CPG CPG Geochemistry & Source Rock Analysis

Question 1

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

Accepted Answer

Good to excellent source rock potential for oil or gas generation

Answer

Reservoir quality with high storage capacity

Answer

Thermal maturity above the oil window

Answer

High permeability for tight gas extraction

Question 2

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

Accepted Answer

~0.6% Ro

Answer

~0.2% Ro

Answer

~1.3% Ro

Answer

~2.5% Ro

Question 3

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

Accepted Answer

Remaining generative potential — hydrocarbons released by thermal cracking of kerogen

Answer

Free hydrocarbons already present in the rock

Answer

Carbon dioxide released from inorganic carbonates

Answer

Volatile hydrocarbons lost during sample preparation

Question 4

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

Accepted Answer

Type II kerogen

Answer

Type I kerogen

Answer

Type III kerogen

Answer

Type IV kerogen

Question 5

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

Accepted Answer

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

Answer

HI = (S1/S2) × 100; declining HI shows increasing permeability

Answer

HI measures inorganic hydrogen in clays; decline indicates dehydration

Answer

HI = TOC/S3; decline indicates carbonate dissolution

Question 6

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

Accepted Answer

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

Answer

Chloroform bitumen extraction gravimetry

Answer

Stable carbon isotope ratio of bulk crude

Answer

Vitrinite reflectance of oil inclusions