Introduction to well logs for use in the petroleum industry

Walter S. Borowski, Eastern Kentucky University
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This exercise uses a suite of well logs (aka electric logs) to interpret lithology within a stratigraphic section and to determine fluid content within borehole rocks.

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This exercise provides an introduction to complete well log interpretation pertinent to petroleum geology. It is designed for undergraduate geology majors.

The exercise:
  1. instructs students to recognize mudstone vs. sandstone lithology using spontaneous potential and gamma ray logs.
  2. Teaches the concepts of resistivity and conductivity and their underlying causes in pore fluids.
  3. Shows how to recognize briny pore fluids and hydrocarbons using resistivity logs.
  4. Instructs how the sonic log can be used to recognize zones of high and low porosity.
  5. Contrasts high resistivity zones occurring due to cementation versus those with resident hydrocarbons.
  6. Uses density and neutron logs to recognize gaseous hydrocarbons in the subsurface.

Skills and concepts that students must have mastered

I use a very similar exercise as my first exercise in a Petroleum Geology course. However, the posted exercise can be parsed to include or delete the use of various logs as any instructor wishes.

I intend to use the exercise as a culminating session that brings together several concepts in a professional context tilted toward the petroleum industry and as an introduction to well logs. Students in sedimentology/stratigraphy should first master sedimentary lithologies and the concept of porosity and permeability.

How the activity is situated in the course

This is a stand-alone exercise to demonstrate how concepts of sedimentology and stratigraphy are used in geologic professions, here referring to the petroleum industry.


Content/concepts goals for this activity

Use of electric logs in determining lithology and fluid content, pertinent to the petroleum industry, showing the practicality of geological knowledge.

Higher order thinking skills goals for this activity

  1. Analysis of data, in particular using a suite of electric logs to arrive at an interpretation of lithology and fluid content.
  2. Hypothesis formation and testing.

Other skills goals for this activity

Use of a constellation of information to reach interpretations involving logic and higher-order thinking skills.

Description and Teaching Materials

Our subject well logs will be 1-inch and 5-inch wells logs from the deep-water of the Gulf of Mexico, offshore Louisiana. The logs are from the wells of Ram-Powell Field (Viosca Knoll Blocks 912 and 956), which was one of the first fields developed in deeper waters.

The exercise uses 5 logs focusing mainly upon 2 different portions of the stratigraphic section – one in which potential reservoir rock (unconsolidated sand) contains brine and one in which reservoir rock contains gaseous hydrocarbons (natural gas or methane). Spontaneous potential and gamma ray logs are used to differentiate between mudstone (or shale) and non-shale (unconsolidated sand) lithologies. Resistivity logs are used to recognize pore fluids – again brine and hydrocarbons. Sonic logs are used to show that cementation within sands can lead to high resistivity, which can be misinterpreted as hydrocarbons. Lastly, density and neutron logs are used to recognize gaseous hydrocarbons due to crossover.
Student handout for Introduction to well logs (Microsoft Word 134kB Jun4 14)
Answers to exercise questions (Microsoft Word 142kB Jun4 14)
Well logs for exercise, Introduction to Well Logs (Microsoft Word 2007 (.docx) 35.9MB Jun4 14)

Teaching Notes and Tips

Instructors should lead this exercise with the entire class working through the problems together because each successive question is dependent upon a correct answer to the preceding question. Groups of 2 to 3 students first address the questions together as the instructor floats about the room giving aid as needed. Then the instructor addresses the question at hand with the entire class demonstrating use of e-logging concepts and any interpretation.


By grading and annotating their lab exercises, making sure that their explanations are sharp and correct.

References and Resources

I used no outside resources. The well logs were purchased in analog form from a well-log broker (Cambe).