petroleum play

1

Geoscience B

G19PG

© Heriot-Watt University. Version: 01/11/2014

Lecturer: Mrs. Siti NuraliaEmail: [email protected]: 43741Office: 15, E3.10

© Heriot-Watt University 2

Topic 1. Introduction to the petroleum play

1.1. CONCEPT OF PETROLEUM PLAY1.1.1. What is the petroleum play1.1.2. Components of the petroleum play

1.2. CONCEPT OF SOURCE ROCK1.3. CONCEPT OF RESERVOIR

1.3.1. Definition of reservoir1.3.2. Factors affecting the reservoir

1.4. CONCEPT OF SEAL1.5. PETROLUEM TRAPS1.6. CONCEPT OF MATURITY1.7. MIGRATION PATHS AND TRAPS1.8. TIMING1.9. PETROLEUM EXPLORATION

Geoscience B

Class 1.3


Migration pathways

The transportation of petroleum from the source rock to the reservoir rocks is called migration

Driven by the buoyancy of petroleum

Can be spilt into three stages:

1) Primary migration2) Secondary migration3) Tertiary migration

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Source: IPE, modified by S. Ilott


Primary migrationPrimary migration- the expulsion of the petroleum from the source rock into adjacent rocks

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Primary migration

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Primary migration- the expulsion of the petroleum from the source rock into adjacent rocks

As generation of takes place, the new oil increases pressure inside the source rock

As pressure builds up, micro-fractures begin to appear in the source rock

The oil is then expelled via the micro-fractures

Oil expulsion is episodic


Secondary migrationSecondary migration- the journey from the source rock to trap. This is the process which concentrates or focuses the petroleum.

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Secondary migrationSecondary migration- the journey from the source rock to trap. This is the process which concentrates or focuses the petroleum.

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It migrates under buoyancy to the reservoir rock

Gravity driven process

Controlled by the pore systems

The pore systems in the carrier rock are normally larger than those of the source rock


Secondary migration

Secondary migration- the journey from the source rock to trap. This is the process which concentrates or focuses the petroleum.

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Capillary entry pressure is the strong controlling mechanism for secondary migration.

The pores of a rock often contain other liquids (normally water).

Oil needs to displace the water to enter the pores

Secondary oil migration will continue until the buoyancy driven flow is restricted by the capillary entry pressure of a caprock (seal).


Secondary migrationCapillary entry pressure-the amount of force, generated by buoyancy, needed for the oil to displace the water in the pores

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Source: S. Ilott


Tertiary migrationTertiary migration- leakage and dissipation of the petroleum at the Earth’s surface.

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Occurs if there is no seal or trap in place or if the seal leaks

Once oil reaches the earths surface it is biodegraded

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Timing

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Oil migration

Source: S. Ilott

If hydrocarbons migrate before:

a) A seal or trap are in place

b) A reservoir rock is formed

…….then they will escape to the surface


Timing-Basin modelling Basin modelling can be used to predict the generation and timing of migration of hydrocarbons

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Can be used with geological history to tell if all the components of the petroleum play were in place before hydrocarbon generation and migration took place

Source: IPE




Petroleum Play- Summary

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SEALimpermeable

RESERVOIRporous and permeable

CARRIER BEDporous and permeable

SOURCE ROCKorganic rich

TRAP

MIGRATION:IF: heat and pressure sufficient to create hydrocarbons from source rock organic matter&: enough is created to cause expulsion&: there are pathways for migration to reservoir

SECONDARY MIGRATION

TRAPPING:IF: trap formation occurs before migration

SEALING:IF: seal is deposited before migration&: it is sufficiently impermeable


Petroleum Exploration

Class 1.3

Defined in several ways:

• Process of exploring for oil and gas resources in the earth’s sedimentary basins.

• Leads to viable prospects to drill and the actual drilling of these prospects with exploratory and appraisal wells.

• Commitment of large amounts of risk capital to explore prospects that have an uncertain outcome.



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1. Play concept2. Leads3. Prospects4. Discovery5. Appraisal

The five stages of petroleum exploration are:

The process by which hydrocarbon accumulations are identified



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The exploration process- building upwards to a successfully producing field

Source: IPE



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1. Play concept- Identifying and mapping high probably areas to investigate

From concept models to actual data…………

Source: Allen & Allen, 1990


Stage 1: Play factors

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Available data used to this stage includes:

• Outcrop data (where rocks of interest such as potential reservoir rocks come to the surface)

• Seismic data (providing subsurface imaging of the rock structure

• Geological studies by government geological surveys or industry contractors

• Scout data (information from discussion with professionals in other companies)


Stage 1: Play factors

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The geologist will: • investigate all of the above data to

• gain an insight into the regional geological history

• identify if the main elements of the petroleum play are present.


Play maps

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Limit of the reservoirFacies distribution

Source rock location

Migration zoneRegional seal

Trap structure

Extra information on oil/ gas deposits

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Play assessment

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Pplay =

Psource x Pmaturity x Ptrap x Pseal x PtimingPresence of source rock Mature

source rock

Trapping structure

Regional seal to trap hydrocarbons

All elements in place before hydrocarbon expulsion

Total play risk

Probabilities can be assigned for each element of the play (reservoir, seal, source, trap and timing) from 0 (meaning impossible) to 1 (certain or very likely)


Play assessment

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Prospect type Probability valueNeeds more work P <0.4High risk prospect 0.4-0.6Low risk prospect 0.6-0.8

Very good prospect P >0.8

Pplay=

Psource x Pmaturity x Ptrap x Pseal x Ptiming


Play assessment

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Probabilities can be used to create a map

Source: Allen & Allen, 1990



Common Risk Segment Map

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Developed for plays to identify areas of high or low probability of finding petroleum accumulations

Generally use a ‘traffic-light’ colouring system: red is low probability of success, green is high probability.

Source: IPE


Common Risk Segment Map

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The point is to rank the different areas and then prospects within those areas, in order to find the most likely prospects. Source: IPE



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2. Leads- Specific locations where traps may exist

3. Prospects- Investigation shows potential accumulations


Prospects

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A prospect is

• a container that has a chance of containing a reservoir rock

• a suitable seal which were present at the time of hydrocarbon migration

• is on the migration pathway.


Prospects

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Prospects must be sufficient (large enough) size to warrant drilling

Prospects have more certainty then leads

Once a prospect has been drilled it will become either: • A proven petroleum field • Dry hole (no gas or oil)



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2. Leads- Specific locations where traps may exist

3. Prospects- Investigation shows potential accumulations

4. Discovery- Drilling and finding hydrocarbons

5. Appraisal- Determining the extent of the field


Appraisal

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The appraisal process is designed to determine the size of the hydrocarbon pool and to decide whether the petroleum accumulation should be developed.

This stage involves collecting high resolution seismic data (3D), to drill more wells and acquire more engineering and geological data to analyse and constrain your prospect.


Appraisal

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The data collected at this stage is used to: • Estimate the size of the petroleum

reserves

• Determine the complexity of the reservoir

• Characterise formation fluids

• Judge production performance


Appraisal

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This is the point at which a decision is made between whether:

• to commercially produce an oil/gas field • to postpone the development of the field • to abandon the field due to it being

uncommercial


Risk of exploration process

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It is important to note that all exploration is risky

• All prospects have uncertainties attached to them.

• The size of a lead or prospect and the likelihood of success are often linked.

• The greater the possible return, the higher the level of risk (possibility of failure) which can be taken.


Risk of exploration process

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Other risks:

• political (the local government might refuse a licence)

• economic (the price of hydrocarbons might decrease making the field uneconomical)

• it is important to qualify and manage the risk associated with the exploration process


References

Allen, P & Allen, J. 2005. Basin Analysis: Principles and applications.Blackwell science Ltd. Students should read the following chapter: Part 4. Application to petroleum play assessment.

Allaby, M. (Ed.). 2013. A Dictionary of Geology and Earth Sciences (4ed.).Oxford University Press.

Bjørlykke, K. 2010. Petroleum Geoscience: From Sedimentary Environments to Rock Physics. Springer.

Gluyas, J and Swarbrick, R. 2004. Petroleum Geoscience. Blackwell science Ltd.



Timing-Basin modelling

Class 1.3

Can be used to tell when (or if) a source rock was in the oil or gas window- Burial history

Source: IPE


Documents

petroleum play