Table 2.
Details of borehole geophysical logging methods commonly applied to fractured rock. The lateral radius of penetration into the formation and resolution of the measurement, are approximate ranges for site investigation. The measured parameters can be derived directly from the acquired data. The recovered properties are obtained through processing and/or inversion of the acquired data.
| Method | Radius of Penetratio n (meters) | Resolution (vertical) (meters) | Measured Parameters | Recovered Properties of Interest | Potential Fractured Rock Targets |
|---|---|---|---|---|---|
| Caliper | N/A | 0.05 | Diameter of borehole | Diameter of borehole | Fracture locations, guidance for packer placement |
| Electro-magnetic induction | 0.5 | 0.5 | induced magnetic fields due to subsurface conductors | Electrical conductivity | Contaminant plume delineation |
| Magnetic Susceptibility | 0.5 | 0.5 | Magnetic susceptibility | Magnetic susceptibility | Iron minerals (magnetite), Treatment monitoring involving metals |
| Sonic logging | 0.2 to 1 | 0.1 | Arrival time of compression, shear, and Stoneley waves | Compressional wave velocity shear wave velocity tube wave velocity | Porosity, lithology, cement bond evaluation; fracture evaluation, lithology, mechanical properties fracture permeability |
| Single Point Resistance | N/A | 0.05 | Resistance | Resistance | Characterization of lithology |
| Normal Resistivity | 0.2 to 1.6 | 0.05 to 1.6 | Electrical potential in response to injected current | Electrical resistivity | Major fracture detection, lithology, solute or amendment monitoring |
| Nuclear Magnetic Resonance | 0.3 | 0.25 to 1 | Decay in nuclear magnetization following radio-frequency pulse | Relaxation time constant | Porosity, permeability |
| Self Potential | N/A | 0.5 | Electrical potentials arising from current sources in the earth | Electro-diffusion potential, redox potential, streaming potential Thermoelectric potential | Groundwater flow directions |
| Fluid conductivity/temperature | None | 0.05 | Fluid electrical conductivity, temperature | Fluid electrical conductivity, temperature | Total dissolve solids, fracture locations, solute or amendment monitoring |
| Television | None | 0.05 | Visual inspection | Video or digital image | Fracture locations, lithology, formation of precipitates, turbidity, flocculation due to amendments |
| Acoustic Televiewer | None | 0.0005 | Ultrasonic reflection, amplitude and traveltime | Acoustic reflectivity and borehole diameter | Fracture locations and orientations, lithology, borehole diameter |
| Optical Televiewer | None | 0.0005 | Visual | Red, green, blue color and light intensity | Fracture locations and orientations, lithology |
| Flowmeter | 1 to 100 | N/A | Heat-pulse travel time or impeller speed | Vertical flow | Transmissivity and far-field head of fractures or layers |