The Petroleum SystemFrom Source to Trap
• A petroleum system encompasses a pod
of active source rock and all genetically
related oil and gas accumulations.
• It includes all the geologic elements and
processes that are essential
• if an oil and gas accumulation is to exist.
LEVELS OF PETROLEUM
INVESTIGATIONS
• Sedimentary Basin Investigations
• Petroleum System Investigations
• Play and Prospect Investigations
Magoon and Beaumont
Petroleum System Investigations
• Petroleum–petroleum geochemical correlation
• Petroleum–source rock geochemical correlation
• Burial history chart
• Petroleum system map
• Petroleum system cross section
• Events chart
• Table of hydrocarbon accumulations
• Determination of generation–accumulation
efficiency
Identifying a Petroleum System
Magoon and Beaumont
Naming a Petroleum System
The name of a petroleum system contains several
parts that name the hydrocarbon fluid system:
1. The source rock in the pod of active source rock
2. The name of the reservoir rock that contains the
largest volume of in-place petroleum
3. The symbol expressing the level of certainty
Magoon and Beaumont
the level of certainty
Magoon and Beaumont
A petroleum system has three
important temporal aspects
• Age
• Critical moment
• Preservation time
age
• The age of a system is the time required
for the process of generation–migration–
accumulation of hydrocarbons.
critical moment
• The critical moment is the time that best
depicts the generation–migration–accumulation
of hydrocarbons in a petroleum system. A map
and cross section drawn at the critical moment
best show the geographic and stratigraphic
extent of the system. The burial history chart
below shows the critical moment and the
essential elements for the fictitious Deer-Boar(.)
petroleum system.
critical moment
Magoon and Beaumont
preservation time
• The preservation time of the petroleum system
begins immediately after the generation–
migration–accumulation process occurs and
extends to the present day. It encompasses any
changes to the petroleum accumulations during
this period. During the preservation time,
remigration, physical or biological degradation,
or complete destruction of the petroleum may
take place. During the preservation time,
remigrated (tertiary migration) petroleum can
accumulate in reservoir rocks deposited after the
petroleumsystem formed.
preservation time
Magoon and Beaumont
Mapping a Petroleum System
• A petroleum system is mapped by showing
the geographic, stratigraphic, and
temporal extent of the system.
Examples of Two Petroleum
Systems
• The Mandal–Ekofisk(!) petroleum system in the Central
Graben of the North Sea contains 21.4 billion bbl of oil
and 39.4 trillion ft3 of gas in 39 fields (Cornford, 1994).
The age of the reservoir rock ranges from Devonian to
Tertiary age with about 85% of the petroleum in rock
adjacent to the Cretaceous–Tertiary boundary,
specifically the Ekofisk Formation of Late Cretaceous
age. Based on geochemical evidence, the Upper
Jurassic (Kimmeridgian) to Lower Cretaceous source
rock is the Mandal Formation. A positive oil–source rock
correlation indicates a known system.
Geologic setting
Comford,1994
Geologic setting
Comford,1994
Burial history chart
Magoon and Beaumont
Petroleum system cross section
Magoon and Beaumont
Oil–source rock correlation
Magoon and Beaumont
Petroleum system events chart
Magoon and Beaumont
Petroleum Systems- Elements
•
•
•
•
•
Source Rock
Migration Route
Reservoir Rock
Seal Rock
Trap
Petroleum System Summary
•
•
•
•
•
Source (Material and Rocks)•
Generation (Maturation)•
Migration •
Trap •
Reservoir
Source Material
Kerogen Types
• Type I –Algal (oil prone) sapropelic
• Type II –Mixed
• Type III –Woody (gas prone) humic
Petroleum System Summary
•Source (Material and Rocks)
•Generation (Maturation)
•Migration
•Trap
•Reservoir
Primary Migration
• Solution:
• Micelles:are molecules that behave like soap, attaching themselves
to a hydrocarbon molecule on one end and to an OH- at the other
end.
• Diffusion:of most hydrocarbons through rocks is also exceedingly
slow.
• Gas phase migration- Compressed gas can dissolve liquid
hydrocarbons. Migration of hydrocarbons dissolved in the gas phase
can facilitate the movement of hydrocarbons through the source
rock, as the gas phase migrates into shallower regions where
temperature is lower, the liquid hydrocarbons come out of solution.
• Oil Phase Migration- The expulsion of the oil out of the source
rock is a dynamic process driven by the oil generation itself.
Secondary Migration
Driving forces for migration:
• Buoyancy: (This force acts vertically and is
proportional to the density difference between water and
the hydrocarbon so it is stronger for gas than heavier oil)
• Hydrodynamic flow: (water potential deflect the
direction of oil migration, the effect is usually minor
except in over pressured zones (primary migration))
Resisting forces:
• Capillary pressure (opposes movement of fluid from
coarse-grain to fine- grain rock, also the capillary
pressure of the water in the reservoir resists the
movement of oil)
Petroleum System Summary
•Source (Material and Rocks)
•Generation (Maturation)
•Migration
•Trap
•Reservoir
Entrapment Style
• High-impedance entrapment style is characterized
by( laterally continuous seals coupled with a
moderate to high degree of structural deformation.
• LOW-impedance entrapment style is characterized
by either a high degree of regional seal continuity and
a low degree of structural deformation, or a low
degree of regional seal effectiveness coupled with a
high or low degree of structural deformation.
Sedimentological traps
• Point bar sands surrounded by flood-plain
clays in a fluvial system.
• Distributary channels within deltaic muds.
• Reefs within lagoonal and marine shales
• Barrier island sands also within lagoonal
and marine shales
Petroleum System Summary
•Source (Material and Rocks)
•Generation (Maturation)
•Migration
•Trap
•Reservoir
seal
Regional seal (determines migration pathway)
• Local seal (seals the trap)
• Best seals: gas hydrates, evaporites (salt),
organic rich shales, clay rich shales, tight
carbonates
Important characteristics of seal rocks:
• Low permeability
Ductility (otherwise they are easily fractured during
deformation)