Logs

Question 1

Induction Log

Answer 1

• Measures magnetic current
(induces electrical current)
- water quality
- lithology & correlation
- locating & monitoring contaminant plumes
∙ uncased/cased with PVC or fiberglass, air or fluid-filled

Question 2

Spectral Gamma Log

Answer 2

• Separates out different gamma rays

• locating & monitoring contaminant plumes
• ID of fluid-migration pathways

Question 3

Dipmeter Log

Answer 3

• Measures orientation of dipping surfaces by resistivity changes
- structural & stratigraphic analysis

[degrees & direction]

Question 4

Neutron Log

Answer 4

• Measures concentrations of hydrogen (water & hydrocarbons) in pores

• porosity & permeability
• water table location
• lithology & correlation

low = anhydrite, limestone, ark. congl., granite
high = alluvium, gypsum, quartz sand, coal

[% porosity]

Question 5

Caliper Log

Answer 5

• Measures size of hole
-hole conditions
-fracture location & characterization
∙wider borehole when in fractures

low = dolomite, arkosic congl.

[cm]

Question 6

Acoustic (Sonic) Log

Answer 6

•Measures velocity of compressional sound waves
  -lithology & correlation
  -porosity & permeability
  -fractures
∙uncased, fluid-filled

low = brittle: limestone, anhydrite, dolomite, gypsum
high = soft: quartz sand, coal, shale, sandstone

[μs/m]

Question 7

Density (Gamma-Gamma) Log

Answer 7

•Measures bulk density
(emits gamma, measures radiation that comes back)
-lithology
∙anhydrite, halite, nonporous carbonates
-porosity & permeability
-eval. well construction

high = alluvium, quartz sand, dolomite, coal
low = limestone, granite, arkosic congl.

[gm/cm3]

Question 8

Gamma-ray Log

Answer 8

•Measures natural radioactivity
(related to K, Th, U)
-lithology & correlation
∙shaliness

high = shale, granite, arkosic congl.
low = coal, limestone, sandstone

[API units]

Question 9

Resistivity Log

Answer 9

•Measures resistance to electric current flow
-lithology & correlation
∙coals, bentonites
-saltwater intrusion
-locating & monitoring contaminant plumes
-ID fluid-migration pathways
∙uncased, fluid-filled

[ohm-meters]

Question 10

Spontaneous Potential (SP) Log

Answer 10

•Measures natural electric potential (natural currents)
-locating & monitoring contaminant plumes
-ID porous zones
-lithology (sometimes): shale (baseline) vs. sand
∙uncased, fluid-filled; conductive mud

[millivolts]

Question 11

Alluvium

Answer 11

very high Neutron & Density logs

high porosity

Question 12

Dolomite

Answer 12

low Acoustic log (brittle)
high Density log (low porosity)
low Caliper log

Question 13

Coal

Answer 13

log Gamma log (while surrounding have high)
high Neutron & Density logs (porosity) (while surrounding have low)
high Acoustic log (soft)
high Resistivity log

Question 14

Fractured Arkosic Conglomerate

Answer 14

Variable = fractured:
(relatively) low Acoustic log (brittle)
low Neutron & Density logs (porosity)
low Caliper log
high Gamma log

Question 15

Limestone

Answer 15

very low Neutron & Density logs (low porosity) (esp. compared to surrounding units)
very low Acoustic log (brittle)
low Gamma-ray log

Question 16

Sandstone

Answer 16

high Acoustic log (soft)
high Resistivity & Single Point logs
(relatively) low Gamma Log (compared to shale)
Porosity (Neutron & Density) ~30-40%

Question 17

Gypsum

Answer 17

high Neutron log (porosity)
high Resistivity log
lower Acoustic log (than surrounding units)

Question 18

Shale

Answer 18

high Gamma log (compared to sandstone)
high Acoustic log (soft) (higher than sandstone)
lower Single Point & Resistivity logs (compared to ss)

Question 19

Quartz Sand

Answer 19

very high Acoustic log (soft)

high Neutron & Density logs (porosity)

Question 20

Anhydrite

Answer 20

very low Neutron log (porosity)
high Resistivity log
low Acoustic log (brittle)

Question 21

Fractured Granite

Answer 21

Variable = fractured:
low Acoustic log (brittle)
low Neutron & Density logs (porosity)
very high Gamma & Resistivity logs