Borehole geophysics is the science of recording and analyzing measurements of physical properties made in wells or test holes.

In the same way that surface geophysics makes it possible to “see” beneath the ground surface, borehole geophysical logging makes it possible to see beyond the walls of a boring or well. To perform borehole logging, sensors (or sondes) that measure different physical properties of the formation around the boring are lowered down the hole to record continuous data (or logs). A multi-conductor cable on a motorized winch controls the sonde, and transmits data back up the hole to a computer and graphic display. Often, multiple logs (called a suite) are recorded for a single boring – each measuring a different property – to allow more complete knowledge of subsurface conditions.

We have used borehole logging to assist clients on projects involving soil and groundwater contamination, groundwater supply, and geotechnical and mining/minerals issues.

• The objects of a geophysical survey are to locate subsurface geological structures or bodies and where possible to measure their dimensions and relevant physical properties. In oil prospecting structural information is sought because of the association of oil with particular features such as anticlines in sedimentary rock. In mining geophysics the emphasis is on detection and determination of physical properties, while in site investigation engineers are interested in both structure and physical properties.
  
  
• A geophysical survey consists of a set of measurements, usually collected to a systematic pattern over the earth's surface by land, sea or air, or vertically in a borehole. The properties of rocks of which most use is made in geophysical prospecting are elasticity, electrical conductivity, density, magnetic susceptibility and remanence and electrical polarizability. To a lesser extent other properties such as degree of radioactivity are also utilized Many factors, geological, economic, logistic and what we might call geophysical govern the choice of method for a particular survey And much more...

Well logging, also known as borehole logging is the practice of making a detailed record (a well log) of the geologic formations penetrated by a borehole. The log may be based either on visual inspection of samples brought to the surface (geological logs) or on physical measurements made by instruments lowered into the hole (geophysical logs). Well logging is done when drilling boreholes for oil and gas, groundwater, minerals, and for environmental and geotechnical studies.

SPECTRO specializes in geophysical well logging and has the tools for carrying out Electrical, Natural Gamma, Gamma-Gamma, Caliper and Neutron loggings.

SPECTRO’s Wire line Geophysical Services has a vast experience in coal, minerals and gas down hole logging. The equipment is state-of-the-art, and maintained/calibrated regularly. SPECTRO maintains a comprehensive suite of tools that provide cost effective dependable and accurate surveys in the subsurface environment for:

• Coal explorations
• Mineral deposits
• Groundwater
• Pollution investigations
• Engineering investigations

SPECTRO's primary logging activities are in CBM and coal explorations. However, engineering and environmental investigations can also be carried out at short notice.

Single Space Density Tool

This tool contains a single detector, focused density system using a 125-mCi Cesium137 source, to record apparent bulk density of the formation. The tool records natural gamma, caliper, and a short guard resistivity also. This tool is generally used in mineral logging and coal production blast hole logging.

Density Tool

The above tool contains a two detector, focused density system using a 125-mCi Cesium137 source, to record apparent bulk density of the formation. This tool also records natural gamma, caliper, and a short guard resistivity. This is the standard coal tool that uses the long spaced density in washout zones that can render the short spaced density data inadequate.

Neutron Tool

The Neutron tool is a multi-parameter slim hole mining and hydrology tool, which contains a single detector, neutron system using a 1.0 Ci, Am241Be source, to record neutron porosity of the formation. This tool also records natural gamma, self potential, single point resistance and borehole deviation (verticality).

Ground Penetrating Radar, also known as GPR, Georadar, Subsurface Interface Radar, Geoprobing Radar, is a totally non-destructive technique to produce a cross section profile of subsurface without any drilling, trenching or ground disturbances. Ground penetrating radar (GPR) profiles are used for evaluating the location and depth of buried objects and to investigate the presence and continuity of natural subsurface conditions and features.

Basic Principle:

The GPR operates by transmitting electromagnetic impulses into the ground through transmitter antenna. The transmitted energy is reflected from various buried objects or distinct contacts between different earth materials, across which there is a contrast in dielectric constant. The antenna then receives the reflected waves and displays them in real time on screen. Data is also saved in appropriate memory for later processing and interpretation.

Ground penetrating radar waves can reach depths upto 60 meters in low conductivity materials such as dry sand or granite. Clays, shale and other high conductivity materials may attenuate or absorb GPR signals, greatly decreasing the depth of penetration.

The depth of penetrating in also determined by the GPR antenna used. Antennas with low frequency obtain reflections from deeper depths but have low resolution. These low frequency antennas are used for investigating the geology of a site, such as for locating sinkholes or fractures, and to locate large, deep buried objects.

Antennas with higher frequencies (300 to 2000 MHz) obtain reflections from shallow depths (0 to 10 meters) and have a high resolution. These high frequency antennas are used to investigate surface soils and to locate small or large shallow buried objects, pipes, cables and rebar in concrete.

GPR can detect objects of any material, metallic or non-metallic.

Application Areas:

Geological and hydro-geological investigations including mapping of bedrock topography, water levels, solution features, glacial structures, soils and aggregates.

Engineering investigations to evaluate dams, sea walls, tunnels, pavements, roadbeds, railway embankments, piles, bridge decks, river scour, buildings and monuments.

Location and evaluation of buried structures including utilities, foundations, reinforcing bars, cavities, tombs, archaeological artifacts, and animal burrows.

Site investigations: location of buried engineering structures and underground storage tanks.

Subsurface mapping for cables, pipes and other buried structures prior to trench-less operations.