assignment 200
Assessment Tool
School/ Department Name School of Engineering/ Petroleum Engineering
Program Code and Title: BEPF15 – Degree of Petroleum Engineering
Course Code and Title: 151PTE 321 – Engineering Geology
Assessment Number and Title: Assessment 3 – Assignment # 1
Assessment Type: Written Assignment
Assessment Location: ACK – Online Submission
Assessment Date: Saturday 9th January, 2021
Assessment Time/Duration: Due: Monday 11th January, 2021 at 11:55 PM
Student Name:
Student ID:
Section (s): G2P1, G2P2
Assessment General
Instructions:
• This is a calculation based project and you may use the class material such
as your lecture notes, online resource, and software such as excel (if
needed).
• You may not discuss or share this project or questions related to the project
with your fellow classmates or other individuals.
• Show your work, you may scan your hand work or insert calculation steps
in this document.
• Please type your answers using Microsoft Words and ensure to type your
equations correctly.
• If you require any assistance during the assessment period, please
communicate through e-mail or MS Teams.
DO NOT WRITE IN THE AREA BELOW
Task Number Maximum Marks Student Marks
1 1.5
2 4
3 1.25
4 1.25
5 2
6 2.5
7 2.5
Total Mark 15
Assessor Feedback:
Assessor Name: Dr. Seyed Mehdi Seyed Alizadeh
Date:
Assessor Signature:
Student Name:
Date:
Student Signature:
Assessment Tool
Task 1:
(1.5 Marks)
What are the processes that are responsible for the marine transgression and regression?
Assessment Tool
Task 2: (4 Marks)
The matrix in figure below is a set of measurements for water saturations (in % points) at
different locations in a reservoir rock formation. The data are plotted on a regular grid with both
horizontal (x) and vertical (y) distance of 1 between neighbouring points of measurement.
a) Write down the general equation for variogram calculation.
(1 Mark)
Assessment Tool
b) Calculate the experimental variogram for horizontal (x or 0°), vertical (y or 90°) and for the
diagonal (45°) direction for the shortest possible nonzero distance in each case.
(3 Marks)
Assessment Tool
Task 3: (1.25 Marks)
Match the following typical deposition with the corresponding basin name. The correspondence is one-
to-one.
RIFT FORELAND
FLEXUR
E
PROTO
OCEANIC
THROUGHS
STAGE
PASSIVE
MARGINS
FOREARC
REGION
Evaporite
s
River
and
Lake
Deposits
Shallow
Marine
and
Clastic
Deposits
Arc
related
volcanics
Deeper
Water
Facies
Assessment Tool
Task 4: (1.25 Marks)
Match the following typical sediments sources with the corresponding basin name. The
correspondence is one-to-one.
RIF
T
OCEAN
BASINS
INTRACRATONIC
BASINS
PASSIVE
MARGINS
ACCRETIONARY
COMPLEXES
Sediments are supplied
from rivers.
Fluvial and lacustrine
sediments.
The clastic sediment
supply is largely
from the adjacent
continental land area.
In the deeper parts
sedimentation is
mainly pelagic,
consisting of fine-
grained biogenic
detritus and clays.
In some places sediments
are carried down the
subduction zone.
Assessment Tool
Task 5: (2 Marks)
Draw a correlation for the three geologic sequences shown in the three locations in Figure 1 using the
fossils to establish the relative age for each sequence.
Outcrops at three different locations
Assessment Tool
Task 6: (2.5 Marks)
In the geologic sequence shown in Figure 1 establish the right time sequence of the five formations,
from the oldest to the youngest.
A
B
E
C D
Assessment Tool
Task 7: (2.5 Marks)
The coefficient of variation for permeability for several core plugs from different rock
formations are as follows:
Rock
Type
Coef. Of
variation of
Permeability
Degree of heterogeneity
Homogeneous Heterogeneous Highly
Heterogeneous
A 0.75
B 1.1
C 0.34
D 1.8
E 0.21
F 0.83
(a) In the table above, specify the degree of heterogeneity for each rock type by a (x) sign in
front of the correct choice.
(1.5 Marks)
(b) Explain why you have selected the choices for the previous part.
(1 Mark)
151PTE321
Engineering Geology
Lecture 6
Learning Outcomes
After completing this chapter the student will:
• familiarize himself with common types of sedimentary basins and their
formation;
• learn the relationship between the formation of sedimentary basins and
tectonics;
• familiarize himself with the different kind of sedimentary rocks deposited in
different sedimentary basins;
• learn what are the most favorable sedimentary basins for O&G
accumulations.
Sedimentary Basins
• Sedimentary basins are regions where sediment accumulates into
successions of hundreds to thousands of metres in thickness over areas of
thousands to millions of square kilometres.
• The underlying control on the formation of sedimentary basins is plate
tectonics and hence basins are normally classified in terms of their position
in relation to plate tectonic settings and tectonic processes.
• Each basin type has distinctive features, and the characteristics of
sedimentation and the stratigraphic succession that develops in a rift valley
can be seen to be distinctly different from those of an ocean trench.
• The sedimentary rocks in a basin provide a record of the tectonic history
of the area.
• They also provide the record of the effects of other controls on deposition,
such as climate, base level and sediment supply.
Sedimentary Basins
Three main settings of basin formation can be recognized:
1. basins associated with regional extension within and between plates;
2. basins related to convergent plate boundaries;
3. basins associated with strike-slip plate boundaries.
Basins Related to Lithospheric Extension
• The motion of tectonic plates produces in some areas the extension of the
lithosphere and in other places compression.
• In the early stages of extension Rifts form and are typically sites of
continental sedimentation.
Sedimentary Basins
Rift Basins
• In regions of extension
continental crust fractures to
produce rifts, which are structural
valleys bound by extensional
(normal) faults.
• The down-faulted blocks are
referred to as graben and the up-
faulted areas as horsts.
• The structural weakness in the
crust and high heat flow
associated with rifting may result
in volcanic activity.
• Sediment is supplied from the
rift flanks or brought in by rivers
flowing along the axis of the rift.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Rift Basins
• In regions of extension
continental crust fractures to
produce rifts, which are
structural valleys bound by
extensional (normal) faults.
• The down-faulted blocks are
referred to as graben and the
up-faulted areas as horsts.
• The structural weakness in the
crust and high heat flow
associated with rifting may result
in volcanic activity.
• Sediment is supplied from the
rift flanks or brought in by rivers
flowing along the axis of the rift.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Intracratonic Basins
• These are areas of broad
subsidence within a
continental block (craton)
away from plate margins or
regions of orogeny.
• Rifts are therefore areas of
high heat flow, a high
geothermal gradient.
• When geothermal gradient is
reduced the crust cools,
contracts and sinks
resulting in thermal
subsidence.
• Fluvial and lacustrine
sediments are commonly
encountered in intra-cratonic
basins.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Proto-oceanic troughs
• As the extension of the continental
crust continues this leads to
thinning and eventually to rupture.
• Basaltic magmas rise to the
surface in the axis of the rift and
start to form new oceanic crust.
• The basin will be wholly or partly
flooded by seawater.
• Rivers will be depositing
sediment to shelf areas and out into
deeper water in the axis of the
trough as turbidity currents.
• Connection to the open ocean may be intermittent during the early stage of
basin formation and in arid areas with high evaporation rates the basin may
periodically desiccate. Evaporites (gypsum or halite) may form in these
circumstances.
• This stage is known as a ‘proto-oceanic trough’ and is the first stage in the
initiation of an ocean basin: the remnant flanks of the rift become the passive
margins of the ocean basin as it develops.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Passive margins
• The regions of continental crust
and the transition to oceanic
crust along the edges of
spreading oceans basins are
known as passive margins.
• Passive because no subduction is
happening in this region.
• The continental crust is
commonly thinned in this region
and there may be a zone of
transitional crust before fully
oceanic crust of the ocean basin
is encountered. Transitional crust
forms by basaltic magmas
injecting into continental crust in a
diffuse zone as a proto-oceanic
trough develops.
• Subsidence of the passive margin is due
to continued cooling of the lithosphere as
the heat source of the spreading centre
becomes further away, augmented by
the load on the crust due to the pile of
sediment that accumulates.
• The clastic sediment supply is largely
from the adjacent continental land area.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Stages in the Development of a Passive Margin
Sedimentary Basins
Passive margins
• The supply of clastic sediments will be low in areas adjacent to desert
areas, and the margin will be a starved margin, experiencing a low clastic
sedimentation rate.
• In contrast, a large river system may carry large amounts of detritus and
build out a large deltaic wedge of sediment onto the margin.
• In the absence of terrigenous detrital supply, the shelf may be the site of
accumulation of large amounts of biogenic carbonate sediment, although
the volume and character of the material will be determined by the local
climate.
• Passive margins are important areas of accumulation of both carbonate
and clastic sediment: they may extend over tens to hundreds of
thousands of square kilometres and develop thicknesses of many
thousands of metres.
• They are also areas that are sensitive to the effects of eustatic changes
in sea level because most of the deposition occurs in water depths of up
to 100 m.
Detailed Cross-section of a Passive Margin
Atlantic Margin
Triassic rift valley sediments
Jurassic salt
Cretaceous &
Cenozoic sediments
What is the relative
age of the basalt?
Sedimentary Basins
Ocean basins
• Basaltic crust formed at mid-oceanic ridges is hot and relatively buoyant.
• As the basin grows in size by new magmas created along the spreading
ridges, older crust moves away from the hot mid-ocean ridge.
• Cooling of the crust increases its density and decreases relative
buoyancy, so as crust moves away from the ridges, it sinks.
• Mid-ocean ridges are typically at depths of around 2500 m.
• The depth of the ocean basin increases away from the ridges to between
4,000 and 5,000 m where the basaltic crust is old and cool.
• The ocean floor is not a flat surface. Spreading ridges tend to be irregular,
offset by transform faults that create some areas of local topography.
• Isolated volcanoes and linear chains of volcanic activity related to
hotspots (mantle plumes) such as the Hawaiian Islands form submerged
seamounts or exposed islands.
Sedimentary Basins
Ocean basins
• The shallow water environment may be a site of carbonate production
and the formation of reefs.
• In the deeper parts of the ocean basins sedimentation is mainly pelagic,
consisting of fine-grained biogenic detritus and clays. Nearer to the
edges of the basins terrigenous clastic material may be deposited as
turbidites.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Basins Related to Subduction
• A trough is created at the contact between the two plates as the downgoing plate
bends to enter the subduction zone : this is the ocean trench.
• The magmas generated by the melting of the subducted plate rise to the surface
through the overriding plate to create a line of volcanoes, or volcanic arc.
• Magma is created when the down going slab reaches 90 to 150 km depth.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Basins Related to Subduction
• Arc–trench systems are regions of plate convergence, however, the upper plate of
an active arc must be in extension in order for magmas to reach the surface and
generate volcanic activity.
• If the angle of subduction is steep then convergence is slower than subduction at
the trench, the upper plate is in net extension and an extensional backarc basin
forms (Dickinson 1980).
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Trenches
Ocean trenches are elongated, gently curving troughs that form where an oceanic plate
bends as it enters a subduction zone.
The bottoms of modern trenches are up to 10,000m below sea level, twice as deep as
the average bathymetry of the ocean floors.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Accretionary Complexes
A subducting plate can be thought of as a conveyor belt bringing ocean basin
deposits, mainly pelagic sediments and turbidites, to the edge of the
overriding
plate.
In some places this sediment is carried down the subduction zone, but in
others it is sliced off as a package of strata that is then accreted on to the
overriding plate.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Forearc Basin
The main source of sediment to the basin is the volcanic arc and, if the arc
lies in continental crust, the hinterland of continental rocks.
Intraoceanic arcs are commonly starved of sediment because the island-arc
volcanic chain is the only source of detritus apart from pelagic sediment.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Backarc Basin
• Extensional backarc basins form where the angle of subduction of the
downgoing slab is steep and the rate of subduction is greater than the rate
of plate convergence.
• Rifting occurs in the region of the volcanic arc where the crust is hotter
and weaker.
• The principal source of sediment in a backarc basin formed in an oceanic
plate will be the active volcanic arc.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Basins related to Crustal Loading
Collision of plates involves a thickening of the lithosphere and the creation
of an orogenic belt, a mountain belt formed by collision of plates.
The Alps have formed by the closure of the Tethys Ocean as Africa has
moved northwards relative to Europe, and the Himalayas are the result of a
series of collisions related to the northward movement of India.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Basins related to Crustal Loading
Thickening of the crust will result in an additional load being placed on the
crust either side and causes a downward flexure of the crust to form
peripheral foreland basins.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Retroarc Foreland Basin
The thickness of the crust increases due to emplacement of magma in a
volcanic arc at a continental margin, resulting in flexure of the crust behind
the arc to form a retroarc foreland basin.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Strike-slip basins
• Most basins in strike-slip belts are
generally termed trans-tensional
basins.
• The overlap of two separate faults
can create regions of extension
between them known as pull-apart
basins.
• Such basins are typically rectangular
or rhombic in plan with widths and
lengths of only a few kilometres or
tens of kilometres.
• They are unusually deep, especially
compared with rift basins.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Strike-slip basins
Where there is a branching of faults a zone of extension exists between the
two branches forming a basin.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
The Wilson Cycle
Rift basins form
and evolve into proto-
oceanic troughs and
eventually into ocean
basins bordered by
passive margins. After
a period of tens to
hundreds of millions of
years the ocean basin
starts to close with
subduction zones
around the margins
consuming oceanic
crust. Final closure of
the ocean results in
continental collision
and the formation of
an
orogenic belt.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
The Wilson Cycle
Rift basins form
and evolve into proto-oceanic
troughs and eventually into
ocean basins bordered by
passive margins. After
a period of tens to hundreds of
millions of years the ocean
basin starts to close with
subduction zones
around the margins consuming
oceanic crust. Final closure of
the ocean results in
continental collision
and the formation of an
orogenic belt.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
The Wilson Cycle
Within the Wilson Cycle,
• Rift basin: may be recognized by river and lake deposits overlying the
basement,
• Proto-oceanic trough stage: recognized by evaporites,
• Passive margin deposition: will be recorded by thick succession of shallow-
marine carbonate and clastic deposits.
• Forearc region: If this passive margin becomes a site of subduction, arc-
related volcanics will occur as the margin is transformed into a forearc
region of shallow-marine, arc-derived sedimentation.
• Upon complete closure of the ocean basin, loading by the orogenic belt may
then result in foreland flexure of this same area of the crust, and the
environment of deposition will become one of deeper water facies.
• As the mountain belt rises, more sediment will be shed into the foreland
basin and the stratigraphy will show a shallowing-up pattern.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
The Major Types of Sedimentary Basins
The major types of sedimentary basins are shown in their plate-tectonic settings.
The major physical cause or causes of subsidence for each case are shown below
the diagram. Some examples are indicated in top.
Michigan Basin
E. AfricaNevada
Offshore Calif.
Indonesia
E. Coast NA
Sedimentary Basins
Strike-slip basins
The curvature of a single fault strand results in bends that are either
restraining bends (locally compressive) or releasing bends (locally
extensional): releasing bends form elliptical zones of subsidence.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Forearc Basin
The inner margin of a forearc basin is the edge of the volcanic arc and the
outer limit the accretionary complex formed on the leading edge of the upper
plate.
The basin may be underlain by either oceanic crust or a continental margin.
The thickness of sediments that can accumulate in a forearc setting is partly
controlled by the height of the accretionary complex: if this is close to sea
level the forearc basin may also fill to that level.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Trenches
They are also narrow, sometimes as little as 5 km across, although they may
be thousands of kilometres long.
Trenches formed along margins flanked by continental crust tend to be filled
with sediment derived from the adjacent land areas. Intra-oceanic trenches
are often starved of sediment because the only sources of material apart from
pelagic deposits are the islands of the volcanic arc.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
Sedimentary Basins
Basins related to Crustal Loading
When an ocean basin completely closes with the total elimination of
oceanic crust by subduction the two continental margins eventually
converge.
Where two continental plates converge subduction does not occur
because the thick, low-density continental lithosphere is too buoyant to be
subducted.
from G. Nichols, “Sedimentology and Stratigraphy”, 2009
151PTE321/GEOL2101
Engineering Geology
Lecture 9
Dr. Seyed Mehdi Seyed Alizadeh
Heterogeneity
Definition
• Formation with two or more non-communicating
sand members.
• Different specific- and relative-permeability
characteristics.
• The reservoir heterogeneity is defined as a
variation in reservoir properties as a function of a
space.
• Oil/Gas reservoirs are complicated geological
heterogeneous bodies.
• There is no homogeneous porous media.
• Well log and core analysis reports show that all
reservoirs are heterogeneous.
• Permeability heterogeneities cause variations in
the fluid movements compared to the equivalent
homogeneous system.
• Efficiency management (RF).
http://www.google.com.kw/url?sa=t&rct=j&q=&esrc=s&source=web&cd=20&ved=0CFsQFjAJOAo&url=http%3A%2F%2Fcaos.fs.usb.ve%2F~srojas%2FVI_
CCFD%2Fpapers%2Ffpm%2FRDawe &ei=H61FU9bzMqqCyAOl6oGwCA&usg=AFQjCNHThSj_QfQoMcpB8ONwRB5E3xujOA&bvm=bv.64507335,d.
bGQ
Reservoir Heterogeneity in Sandstone
Heterogeneity May
Result From:
Depositional Features
Diagenetic Features
(Whole Core Photograph, Misoa
Sandstone, Venezuela)
Heterogeneity
Segments Reservoirs
Increases Tortuosity of
Fluid Flow
Reservoir Heterogeneity in Sandstone
Heterogeneity Also May
Result From:
Faults
Fractures
Faults and Fractures may
be Open (Conduits) or
Closed (Barriers) to Fluid
Flow
(Whole Core Photograph, Misoa
Sandstone, Venezuela)
Scales of Geological Reservoir Heterogeneity
F
ie
ld
W
id
e
In
te
rw
e
ll
W
e
ll
-B
o
re
(modified from Weber, 1986)
Hand Lens or
Binocular Microscope
Unaided Eye
Petrographic or
Scanning Electron
Microscope
Determined
From Well Logs,
Seismic Lines,
Statistical
Modeling,
etc.
10-
100’s
m
m
10-100’s
mm
1-
10’s
m
100’s
m
10’s
m
1-10 km
100’s m
Well Well
Interwell
Area
Reservoir
Sandstone
Scales of Investigation Used in
Reservoir Characterization
Gigascopic
Megascopic
Macroscopic
Microscopic
Well Test
Reservoir Model
Grid Cell
Wireline Log
Interval
Core Plug
Geological
Thin Section
Relative Volume
1
10
14
2 x 10
12
3 x 10
7
5 x 10
2
300 m
50 m
300 m
5 m 150 m
2 m
1 m
cm
mm – mm
(modified from Hurst, 1993)
& Seismic
Primary objective of geological characterization is
concerned with predicting the spatial variation of geological
variables.
Variable :
• is any property of the geological subsurface that exhibits
spatial variability and can be measured in terms of real
numerical values.
Spatial Variation:
• Typically the subsurface is anisotropic, spatially complex
and sedimentary bodies are internally heterogeneous.
Geological Modeling
Reservoir Characterisation
• Modern reservoir characterisation started around 1980:
• Reason: deficiency of oil recovery techniques (inadequate
reservoir description)
• Aim: predict inter-well distributions of relevant properties (φ, K)
• Subsurface (inter-well) heterogeneity cannot be measured:
• Seismic data (large support, low resolution)
• Well data (small support, high resolution)
• Complementary sources of information:
• Geological models
• Statistical models
• Combine data and models ‘static’ reservoir model
Static reservoir models
• Reservoir geology is the science (art?) of building
predictive reservoir models on the basis of geological
knowledge (= data, interpretations, models)
• A reservoir model depicts spatial variation of lithology
(porosity and permeability): “static” model
• Simulations of multi-phase flow (“dynamic” models)
require high-quality “static” reservoir models
• Static reservoir models are improved through analysis
of dynamic data: iterative process
Geological Modeling: different tracks
Static
Reservoir Model
Reservoir Data
Seismic, borehole and wirelogs
Sedimentary
Process Model
Stochastic ModelDeterministic
Model
Data-driven modeling Process modeling
Flow Model
Upscaling
14
Geological model
•Elements of the
geological model:
1. Bounding surfaces
2. Distributions of
physical properties
between surfaces
3. Faults
4. OWC, GWC, GOC
5. Conditioned to well
data ?
15
Why is geological modeling difficult
• The output of many natural systems exhibits apparent
randomness, which is usually caused by extreme sensitivity to
initial conditions. Initial conditions and physical laws of such
systems cannot be inferred from the output.
• Measurements are a finite sample of the output (all possible
realisations of the system).
• Statistical models may be used to describe such
measurements in the absence of a physical model.
• Geological modeling software (a worst-case scenario):
• Designed by statisticians who know little about geology
• Applied by geologists / engineers who know little about
statistics
• Many things can and will go wrong !
16
Upscaling issues
• In addition to the natural scales of heterogeneity in the
system and the scale of the measurements, there is also the
scale of the discrete elements (grid blocks) in a reservoir
model.
• Upscaling measurements to grid-block scale is a critical
issue in geological modeling and the object of active
research
• Common errors in numerical reservoir models:
• Discretisation errors
• Upscaling errors
• Input errors
• Geological modeling aims at minimizing these
errorsrrorsnput errors to
improve reservoir-model performance
151PTE32
1
Engineering Geology
Lecture 8
Learning Outcomes
At the end of this chapter the student will be able to:
• Learn about the concept of Petroleum System;
• Understand the process of Oil and Gas generation;
• Recognize the different elements of a Petroleum System;
• Recognize the different kind of hydrocarbons generated by the source rock;
• Recognize the different kind of environments needed for the generation of
hydrocarbons;
Disclaimer:
These notes are not intended to cover all the necessary knowledge for a Petroleum Geology course for engineering students. The notes were
created with the intention of serving as a guide and summary on the subject. For more detail it is recommended that the student consults any of
the textbooks recommended by the instructor.
Petroleum Systems
Elements
Source Rock
Migration
Route
Reservoir
Rock
Seal Rock
Trap
Processes
Generation
Migration
Accumulation
Preservation
A Petroleum System requires that certain geologic factors and geologic events
happen at coordinated times.
Geological conditions and geochemical
processes
1. Occurrence of source rocks which generate petroleums under proper
subsurface temperature conditions.
2. Sediment compaction leading to expulsion of petroleum from the source
and into the reservoir rocks (primary migration).
3. Occurrence of reservoir rocks of sufficient porosity and permeability
allowing flow of petroleum through the pore system (secondary migration).
4. Structural configurations of sedimentary strata whereby the reservoir
rocks form traps, i.e. closed containers in the subsurface for the
accumulation of petroleum.
5. Traps are sealed above by impermeable sediment layers (cap rocks) in
order to keep petroleum accumulations in place.
6. Correct timing with respect to the sequence by which the processes of
petroleum generation/migration and trap formation have occurred during
the history of a sedimentary basin.
7. Favorable conditions for the preservation of petroleum accumulation
during extended periods of geologic time, i.e. absence of destructive, such
as the fracturing of cap rocks leading to dissipation of petroleum
accumulations, or severe heating resulting in the cracking of oil into gas.
modified from Magoon and Dow, 1994
Source Rocks
• Most major source rocks are fine grained, clay-rich siliciclastic rocks
(mudstones and shales) and biogenic limestone’s. Coal may also be
considered as a source rock, even though it is present in relatively small
quantities within the earth when compared to shale’s and biogenic
limestone’s.
• Hydrocarbon originates from micro organisms in seas and lakes. When
they die, they sink to the bottom where they form organic-rich “muds” in
fine sediments.
• In subaerial environments organic matter is readily destroyed by
chemical and microbial oxidation shortly after deposition.
• Good quality petroleum source rocks can be deposited in marine or lake
environments as organic-matter-rich muds providing that bottom waters are
oxygen-deficient, i.e. that reducing conditions prevail.
Plankton (singular plankter) are the diverse collection of organisms that
live in large bodies of water and are unable to swim against a current.
They provide a crucial source of food to many large aquatic organisms,
such as fish and whales (wikipedia).
PLANKTON
These organisms include bacteria, archaea, algae, protozoa and
drifting or floating animals that inhabit—for example—the pelagic zone of
oceans, seas, or bodies of fresh water. Essentially, plankton are defined
by their ecological niche rather than any phylogenetic or taxonomic
classification.
Though many planktonic species are microscopic in size, plankton
includes organisms over a wide range of sizes, including large
organisms such as jellyfish. Technically the term does not include
organisms on the surface of the water, which are called pleuston – or
those that swim actively in the water, which are called nekton.
PLANKTON
PLANKTON Distribution
A schematic showing the abundance of plankton in the oceans. The schematic was based on
an image in the book “Waardeer de oceanen” by Lawrence Williams. Plankton is a fish feed
giving an indication of the richness of fish species and their numbers in that part of the ocean.
It is an ocean fertiliser natural in origin (eg unlike others as ammonium-nitrate). Its variation
in abundance shows what parts of the ocean are in more need of protection. Plankton is
richer near land surfaces (trough soil runoff carrying nutrients) It is especially rich near
river mouths.
Source Rocks
• If the concentration of oxygen dissolved in these waters is less than 0.1
ml/l the environment is referred to as anaerobic,
• If it is in the range of 0.1-1.0 ml/l the environment is referred to as
dysaerobic
• If higher oxygen concentrations prevail, the environment is known as
oxic.
• Anaerobic or dysaerobic environments require stagnant water
conditions, because turbulent water circulation results in the replenishment
of oxygen contents.
• A petroleum source is characterized by three essential conditions: it must
have a sufficient content of finely dispersed organic matter of biological
origin; this organic matter must be of a specific composition, i.e.
hydrogen-rich (reducing environment, strips oxygen from sediments);
and the source rock must be buried at certain depths and subjected to
proper subsurface temperatures in order to initiate the process of
petroleum generation by the thermal degradation of kerogen.
Source Rocks
• The sediments are compacted to form organic-rich rocks with very low
permeability.
• With increasing depth, temperature increases, geologic time passes,
and chemical action occurs, converting the organic debris into
hydrocarbons.
• In most geologic situations, the resultant hydrocarbons formed have been
forced out of the sediments during lithification.
• The hydrocarbon can migrate very slowly to nearby porous rocks,
displacing the original formation water.
Models of Deposition of Organic Matter
• There are three basic depositional scenarios which ensure favorable
conditions for the preservation of organic matter.
• The depositional system of the so called stagnation model requires a
restricted basin, i.e. a marine basin which has highly restricted water
circulation with the open ocean. This is the case today, e.g. of the Black Sea
which is up to 2,500 m deep but only has a narrow 25 m deep connection to the
Mediterranean Sea.
from D Leythaeuser, “Encyclopaedia of Hydrocarbons”
Models of Deposition of Organic Matter
• The second principal depositional system in this context is the so-called
productivity model. In certain areas of today’s world oceans, nutrient-rich
bottom water currents upwell across the shelf edges from deep parts of the
continental slopes. When they reach the near-surface interval penetrated by
sun light (photic zone), a massive growth of marine algae occurs
(phytoplanctonic blooms). Enormous quantities of algal biomass are produced
by this photosynthetic activity. This is the basis of the marine food chain, i. e.
algae are eaten by zooplankton which in turn are eaten by fish, etc.
from D Leythaeuser, “Encyclopaedia of Hydrocarbons”
• Currents of water masses of higher density originate in Arctic and Antarctic
oceanic realms and flow along the deep ocean topography towards lower
latitudes.
• Wherever they encounter major topographic elevations they displace
nutrient-rich bottom water masses towards the surface of the ocean. In this
way, a series of processes and effects are initiated which are similar to those
in the upwelling regime leading to the establishment of an open-ocean
oxygen-minimum zone. Wherever this oxygen minimum zone impinges on a
continental shelf, organic matter-rich sediments are deposited.
Models of Deposition of Organic Matter
from D Leythaeuser, “Encyclopaedia of Hydrocarbons”
Models of Deposition of Organic Matter
• All the depositional environments of marine and freshwater systems can also
receive an input of organic matter derived from higher land plants
transported by rivers or glaciers, or wind-blown.
• In contrast to algal or bacterial biomass which is rich in hydrogen, land
plant-derived organic matter tends, due to high contributions by cellulose
and lignin-derived precursor materials, to be rich in oxygen.
from D Leythaeuser, “Encyclopaedia of Hydrocarbons”
• The great variety of kerogens occurring
in nature can be classified into three
broad categories referred to as type I-,
type II- and type III-kerogens (Tissot
and Welte, 1984).
• The high H/C-ratio of type I-kerogens,
goes back to a high input of algae and
bacterial biomass.
• The elevated H/C-ratio of type II-
kerogens is mostly derived from a high
contribution of algal biomass.
Models of Deposition of Organic Matter
from D Leythaeuser, “Encyclopaedia of Hydrocarbons”
• It is the relative abundance of each of
these organic materials which
determines whether the resulting source
rock will generate predominantly oil or
gas upon burial.
• The solid organic matter in source rocks
which is insoluble in low-boiling organic
solvents is called kerogen.
Models of Deposition of Organic Matter
• Kerogens of type III, in contrast, have high O/C- and low H/C-ratios.
• The elevated oxygen content, is either due to a high input of higher land
plants, which are always rich in cellulose and lignin-derived structures, or to
the deposition of any kind of organic matter derived from marine organisms
under dysaerobic to oxic environments.
• Most prolific source rocks for oil have type II-kerogens.
• Type I-kerogens are rare in terms of worldwide occurrence and mostly
restricted to oil shales (rocks which do not contain oil, but high concentrations
of kerogen, which yield oil artificially when the rock is heated to 500°C in an
inert atmosphere).
• Source rocks bearing type III-kerogen generate little oil but more gas and
condensate upon exposure to proper subsurface temperatures.
Organic Matter in Sedimentary Rocks
• Based on empirical evidence, minimum concentration levels of 1.5% and
0.5% total organic carbon (TOC) in source rocks of siliclastic and carbonate
lithologies respectively have been established (Hunt, 1996).
• The organic carbon concentration is an approximate measure of the organic
matter content of a rock.
• Organic matter is predominantly composed of organic carbon, but also
contains minor amounts of N, S, and O.
• This minimum concentration of organic carbon in source rocks is controlled by
the relationship between the quantity of petroleum generated and the
internal storage capacity of the rocks in terms of their porosity.
• If too little organic matter is present, the small quantities of petroleum
generated will not exceed the storage capacity of the rock, i.e. no petroleum
expulsion will take place.
Interpretation of Total Organic Carbon (TOC)
Hydrocarbon
Generation
Potential
TOC in Shale
(wt. %)
TOC in Carbonates
(wt. %)
Poor 0.0-0.5 0.0-0.2
Fair 0.5-1.0 0.2-0.5
Good 1.0-2.0 0.5-1.0
Very Good 2.0-5.0 1.0-2.0
Excellent >5.0 >2.0
The reason why petroleum source rocks of carbonate lithologies tend
to have significantly lower TOC concentrations has to do with the quality
and composition of the organic matter present. In carbonate source
rocks, the organic matter tends to be richer in hydrogen.
Temperature window for Hydrocarbon Generation
Sea level
Depth in feet
-5,000
-10,000
-15,000
Oil window
Gas
formed
only
50
Temperature oF
662
104
• In order for hydrocarbons
to be generated from
organic deposition,
temperatures must rise
above 104ºF (40ºC) but not
exceed 662ºF (350ºC).
• Higher temperatures will
destroy any remaining
organic materials or
hydrocarbons already
generated.
• In order for hydrocarbons
to be generated, a proper
sequence of geologic
events and conditions must
occur.
Hydrocarbon Migration
from “Petroleum Geology”, Schlumberger.
Hydrocarbon migration takes place in two stages:
Primary migration – from the source rock to a porous rock. This is a complex
process and not fully understood. It is probably limited to a few hundred metres.
Secondary migration – along the porous rock to the trap. This occurs by
buoyancy, capillary pressure and hydrodynamics through a continuous water-
filled pore system. It can take place over large distances.
Reservoir Rock
The term “reservoir” implies storage.
Reservoir rock is rock where hydrocarbons are stored and from which they can
be produced.
This reservoir rock may or may not be source rock.
The fluids of the subsurface migrate according to density.
The dominant fluids in hydrocarbon regions are hydrocarbon gas,
hydrocarbon liquids, and salt water.
Since hydrocarbons are the less dense of these fluids, they will tend to migrate
upward, displacing the heavier salt water down elevation.
Hydrocarbons may therefore be forced from their source rock during
lithification, and migrate into the reservoir rock in which they are stored.
The fluids present will separate according to density as migration occurs.
In order for a rock to be a potential reservoir rock, two properties, porosity and
permeability, must exist of sufficient magnitudes to justify economic
development of the hydrocarbon reservoir.
Basic Geological Conditions that Create
Petroleum Traps
• Hydrocarbon traps are any combination of physical factors that
promote the accumulation and retention of petroleum in one location.
• Traps can be structural, stratigraphic, or a combination of the two.
• Geologic processes such as faulting, folding, and deposition and
erosion create irregularities in the subsurface strata which may cause
oil and gas to be retained in a porous formation, thereby creating a
petroleum reservoir.
• The rocks that form the barrier, or trap, are referred to as caprocks.
Down figure illustrates the basic morphology and terminology of an
anticlinal trap.
Note also that the gross pay is the vertical thickness from the top
of the reservoir to the oil-water contact.
Basic Parameters of a Trap
from “Petroleum Geology”, Prof. Farooq Shareef
• Structural traps are due to post-depositional tectonic processes (e.g., folds
and faults).
• Structural traps are created by the deformation of rock strata within the earth’s
crust. This deformation can be caused by horizontal compression or tension,
vertical movement and differential compaction, which results in the folding,
tilting and faulting within sedimentary rock formations.
• Stratigraphic traps are due to syn-depositional sedimentary processes (reefs)
or post-depositional diagenetic ones (dolomitization).
• Hydrodynamic traps are caused by flowing water.
Classification of Hydrocarbon Traps
Structural Traps
There are three main types of structural traps. One type is the anticline, or
upfold of rock. These are
illustrated in Figure.
Diagrams depict compressional and compaction anticlines.
from “Petroleum Geology”, Prof. Farooq Shareef
Structural Traps
Anticlinal and Dome Trap
The rock layers in an anticlinal trap were originally laid down horizontally then
folded upward into an arch or dome. Later, hydrocarbons migrate into the porous
and permeable reservoir rock. A cap or seal (impermeable layer of rock) is required
to permit the accumulation of the hydrocarbons.
from “Basic Petroleum Geology and Log Analysis”, Halliburton, 2001
Structural Traps
A second type of structural trap is the fault trap, where porous, permeable
reservoir beds are faulted against impermeable beds. Some fault planes seal,
others act as permeable conduits. These are illustrated in Figure.
from “Petroleum Geology”, Prof. Farooq Shareef from “Basic Petroleum Geology and Log Analysis”, Halliburton, 2001
Structural Traps
The third type is the growth fault, which shows sediment thickening on the
downthrown side. These are illustrated in Figure.
Diagrams depicts a growth fault with associated rollover anticline.
from “Petroleum Geology”, Prof. Farooq Shareef
Hydrodynamic Traps
The downward flow of water in a permeable bed may cause oil to be trapped in
flexures which lack vertical closure. This is a type of pure hydrodynamic trap,
illustrated in Figure.
Cross section to illustrate oil trapped hydrodynamically by flowing water.
from “Petroleum Geology”, Prof. Farooq Shareef
A trap created by piercement or
intrusion of stratified rock layers from
below by ductile nonporous salt.
The intrusion causes the lower
formations nearest the intrusion to
be uplifted and truncated along the
sides of the intrusion, while layers
above are uplifted creating a dome
or anticlinal folding.
Hydrocarbons migrate into the
porous and permeable beds on the
sides of the column of salt.
Hydrocarbons accumulate in the
traps around the outside of the salt
plug if a seal or cap rock is present.
from “Basic Petroleum Geology and Log Analysis”, Halliburton, 2001
Salt Dome or Salt Plug Trap
Stratigraphic Traps
Stratigraphic traps are formed as a
result of differences or variations
between or within stratified rock
layers, creating a change or loss of
permeability from one area to
another. These traps do not occur
as a result of movement of the
strata.
from “Basic Petroleum Geology and Log Analysis”, Halliburton, 2001
• An angular unconformity is one in which
older strata dips at an angle different
from that of younger strata.
• An angular unconformity trap occurs
when inclined, older petroleum bearing
rocks are subjected to the forces of
younger non-porous formations.
• This condition may occur whenever an
anticline, dome or monocline are eroded
and then overlain with younger, less
permeable strata.
Figure 40 Eroded anticline
Figure 41 Eroded monocline
from “Basic Petroleum Geology and Log Analysis”, Halliburton, 2001
Angular Unconformity Trap
from “Basic Petroleum Geology and Log Analysis”, Halliburton, 2001
Angular Unconformity Trap
Fractured Basement
from “Petroleum Geology”, Schlumberger.
Re-distribution of petroleum
• Of the total amount of petroleum generated in the source rocks 75% is
expelled in the course of primary migration into nearby high porosity/
permeability carrier beds.
• During secondary migration, about 50% of the petroleum which has
entered the carrier beds remains in the form of impregnations adsorbed
on mineral surfaces.
• About 40% has, at an earlier stage in the history of this sedimentary basin,
accumulated in reservoir traps.,
• The remaining 10% is on its secondary migration route bypassing all
traps and eventually leaking out at the Earth’s surface. This process is
called petroleum seepage.
• About 25% of the original petroleum accumulated gets lost by cap rock
leakage occurring at a slow rate over long periods of geologic time.
• Of the remaining petroleum, another 25% gets lost in the course of
chemical, physico-chemical and bacterial processes (discussed above).
• In summary, only about
10% of the petroleum
generated in the source
rocks can be discovered
by exploration and
produced for economic
usage.
• There are only a few
reported cases that fall
into this category. These
include the La Luna-
Misoa petroleum
system of Venezuela
and the Arabian/Iranian
Basin in the Middle
East.
from D Leythaeuser, “Encyclopaedia of Hydrocarbons”
Distribution of oil and gas fields based on
geologic age
It is important to know the geologic age of reservoir rocks because rocks of
different ages frequently have different petroleum characteristics and
productivity. It is also important to note that the age of the rock does not
necessarily coincide with the time of oil accumulation. You can only know
that it accumulated sometime after the formations deposition.
Geologic Age
Era Period % of Fields
Cenozoic
Neogene 18
Palaeogene 21
Mesozoic
Cretaceous 27
Jurassic 21
Permo-Triassic 6
Paleozoic
Carboniferous 5
Devonian 1
Cambrian-
Silurian
1
TOTAL 100
What’s so special about the Mesozoic?
• The worldwide climate was tropical.
• Plankton were abundant in the ocean.
• Ocean bottoms were stagnant and anoxic, unlike today’s ocean.
• Black, organic-rich muds accumulated to form later source rocks.
Distribution of oil and gas fields based on
geologic age
Warm
water
Low-oxygen
layer
Cold
water
Modern Ocean
Mesozoic Ocean
Distribution of oil and gas fields based on
geologic age
151PTE321Engineering Geology
Lecture 7
Dr. Seyed Mehdi Alizadeh
Sedimentology
Sedimentology is the study of the processes of formation, transport
and deposition of material that accumulates as sediment in
continental and marine environments and eventually forms
sedimentary rocks.
Stratigraphy is the study of rocks to determine the order and timing of
events in Earth history: it provides the time frame that allows us to
interpret sedimentary rocks in terms of dynamic evolving
environments.
The stratigraphic record of sedimentary rocks is the fundamental
database for understanding the evolution of life, plate tectonics
through time and global climate change.
Sediment Sources, Transport,
and Deposition
Why are rounding and sorting important in sediments
and sedimentary rocks?
Both are important in determining how liquid water, ice, and
wind move through sediments and sedimentary rocks.
The amount of rounding and sorting depends on particle
size, distance of transportation, and depositional
processes.
Rounding and size control, also how important subsurface
resources such as groundwater and petroleum, move
through sedimentary rocks and sediment
Sediment Sources, Transport,
and Deposition
Eventually, the sediment comes to rest in a
depositional
environment.
Depositional environments are areas of
sediment deposition that can be defined by their
physical characteristics (topography, climate,
wave and current strength, salinity, etc.).
Depositional environments provide clues as to
how the rock formed and what the geologic past
was like.
Sediment Sources, Transport,
and Deposition
Major depositional settings are continental (including freshwater),
transitional (shore or near shore marine), and marine.
Each of these depositional settings includes several
specific subenvironments.
How Does Sediment Become
Sedimentary Rock?
Through the process of lithification,
sediment is converted into sedimentary rock.
How Does Sediment Become
Sedimentary Rock?
Lithification involves two processes:
1. Compaction – The volume of sediment
decreases as the weight of overlying sediment
causes a reduction in pore space (open space) as
particles pack more closely together.
Compaction alone is sufficient for lithification of
mud into shale.
How Does Sediment Become
Sedimentary Rock?
Lithification involves two processes:
2. Cementation is a process that glues the
sediments together.
The most common cements are calcium carbonate
and silica, but iron oxide and iron hydroxide are
important in some rocks.
Compaction alone will not form rocks from sand and
gravel. Cementation is necessary to glue the
particles together into rocks.
How Does Sediment Become
Sedimentary Rock?
Sedimentary Facies
Geologists realize that if they laterally trace a
sedimentary layer far enough, it will undergo
changes in composition and/or texture.
Bodies of sediment or sedimentary rocks which are
recognizably different from adjacent sediment or
sedimentary rocks and are deposited in a different
depositional (sub) environment are known as
sedimentary facies.
Today we recognize modern facies changes when we go
from an inland area with rivers to the beach.
The environment at any point on
the land or under the sea can be
characterized by the physical and
chemical processes that are
active there and the organisms
that live under those conditions at
that time.
In the description of sedimentary
rocks in terms of depositional
environments, the term ‘facies’ is
often used. A rock facies is a body
of rock with specified
characteristics that reflect the
conditions under which it was
formed.
Sedimentary Environments And Facies
Rock Formation
A formation is the basic rock unit in geology. IT IS NOT A TIME UNIT. It
is defined by its properties: type (sandstone, limestone, etc. e.g. (Bell
Shale), color (Brown Niagrian), texture, geometry. The choice is fairly
obvious in A, but more difficult in B. In B and C the choice of
subdivisions is somewhat arbitrary.
Depositional Environments and
Sedimentray Facies
Lateral variations of strata not fully appreciated
until 1838
Facies concept relates sediments to their
depositional environment
Block diagram
showing proximal (near
source) and distal (distant
from source) facies
relationships in a shoreline
environment.
The source area is the
uplifted “island” which is
supplying sediment
(gravel, sand, mud in
that order) as it erodes)
Facies- Example
Facies- Example
A = Sandstone facies (beach environment)
B = Shale facies (offshore marine environment)
C = Limestone facies (far from sources of
terrigenous input)
Each depositional environment grades laterally into other environments.
Sedimentary Facies
Sedimentary facies are used to identify ancient
changes in sea level, called marine
transgressions and regressions.
Sedimentary Facies
A marine transgression
occurs when sea level
rises with respect to the
land, resulting in offshore
facies overlying nearshore
facies.
Marine Transgressions and Regressions
Sedimentary Facies
A marine regression,
caused when the land
rises relative to sea
level, results in
nearshore facies
overlying offshore facies.
Note the difference in
the vertical rock
sequence that occurs
in a transgression
versus a regression.
Marine Transgression and Regression
Onlap (Transgressive) Sequences
Shifting Facies through Time
Beach moves farther away
Water gets deeper
Sediment becomes finer
Time Rock Unit
Time Rock Unit
Time Rock Unit
Time Rock Unit
Time Rock Unit
Time Rock Unit
Beach
sandstone
Near Shelf
shale
Far Shelf
limestone
FUS – Fining Upward Sequence
= Transgressive Sequence
Offlap (Regressive) Sequences
Shifting Facies through Time
Beach
sandstone
Near Shelf
shale
Far Shelf
limestone
Beach moves closer
Water gets shallower
Sediment gets coarser
Prograding Regression
Time Transgressive Rock Unit
CUS – Coarsening Upward Sequence
= Regressive Sequence
Transgressive Sequence
Regressive Sequence
Beach
sandstone Near Shelf
shale
Far Shelf
limestone
Beach moves closer
Water gets shallower
Sediment gets coarser
Prograding Regression
Time Transgressive Rock Unit
Beach moves farther away
Water gets deeper
Sediment becomes finer
Beach
sandstone
Near Shelf
shale
Far Shelf
limestone
Depositional Environments
Areas of the Earth’s surface where distinct processes
generate specific geological (sedimentary) products:
Physical
Biological
Chemical
Depositional Environments
Continental environments
Transitional environments
Marine
environments
Desert environments contain an association
of features found in
sand dune deposits,
alluvial fan deposits,
playa lake deposits
Desert Environments
A dune is a hill of sand built by wind or the flow of
water.
Dunes occur in different shapes and sizes, formed by
interaction with the flow of air or water.
Most kinds of dunes are longer on the windward side
where the sand is pushed up the dune and have a
shorter “slip face” in the lee of the wind.
Windblown dunes are typically composed of:
well-sorted, well-rounded sand
cross-beds meters to tens of meters high
land-dwelling plants and animals make up any fossils
Sand Dunes
A desert basin
showing the
association of:
alluvial fan,
sand dune,
playa lake
deposits
Associations in Desert Basin
Alluvial fans form best along the margins of
desert basins :
where streams and debris flows discharge
from mountains onto a valley floor
They form a triangular (fan-shaped) deposit of
sand and gravel
Alluvial Fans
Transitional Environments
Transitional environments
Simple Deltas
1) topset beds
2) foreset beds
3) bottomset
beds
The simplest deltas are those in lakes and
consist of :
– As the delta builds outward it progrades and forms a vertical
sequence of rocks that becomes coarser-grained from the
bottom to top.
– The bottomset beds may contain marine (or lake) fossils,
– whereas the topset beds contain land fossils.
Wave-dominated
deltas
such as the Nile
Delta of Egypt
also have
distributary
channels
but their
seaward margin
is modified by
wave action
Wave-Dominated Deltas
Marine Environments
Marine
environments
Factors that control sedimentation include particle size
and the turbulence of the depositional environment.
Terrigenous sediments are those derived from the erosion of
rocks on land; that is, they are derived from terrestrial
environments.
Terrigenous sediments strongly reflect their source and are
transported to the sea by wind, rivers and glaciers.
Rate of erosion is important in determining nature of
sediments.
Average grain size reflects the energy of the depositional
environment.
4-1 Sedimentation in the Sea
Hjulstrom’s Diagram
Hjulstrom’s Diagram graphs the relationship between
particle size and energy for erosion, transportation and
deposition.
The gently sloping area adjacent to a continent
is a continental shelf
It consists of a high-energy inner part that is
periodically stirred up by waves and tidal currents
Its sediment is mostly sand, shaped into large cross-
bedded dunes
Bedding planes are commonly marked by wave-
formed ripple marks
Marine fossils and bioturbation are typical
Detrital Marine Environments
Shelf, slope and rise environments
The main avenues of sediment transport across the shelf are submarine
canyons
Detrital Marine Environments
Turbidity currents
carry sediment
to the
submarine fans
Sand with
graded bedding
and mud settled
from seawater
Beyond the continental rise, the seafloor is
nearly completely covered by fine-grained deposits
no sand and gravel
or no sediment at all
near mid-ocean ridges
The main sources of sediment are:
windblown dust from continents or oceanic islands
volcanic ash
shells of microorganisms dwelling
in surface waters of the ocean
Deep Sea Environments
Types of sediment are:
pelagic clay, which covers most of the deeper parts
of the seafloor
calcareous (CaCO3) and siliceous (SiO2) oozes
made up of microscopic shells
Deep Sea Environments
151PTE321/GEOL2101
Engineering Geology
Lecture 9
Dr. Seyed Mehdi Seyed Alizadeh
Heterogeneity
Definition
• Formation with two or more non-communicating
sand members.
• Different specific- and relative-permeability
characteristics.
• The reservoir heterogeneity is defined as a
variation in reservoir properties as a function of a
space.
• Oil/Gas reservoirs are complicated geological
heterogeneous bodies.
• There is no homogeneous porous media.
• Well log and core analysis reports show that all
reservoirs are heterogeneous.
• Permeability heterogeneities cause variations in
the fluid movements compared to the equivalent
homogeneous system.
• Efficiency management (RF).
http://www.google.com.kw/url?sa=t&rct=j&q=&esrc=s&source=web&cd=20&ved=0CFsQFjAJOAo&url=http%3A%2F%2Fcaos.fs.usb.ve%2F~srojas%2FVI_
CCFD%2Fpapers%2Ffpm%2FRDawe &ei=H61FU9bzMqqCyAOl6oGwCA&usg=AFQjCNHThSj_QfQoMcpB8ONwRB5E3xujOA&bvm=bv.64507335,d.
bGQ
Reservoir Heterogeneity in Sandstone
Heterogeneity May
Result From:
Depositional Features
Diagenetic Features
(Whole Core Photograph, Misoa
Sandstone, Venezuela)
Heterogeneity
Segments Reservoirs
Increases Tortuosity of
Fluid Flow
Reservoir Heterogeneity in Sandstone
Heterogeneity Also May
Result From:
Faults
Fractures
Faults and Fractures may
be Open (Conduits) or
Closed (Barriers) to Fluid
Flow
(Whole Core Photograph, Misoa
Sandstone, Venezuela)
Scales of Geological Reservoir Heterogeneity
F
ie
ld
W
id
e
In
te
rw
e
ll
W
e
ll
-B
o
re
(modified from Weber, 1986)
Hand Lens or
Binocular Microscope
Unaided Eye
Petrographic or
Scanning Electron
Microscope
Determined
From Well Logs,
Seismic Lines,
Statistical
Modeling,
etc.
10-
100’s
m
m
10-100’s
mm
1-
10’s
m
100’s
m
10’s
m
1-10 km
100’s m
Well Well
Interwell
Area
Reservoir
Sandstone
Scales of Investigation Used in
Reservoir Characterization
Gigascopic
Megascopic
Macroscopic
Microscopic
Well Test
Reservoir Model
Grid Cell
Wireline Log
Interval
Core Plug
Geological
Thin Section
Relative Volume
1
10
14
2 x 10
12
3 x 10
7
5 x 10
2
300 m
50 m
300 m
5 m 150 m
2 m
1 m
cm
mm – mm
(modified from Hurst, 1993)
& Seismic
Primary objective of geological characterization is
concerned with predicting the spatial variation of geological
variables.
Variable :
• is any property of the geological subsurface that exhibits
spatial variability and can be measured in terms of real
numerical values.
Spatial Variation:
• Typically the subsurface is anisotropic, spatially complex
and sedimentary bodies are internally heterogeneous.
Geological Modeling
Reservoir Characterisation
• Modern reservoir characterisation started around 1980:
• Reason: deficiency of oil recovery techniques (inadequate
reservoir description)
• Aim: predict inter-well distributions of relevant properties (φ, K)
• Subsurface (inter-well) heterogeneity cannot be measured:
• Seismic data (large support, low resolution)
• Well data (small support, high resolution)
• Complementary sources of information:
• Geological models
• Statistical models
• Combine data and models ‘static’ reservoir model
Static reservoir models
• Reservoir geology is the science (art?) of building
predictive reservoir models on the basis of geological
knowledge (= data, interpretations, models)
• A reservoir model depicts spatial variation of lithology
(porosity and permeability): “static” model
• Simulations of multi-phase flow (“dynamic” models)
require high-quality “static” reservoir models
• Static reservoir models are improved through analysis
of dynamic data: iterative process
Geological Modeling: different tracks
Static
Reservoir Model
Reservoir Data
Seismic, borehole and wirelogs
Sedimentary
Process Model
Stochastic ModelDeterministic
Model
Data-driven modeling Process modeling
Flow Model
Upscaling
14
Geological model
•Elements of the
geological model:
1. Bounding surfaces
2. Distributions of
physical properties
between surfaces
3. Faults
4. OWC, GWC, GOC
5. Conditioned to well
data ?
15
Why is geological modeling difficult
• The output of many natural systems exhibits apparent
randomness, which is usually caused by extreme sensitivity to
initial conditions. Initial conditions and physical laws of such
systems cannot be inferred from the output.
• Measurements are a finite sample of the output (all possible
realisations of the system).
• Statistical models may be used to describe such
measurements in the absence of a physical model.
• Geological modeling software (a worst-case scenario):
• Designed by statisticians who know little about geology
• Applied by geologists / engineers who know little about
statistics
• Many things can and will go wrong !
16
Upscaling issues
• In addition to the natural scales of heterogeneity in the
system and the scale of the measurements, there is also the
scale of the discrete elements (grid blocks) in a reservoir
model.
• Upscaling measurements to grid-block scale is a critical
issue in geological modeling and the object of active
research
• Common errors in numerical reservoir models:
• Discretisation errors
• Upscaling errors
• Input errors
• Geological modeling aims at minimizing these
errorsrrorsnput errors to
improve reservoir-model performance
151PTE321 Engineering Geology
Lecture 5
Dr. Seyed Mehdi Alizadeh
General Aspects of Sedimentary Rocks
Composition of grains/clasts: tells about source.
Age of grains: tells about age of source and transportation
history (e.g., zircon).
Texture/
Maturity
: tells about transportation history.
Sedimentary structures: tell about depositional
environment.
Fossils: tell about depositional environment and age of
deposit.
Grade Scales
• A grade scale provides such a standard for verbally expressing
and quantitatively describing grain size.
• Any good grade scale should:
(i) Define ranges or classes of grain size (grade is the size of particles
between two points on a scale. e.g., “very fine sand”, is a grade
between maximum and minimum size limits)
(ii) Proportion the grade limits so that they reflect the significance of the
differences between grades.
• For example, the change in size from 1 mm to 2 mm diameter sand is
an increase of 100%, however, the change in size from 10 mm to 11
mm is on the order of 10%. Therefore, a grade scale in which grade
limits vary by 1 mm would not be useful.
• The most widely-used grade scale is the Udden-Wentworth Grade
Scale (Table R-5). Note that most of the grade boundaries increase by a
factor of 2, reflecting significant changes in grain size. Also, the scale
defines limits for the verbal expression of grain size. “Very fine sand” is
sand which ranges in size from 0.0625 mm to 0.125 mm
• Krumbein (1934) introduced a logarithmic transformation of
the scale which converts the boundaries between grades to
whole numbers. This scale is known as the Phi Scale, it’s
values being denoted by the Greek symbol (φ):
Udden-Wentworth Tale
φ = -log d(mm)
2
where d(mm) is
just the grain size
expressed in
millimetres.
Maturity is a function of sediment transport
• Textural maturity refers to:
– The degree of roundness of the grains
– The amount of sorting of the grain sizes
•
Texturally mature sandstones have well-rounded
and well-sorted grains, immature if not
• Mineralogical maturity refers to the percentage of
quartz grains
Feldspars break down with transport
Quartz grains more resistant
• Mineralogically mature sandstones have mostly
quartz grains
• Arkose is mineralogically immature
Maturity
•
Sorting
is the degree of similarity in particle size in a sedimentary
rock.
• For example, if all the grains in a sample of sandstone are about
the same size, the sand is considered well sorted. Conversely, if
the rock contains mixed large and small particles, the sand is said
to be poorly sorted (see figure 6.5)
• The shapes of sand grains can also help decipher the history of a
sandstone (Figure 6.5B).
• When streams, winds, or waves move sand and other larger
sedimentary particles, the grains lose their sharp edges and
corners and become more rounded as they collide with other
particles during transport.
• Thus, rounded grains likely have been airborne or waterborne.
Sorting
Particle sorting – comparison chart
Increasing Roundness=increasing maturity
• Example: a poorly sediment containing
glassy angular volcanic fragments,
olivine crystals and plagioclase is
texturally immature because the
fragments are angular.
• This indicates they have not been
transported very far and the sediment is
poorly sorted, indicating that little time
has been involved in separating larger
fragments from smaller fragments.
• A well sorted beach sand consisting
mainly of well rounded quartz grains is
texturally mature because the grains are
rounded, indicating a long time in the
transportation cycle.
• Such sediment is well sorted, also
indicative of the long time required to
separate the coarser grained material
and finer grained material from the
sand.
Clastic Sediment Textures
Roundness/Angularity:
Transport by wind or water – rounding occurs.
Transport by ice or gravity – angular.
Degree of Sorting:
Selection/separation of grains is on the basis
of size, shape, specific gravity.
Poorly sorted: fast deposition, high energy.
Well sorted: slow deposition, less chaotic.
Poorly
Sorted
Sample
Sedimentary Structures
Other than rock type (lithology), one of the
best ways to determine depositional
environment is by observing sedimentary
structures:
bedding – flat layering
cross-bedding – sediment moved by wind or water
deposited at an incline
ripple marks – deposition by wave oscillating
graded bedding – coarser sediment on bottom,
finer on top (currents dropping load)
mud cracks – sediment drying up and shrinking
Sedimentary Structures
• Give evidence of depositional environments.
• Sedimentary rocks are deposited originally
in horizontal beds.
• Later deformation causes the beds to be inclined.
• Which was the original way up?
Structures can give that information.
Bedding – horizontal sheets differing in composition.
Sedimentary structures can give idea of paleocurrents.
Bedding & Cross-Bedding
• In geology a bed is the smallest division of geologic formation or
stratigraphic rock series marked by well-defined divisional planes
(bedding planes) separating it from layers above and below.
• The term is generally applied to sedimentary strata, but may also be
used for volcanic flows or ash layers.
• An important feature of a bed is its internal structure, which is
characterized by conditions of deposition.
• A bedding type can be recognized and named on the basis of a
single bed; or it is only possible when same type of bed is repeated
a several times- a bedset; or it is then possible when two or more
beds of different natures are repeated in certain sequences.
• Thus a bedding type can be made of the same type of beds (cf.
Reineck and Wunderlich 1969).
Examples – various bedding types
Cross Bedding (formation)
• Cross beds form as sand blows up the windward side of a dune and then accumulates on
the slip face. At a later time we see that the dunes migrate, and eventually bury the layers
below.
• Cross-bedded strata can be seen on this cliff face of sandstone in Zion National Park.
We are looking at the remnants of ancient sand dunes. Cross beds indicate the wind direction
during deposition.
• With time the dune crest moves
Development of Cross Bedding
Cross Bedding (Field Example)
Ripple Marks
• Ripple marks are sedimentary structures (i.e. bedforms of the lower flow
regime) and indicate agitation by water (current or waves) or wind.
(A) A current that always flows in the same direction (like in a stream)
produces asymmetric ripples.
(B) A current that moves back and forth (like on a wave-washed beach)
produces symmetrical ripples.
(A) (B)
Ripple Marks – wave action, form on top of beds.
Ripple Marks
• A ripple is conventionally described in terms of its size and shape. Traditionally, ripple
marks are represented and described in terms of vertical profile parallel to flow, at right
angle to the ripple crest. A ripple is composed of a crest and a trough.
Ripple Mark Description
Ripple Marks
• A graded bed is one characterized by a systematic
change in grain or clast size from the base of the bed
to the top. Most commonly this takes the form of
normal grading, with coarser sediments at the base,
which grade upward into progressively finer ones.
• In above example of a graded bed, pebbles lie at the bottom
of the bed and silt at the top
Graded Bedding
Graded Bedding
(turbidity current) – beds
grade from coarse grained
at the bottom to fine
grained at the top.
Graded Bedding
• Mudcracks (also known as desiccation cracks or mud cracks) are
sedimentary structures formed as muddy sediment dries and
contracts.
• They are formed as a result of drying on top of bed
Mud Cracks
END