Before the Case is Cracked: How Borehole Logging Reveals the Evidence
Borehole geophysical logging/imaging allows you to see the walls (and beyond) of borings/wells to determine the depths and orientations of features such as lithology, bedding, water-bearing fractures (which can serve as fluid migration pathways), etc. Sondes – which measure different physical properties of the subsurface materials – are lowered through the hole to record continuous data or “logs.” A multi-conductor cable/winch controls the sondes and transmits data up the hole to a computer for digital recording and real-time graphic display. Often, multiple logs are recorded, each measuring a different property to understand subsurface conditions better.
Logging What Lies Beneath: Cracking the Case of Hidden Fractures
RETTEW conducted a geophysical borehole logging survey in a 100-foot-deep well at a retail gas station to reveal hidden fractures within the earth that might serve as pathways for water or contaminants beneath the property. To unlock these underground mysteries, RETTEW completed a suite of tests through the entire well length, including Optical Televiewer (OTV), Acoustic Televiewer (HRAT), 3-Arm Caliper (CAL), Fluid Temperature (T), Fluid Conductivity (C), Natural Gamma (y), Short and Long Normal Resistivity (RES), Spontaneous Potential (SP), Single Point Resistance (SPR), and Heat Pulse Flowmeter (HPFM) measurements.
Highlighted logs from 48 to 63 feet below grade reveal story-rich digital images via OTV and HRAT, showing fractures as horizontal lines or sinusoids — hints of their strike and dip — as shown in the accompanying figure. Caliper logs measure borehole diameter, while Fluid T and C logs often spike where water enters through fractures. Natural gamma logs indicate increased clay content of surrounding beds. RES, SP, and SPR logs measure different electrical properties of rock layers, and HPFM logs track how fast and in what direction water flows into or out of the well.
By revealing underground water movement or potential contaminants, the geophysical borehole logging survey became a pivotal step in identifying key concentrations and designing a comprehensive remediation plan that safeguards the site’s future.
Introducing Erica Carbaugh
Project Technician
Balancing family fun, community races, and a little book-club downtime, Erica Carbaugh brings the same can-do energy to life outside of work as she does supporting geophysics and SUE projects. Read on to get to know Erica—and catch the unexpected twist that made one workday especially memorable.
