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Vibrometric’s extensive portfolio includes specialized seismic imaging techniques for nuclear waste site characterization, mineral exploration, ore prospecting, advanced 3D imaging for tunnel construction, and fractured reservoir characterization, amongst others.
The structural aspect has been documented relatively well in the past four decades and consists mainly of mapping faults, fracture zones, and dissolution features, bearing an impact on geotechnical models and designs.
Mineral resource delineation by seismic techniques is a later addition to the seismic application menu and has been proven as a valuable technique over more than two decades. Structural and lithological delineation is seen as an emerging mining application of seismic imaging. The general benefits expected from applying delineation techniques include: reduced economic risk, shorter project time-lines, and more accurate resource evaluations.
In Finland, the site selection research programme has been conducted from 1983 until 2000. The Olkiluoto site has been selected for deep geological disposal of spent nuclear fuel in 2001. Extensive geophysical data and imaging have been used to produce and refine a 3D model of the site. An underground research, testing and demonstration facility, ONKALO, was built at Olkiluoto for detailed characterisation of the planned nuclear waste repository host rock.
Hardrock investigations target characterisation of crystalline bedrock features that may have any orientation and may display discontinuous and diffuse boundaries. The investigations for high level nuclear waste repositories must be focused on deep and relatively small volumes of rock: target investigation depths are larger than typical depth of a repository (500 m – 1000 m) and resolution of determinations needs to be better than the typical transverse size of relevant site features (1-2 m). Seismics is the only geophysical method to accommodate both requirements.
Research and demonstration programs are conducted during the construction of a nuclear waste repository with the primary objective of ensuring that the bedrock is suitable for the final disposal. Large fractures need to be identified during construction of the deposition tunnels and the deposition holes, as they could experience secondary movements which could affect the mechanical integrity of the disposal canisters. 3D seismic imaging around tunnels is done to detect seismically responsive deformation structures and large fractures before the excavation of deposition tunnels and to identify needs for additional development.
By using highly accurate, time efficient and repeatable tunnel-wall and borehole seismic sources, very diverse frequency, multi-component receivers (10 – 40000Hz) and rock coupling methods, processing & Imaging techniques that work in a truly 3D environment and interpretation tools able to verify and reciprocally validate results of various geoscientific disciplines it is possible to image target features displaying very diverse orientations and character.
EDZ Seismic Investigations in ONKALO, 2009
Factual Report
Elastic properties may change due to excavation, as blasting breaks the rockmass. As direct consequence a decrease of acoustic P and S wave velocities and increase in attenuation can be observed. The S wave velocity is affected only by the mechanical integrity of the rockmass. The P wave velocity is affected also by the water saturation in
the rock. Reflectivity or scattering (diffraction) of the seismic energy increases due to EDZ. Excavation generated fractures (and their effective porosity) and natural fractures open or close due to stress field, which affects the measurable properties in complex ways. Micro-fracturing or porosity changes the water content in the rock and plays a
decreasing factor in the velocity of the acoustic waves.
The investigation of the properties of the Excavation Damage Zone (EDZ) in the Olkiluoto bedrock was a part of the research activities undertaken by Posiva Oy.
The rock was probed by ultra-high resolution seismics. Baseline data were acquired before the excavation of a demo tunnel, the EDZ niche, the measurements being repeated after excavation.
The objective of the study has been to confirm the existence of the EDZ phenomenon at Olkiluoto, to evaluate its extent and determine its physical characteristics. High frequency seismic signals (5 – 65kHz) were produced and recorded by the PS-8R system.
Side-scan seismic profiling and cross-hole investigations were done, measured data was processed, analyzed and interpreted and the existence of the EDZ has been proven beyond doubt and it was concluded that the extent and magnitude of the EDZ can be quantified from both transmission and reflection measurements.
Research and demonstration programs are conducted during the construction of a nuclear waste repository having as primary objective to ensure that the bedrock is suitable for the final disposal. Large fractures need to be identified during construction of the deposition tunnels and the deposition holes, as they could experience secondary movements which could affect the mechanical integrity of the disposal canisters. 3D seismic imaging around tunnels is done to detect seismically responsive deformation structures and large fractures before the excavation of deposition tunnels and to identify needs for additional development.
By using highly accurate, time efficient and repeatable tunnel-wall and borehole seismic sources, very diverse frequency, multi-component receivers (10 – 40000Hz) and rock coupling methods, processing & Imaging techniques that work in a truly 3D environment and interpretation tools able to verify and reciprocally validate results of various geoscientific disciplines it is possible to image target features displaying very diverse orientations and character.
Surface seismic reflection has successfully been used for the mapping of a coal deposit and associated structural setting. An area of approximately 4500m x 5000m was covered by the survey using roll-along geophone arrays and a multi-impact VIBSIST-1000 source.
The purpose of the work has been to acquire and process multi-lines 2D seismic data, which would allow the mapping of the coal seam, believed to be at a depth of 200 – 500 m, the evaluation of the thickness of the coal seam, and the identification of normal faults with a vertical displacement larger than 5m-10m.
Borehole seismic methods have been proven useful in delineating the kimberlite–country rock contact. Investigation range is typically more than 150 m in a working mine conditions. If applied routinely, borehole seismic methods provide a cost effective way to increase knowledge of geology, raise confidence in the geological model and reduce the risk with resource estimation.
The CO2SINK project has been the first onshore European CO2 injection experiment. The seismic characterization of CO2 storage at Ketzin consisted of several investigation and monitoring elements covering different experimental scales mutually validating and potentially complementing each other. The objective has been to cover the kilometer scale encompassing the region where the CO2 can migrate, while resolving at a meter scale the potential heterogeneities of the aquifer in the vicinity of the injection site. The crosshole measurements were meant to cover the smallest scale of all measurements performed, between wells approximately 100 m apart. Crosshole tomographic surveys were repeated between the observation wells in order to provide a high-resolution model for the reservoir near the injection and to observe the change of seismic velocities between the observation wells.
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