Basin Petroleum Systems Modeling

8/13/2019 Basin Petroleum Systems Modeling

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Petroleum System

• Definitions

• Source / Reservoir / Trap / Seal

• Timing!

• Migration

• Petroleum Systems Model

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.

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)



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.







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

• generation started

• traps exist

• migration possiblePod of Active

Source Rock

Reservoirs

A-A’ Cross Section


(from Magoon and Dow, 1994)

Geograpic Extent




Burial Chart

Events Chart

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

• generation started

• traps exist

• migration possible


(from Magoon and Dow, 1994)

Combined with Events Chart



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 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 Rock

A subsurface volume of rock that has sufficient porosity and permeability to permit

the migration and accumulation of petroleum under adequate trap conditions.


• 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.


• 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 historychart 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 the

Paris Basin Petroleum System





Paris Basin, from Tissot & Welte, 1978





Paris Basin, from Tissot & Welte, 1978



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.

• 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)


• Petroleum System – Petroleum System Elements



from TISSOT & WELTE (1984)


• 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 sourcerock (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 phasefrom the higher potential to a lower potential

on the direct way

topography driven

How do hydrocarbons migrate?



Generated HC Massesfrom Source

Topography driven

buoyancy driven

f r o m H a n t s c h e

l & K a u e r a u f ( 2 0 0 9 )

c pww p ph g uu )(

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 )



0.01 0.1 1.0 10.0 100.0 1000.0

gas oil

Viscosity [mPa s]

P e r m e a b i l i t y [ m D

]

104

103

102

101

10-1

10-2

10-3

10-4

10-5

100

Silt@ 20% porosity

Sand

@ 20% porosity

Petroleum Migration Rates

p grad k

dx

dpk

A

Qv



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 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

B u r i a l D e p t h

Pressure

Lithostatic

Pressure

Hydrostatic

Pressure

Pore

Pressure

Fluidflow

Compaction

Z o n e o f

O v e r p r e s s u r e

h P

u

l P : Effective Overburden Pressure (MPa)

u : Excess Pore Pressure (MPa)

l P

h P

: Lithostatic Pressure (MPa)

: Hydrostatic Pressure (MPa)

e P

normal / hydrostatic

pressure

overpressure





Sediment Compaction

p grad k

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 P o r o s i t y - E f f e c t i v e S t r e s s F u n c t i o n

k e

101)(

gz k wl e z

))(1(00

0

1)1()(

P o r o s i t y - D e p t h F u n c t i o 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.

q 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 interface

adhesive forces at the solid-fluid interface



Example:

Capillary Imbibition



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

P c = P

nw - P

w

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 > 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

c pw

w p P h g uu )(

The petroleum potential

: Excess Pore Pressure (Overpressure)

: Petroleum Density

: Petroleum Potntial

: Water Density

: Capillary Pressure

u p

uw

g

P c

: acceleration due to gravity

ρ p

ρw

: column heighth



5000m

4500m

2500m

2000m

3000m

2000m

2500m

B A C

A

A’


Hydrocarbons migrate as a

separate phase from the

higher potential to a lowerpotential 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 & C

2) Draw the hydrocarbon flow

lines towards each trap

1500

2000

2500

3000

3500

4000

4500

5000

A A’




5000m

4500m

2500m

2000m

3000m

2000m

2500m

B A C


• Petroleum System – Migration - Exercise




B A 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 specificmethod 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





„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 gashave 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 timingproblems. For example, when oil and gas was generated early and the structures were createdmuch later:

Petroleum Migration & AccumulationCould they have migrated to the prospect?Modeling of the dynamic process of generation, expulsion and migration makes it possible todetermine 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 lossmakes it possible to determine oil vs. gas probabilities and even predict properties such as API

gravities and GORs.





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!


Definition: Charge is the

volume of hydrocarbons

available for entrapment


Documents

Basin Petroleum Systems Modeling