Sedimentology and Petroleum Geology

Sedimentology and Petroleum Geology

Homework A & B

Petroleum source rocksevaluation


General instructions


Provided isa spreadsheet with publically available Rock-Eval data generated for petroleum source rocks (or low permeability reservoir rocks) in Montana (from a U.S. Geological Survey database). It is your task to:

  • Calculate values (Hydrogen index, Oxygen Index, and others) and create:
    1. modified van Krevelen diagrams showing the data for all source rocks
      1. Hint: compare the values on the axes to the “modified Van Krevelen diagram” in the notes!
    2. S2 vs TOC plot like those shown in the 1990 AAPG article
    3. Pyrolysis Tmax versus HI as shown in lecture notes
  • Compare the oil- or gas-generating potential of the different source rocks (the geologic names of the formations are given), and
  • Summarize whatyou can from the data analysis by answering questions on Moodle> Assignments > Homework –Rock Eval
  • Each student must turn in their work only. Multiple students turning in identical work will each get zero points for the assignment.


Sedimentology and Petroleum Geology Specific instructions


You will need to use a spreadsheet program, such as Excel, to do this work. If you are not familiar with the program, this will be a good introduction to graphing and data analysis. You will need to do calculations of fields, X:Y Cartesian (“scatter”) plots (not bar, column, or line plots), and to plot data points as different series (based on the formation of the source rock).


  • Download:
    1. Spreadsheet Rock-Eval Data source rock.xls
    2. Book pages from Tissot and Welte 1978.pdf
    3. Short article Rock-Eval analysis methods AAPG1990.pdf
  • Read the discussion of Rock sampling and analysis in G&S (2004), p 48-49 and or pages from Tissot and Welte (1978).
  • The results of about 750analyses are in the spreadsheet. The fields of interest (which are incomplete on many samples) are:
    1. Formation Name, Lith, Period
    2. S1 – the amount of free hydrocarbons (gas and oil) in the sample (in milligrams of hydrocarbon per gram of rock).
    3. S2 – the amount of hydrocarbons generated through thermal cracking of nonvolatile organic matter(in milligrams of hydrocarbon per gram of rock).
    4. S3 – the amount of CO2 (in milligrams CO2 per gram of rock) produced during pyrolysis of kerogen.
    5. TOC – total organic carbon in the sample (in weight percent of the rock).
    6. TMAX – the temperature at which the maximum release of hydrocarbons from cracking of kerogen occurs during pyrolysis (top of S2 peak).


Petroleum Geology

Analysis: For plots label the axes with fields and units. Save all the graphs as PDF files.


  1. Calculate new fields in the spreadsheet that you will need for plotting modified van Krevelen diagrams, measures of sample maturity, and other source rock indicators. These include:
    1. HI = hydrogen index (HI = [100 x S2]/TOC).
    2. OI = oxygen index (OI = [100 x S3]/TOC).
  • Oil and gas genetic potential S1+S2 (kg/ton of rock)
  1. Maturation indices
    1. transformation ratio (or production index) = S1/S1+S2
    2. Look at the range in TMAX (peak temperatures) – source rock samples exposed to high temps will have a higher TMAX


(see G&S, 2004, fig. 2.26 on p. 49; Tissot and Welte, 1978; and AAPG, 1990)


  1. Make a modified van Krevelen plot of the data (HI vs OI), showing different symbols for source rocks from different formations. Label the axes with fields and units. Use the following categories:
    1. Upper Bakken Shale
    2. Lower Bakken Shale
  • Middle Bakken
  • Phosphoria
  1. Fort Union
  2. All Cretaceous combined
  3. All others combined
  1. Make S2 vs TOC Cartesian plotsfor the same categories (described in the short article Rock-Eval analysis methods AAPG1990.pdf).
  2. To understand the maturation of the samples, make one or more Tmax versus HI index plots for the same categories.


  • Evaluate the oil and gas genetic potential of the source rocks to determine whether they have good, moderate, or only some potential to generate petroleum, where 1 ton [long, UK] = 1 016.05 kilogram.

The following classification of the source rocks is suggested:

  1. <1% organic carbon and/or <2 kg/ton: no oil source rock, some potential for gas
  2. 1–5% organic carbon and/or 2–6 kg /ton: moderate source rock
  3. >5% organic carbon and/or >6 kg/ton: good source rock


  • How do these Montana and Wyoming source rocks compare to the Kimmeridge Clay source rock in the UK, that yields 15-20 kg hydrocarbons per ton (see Tissot and Welte, 1978, and G&S, 2004).
    Turn in:
Sedimentology and Petroleum Geology Homework
  • (12 points)

Upload PDF versions of all graphs(modified Van Krevelen, S2/TOC, and HI/Tmax) to Moodle (do your own work – identical graphs will be given grades of “0”)




  • Answer the following questions online:
Name Homework  – Rock Eval
Description These are the questions to be answered online for Homework Rock-Eval.
Instructions Base your answers on the modified van Krevelen diagrams and S2 vs TOC Cartesian plots you made.
Question 1 Question 2 Question 3 Question 4 Question 5 Question 6 Question 7 Source Rock Ranking 3 points
Question Based on your calculations, rank the average genetic potential for oil generation of the six classes of source rocks  by matching them their ranking number
Display Order
Cretaceous formations
Phosphoria Formation
Bakken Shales
Bakken Middle Member
Fort Union
Other rocks combined


Question 2 (2 points)

How do the two best Montana-Wyoming source rocks compare to the Kimmeridge Clay source rock in the UK, that yields 15-20 kg hydrocarbons per ton (G&S, 2004).

Select one:

  1. One of the Montana-Wyoming source rocks is richer than the Kimmeridge Clay
  2. Both of the Montana-Wyoming source rocks are richer than the Kimmeridge Clay
  3. None of the Montana-Wyoming source rocks is richer than the Kimmeridge Clay



Question 3 (1 point)

From the Tmax versus HI plot, which source rocks have produced more natural gas:


Bakken and Phosphoria

Cretaceous and Fort Union

Fort Union and Bakken

Phosporia and Cretaceous


Question 4 (2 points)


From the Tmax versus HI plot, which source rock samples represent the largest ranges of maturity:




Fort Union

Sedimentology and Petroleum Geology

Best affordable essay writers online in USa

Last Updated on February 11, 2019 by EssayPro