Environmental Engineering Reference
In-Depth Information
Table 5.2.
Applications and limitations of borehole logging methods (adapted from Fell et al., 2000 and
McGuffey et al., 1996).
Method
Parameter measured
Applications
Limitations
Ultra-sonic log
Determination of sonic
Shows fractures, other
Requires uncased hole.
velocities, attenuation of
discontinuities
Image less clear than
shear velocity in shear
borehole camera
zones, or imaging the
sides of the borehole wall
Thermal profile
Temperature
Zones of inflow (lower/
Open hole not
higher temperature water)
necessarily required
Caliper log
Borehole diameter
Infers lithology by borehole
Requires an uncased
enlargement by erosion
hole
during drilling by drill fluid
Induction log
Electrical conductivity
Infers lithology by clay
Lower resolution than
content, permeability,
resistivity log, but can
degree of fracturing
evaluate unsaturated
zone and PVC cased
boreholes
Resistivity
Electrical resistivity
Infers lithology, (particularly
Applicable only in
between sand and clay)
saturated zone;
requires open hole
Self potential
Electrical potential from
Infers lithology, oxidation/
Applicable only in
mineral reaction and
reduction zones, subsurface
saturated zone; requires
groundwater flow
flows
open hole. Data
difficult to interpret.
Natural gamma
Natural gamma radiation
Infers presence of clay and
Mud coating on
shale
borehole wall may
affect results
Gamma gamma
Natural density
Provides log of density, from Provides only density.
which lithology may be inferred Health and safety issues.
Neutron neutron Moisture content (above
Log of moisture content, from
Provides only water
water table). Porosity
which lithology or wetter
contents. Health and
(below water table)
zones may be inferred
safety issues
Borehole camera
Visual image of fractures
Can identify structure. May
Requires uncased hole.
or video e.g.
and structure
be able to interpret dip of
Images affected by
RAAX
fractures and opening of
water quality, smearing
joints, and bedding partings
of sides of hole
Acoustic
Acoustic reflections
Can identify lithology and
Requires uncased hole
reflectivity
structure. May be able to
interpret dip of fractures
and orient cores
Profiles of electrical resistivity, self potential, gamma-ray emission and neutron absorption
are routinely obtained during exploration for oil and coal, where most boreholes are uncored.
Geophysical logging of each hole produces graphical plots from which the characteristic fea-
tures of the different lithological formations can be recognised (Whiteley, 1983; Whiteley et al.,
1990a). The development of commercial software packages for the interpretation of the data
has considerably assisted its analysis.
The logging commonly requires uncased and water or mud-filled holes. The equipment
is expensive and surveys have to be coordinated with the drilling programme.
Dam site investigations involve many shallow holes and nearly all holes are sampled or
cored. Geophysical logging can assist in correlation between boreholes, the location of
potential leakage zones and in the assessment of the properties of valley floor sediments.
In the opinion of the authors in many cases the additional cost of retaining the expensive
