Petroleum System

1
Basin Petroleum Systems Modeling

• Petroleum System
• Definitions
• Source / Reservoir / Trap / Seal
• Timing!
• Migration
• Petroleum Systems Model

2
Basin Petroleum Systems Modeling

• Petroleum System Definitions

• What is a Petroleum System?
• A Petroleum System is defined as a natural
  system that encompasses a pod of active source
  rock and all related oil and gas which includes
  all of the geologic elements and processes that
  are essential if a hydrocarbon accumulation is to
  exist.

Magoon and Dow, 1994
3
Basin Petroleum Systems Modeling

• Petroleum System Definitions

Petroleum A mineral oil occurring in subsurface
rocks and at the surface which is a naturally
occurring mixture of hydrocarbon and
non-hydrocarbon compounds. It may occur in the
gaseous, liquid, or solid state depending on the
nature of these compounds and the existent
conditions of temperature and pressure. Common
synonyms are hydrocarbons and oil and gas.
System A regularly interacting or
interdependent group of items forming a unified
whole whose organization forms a network for
distributing something, for example telephone,
highway, blood, or petroleum.
(after Magoon and Dow, 1994)
4
Basin Petroleum Systems Modeling

• Petroleum System Definitions

Geographic Extent The area over which the
petroleum system occurs, defined by a line that
circumscribes the pod of active source rock as
well as all the discovered petroleum shows,
seeps, and accumulations that originated from
that pod. The geographic extent is mapped at the
critical moment. Also the known extent. Burial
History Chart A burial history curve or
geohistory diagram constructed to show the time
over which hydrocarbon generation occurs. Depicts
the essential elements and the critical moment
for the petroleum system. Events Chart A chart
for a petroleum system showing when the essential
elements and processes took place as well as the
preservation time and critical moment of the
system.
(after Magoon and Dow, 1994)
5
Basin Petroleum Systems Modeling

• Petroleum System Definitions

Geograpic Extent
(from Magoon and Dow, 1994)
A-A Cross Section

• Deer Boar Petroleum System_at_ 250 Ma -gt Critical
  Moment
• generation started
• traps exist
• migration possible

6
Basin Petroleum Systems Modeling

• Petroleum System Definitions

Burial Chart
Combined with Events Chart
Events Chart

• Deer Boar Petroleum System_at_ 250 Ma -gt Critical
  Moment
• generation started
• traps exist
• migration possible

(from Magoon and Dow, 1994)
7
Basin Petroleum Systems Modeling

• Petroleum System Source / Reservoir / Trap /
  Seal

Source Rock A rock unit containing sufficient
organic matter of suitable chemical composition
to biogenically or thermally generate and expel
petroleum. Pod of Active Source Rock A
contiguous volume of source rock that is
generating and expelling petroleum at the
critical moment and is the provenance for a
series of genetically related petroleum shows,
seeps, and accumulations in a petroleum system. A
pod of mature source rock may be active, inactive
or spent. Reservoir Rock A subsurface volume of
rock that has sufficient porosity and
permeability to permit the migration and
accumulation of petroleum under adequate trap
conditions.
(after Magoon and Dow, 1994)
8
Basin Petroleum Systems Modeling

• Petroleum System Source / Reservoir / Trap /
  Seal

Seal A shale or other impervious rock that acts
as a barrier to the passage of petroleum
migrating in the sub-surface it overlies the
reservoir rock to form a trap or conduit. Also
known as roof rock and cap rock. Overburden
Rock The sedimentary rock above which compresses
and consolidates the material below. In a
petroleum system the overburden rock overlies the
source rock and contributes to its thermal
maturation because of higher temperatures at
greater depths.
(after Magoon and Dow, 1994)
9
Basin Petroleum Systems Modeling

• Petroleum System Exercise

PARIS BASIN Petroleum System Analysis

• Follow the below listed instructions to analyze
  the Paris Basin petroleum system
• Draw a line (map) around the pod of active source
  rock (green-colored pencil).
• Draw a line (map) around the geographic extent of
  the petroleum system (red-colored pencil).
• Draw a line (map) of cross-section on the map
  (brown-colored pencil) that would best show the
  relation of the pod of active source rock to the
  petroleum migration paths and accumulations.
• Draw an asterisk on the map (brown-colored
  pencil) where a burial history chart would best
  show the onset and end of petroleum generation
  and the critical moment.
• Draw a few arrows (green-colored pencil) to
  indicate the directions of oil and gas migration.

10
Basin Petroleum Systems Modeling

• Petroleum System Exercise

Use the following symbols to analyze theParis
Basin Petroleum System

• Pod of active source rock
• Geographic extent
• Cross section location
• Burial history chart location
• Petroleum migration

11
Basin Petroleum Systems Modeling

• Petroleum System Exercise

Paris Basin, from Tissot Welte, 1978
12
Basin Petroleum Systems Modeling

• Petroleum System Exercise

Paris Basin, from Tissot Welte, 1978
13
Basin Petroleum Systems Modeling

• Petroleum System Timing!

Critical Moment The time that best depicts the
generation migration accumulation of
hydrocarbons in a petroleum system. A map and a
cross section drawn at the critical moment best
shows the geographic and stratigraphic extent of
the System. The four elements Source Rock,
Reservoir Rock, Seal Rock and a sufficient Amount
of Overburden have to be in place before the
Critical Moment.
Petroleum System Age The time over which the
process of generation-migration accumulation of
hydrocarbons in the system takes place on the
events chart. Preservation Time The time after
generation-migration-accumulation of petroleum
takes place and encompasses any changes to the
petroleum accumulations up to present day.
(after Magoon and Dow, 1994)
14
Basin Petroleum Systems Modeling

• Petroleum System Petroleum System Elements

• 2 Processes are essential for a working Petroleum
  System
• Generation Migration Accumulation
• (driven by temperature)
• Trap Formation!
• (structural evolution or stratigraphic
  framework)

15
Basin Petroleum Systems Modeling

• Petroleum System Migration

(Expulsion)
from TISSOT WELTE (1984)
16
Basin Petroleum Systems Modeling

• Petroleum System Migration

• Migration is the process, whereby hydrocarbons
  move from source rocks to traps.
• Migration is divided into four categories
• Primary migration The process of loss of
  hydrocarbons from the source rock (also
  Expulsion).
• Secondary migration Migration from source to
  reservoir rock in trap configuration along a
  carrier system. Including the migration within
  the reservoir rock itself.
• Tertiary migration Migration to the surface,
  either from the reservoir or source rock
  (dismigration).
• Re-migration Migration from one reservoir
  system position through an intervening section
  into another reservoir position (trap) in the
  same or a different reservoir.

17
Basin Petroleum Systems Modeling

• Petroleum System Migration

Why do hydrocarbons migrate?

• Fluids migrate along a pressure gradient
• ? pressure driven
• Density contrasts between hydrocarbons and water
• buoyancy driven
• Diffusion due to concentration differences
• ? chemical gradient driven

from Hantschel Kauerauf (2009)
buoyancy driven
How do hydrocarbons migrate?
Hydrocarbons migrate as a separate phase from the
higher potential to a lower potential on the
direct way ? topography driven
Topography driven
Generated HC Masses from Source
Overpressure Buoyancy Capillary
Pressure
18
Basin Petroleum Systems Modeling

• Petroleum System Migration

Petroleum Migration Rates
Buoyancy GAS
Diffusion
?
Compactionally driven flow
?
Hydrodynamic
1
10
102
103
104
0.1
10-2
10-4
10-5
10-6
10-7
10-3
Fluid velocity m/a
19
Basin Petroleum Systems Modeling

• Petroleum System Migration

Petroleum Migration Rates
for a distance of 500m and a pressure gradient
of 5MPa/km ( Darcy Law )
20
Basin Petroleum Systems Modeling

• Petroleum System Migration

The following main driving mechanisms can be
distinguished Pressure Gradient Driven Sediment
Compaction ? - overpressure (grad u),
compaction driven fluid movement,
permeability Capillary imbibition ? -
capillary pressure differences between fine and
coarse grained layers (leads to downward
expulsion) - capillary fluid flow depends on
fluid components involved, relative
permeability Buoyancy Driven Fluid
composition ? density contrast between
hydrocarbons and water Temperature ?
Temperature increase leads to increasing
buoyancy - primary effect - the density
contrast between water an HCs increase -
secondary effect - cracking to lighter
HCs Pressure ? Pressure increase leads to
decreasing buoyancy - primary effect - the
density contrast between water an HCs
decrease - secondary effect - dissolving of
lighter HCs into the liquid phase Chemical
potential ? concentration differences
(diffusion)
21
Basin Petroleum Systems Modeling

• Petroleum System Migration

Sediment Compaction
Pressure
Lithostatic Pressure (MPa)
normal / hydrostatic pressure
Hydrostatic Pressure (MPa)
Effective Overburden Pressure (MPa)
Excess Pore Pressure (MPa)
Fluidflow
Zone of Overpressure
Compaction
overpressure
Burial Depth
Lithostatic Pressure
Hydrostatic Pressure
Pore Pressure
22
Basin Petroleum Systems Modeling

• Petroleum System Migration

Sediment Compaction
A pressure gradient dependent fluid flow can be
quantified by the Darcy Law
23
Basin Petroleum Systems Modeling

• Petroleum System Migration

Sediment Compaction
f
f
Porosity-Effective Stress Function
Porosity-Depth Function
s
z
Permeabilities
24
Basin Petroleum Systems Modeling

• Petroleum System Migration

Capillary Imbibition
When a drop of one immiscible fluid is immersed
in another and comes to rest on a solid surface.
The shape of the resulting interface is governed
by the balance of adhesive and cohesive forces.
Example
Oil
Water
q
SOLID SURFACE
The surface area at the fluid-fluid contact is
minimized by the interaction of these
forces cohesive forces at the fluid-fluid
interface adhesive forces at the solid-fluid
interface
25
Basin Petroleum Systems Modeling

• Petroleum System Migration

Capillary pressure is the difference in pressure
across the interface between two immiscible
fluids, and thus defined as
Pc Pnw - Pw
Pw wetting phase Pnw non-wetting phase
In oil-water systems, water is typically the
wetting phase, while for gas-oil systems, oil is
typically the wetting phase.   When adhesion gt
cohesion, adhesive forces draw the fluid up the
tube until they are balanced by the weight of the
fluid column.   When cohesion gt adhesion,
cohesive forces drag fluid down the tube until
they are balanced by the weight of the head
difference forcing fluid upwards.
26
Basin Petroleum Systems Modeling

• Petroleum System Migration

Capillary Imbibition
27
Basin Petroleum Systems Modeling

• Petroleum System Migration

drainage
imbibition
Oil phase
As HC migrate into a water-wet rock - They first
enter the pores with the largest pore throats
(capillaries) leaving the wetting phase in the
pores with the smaller throats (insufficient
pressure). - Can also leave the wetting phase in
irregular nooks and crannies. - As the
hydrocarbon column rises, Pc rises (buoyancy) and
forces hydrocarbons into pores with smaller and
smaller throats
28
Basin Petroleum Systems Modeling

• Petroleum System Migration

Sediment Compaction
The petroleum potential
up
Petroleum Potntial
uw
Excess Pore Pressure (Overpressure)
?w
Water Density
Petroleum Density
?p
g
acceleration due to gravity
h
column height
Pc
Capillary Pressure
29
Basin Petroleum Systems Modeling

• Petroleum System Exercise

A

• Hydrocarbons migrate as a separate phase from the
  higher potential to a lower potential on the
  direct way, usually from the deepest to the
  shallowest part of the basin, depending on the
  drainage area.
• Identify the drainage area for trap A, B C
• Draw the hydrocarbon flow lines towards each
  trap

A
30
Basin Petroleum Systems Modeling

• Petroleum System Migration - Exercise

31
Basin Petroleum Systems Modeling

• Petroleum System Migration - Solution

B
A
C
32
Basin Petroleum Systems Modeling

• Petroleum System Migration

• There are a variety of modelling methods in
  computerized Basin Modelling, out of which three
  basic concepts can be indentified
• Darcy Flow Based on equations of flow through
  porous media
• Flow Path Geometrical surface analysis
  (buoyancy driven migration)
• Invasion Percolation Flow controlled by
  capillary forces only
• A combination of methods A combination of
  different methods needs the introduction of
  threshold values to enable the program to decide
  when a specific method is used, advantages of
  each method can be combined in a time effective
  and accurate simulation of the migration and
  accumulation processes

33
Basin Petroleum Systems Modeling

• Petroleum System Migration

3D Modeling Requirements
Petroleum Systems Components
34
Basin Petroleum Systems Modeling

• Petroleum Systems Model

A Petroleum Systems Model is a digital data
model of an entire petroleum system in which the
interrelated processes and their results can be
simulated in order to understand and predict
them. The model is dynamic and provides a
complete record through geologic time.
from Magoon and Dow, 1994
35
Basin Petroleum Systems Modeling

• Petroleum Systems Model

Key Questions and Tasks of Petroleum Systems
Modeling

• Petroleum Generation
• Have hydrocarbons been generated?
• Resource assessment studies and initial charge
  risking. There are basins in which no oil and gas
  have been generated!
• Where were hydrocarbons generated?
• If hydrocarbons were generated, we can define
  their locations quite accurately.
• When were hydrocarbons generated?
• There are many clear examples of where
  basins/plays/prospects have failed due to timing
  problems. For example, when oil and gas was
  generated early and the structures were created
  much later

Petroleum Migration Accumulation Could they
have migrated to the prospect? Modeling of the
dynamic process of generation, expulsion and
migration makes it possible to determine if the
oil and gas charge could reach the trap. What
are the properties of the hydrocarbons? Modeling
of the phase behaviour of the hydrocarbons during
migration, accumulation and loss makes it
possible to determine oil vs. gas probabilities
and even predict properties such as API gravities
and GORs.
36
Basin Petroleum Systems Modeling

• Petroleum Systems Model

Trap Risk for example - Prospect geometry -
Reservoir quality (por/perm) - Seal quality
seal
carrier/ reservoir

• Charge Risk
• for example
• - Source rock quality
• Source rock maturity
• Generated petroleum

Timing and Migration Risk! - relates the charge
to the trap ... migration! - takes dependencies
and processes into account! - takes dynamics into
account!
carrier
source
This is what Petroleum Systems Modeling
technology does!
37
Basin Petroleum Systems Modeling

• Petroleum System - References

Allen, P.A. Allen, J.R. (2005) Basin Analysis
Principles and Applications, Blackwell Science,
Malden, MA, USA 560pp. Hantschel, T., Kauerauf,
A.I. (2009) Fundamentals of Basin Modeling,
Springer Verlag, Berlin, Germany, 476pp Magoon,
L.B. Dow, W.G. (1994) The Petroleum System
from Source to Trap, AAPG Memoir 60, Tulsa, OK,
USA 655pp. Tissot, B.P. Welte, D.H. (1984)
Petroleum Formation and occurrence. 2nd
Edition, Springer Verlag