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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.
1
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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
2
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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
5
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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.
Introduction/Origin of petroleum/conversion
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Conversion (Effect of temperature):
Introduction/Origin of petroleum/conversion
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.
Conversion (Effect of temperature):
Introduction/Origin of petroleum/conversion
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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)
Introduction/Origin of petroleum/Entrapment
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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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.
Introduction/Origin of petroleum/Entrapment
http://www.drillingfunds.com/common_traps.html
Surface gravel
LimestoneSandstone
Salt
Shale
Oil
Gas
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Structural trap (Thrust fault)
Introduction/Origin of petroleum/Entrapment
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.
Introduction/Origin of petroleum/Entrapment
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
Introduction/Origin of petroleum/Entrapment
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Stratigraphic trap (pinch out)
Introduction/Origin of petroleum/Entrapment
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)
Introduction/Origin of petroleum/Entrapment
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/Origin of petroleum/Entrapment
Introduction to Oil and Gas Production, API, Dalla, Texas, 1983, 4.
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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.
Introduction/Origin of petroleum/Entrapment
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Introduction/Origin of petroleum/Entrapment
http://www.carbonet.net/bjarne/Stoupakova%20et%20al%202006.swf
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23DIFFERENTIAL TRAPPING OF HYDROCARBONS, WM. C. GUSSOW. CONSULTANT.
Introduction/Origin of petroleum/Entrapment
C.4. Differential Traps:
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Introduction/Origin of petroleum/Entrapment
C.4. Differential Traps:
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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25
Introduction/Origin of petroleum/Entrapment
C.4. Differential Traps:
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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Introduction/Origin of petroleum/Entrapment
C.4. Differential Traps:
Stage 3
Gas spills up dip as more gas enters trap. Oil by-passes the
trap and continues up dip.
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Introduction/Origin of petroleum/Entrapment
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.
Introduction/Petroleum Engineering
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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.
Introduction/Petroleum Engineering
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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.
Introduction/Petroleum Engineering
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Introduction/Petroleum Engineering
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