petroleum system definitions source / reservoir / trap / seal timing! migration petroleum systems...

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

Basin & Petroleum Systems Modeling

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

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.

SystemA 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)

Geographic ExtentThe 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 ChartA 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 ChartA 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.




Deer Boar Petroleum System@ 250 Ma -> Critical Moment:

• generation started• traps exist• migration possible

Pod of ActiveSource Rock

Reservoirs

A-A’ Cross Section

• Petroleum System – Definitions

(from Magoon and Dow, 1994)

Geograpic Extent

Basin & Petroleum Systems ModelingBurial Chart

Events Chart

Deer Boar Petroleum System@ 250 Ma -> Critical Moment:

• generation started• traps exist• migration possible

• Petroleum System – Definitions

(from Magoon and Dow, 1994)

Combined with Events Chart

Source RockA rock unit containing sufficient organic matter of suitable chemical composition to biogenically or thermally generate and expel petroleum.

Pod of Active Source RockA 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 RockA subsurface volume of rock that has sufficient porosity and permeability to permit the migration and accumulation of petroleum under adequate trap conditions.

Basin & Petroleum Systems Modeling• Petroleum System – Source / Reservoir / Trap / Seal


SealA 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 RockThe 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.

Basin & Petroleum Systems Modeling• Petroleum System – Source / Reservoir / Trap / Seal


• Petroleum System – Exercise


Follow the below listed instructions to analyze the Paris Basin petroleum system

1. Draw a line (map) around the pod of active source rock (green-colored pencil).2. Draw a line (map) around the geographic extent of the petroleum system (red-

colored pencil).3. 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.

4. 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.

5. Draw a few arrows (green-colored pencil) to indicate the directions of oil and gas migration.

PARIS BASIN – Petroleum System Analysis

• Pod of active source rock

• Geographic extent

• Cross section location

• Burial history chart location

• Petroleum migration



Use the following symbols to analyze theParis Basin Petroleum System



Paris Basin, from Tissot & Welte, 1978

Critical MomentThe 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 AgeThe time over which the process of generation-migration accumulation of hydrocarbons in the system takes place on the events chart.

Preservation TimeThe time after generation-migration-accumulation of petroleum takes place and encompasses any changes to the petroleum accumulations up to present day.

• Petroleum System – Timing!


2 Processes are essential for a working Petroleum System

• Generation – Migration – Accumulation(driven by temperature)

• Trap Formation!(structural evolution or stratigraphic framework)

Basin & Petroleum Systems Modeling• Petroleum System – Petroleum System Elements

from TISSOT & WELTE (1984)

Basin & Petroleum Systems Modeling• Petroleum System – Migration

(Expulsion)

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.


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

Hydrocarbons migrate as a separate phase from the higher potential to a lower potential on the direct way topography driven

How do hydrocarbons migrate?


Generated HC Masses from Source

Topography driven

buoyancy driven

from

Han

tsch

el &

Kau

era

uf

(2009)

cpwwp phguu )( Overpressure Buoyancy Capillary Pressure

Migration Mechanism Migration Rate

Hydrodynamic (pressure driven) 10-3 to 1000 m/a

Compaction (drainage!) 10-5 to 1 m/a

Buoyancy Meters per day (gas)

Diffusion 1 to 10 m / Ma

Petroleum Migration Rates


Fluid velocity [m/a]

1 10 102 103 1040.110-210-410-510-610-7 10-3

Buoyancy GAS

Hydrodynamic?

? Compactionally driven flow

Diffusion

for a distance of 500m and a pressure gradient of 5MPa/km ( Darcy Law )

• Petroleum System – Migration


0.01 0.1 1.0 10.0 100.0 1000.0

gas oil

Viscosity [mPa s]

Perm

eabi

lity

[mD

]

104

103

102

101

10-1

10-2

10-3

10-4

10-5

100

1 day

1000 yearsSilt@ 20% porosity

1 year

Sand @ 20% porosity

Petroleum Migration Rates

pgradk

dx

dpk

A

Qv

The following main driving mechanisms can be distinguished

Pressure Gradient DrivenSediment Compaction - overpressure (grad u), compaction driven fluid movement,

permeabilityCapillary 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 DrivenFluid composition density contrast between hydrocarbons and waterTemperature Temperature increase leads to increasing buoyancy

- primary effect - the density contrast between water an HC’s increase

- secondary effect - cracking to lighter HC’s

Pressure Pressure increase leads to decreasing buoyancy- primary effect - the density contrast between water an

HC’s decrease- secondary effect - dissolving of lighter HC’s into the

liquid phase

Chemical potential concentration differences (diffusion)




Sediment Compaction

Bu

rial D

ep

th

Pressure

LithostaticPressure

HydrostaticPressure

PorePressure

Fluidflow

Compaction

Zo

ne

of

Ove

rpre

ssu

re

hP

u σ

lP : Effective Overburden Pressure (MPa)

u : Excess Pore Pressure (MPa)

lP

hP

: Lithostatic Pressure (MPa)

: Hydrostatic Pressure (MPa)

eP

normal / hydrostaticpressure

overpressure



Sediment Compaction

pgradk

dx

dpk

A

Qv

A pressure gradient dependent fluid flow can be quantified by the Darcy Law

: volumetric flow [m3 / s]

: permebility [ m2 ]

: darcy velocity (discharge velocity) [m / s]

: flow specific surface [m2]

: pressure gradient [Pa / m]

Q

v

η

dp/dx

: dynamic viscosity [ Pa s ]

k

A



Sediment Compaction

Permeabilities Po

rosi

ty-E

ffe

ctiv

e S

tre

ss F

un

ctio

n

ke 101)(

gzk wlez

))(1(00

01)1(

)(

Po

rosi

ty-D

ep

th F

un

ctio

n

z

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.

SOLID SURFACE

OilWater

The surface area at the fluid-fluid contact is minimized by the interaction of these forces:

cohesive forces at the fluid-fluid interfaceadhesive forces at the solid-fluid interface



Example:

Capillary Imbibition

Capillary pressure is the difference in pressure across the interface between two immiscible fluids, and thus defined as:

Pc = Pnw - Pw

Pw = wetting phasePnw 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 > cohesion, adhesive forces draw the fluid up the tube until they are balanced by the weight of the fluid column. When cohesion > adhesion, cohesive forces drag fluid down the tube until they are balanced by the weight of the head difference forcing fluid upwards.





Capillary Imbibition

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



Sediment Compaction

cpwwp Phguu )(

The petroleum potential

: Excess Pore Pressure (Overpressure)

: Petroleum Density

: Petroleum Potntial

: Water Density

: Capillary Pressure

up

uw

g

Pc

: acceleration due to gravity

ρp

ρw

: column height h

5000m

4500m

3000m

4000m

3500m

2500m

2000m

3000m

2000m

5000m

4500m

4000m

2500m

BA C

A

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.

1) Identify the drainage area for trap A, B & C2) Draw the hydrocarbon flow

lines towards each trap

1500

2000

2500

3000

3500

4000

4500

5000

A A’


5000m

4500m

3000m

4000m

3500m

2500m

2000m

3000m

2000m

5000m

4500m

4000m

2500m

BA C

Basin & Petroleum Systems Modeling• Petroleum System – Migration - Exercise


BA C

• Petroleum System – Migration - Solution


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

Dynamics ++ - -

Scaling - + +

Processing speed -- + + -

Data availability + + +

Source and expulsion + - -

Migration – low perm. units + -- +

Migration – high perm. carriers - ++ +

Reservoir bodies -- ++ +

Petroleum Systems Components:

3D Modeling Requirements:


Darcy Flowpath Percolation

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

Key Questions and Tasks of Petroleum Systems ModelingPetroleum 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 & AccumulationCould 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.

Basin & Petroleum Systems Modeling• Petroleum Systems Model

source

carrier

Trap Riskfor example:- Prospect geometry- Reservoir quality (por/perm)- Seal quality

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!

sealcarrier/

reservoir

This is what Petroleum Systems Modeling technology does!

• Petroleum Systems Model

Definition: Charge is the volume of hydrocarbons available for entrapment
