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Heidelberg, Canada

Beauheim R.L.,Consulting Hydrogeologist | Roberts R.M.,HydroResolutions LLC | Avis J.D.,Geofirma Engineering Ltd.
Journal of Hydrology

Straddle-packer hydraulic testing was performed in 31 Silurian intervals and 66 Ordovician intervals in six deep boreholes at the Bruce nuclear site, located near Tiverton, Ontario, as part of site-characterization activities for a proposed deep geologic repository (DGR) for low- and intermediate-level radioactive waste. The straddle-packer assembly incorporated a hydraulic piston to initiate in situ pulse tests within low hydraulic conductivity (<1E-10. m/s) test intervals. Pressure transient data collected during the hydraulic tests were analyzed using the well-test simulator nSIGHTS to estimate the hydraulic properties specified as fitting parameters for the tested intervals, quantify parameter uncertainty, and define parameter correlations.Horizontal hydraulic conductivities of the Silurian test intervals range from approximately 4E-14 to 4E-8. m/s. The average horizontal hydraulic conductivities of the Ordovician intervals range from 2E-16 to 2E-10. m/s. The Lower Member of the Cobourg Formation, the proposed host formation of the DGR between 660 and 688 meters below ground surface, was found to have a horizontal hydraulic conductivity of 4E-15 to 3E-14. m/s.The formation pressures inferred from the hydraulic testing, confirmed by long-term monitoring, show that the Upper Ordovician and Middle Ordovician Trenton Group are significantly underpressured relative to a density-compensated hydrostatic condition and relative to the overlying Silurian strata and underlying Black River Group and Cambrian strata. These underpressures could not persist if hydraulic conductivities were not as low as those measured. © 2013 Elsevier B.V. Source

Avis J.D.,Geofirma Engineering Ltd. | Calder N.,Geofirma Engineering Ltd. | Kremer E.P.,Nuclear Waste Management Organization of Canada
15th International High-Level Radioactive Waste Management Conference 2015, IHLRWM 2015

The NWMO has undertaken a postclosure safety assessment of a conceptual deep geological repository for used nuclear fuel at a hypothetical sedimentary rock site in the Michigan Basin in Ontario. The assessment includes a Disruptive Scenario where container failure 10,000 years post-closure exposes steel components of the containers to groundwater. The migration of gas generated by steel corrosion processes is assessed through simulations conducted with the T2GGM code at the placement-room and repository scales. The model results indicate: 1) that room resaturation (in the absence of gas generation) is 90 percent complete by 10,000 years, 2) pore pressure in the host rock never exceeds 80 percent of the lithostatic stress, and 3) gas transport is primarily in gaseous (as opposed to dissolved) form and is substantially confined to the engineered sealing materials and excavation-damaged zone. The different scale models were linked through a manual iterative process, where gas flows calculated using the Room-Scale Model were provided to the Repository-Scale Model. End-of-room boundary conditions on the Room-Scale Model were adjusted based on Repository-Scale Model results and the process repeated until sufficient congruence was attained. Recent T2GGM code developments have included the capability to link different scale models explicitly. Preliminary results are presented that illustrate the advantages of this approach. Source

Walsh R.,Geofirma Engineering Ltd. | Nasir O.,Geofirma Engineering Ltd. | Leung H.,Nuclear Waste Management Organization of Canada | Avis J.,Geofirma Engineering Ltd.
15th International High-Level Radioactive Waste Management Conference 2015, IHLRWM 2015

The HG-A experiment, led by NAGRA from 2004 to the present, examined gas and water flow in the Excavation Damaged Zone (EDZ) of a tunnel in Opalinus clay. The experiment provided evidence for EDZ permeability changes due to swelling of the damaged rock in the presence of water and hydromechanical coupling following changes in pore and confining pressure. There is also evidence that low effective stress caused leakage of fluids along the packer-rock interface. Initially a two-phase flow model with variable EDZ permeability was used to model the system. This approach successfully reproduced pressure measurements in the HG-A test section. Modeling the gas injection tests did not require large changes in EDZ permeability, indicating that the EDZ properties were stabilizing at this stage of the test. We developed the T2GGM-FLAC model which simulates two-phase flow in T2GGM and mechanical processes in FLAC3D to model the EDZ. This coupled model predicted the development of EDZ around the HG-A tunnel, and then modeled the EDZ permeability as a function of time (self sealing) and packer pressure (hydromechanical coupling). The model predicted damage distribution around the HG-A tunnel corresponded well to available measurements of damage from post-excavation laser scans of the tunnel wall. Source

Dusseault M.,University of Waterloo | Jackson R.,Geofirma Engineering Ltd.
Environmental Geosciences

Hydraulic fracture stimulation (HFS) of unconventional oil and gas reservoirs is of public concern with respect to fugitive gas emissions, fracture height growth, induced seismicity, and groundwater quality changes. We evaluate the potential pathways of fugitive gas seepage during stimulation, in production, and after abandonment; we conclude that the quality of the casing installations is the major concern with respect to future gas migration. The pathway outside the casing is of particular concern as it likely leads to many wells leaking natural gas from thin intermediate-depth gas zones rather than from the deeper target reservoirs. These paths must be understood, likely cases identified, and the probability of leakage mitigated by methods such as casing perforation and squeeze, expanding packers of long life, and induced leakoff into saline aquifers. HFS itself appears not to be a significant risk, with two exceptions. These occur during the high-pressure stage of HFS when (1) legacy well casings are intersected by fracturing fluids and when (2) these fluids pressurize nearby offset wells that have not been shut in, particularly offset wells in the same formation that are surrounded by a region of pressure depletion in which the horizontal stresses are also diminished. This paper focuses on the issue of gas migration from deeper than the surface casing that occurs outside the casing caused by geomechanical processes associated with cement shrinkage, and we review the origin of the gas pulses recorded in noise logs, landowner wells, and surface-casing vents. Copyright © 2014. The American Association of Petroleum Geologists. Source

Clark I.D.,University of Ottawa | Al T.,University of New Brunswick | Jensen M.,Nuclear Waste Management Organization of Canada | Kennell L.,Nuclear Waste Management Organization of Canada | And 3 more authors.

Consideration of the geosphere for isolation of nuclear waste has generated substantial interest in the origin, age, and movement of fluids and gases in low-permeability rock formations. Here, we present profiles of isotopes, solutes, and helium in porewaters recovered from 860 m of Cambrian to Devonian strata on the eastern flank of the Michigan Basin. Of particular interest is a 240-m-thick, halite-mineralized, Ordovician shale and carbonate aquiclude, which hosts Br--enriched, post-dolomitic brine (5.8 molal Cl) originating as evaporated Silurian seawater. Authigenic helium that has been accumulating in the aquiclude for more than 260 m.y. is found to be isolated from underlying allochthonous, 3He-enriched helium that originated from the rifted base of the Michigan Basin and the Canadian Shield. The Paleozoic age and immobility of the pore fluids in this Ordovician aquiclude considerably strengthen the safety case for deep geological repositories, but also provide new insights into the origin of deep crustal brines and opportunities for research on other components of a preserved Paleozoic porewater system. © 2013 Geological Society of America. Source

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