CPG Study Guide 2026
Everything you need to pass the CPG exam in one place: the exam format, every topic to study, real practice questions with explanations, flashcards, and full-length practice tests. Free, no sign-up needed.
📋 CPG Exam Format at a Glance
📚 CPG Topics to Study (27)
✍️ Sample CPG Questions & Answers
1. Which log measurement is the primary direct indicator of formation fluid pressure in permeable zones while drilling?
The Repeat Formation Tester (RFT) or Modular Dynamic Tester (MDT) directly samples formation fluid and measures pore pressure at discrete depth intervals.
2. The vitrinite reflectance value (Ro) of approximately 0.5–0.6% corresponds to which stage of organic matter maturation?
Ro values of 0.5–0.6% mark the onset of the early oil window, where sufficient thermal energy has been reached to begin cracking kerogen into liquid hydrocarbons.
3. What is porosity in a reservoir rock?
Porosity in a reservoir rock refers to the percentage of the total rock volume that is made up of void spaces or pores. These interconnected pores are crucial because they are where hydrocarbons (oil and gas) and water are stored within the rock formation. High porosity is essential for a rock to be an effective reservoir, determining its storage capacity.
4. In NMR logging, what does the T2 distribution primarily represent?
The NMR T2 transverse relaxation time is inversely proportional to the surface-area-to-volume ratio of pores, making larger pores correspond to longer T2 times.
5. Which factor influences reservoir permeability?
Permeability is a measure of a rock's ability to allow fluids to flow through it. While porosity indicates the amount of space, pore throat size (the size of the connections between pores) dictates how easily fluids can move. Larger, well-connected pore throats result in higher permeability, which is vital for efficient hydrocarbon production from a reservoir.
6. Which mechanism drives primary migration of hydrocarbons out of source rocks?
Primary migration is driven by abnormally high pore pressures in compacting source rocks and molecular diffusion, allowing hydrocarbons to move through microporosity and microfractures into carrier beds.
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How this page was made: written with AI tools and published by Nathan Beja, founder of Practice Test Geeks, who is responsible for its content. Exam facts are checked against the official sources listed below. Not reviewed by a subject-matter expert. Editorial policy
Sources & references
Exam facts on this page (fees, format, dates, passing scores) are checked against these official sources; the date is our last check. Editorial policy
- aapg.org — Fees, eligibility, renewal, score validity · verified Oct 2026