In-Borehole Geophysical Surveys (Borehole Logging)

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In-borehole geophysical surveys are a critical stage of quality control and assessment during the construction of new water boreholes. Measurements are carried out immediately after drilling and before final utilisation, providing reliable data on the behaviour and dynamics of the aquifer system.

Using modern Mount Sopris Instruments equipment, we carry out comprehensive high-resolution recordings at real depth, supporting technical services (Municipalities, DEYA), consultants and private individuals in making well-documented decisions.

The main logs include:

Electrical resistivity (Resistivity) for locating aquifer zones

Electrical resistivity logging (borehole resistivity logging) is a fundamental method for assessing aquifer formations within a borehole, providing immediate information at real depth. The resistivity curves allow a clear distinction between zones of different water quality: high values usually correspond to fresh water and clean formations, while low values indicate brackish or saline water and increased conductivity. Through multi-electrode (multi-spacing) logging, investigation is achieved both close to the wall and deeper into the formation, offering a reliable interpretation of the aquifer. The method supports the definition of productive zones, the correct design of screens and the assessment of salinisation risks, making it a critical tool for technical services, consultants and private individuals who require well-documented and applicable data.

Gamma Ray for lithological discrimination

Natural radiation logging (Gamma Ray – GR) is a fundamental in-borehole geophysical method for the lithological discrimination of formations. The method is based on measuring the natural radioactivity of the rocks, with high values associated mainly with clay formations and low values with clean, permeable layers such as sands and gravels. The GR curves provide an immediate and reliable picture of the stratigraphy, allowing the precise definition of screen positions and the optimisation of the borehole utilisation. In combination with other logs (e.g. resistivity), the interpretation of the aquifer and the quality of the formations is significantly enhanced, making it a fundamental tool for technical services, consultants and private individuals who require highly reliable, well-documented data.

Conductivity & temperature for identifying different types of aquifer formations in relation to depth

Conductivity and temperature logging is a specialised borehole logging method for analysing the behaviour of water within the borehole. Variations in the conductivity curves capture differences in water quality (fresh, brackish, saline), while temperature anomalies indicate active inflows or circulation zones. The combination of the two parameters allows the precise location of aquifer layers and supply points, even in complex hydrogeological environments. The method is used to check the operation of the borehole, assess performance and detect problems (water mixing, undesirable inflows), providing critical data for the correct management and optimisation of the project.

3-axis Caliper for orientation and structural analysis

Borehole diameter logging (Caliper logging) is a fundamental quality control method, usually applied as the first log after drilling. Using QL40-CAL type equipment by Mount Sopris Instruments, the borehole diameter is measured continuously by means of three mechanical arms in contact with the walls.

The method allows immediate assessment of the borehole condition, identifying enlargements (washouts), cavities, fractures and zones of instability that affect both the performance and the safety of the work. At the same time, it is used to calculate the borehole volume before completion (casing, cementing) and to correct and improve the interpretation of other geophysical logs.

It is a critical tool for:

• Quality control of borehole construction
• Identification of problematic zones and discontinuities
• Correct design of casing and screens
• Assessment of conditions before carrying out other logging

Caliper logging provides reliable and immediate data on the actual geometry of the borehole, constituting a fundamental prerequisite for technically sound decisions at the completion and utilisation stage of the work.

Acoustic Televiewer for imaging fractures and discontinuities

Acoustic Televiewer (ABI) logging is the most advanced in-borehole imaging method, providing a full 360° unwrapped and three-dimensional image of the walls at real depth. The QL40-ABI-2G type equipment by Mount Sopris is based on emitting an ultrasonic signal towards the formation and recording the travel time and amplitude of the reflected wave, allowing a detailed analysis of the geometry and physical properties of the rock.

The logs are rendered as an “unwrapped” image, in which fractures, discontinuities, layers and structural elements are accurately captured, while an accurate calculation of the borehole diameter is also obtained through the travel time.

The method is used for:

• Locating and orienting fractures and permeability zones
• Structural and tectonic analysis of formations
• Checking borehole deformations (stress analysis)
• Casing inspection (thickness, corrosion, condition)
• Analysis behind casing (PVC or steel)

It is a high-resolution tool for projects with increased requirements, providing data that cannot be obtained by any other in-borehole geophysical method, and directly supports the making of critical technical decisions.