Near Surface Characterization
The Full Spectrum of Geophysical Methods
- RESISTIVITY & INDUCED POLARIZATION
- DIRECT-CURRENT (DC) RESTIVITY
- ELECTROMAGNETIC METHODS
The Induced Polarization (IP) method reliably detects disseminated sulphides which are often associated with economic base metal and gold deposits. This method, along with resistivity, is also used for geological mapping and groundwater studies. S3 uses industry standard equipment to acquire high-quality time-domain IP and resistivity data. Transmitters ranging from portable battery-powered models to high-powered systems are used to ensure the equipment is best suited to the application, the location and to optimize transmitter current and power.
Direct-Current (DC) Resistivity
DC resistivity methods can reliably detect resistivity contrasts from the near-surface to depths of 500-600 m. The resistivity of soils and rock is measured as a function of depth and of position. Porosity, permeability, ionic content of the pore fluids, clay content and facies are characterized by such measurements. In particular, we use electrical resistivity methods to highlight facies and thus to estimate velocity variations in the shallow part of the subsurface.
In a shallow water environment, where refraction (LVL) and uphole surveys costs are prohibitive, the near-surface velocity model can be derived using a towed resistivity streamer survey. The near-surface velocity model obtained by converting the resistivities into velocities can then be used to compute the static corrections.
MagnetotelluricsWith advances in instrumentation, processing and modeling, MT has become a very important tool in deep subsurface reconnaissance. Magnetotelluric services aim to image the Earth’s subsurface by measuring natural variations in electrical and magnetic fields at the Earth’s surface, ranging from very shallow depths by recording higher frequencies(Audiomagnetotelluric or AMT), down to depths of 10,000 meters by recording low frequencies (Magnetotelluric or MT). Under conductive overburden, MT provides unique penetration. Our AMT and MT services include high-quality data acquisition, processing, inversion, modeling and interpretation. Complementary to seismic, MT surveys are used for: geologic mapping, in particular mapping sub-basalt structures, foothills, thrust and fold belts; frontier play exploration; reservoir characterization and monitoring; mapping of various base metals, nickel, Cu-porphyry (+/- Au,Mo), VMS, IOCG, kimberlites diamond, graphite; groundwater exploration.
GPR (Ground Penetrating Radar)
• Seismic refraction and high-resolution reflection for near-surface characterization
• Surface waves inversion
• Weathering Reflection Surveys (WRS)
• Shallow well geophysics including: uphole/shallow VSP surveys; wireline logging; cross-well geophysics
We have decades of expertise in applying the full spectrum of geophysical methods for a wide range of industries. We draw on this expertise to design customized geophysical surveys, for which we then collect, process and interpret geophysical data of the highest quality. Integration of information from complementary datasets is a powerful part of our interpretation workflow that leads to a comprehensive understanding of the targets and their setting.We provide assistance in coordination with local authorities, safety and security issues.
A wide range of industry applications
Near-surface multi-physics studies, integrating land microgravity, DC resistivity and seismic data, deliver effective refraction static corrections leading to a more accurate seismic image of the subsurface and an improved well-to-seismic tie.
Microgravity, 4D time-lapse gravity surveys and continuous gravity monitoring assist reservoir characterization and estimation of reservoir depletion.
Reducing risks along the mine lifecycle
- Based on our knowledge of the mineral deposits, environments and associations, we select the most appropriate technologies to reduce the risks encountered along the mine lifecycle. For instance, in the planning stage of a new coal mine, gravity, magnetic and resistivity investigations can be performed to get a better understanding of basin geometry, thickness of lithic fill, morphology of the basement/ bedrock, location of sub-basins and detachments, faults and location of dykes.
- For identification of Kimberlite-Clan-Rocks (KCR) strewn in clusters at the intersections of mantle reaching faults in cratonic areas, we can use gravity and magnetic mapping complemented with resistivity imaging.
- To identify uranium and Platinum Group of Metals (PGE), we generally employ gravity and magnetics in association with induced polarization (IP) and time domain electromagnetics (TDEM).
- For gold exploration, depending on the host rock environment, the most common technologies used are a suite of resistivity surveys, including induced polarization (IP), surface and borehole time domain electromagnetics (TDEM) and controlled source electromagnetics (CSEM) in case of deep exploration programs.
- Inversion of broadband magnetotellurics (MT) data, integrated with other ancillary data, lead to 2D and 3D depth models for reliable answers in the exploration of many minerals, including graphite, hydrothermal magnetite, copper and gold, KCR, magmatic nickel and copper, uranium and volcanogenic massive sulphides (VMS).
Tangible deliverables reducing risks
To help developers and engineers effectively reduce risks through the lifecycle of their projects, we deliver interpretation of geophysical data that we have previously acquired on site and processed. Our deliverables include :
• Cavity distribution map for a safe pile planning
• Ground stiffness evaluation for foundation design
• Structural imaging for seismic risk evaluation
• Imaging of cavities, angled fractures and lithological series for railways routes planning using high resolution seismic reflection surveys
Geophysics answering geotechnical challenges
Geophysical methods are selected according to the challenge and prevailing environmental conditions, in addition to the geological data available. Surface and borehole geophysics techniques include:
• Seismic reflection, seismic refraction and surface wave seismic
• Advanced wireline logging methods
• Resistivity methods (DC and electromagnetism)
• High resolution ground penetrating radar (GPR)
• GPR and electromagnetic methods can be used for pipes detection
Assisting search of groundwater
S3 designs geophysical programs specially tailored for groundwater. They provide solutions for :
• Detection of aquifer zones and cap rocks and estimation of their thickness in a sedimentary terrain
• Mapping of faults/shears both vertical and sub-horizontal in hard rock (metamorphic terrains) which controls water pools and its movement
• Detection of perched water tables
• Differentiate between saline water incursions in near shore area from the fresh water pools
• Detection of large water resources in solution cavities and in palaeochannels
Environmental monitoring requires accurate identification of existing or potential causes of pollution and the definition of the lithology and quality of shallow strata (mainly the first twenty meters). Thus, precise measurement of geophysical parameters at a generally smaller scale than employed for exploration surveys, are needed.
Micro-gravity surveys have been used to detect land subsidence or areas likely to subside (decompressed terrain and hollows).
Buried objects are detected by ground-penetrating radar and, in case of metallic buried objects and pipelines, magnetic surveys have been used as well. Gamma ray spectroscopy is used to detect man-made radioactivity and map soil structure. Electromagnetic (EM) and resistivity methods are used most often for mapping groundwater location, salinity and caverns and also to identify electrically resistant pollutants. Multi-physics recordings (tomography, resistivity, radar, micro-gravity) are used to locate pollution rapidly, establish its causes and monitor spreading.
24, rue Louis Blanc
Tél. : 06 83 01 47 68