cutting device that, upon insertion
to the required depth, cut the PVC casing and grout and could then
create a 5 ft long vertical cut in the soil extending upwards to
20 ft high. This fracture initiation device was developed for two
(2) markets; the shallow environmental application of constructing
vertical groundwater permeable treatment walls (iron PRBs) and the
much deeper application for petroleum recovery applications in existing
hydrocarbon reservoirs. |
|
| |
|
| |
 |
| |
|
|
|
Two major technology advances occurred
during 1998 and early 1999;
1) the development of a rapid breaking enzyme capable of
breaking even the highest pH iron gel mixtures, and
2) the development of the orientated metal frac initiation
casing system allowing repeated multiple frac injections at various
depth (stacked) horizons in order to form a continuous vertical
wall. The new enzyme gel breaker assured the rapid (within 1-2 hours)
and clean breakdown of all iron gel mixtures, even those with pH
>10. |
|
| |
The new casing system was a major breakthrough
and provided four new major advantages for the construction of PRBs; namely: |
| |
 |
Made it possible to induce repeated frac
injections at the same horizon. |
|
 |
|
Made it possible, through the use of
casing delimiters and pore pressure relief, to ensure fracture coalescence
between frac injection wells, even with slight drilling offsets
and/or casing orientation mis-alignment. |
|
|
|
The stronger and more robust casing system
provided a more stable tool for the frac injections of the iron
gel mixture. |
|
|
|
Resulted in greater productivity due
to its reusability and contribution to more logical sequencing of
tasks and simplification of PRB construction processes. |
|
| |
|
