CPG Geochemistry & Source Rock Analysis Flashcards

What does a Total Organic Carbon (TOC) value of 2.0 wt% or greater generally indicate about a source rock?

Answer: Good to excellent source rock potential for oil or gas generation

A TOC of 2.0 wt% or higher indicates good to excellent organic richness, meaning the rock contains sufficient organic matter to generate commercial quantities of hydrocarbons.

Vitrinite reflectance (%Ro) is used as a thermal maturity indicator. What %Ro value marks the onset of the main oil generation window?

Answer: ~0.6% Ro

The main oil generation window typically begins at approximately 0.6% Ro, where sufficient thermal energy has been applied to crack kerogen into liquid hydrocarbons.

In Rock-Eval pyrolysis, what does the S2 peak represent?

Answer: Remaining generative potential — hydrocarbons released by thermal cracking of kerogen

The S2 peak measures the hydrocarbons generated by thermal cracking of kerogen during pyrolysis, representing the rock's remaining generative potential.

Which kerogen type is primarily associated with marine algal organic matter and has the highest oil-generation potential?

Answer: Type II kerogen

Type II kerogen, derived largely from marine phytoplankton and algae mixed with bacterial material, has a high hydrogen index and excellent oil-generation potential.

What is the 'Hydrogen Index' (HI) in Rock-Eval pyrolysis, and what does a declining HI with increasing maturity indicate?

Answer: HI = (S2/TOC) × 100; declining HI shows kerogen is being consumed as it generates hydrocarbons

Hydrogen Index equals (S2/TOC) × 100 and decreases with maturity because hydrogen-rich kerogen is progressively converted into expelled hydrocarbons.

What geochemical correlation technique is used to 'fingerprint' crude oil and match it to its source rock?

Answer: Biomarker analysis (sterane and hopane ratios) by GC-MS

Biomarker analysis using gas chromatography–mass spectrometry identifies molecular fossils (steranes, hopanes, terpanes) whose ratios are diagnostic of source rock age, depositional environment, and maturity.