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
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
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