1. The document summarizes two case studies on gas and oil geochemistry: one on the Barbados area focusing on gas characterization, thermal maturity interpretation, and biodegradation trends; and one on the Tarim Basin focusing on oil derivation from Triassic lacustrine mudstones. 2. In the Barbados area study, several major gases were characterized including methane, ethane, and propane. Thermal maturity was interpreted from gas isotope values and gas mixtures. Biodegradation trends were identified from gas composition plots. 3. In the Tarim Basin study, oils were discovered and classified into two genetic groups based on isotope and biomarker values. Source rocks were identified for each group through cross plots of

1. 1
Course Presentation : ORGANIC GEOCHEMISTRY
Presented by

2. 3.1. Gas Geochemistry
3.2.3. Derivation of liquids Oils dominantly from the Triassic Lacustrine mudstone 2

3. FOCUS OF MY PERSENTATION
Part # 1 : 3.1 Gas Geochemistry
Case study of Barbados Area
Characterized by Several major
gases in Barbados source rock
Thermal maturity interpretation
for gases
Biodegradation trends for gases
Sampling and methods
Conclusion
3

4. accretionary prism
Caribbean island, Barbados area
4

5. INTRODUCTION OF GAS GEOCHEMISTRY
Gas sampling,
storage, and
analysis
of gas samples
Important scientific
tool in constraining
processes occurring
in geosciences.
Quantitative
techniques: CO2 &
methane
migration(Climate)
Analytical
techniques :
Hydrocarbon, CO2,
N2, H2, CO and HG
vapour are
measured advance
method.
Hydrocarbon:
Isotopic Studies,
Gas
Chromatography
and Spectrometry.
CO2 & CH4, H2S and
HG vapour:
Seismotectonic and
biogeochemical
models
Gas sample from Thermal feature
Noble gases of Cosmo geochemistry
Volcanic Gas geochemistry Gas seepages sampling
5

6. CASE STUDY OF BARBADOS AREA
Cretaceous Marine Shale Deposit
Demonstrated petroleum systems: Minor oil & gas production, Several
oil seepages
Sample collection : Cutting & Core from Marine Shale outcrops
Geochemically define petroleum systems :
TOC(Total organic content ): <1 to 10 + weight percent.
HI (Hydrogen index) Rock _ Eval Pyrolysis : < 100 to 600+
Vitrinite reflectance analysis (%R < 0.6)
Tertiary Shale : oil window (0.6 – 1.4%), Gas Window(1.4 – 2.0%)
Study Area .(Hill and Schenk 2005)
Woodbourne Trough oil field 6

7. CHARACTERIZED BY SEVERAL MAJOR GASES IN
BARBADOS SOURCE ROCK
CO2
H2S
Methane
Ethane
Propane
n-butane
i-butane
n-pentane
i-pentane
7

8. Methane content :
ranges from 85 to
97 mol% with one
sample having a
value of 62%.
Carbon dioxide:
<0.60 mol% for all
samples
No H2S was
detected.
Methane carbon
isotope : - 38 to -
49‰.
Ethane from -32 to
- 35‰,
propane from K26
to K32‰
8
(Hill and Schenk 2005)

9. THERMAL MATURITY INTERPRETATION FOR GASES
Ranges of gas
thermal maturity
Gas mixtures
sampled collected
from sources
packages of
accretionary
prism
Fig. Carbon isotope plot for gas components, R0 = 0.7 and 1.0%
9
(Hill and Schenk 2005)

10. BIODEGRADATION TRENDS FOR GASES
Gas composition plot for thermal maturity and biodegradation trends.
10
(Hill and Schenk 2005)

11. METHODS
SAMPLING #
11

12. METHOD : GAS ANALYSIS
With flame ionization detector(FID), Thermal Conductivity detectors(TCD).
C1 – C5 hydrocarbon : Analysis using helium carrier gas, 2 Wasson KC5 columns & HP FID. Detection.
CO2, H2S, O2/Ar, N2 and CO non- hydrocarbon: Wasson K1 and K2S packed column & HP TCD.
Fig. Hewlett Packard(HP) 6890 GC by Wasson ECE Instrumentation
12

13. Fig. δ13C isotopic analysis for C1 – C4 and CO2 Gas
Micro mass Optima interfaced with a HP 6890 gas chromatograph: Pee Dee Belemnite Standard. 13

14. 14

15. Part # 2: 3.2.3. Derivation of liquids Oils
dominantly from the Triassic Lacustrine mudstone
Case study of Tarim Basin
Samples & Methods
Hydrocarbons Discovered in kuqa depression
Crude oils classified in kuqa depression
Isotopic and biomarker interpretation for gases and
oils samples
Cross plots geochemically relationship groups of oil
& sources rocks
Conclusion
FOCUS OF MY PERSENTATION
15

16. CASE STUDY OF TARIM BASIN
Natural Gas, Condensate resources and small amount of black oil
High maturity level in Jurassic coal-bearing sequences : Peak stage of Dry gas generation
Sources rocks types: M- L- Jurassic coal-bearing with associated clastic and U- Triassic lacustrine
Mudstone : Stable carbon isotopes & Molecular Biomarker.
Triassic sources rock : Peak stage of oil generation occurred (early Miocene)
Gas and oil migrated : along fault relatively short lateral distance.
Traps formation : N to S margins and a late injection of gas into oil accumulation.
16

17. HYDROCARBONS DISCOVERED IN KUQA DEPRESSION
Bulk Carbon
isotopic values
ranges :
-24.6 to -31.6%.
Depletion 13C2
in Gas sample
13C2 values
ranges : -18.25
to -23.74%
>-24% : tighter
cluster
17
Table.1. showing the Stable carbon isotopes and pristine/phytane
ratio of oils, condensate, and oil seepages .

18. •Group .1 : Low δ13C(-27 to -31.6%) low pristine/phytane values(<2.5,
mostly <2.0)
•Group. 2 : High δ13C(-24 to -26.6%) High pristine/phytane
values(>2.5 )
Crude Oils
classified into two
genetic groups
CRUDE OILS CLASSIFIED IN KUQA DEPRESSION
18

19. Fig. δ13 C values for C1- C4 gaseous alkanes in the samples collected from the major gas fileds
ISOTOPIC AND BIOMARKER INTERPRETATION FOR GASES
AND OILS SAMPLES :
19

20. Table. Distribution of Jurassic and Triassic source rocks sample interpretation on the basis of Biomarker and Stable isotope
20

21. Secondary Classification criteria : Sterane & Terpane Distribution
Fig. Correlation of oil- condensate with potential sources rocks
Cross plots
Relationship
between the
two groups
of oils and
Source rocks
CROSS PLOTS GEOCHEMICALLY RELATIONSHIP GRPS OF
OIL & SOURCES ROCKS
21

22. Group 1 oils
Low in δ13C values, pristine/pythane & C24 tetracyclic/C26 Tricyclic terpane ratios but high C27 Steranes
22

23. Group 2 oils
Small reserves, Correlation with the extracts of Jurassic coal & mudstone
23

24. SAMPLES & METHODS
Gas samples : 13 oils & gas fields from Kuqa
Depression
Black oil : 5 samples
Condensate : 15 samples collected from 14 oil &
gas fields
Oil - Seepages : 3 samples
Oil- sand : 3 samples
Correlative based: 21 Mudstone & 19 Coal samples(
extraction with organic solvents Tr & Jr age)
24

25. METHODS
HP6890 Chromatograph fitted. MAT-252 mass spectrometer
25

26. Gas chromatography–mass spectrometry Vitrinite reflectance microscopy
26

27. 27

28. 28