| Type of Log |
Properties Measured |
Potential Application |
Required Hole Conditions |
Other Limitations |
| Spontaneous Potential (SP) |
Electrical potential caused by salinity differences in borehole and interstitial fluids |
Lithology, shale content, water quality |
Open hole filled with conductive fluid |
Salinity difference required between borhole and interstitial fluid |
| Single Point Resistance (SPR) |
Resistance of rock, saturating fluid, and borehole fluid |
High-resolution lithology, fracture location with differential SPR |
Open hole filled with conductive fluid |
Not quantitative, hole diameter effects significant |
| Multi-Electrode Resistivity |
Resistivity, in ohm-meters of rocks and saturating fluids |
Quantative data on salinity of interstitial water |
Open hole filled with conductive fluid |
Normal resistivity spacing must be smaller than bed thickness to measure bed accurately |
| Electrical Induction |
Conductivity of rock and saturating fluids |
Quantitative data on salinity of interstitial water, lithology |
Open or non conductive casing |
Skin effects for highly conductive formations |
| Natural Gamma, Spectral Gamma |
Gamma radiation from natural or artificial radioisotopes |
Lithology related to clay (silt) content and permeability. Spectral gamma identifies gamma-emitting radioisotopes |
Any hole conditions, except very large, or very thick casing and cement |
Very high count rates need to be corrected for dead-time. |
| Gamma-Gamma Density |
Total electron density |
Bulk density, porosity, moisture content, lithology |
Best results in uncased hole; qualitative through casing or drill stem |
Hole diameter effects |
| Neutron |
Hydrogen Content, Elemental spectra |
Saturated porosity, moisture content, activation analysis, lithology |
Best results in open hole; can be calibrated through casing |
Hole diameter and chemical effects |
| Acoustic (Full Waveform) Velocity |
Compressional, shear, & tube wave velocities |
In-situ engineering properties, porosity, fracture location, & character, cement bond |
open or cased fluid filled holes |
Does not "see" secondary porosity |
| Acoustic Televiewer |
Acoustic reflectivity of borehole wall |
Location, orientation, & character of fractures and solution openings, strike and dip of bedding, casing inspection |
Fluid filled hole |
Heavy mud or mud-cake attenuates signal |
| Optical Televiewer |
Optical borehole wall imagery |
Location, orientation, & character of fractures and solution openings, strike and dip of bedding, casing inspection. Mineralogy (color and light reflectance) |
Air or clear fluid |
Optics diminish as hole is disturbed |
| Caliper |
Hole or casing diameter |
Hole diameter corrections to other logs, lithology, fractures, hole volume for cementing |
Any conditions |
Deviated holes may skew measurement |
| Fluid Temperature |
Temperature of fluid near sensor |
Geothermal gradient, in-hole flow, location of injected water, correction of other logs, curing cement |
Any conditions |
Best in undisturbed holes |
| Water Quality |
Several measurements available: Fluid Cond., pH, Redox, Salinity, Pressure, Sulphides, Nitrates, Chlorides, Ammonia, Copper |
Municipal water supply testing, environmental compliance, drinking water safety |
Fluid filled hole |
Some sensors require regular maintenance and / or replacement |
| Flow |
Velocity of net flow in borehole |
In-hole flow, location and apparent hydraulic conductivity of permeable interval |
Fluid-filled hole |
Spinners require higher velocities and centralization |
| Magnetic Susceptibility |
Magnetic field or some derivative |
Location of magnetic media |
Air or fluid, non magnetic casing |
Mostly qualitative, but can be calibrated if borehole diameter is known |
| Induced Polarization |
Formation chargeability over a time or frequency domain |
Location of conductive zones |
Open fluid-filled hole |
Best measurement requires relatively high current to be transmitted into formation |
| Deviation |
Inclination & Bearing of borehole |
Subsurface geometry, location of specific targets |
Gyro required in magnetic cased holes |
Surface coordinates must be known for gyro |
