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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. |
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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. | |
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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. | |
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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. | |
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The new casing system was a major breakthrough and provided four new major advantages for the construction of PRBs; namely: |
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Made it possible to induce repeated frac injections at the same horizon. |
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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. |
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The stronger and more robust casing system provided a more stable tool for the frac injections of the iron gel mixture. |
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Resulted in greater productivity due to its reusability and contribution to more logical sequencing of tasks and simplification of PRB construction processes. | |
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