Basic Petrophysics · Module B2
Log Reading & Contact Picking
How to read a standard combined log display and pick the evidence for hydrocarbons and fluid contacts: resistivity separation as an invasion indicator, the density–neutron crossover in gas, and where a contact is picked on the resistivity log. It closes with a pay flag built from documented cut-offs.
- Level
- Beginner
- Position
- Module 2 of 7
- Video
- About 18 minutes, narrated
- Format
- Narrated video lesson with chapters; with the certified option, a graded module quiz.
What the module covers
- Reading the gamma ray, resistivity and density–neutron tracks together
- Deep and shallow resistivity separation, and what invasion tells you
- The density–neutron crossover in gas
- Picking an oil–water contact on the resistivity log
- Handling a capillary transition zone in a first-pass interpretation
- Building a pay flag from documented cut-offs
Learning outcomes
After the module you should be able to:
- Identify hydrocarbon-bearing intervals on a combined log display
- Pick a fluid contact on the resistivity log and justify it
- Build a pay flag whose cut-offs are written down with their source
A short preview
In a gas zone the neutron porosity reads low and the density porosity reads high, so on a compatible scale the two curves cross. The reasons are hydrogen and density: gas carries far less hydrogen per unit volume than water or oil, so the neutron tool sees less pore space, and gas is light, so the density tool sees more. The crossover is one of the most dependable gas indicators on an open-hole log, and one of the easiest to miss when shale pushes the neutron the other way and hides it.
Who it is for
Geoscientists, reservoir and production engineers, and graduates who need to read a standard log suite and build a first-pass interpretation they can defend.
Prerequisites: None beyond basic geology and algebra.
Take the module in the Learning Hub
Basic Petrophysics: Seven foundational modules with narrated lessons and chapter-based navigation. The lesson opens in the Learning Hub once the track is purchased; graded quizzes and the certificate come with the certified option.