World Geology Library

HANFORD ERUPTION?
A steam cloud rises over Goose Egg Hill on the U.S. Department of Energy's Hanford Site. True, but the coincidental steam cloud originates from WPPSS #2 nuclear reactor 7 miles away. The distinctive conical shape of Goose Egg Hill, similar to a volcanic vent, is apparently that of a Pleistocene bergmound - deposited by an especially large iceberg during one of the many ice-age megafloods. Indicated by many ice-rafted, erratic boulders exposed on the surface of Goose Egg Hill. — at Hanford Site.

Here is a simple overview of some common logs used in well logging:

• Gamma Ray (GR):
Measures the natural radioactivity of rocks. It is mainly used to distinguish between (shale and clean formations) like sandstone or limestone, since shale usually shows higher gamma radiation.

• SP (Spontaneous Potential):
Measures the natural electrical potential difference between the borehole and surrounding formations. Used to identify permeable beds and bed boundaries, and Helpful for sand–shale discrimination.
Requires conductive mud and permeable formations.

• Resistivity Log (RES):
Measures how strongly the formation resists electrical current. High resistivity may indicate hydrocarbons (oil or gas), while low resistivity usually suggests water-bearing formations.

• Density Log:
Measures the bulk density of the formation using gamma rays. It helps estimate (porosity) and identify different rock types.

• Neutron Log:
Measures the hydrogen content in the formation, which is mainly related to fluids in the pores. It is commonly used to estimate (porosity) and detect possible gas zones.

• Acoustic (Sonic) Log:
Measures the travel time of sound waves through the formation. It is useful for estimating (porosity), rock mechanical properties, and seismic interpretation.

• Caliper Log:
Measures the diameter of the borehole. It helps detect washouts, borehole enlargement, and improves the interpretation of other logs.

Understanding these tools is essential for interpreting subsurface formations and evaluating potential hydrocarbon reservoirs.

One of the key lessons from studying well logs is that "no single log tells the whole story". The real interpretation comes from combining multiple logs together to better understand the subsurface formations.