Petrochemical Engineering - Petroleum Entrapment

8/13/2019 Petrochemical Engineering - Petroleum Entrapment

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By the end of chapter 1, you will be able to:

Explain different steps involved in the generation of the petroleum.

Describe the effect of pressure and temperature in the migration

and conversion of petroleum.

Explain different entrapments which can hold the petroleum in

place underground.

Name some of the duties of reservoir, production, formation and

drilling engineers.

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Petroleum and reservoirs

Main elements of a reservoir

Origin of petroleum

o Organic material deposition

o Migration and conversion

o Entrapment

Quality of reservoir rock

o Porosity

o Permeability

Petroleum Engineering

Formation Evaluation

Drilling Engineering

Reservoir Engineering

Production Engineering

Chapter_1_Introduction

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Introduction/Main elements of a reservoir

Source rock (source of hydrocarbons)

Reservoir trap (structural or stratigraphic)

Reservoir seal (to contain hydrocarbons within reservoir trap)

Quality of reservoir rock (reasonable porosity and permeability)

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Introduction/Origin of petroleum/Organic deposition

Petroleum reservoirs are created through three sequential steps:

deposition, migration/conversion and entrapment.

A. Organic material deposition:

Petroleum originates mainly from algae and plankton (fatty

molecules called lipids).

This organic material must be buried under a sediment or silt.

The silt guards the organic material from aerobic consumption.

Deposition process normally takes place in the river deltas or

between shores and reefs (stagnant flow zone).

The organic material and sediment form a source bed which is

required for the remaining steps in the process.

This is often called black shale or sedimentary rock. Black

shale contains an organic feature called Kerogen enriched in

high molecular weight organic chemicals.

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Introduction/Origin of petroleum/Organic deposition

B. Migration/Conversion:

Pressure: Responsible for the primary migration

Buoyancy: Responsible for the secondary migration

Temperature: Responsible for petroleum generation

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Introduction/Origin of petroleum/migration

Primary migration: The release of petroleum compounds after they are

generated from Kerogen in source beds. The cause of expulsion of

petroleum is due to the overburden pressure on the source rock, pushing

out water and hydrocarbons.

Secondary migration: The expelled oil from the source bed passes through

wider pores of more permeable porous rocks. Small droplets of petroleum

coalesce to form larger volumes. Surrounding water pushes the oil and gas,which have a lower density, upward through the reservoir rock layer until

they are accumulated in traps. This is caused by buoyancy forces.

Petroleum Formation and Occurance2ndedition, Tissot, B.P. and Welte, D.H., Springer-Verlag, Berlin, 1984, 294.6


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Introduction/Origin of petroleum/conversion

For a reservoir to be formed, a porous rock (such as sandstone,

dolomite and so on) must form above the source bed rock.

Petroleum Formation and Occurance2ndedition, Tissot, B.P. and Welte, D.H., Springer-Verlag, Berlin, 1984, 294.


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Conversion (Effect of temperature):

The series of events involved in the transformation of organics intopetroleum is not well known. This conversion takes place duringboth the primary and secondary migrations.

Temperature plays a major role in the conversion.

Temperature in the porous rock is determined by the averagesurface T and the geothermal gradient. An average value is 30C/km. In western Canada these values are: 0 C and 38 C/km.

Some Types of Kerogen release crude oil and natural gas above 50

C.

Although the overburden pressure is the driving force for theprimary migration, it does not appearto be an important parameterin the chemistry of converting organic material to petroleum since asimilar crude oil is obtained at a wide range of well depths at

different locations in the world.


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Generation of crude oil is promoted at temperature between

50 C (1.3 km) and 160 C ( 4.2 km) considering an average

geothermal gradient of 38 C/km.

At temperatures higher than 160 C, the petroleumundergoes thermal degradation to form gas. At temperatures

over 225-250 C, organic matter loses all its hydrogen and

transforms into graphite.

At temperatures lower than 50 C, Kerogen tends to be

selectively degraded by bacteria where the lower density

components are consumed and the higher density fluids remain

(e.g. Bitumen within the Oilsands)

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Hydrocarbon Exploration and Production,Jahn, F., Cook, M., Graham, M., Elsevier, 2008, 2ndEdition 22.



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Introduction/Origin of petroleum/Summary

Earth, portrait of a Planet, 4th edition, Stephen Marshak, W.W. Norton & company, 201211


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C. Entrapment:

Entrapment occurs when the petroleum reaches an impermeable layerwhere no further migration can occur. This rock layer is known as a trap.

There are four types of traps: structural, stratigraphic, combination

and differential.

C.1. Structural traps:

Structural traps are formed by folding (Anticline) or faulting (normal or

thrust) or salt dome.

Folding occurs from compression and tension in the earths crust

including uplifts caused by salt or shale. The inverted U-shape of

the fold (the anticline) results in a trap where the upper layer (the

cap rock) is impermeable to the oil.

Fault traps result from shifting and displacement along a fault line,

which places a reservoir layer adjacent to an impermeable layer.

Introduction/Origin of petroleum/Entrapment

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Structural trap (Anticline)


Where rock layers are folded into anticlines and synclines, the oil and

gas migrates to the crests of the anticlines within the reservoir rock,

and are trapped if overlain by an impermeable layer. If fractures occur,

oil and gas may seep to the surface. Examples include the Bubbles

and Jedney gas fields in northeastern British Columbia.http://www.drillingfunds.com/common_traps.html

Surface gravel

Shale

Salt

Sandstone

Limestone

Gas

OilGas

Oil

Anticline

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http://www.drillingfunds.com/common_traps.htmlhttp://www.drillingfunds.com/common_traps.html


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Structural trap (Normal fault)

Faults drop one side down and push the other side up to place the

reservoir rock against impermeable sealing rocks, forming a structural

fault trap. An example is the Dunvegan gas field in northwestern

Alberta.


http://www.drillingfunds.com/common_traps.html

Surface gravel

LimestoneSandstone

Salt

Shale

Oil

Gas

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Structural trap (Thrust fault)


In the foothills of Western Canada, east of the Rockies, the original

limestone layer was first folded and then thrust-faulted over itself. An

overlying seal of impermeable rock completes the structural trap.

Examples include the Turner Valley oil and gas field and Jumping

Pound gas field, both in south-western Alberta.http://www.drillingfunds.com/common_traps.html

Shale

Sandstone

Limestone

Gas

Oil

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Structural trap (Salt dome)

Under the weight of overlying rock layers, layers of salt will push their

way toward the surface in salt domes and ridges. Oil and gas are

trapped in folds and along faults above the dome and within upturned

porous sandstones along the flanks of the dome. Examples are found

off Canada's East Coast.


http://www.drillingfunds.com/common_traps.html

Sandstone Shale

Salt dome

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C.2. Strarigraphical Traps:

Stratigraphic traps are formed by a change in the character of

the reservoir rock (less permeable) or a change in the deposition

environment where an impermeable layer is deposited around

the reservoir rock. The layering must have both a vertical and

lateral aspect to act as a trap. Three common stratigraphictraps: Pinch out, Reef, and Unconformity.

Examples:Reservoir Rock Impermeable

Layer

Sandstone Shale

Deolomite Limestone

Reef limestone Limestone


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Stratigraphic trap (pinch out)


This occurs where the porous limestone reservoir loses its porosity

and becomes impermeable limestone, or the porous sandstone

reservoir simply thins and pinches out. Overlying impermeable rocks

act as seals. Examples include the D-1 Crossfield sour gas field and

many oil and gas fields in Saskatchewan.http://www.drillingfunds.com/common_traps.html

Sandstone

Limestone Shale

Gas

Oil

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Stratigraphic trap (reef)


Porous ancient coral reefs grew in the warm seas that once covered

much of Western Canada. They now provide prolific oil and gas

reservoirs. Often overlying porous rock layers are "draped," or folded

over the reefs and form separate traps. Overlying impermeable shales

act as seals to the reservoirs. An example is the Leduc oil and gas

field in Alberta.http://www.drillingfunds.com/common_traps.html

Limestone

Limestone

Shale

Shale

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Stratigraphic trap (unconformity)

An unconformity is a break in the depositional sequence of rocks. If the

underlying beds were tilted, eroded and then covered with flat laying

impermeable rocks, then oil and gas may be trapped at the

unconformity. The reservoirs are commonly covered by shale.http://www.carbonet.net/bjarne/Stoupakova%20et%20al%202006.swf


Introduction to Oil and Gas Production, API, Dalla, Texas, 1983, 4.

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http://www.carbonet.net/bjarne/Stoupakova%20et%20al%202006.swfhttp://www.carbonet.net/bjarne/Stoupakova%20et%20al%202006.swf


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C.3. Combination traps:

Combination traps have characteristics of both structural andstratigraphic traps. A trap is created due to a salt dome or salt

plug moving upward. As the salt dome pushes upward through

the sedimentary layers (stratigraphic component), it causes

folding and faulting (structural component). This results in

formation of combination traps.


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http://www.carbonet.net/bjarne/Stoupakova%20et%20al%202006.swf
http://www.carbonet.net/bjarne/Stoupakova%20et%20al%202006.swfhttp://www.carbonet.net/bjarne/Stoupakova%20et%20al%202006.swf


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23DIFFERENTIAL TRAPPING OF HYDROCARBONS, WM. C. GUSSOW. CONSULTANT.


C.4. Differential Traps:


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Stage 1

Both oil and gas continues to be trapped while water is displaced. Stage 1ends when oil water interface reaches the spill points.

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Stage 2

Gas continues to be trapped while oil is spilled up dip. Stage 2ends when oil-gas interface reaches spill point and coincides with

the oil-water interface


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Stage 3

Gas spills up dip as more gas enters trap. Oil by-passes the

trap and continues up dip.


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Summary of traps

1. Structural (89%)

Folding (Anticline)

Faulting

Normal fault

Thrust fault Salt dome

2. Stratigraphic (9%)

Pinch out

Reef

Unconformity

3. Combination (2%)

4. Differential 27


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Porosity:

Connected porosity to store economic volume of hydrocarbons.

Permeability:

The ease with which fluids can flow through the porous rock.

Introduction/Reservoir rock

Hydrocarbon Exploration and Production,Jahn, F., Cook, M., Graham, M., Elsevier, 2008, 2ndEdition, 96, 165.28


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Petroleum and reservoirs

Main elements of a reservoir Origin of petroleum

o Organic material deposition

o Migration and conversion

o

Entrapment Quality of reservoir rock

o Porosity

o Permeability

Petroleum Engineering

Formation Evaluation

Drilling Engineering

Reservoir Engineering

Production Engineering

Introduction

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1) Formation Evaluation:

Objective:

Formation evaluation activities attempt to develop a composite

description of the reservoir.

Seismic testing (e.g. sonic waves)

Well logging (e.g. electrical resistivity of the reservoir)

Well testing (e.g. determination of the flow behaviour)

Information from the formation evaluation will determine the extent of thereservoir and provide an estimate of the amount of oil available and the

difficulty in obtaining the oil. The preliminary feasibility of the reservoir

can be determined from this information. The results also guide the work

of the other disciplines in determining the most effective method to

produce oil from the field.

Introduction/Petroleum Engineering

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2) Drilling Engineering

Objective:

Determine the optimum approach to create an oil well.

Plan and execute the drilling process and all related activities

such as well logging, cementing, completion, stimulation.

Responsibilities also include the design of networks of horizontal wells.

A key concern of the drilling engineer is to limit the extent of wellbore

damage during drilling.


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3) Reservoir Engineering

Objective: Determine the best method to operate all the wells in the

oil field using:

Well testing

Material balance

Reserve estimation update

Stimulation

This work involves modelling the entire oil field. There are a number of

modeling and simulation software in the market.


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4) Production Engineering

Objective: Determine the best method to operate individual wells

using:

Well testing

Well work-over

Stimulation

Artificial lift

The production engineer must obtain the maximum production from oneor more wells at the minimum cost.


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Identify the type of engineering work in each video.

http://www.youtube.com/watch?v=vSTLyEC6QqM

http://www.youtube.com/watch?v=c83CvjQ6nYE

http://www.youtube.com/watch?v=RX4jHN4Fu-k
http://www.youtube.com/watch?v=vSTLyEC6QqMhttp://www.youtube.com/watch?v=c83CvjQ6nYEhttp://www.youtube.com/watch?v=RX4jHN4Fu-khttp://www.youtube.com/watch?v=RX4jHN4Fu-khttp://www.youtube.com/watch?v=RX4jHN4Fu-khttp://www.youtube.com/watch?v=c83CvjQ6nYEhttp://www.youtube.com/watch?v=vSTLyEC6QqM

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Petrochemical Engineering - Petroleum Entrapment

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