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module about how to determine oil or gas generation in oil field
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Wiekert Visser
Oil & Gas typing
Introduction & bulk properties
Petroleum systems mapping work flow
Oil Oil correlation
Oil Gas correlation
Gas Gas correlationOil/gas family map
Oil Source rock correlation
Gas Source rock correlationDefine Petroleum Systems
Rock Eval analyses (wells)
Seismic isopachs mapSource rock quality maps
Maturity data (wells) Source rock kitchen maps
(Once) Active Petroleum Systems maps
Note: modern 3D modeling tools need much more data & deliver superior results
Objectives of oil and gas typing in Exploration
Typing of oil, gas, and source rock extracts is a key
element of Petroleum Systems Analysis. This work
aims at:
Assessment of the source of the hydrocarbons (type and age)
Assessment of the maturity of the source at the time of expulsion
Estabishing the petroleum system (i.e. The link betweensource rock and trapped hydrocarbons)
Oil family mapping: is there more than 1 petroleum system in the basin?
Reduction of exploration risk by the above activities.
Example exploration question
AB C
Source rock A (KK)
Oil field1
2
3
4
0
Top oil window (VR=0.6)
? Source rock B (JJ) ?
Depth
(km
)
Question: Is the oil derived from the Cretaceous or the
Jurassic source rock?
Mature
Immature
D
Fundamentals of oil & gas chemistry
Crude oil is a mixture of thousands of organic
components. Chemical analysis of these complex
mixtures gives information about:
Economic value of the oil/gas
The source & charge history
Post-trapping alterations
A condensate is operationally defined as any fluid which is a gas in the
subsurface but a liquid at the surface. This depends on the PVT
conditions. For geochemical purposes, a condensate is a fluid with most
of its mass below C15.
Gas Condensate Oil
API gravity n.a. >45 20 %
Methane content > 95 % 60-85 % < 20 %
GOR (scf/bbl) > 100.000 3000 100.000 < 3000
Bulk Characteristics of Petroleum Fluids
Oil and Gas compounds, fundamentals
n-Alkanes: CnH2n+2
Cyclo-pentane
H2 H2
H2 H2
H2H2
Cyclo-hexane
C6H12
Benzene
C6H6
H
|
H C H
|
H
H H H H H
| | | | |
H C C C C C H
| | | | |
H H H H H
Methane Pentane
C5H12C1 C5 Iso-C6
Pentane
Paraffins/Alkanes
Cyclo-alkanes
(Naphtenes)
n-alkanes
iso-alkanes
Aromatics
Non-saturates
Saturates: alkanes
Saturates: naphtenes
Naphtalene
Composition of a 35 API & a 16 API crude
16 API
0
Main boiling fractions of oilDown-stream purposes
Normal black oil
Bulk properties of oils for E&P
API gravity (density)
weight-loss on topping
% Sulfur
Heavy metals
Carbon Isotopes
Gross Composition:
% Saturates,
% Aromatics
% Hetero compounds
Total Acid Number (TAN)
Viscosity
Pour point
Cloud point
Wax content
Asphaltene content
Geological Applications (Reservoir) Engineering
i
i
i
F
API gravity - density relationship
Specific gravity
Condensate
Oil
API gravity
Tar
Degrees API= -131,5141,5 specific gravity
R
Tambaredjo Oil
API Gravity versus %S
Global data set trend
Amongst heavy oils
the Tambaredjo crude
is of high quality, and very
exceptional in composition
Sulphur in Shaly Marine Oils
The percentage of Sulphur is
important for crude market price,
and for corrosive effects.
Masila: 30.5 / 0.67%
Marib Light: 48 / 0.08%
Hemiar: 22.2 / 1.23%
The variation in the percentage of
Sulphur in the Yemeni crudes is
related to biodegradation.
These data are from the Jurassic Madbi marly shales in Yemen
Interpreting Sulfur
Sweet low sulfur crudes indicate the source is:
High API gravity shaly marine
Lacustrine (in case of elevated wax content)
Landplant (in case of high wax content)
Souer high sulfur crudes indicate that:
Source is a limestone (with very low shale content)
Crude has been biodegraded (in case of low API)
Crude is a low maturity early expulsion product (in case of
low API)
R
C = -1 *100013 C / C (sample)
13 12
C / C (standard)13 12
[ ]
The standard is the belemnite from the PeeDee Formation in South Carolina
PDB C = 013
Carbon isotopes
The atom Carbon has three different isotopes 12C, 13C, 14C, with atomic
weight of 12, 13, and 14 gram/mol respectively.
12C is most abundant, and living organisms prefer 12C over 13C
14C is least abundant and is radio-active. It can be used as dating tool.
Carbon Isotopes in Nature
-100 -80 -60 -40 -20 0 20
-100 -80 -60 -40 -20 0 20
13 CPDB ()
Diamond
Animal Bone
Thermal Gas
Bacterial Gas
Wood
Peat
Non-marine Carbonate Minerals
Groundwater HCO3
Plankton
Land Plants (C4)
Land Plants (C3)
Marine HCO3
Marine Plants
Marine Carbonate Minerals
Atmospheric CO2
Coal
Bakken Shale
West Africa
North Sea
Cretaceous
Kimmeridge
WyomingPhosphoria
Williston Basin
Ordovician Texas
-20-25-30-35
Monterey
Oils / Source Rocks
Oils/SR
Carbon isotopes are
very useful for Oil Oil
and Oil Source rock
correlations
R
Isomers of alkanes
C2 C5C4 C9C8C7C6 C11 C13
1 92 3 5 18 35 159 802
1 42 2 3 5 6 7 8
Carbon atoms in molecule
Isomers
Possible
Significant in
crude oils
The number of isomers in crude oils explodes with increasing carbon number.
Analysing all these compounds required excellent separation techniques, such as
liquid and/or gas chromatography, and mass spectrometry
C-C-C-C-C-C-C
n-C7Branched alkanes C7 ring compounds
Example of branched alkanes: C7 isomers
1* Tri-branched
3* Mono-branched
4* Di-branched
Long chain iso-alkanes: Pristane and Phytane
CH3
CH3 CH3 CH3
CH3
CH3
CH3
CH3 CH3 CH3
CH3
CH3
Phytane
Pristane
Pristane and Phytane occur in all crude oils
Both compounds are fragments of Chlorophyll,
which occurs in many living organisms
C20
C19
Pristane and Phytane are simple indicators for environment of
deposition and a basic tool for correlation. They are maturity
dependent, but reasonably resistant to biodegradation.
Biomarkers in oil and in living organisms
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
HO
CholesterolPresent in living organisms
CholestanePresent in crude oil
This biomarker occur in virtually all crude oils
Many biomarkers are detailed indicators for environment of
deposition and age of the source rock and are the most
important tool for correlation. They are slightly maturity
dependent, but resistant to biodegradation. Biomarkers are
the work-horse for exploration geochemists.
Conclusions
Analyses of oil and gas are essential input for the
assessment of Petroleum Systems
Fluid properties contain geological information that
can be used for inpout as well as for calibration of
petroleum systems models.