FUNDAMENTALS_OF_PETROLEUM_GEOLOGY_1725100092.pdf

Hanafy El Naggar
SOUTH VALLEY EGYPTIAN HOLDING PETROLEUM COMPANY
Prepared by
FUNDAMENTALS OF PETROLEUM GEOLOGY

Petroleum geology:
Petroleum geology is a branch of geological sciences using concepts and techniques which are
applicable for exploration and exploitation of petroleum deposits in sedimentary rocks.
INTRODUCTION
A B
Fig. 1: (A, B)The stages of petroleum formation and petroleum deposits in sedimentary rocks

Petroleum Geology means the geology of sedimentary basins because in sedimentary basins
the commercial accumulations of petroleum occur. It is therefore essential to have a clear idea
from the outset of what a sedimentary basin is.
INTRODUCTION
(3) The nature of the sediments that accumulate in a sedimentary basin is related to the
environments of the physiographic basin from which the sediments were derived and in which
they were deposited.
(1) Sedimentary basins are areas in which sediment accumulated at a significantly greater rate
than sediments of the same age in neighboring areas, so accumulating a greater thickness.
The sediments accumulate by virtue of subsidence.
(2) The geological concept of a sedimentary basin is distinct from the geographical concept of
a physiographic basin. Sediment accumulation is also distinct from sedimentation and
deposition, because not all sediment deposited accumulates for a significant period of time in
the geological record.
□ Petroleum Geology and its relations with the sedimentary basins:

(7) Sedimentary basins are deformed by faults sediment and the sedimentary column is still
subsiding
(4) Sedimentary basins typically begin with a transgressive sequence and end with a
regressive sequence, but they may have a long and complicated history. Transgressive
sequences record a general deepening of the sea, with reduction of the land area and
migration of the facies towards the land. Regressive sequences record a general shallowing of
the sea, with extension of the land and migration of the facies seaward.
(5) Most significant carbonate sequences are transgressive:
arenaceous sequences may be transgressive or regressive. All important regressive sequences
are arenaceous.
(6) Eustatic changes of sea level leave a record in all active sedimentary basins that are
accumulating sediment. Changes of sea level due to changes in the shape of the geoid may lead
to transgressive sequences in some parts of the world contemporaneously with regressive
sequences in others
INTRODUCTION

Its goal is to describe the amount, type and thermal maturation of the sedimentary organic matter
and to use this knowledge to the exploration and development of petroleum.
Petroleum Geochemistry is one of the newest tools to be used in the search for petroleum.
Organic geochemistry is the study of organic matter in sedimentary rock, and the use of
chemical principles to study the origin, migration, accumulation, and alteration of petroleum (oil
and gas).
a. The concentration of organic matter.
b. The quality of the organic matter.
c. The state of metamorphism.
d. The amounts of hydrocarbon.
It also allows us to determine how and where organic matter in sediment is converted into gas and
oil by defining:
INTRODUCTION
Petroleum Geochemistry:

Fig. 2: Carbon Cycle and Petroleum Formation.
INTRODUCTION

Crude oils:
- Are complex mixtures containing many different hydrocarbon compounds that vary in
appearance and composition from one oil field to another.
- Crude oils range in consistency from water to tar-like solids, and in color from clear to black.
- An "average" crude oil contains about 84% carbon, 14% hydrogen, 1%-3% sulfur, and less
than 1% each of nitrogen, oxygen, metals, and salts.
Fig. 3: (A)Oil production concept. (B)Crude oil spilled in the shape of Earth
INTRODUCTION
A B

ORIGIN OF PEROLEUM
ORGANIC
INORGANIC
COSMIC THEORY
ALKALI METAL
CARBIDE THEORY
VOLCANIC IMANATION
PLANTS AND ANIMALS
The Theories of Origin of
petroleum:
INTRODUCTION
Fig. 4: The organic concept of oil and national gas formation.

Supports :
▪ Methane is a main constituent in the atmosphere of major plants.
▪ Existence of hydrocarbon in meteorites which indicate the nature of the earth's core.
Against (Opposite):
▪ IF so, hydrocarbon should be uniform ably distributed over the earth and older rocks.
▪ hydrocarbon should be uniformably distributed throughout the geologic column.
▪ Pre Cambrian, Cambrian, Triassic and Pliestocene rocks are low in hydrocarbon content
Supports:
▪ Existence of alkalies as traces in petroleum.
Against:
▪ Existence of free alkalies not proved yet.
▪ Existence of alkalies in petroleum should be high percentage
Supports:
▪ Existence of Carbide as traces in petroleum.
Against:
▪ Existence of iron carbides in the earth not proved yet.
▪ Water will not perculate to great depths sufficient to this reaction.
Supports:
▪ liquid oils and solid paraffins have been found in the basaltic lava near volcanoes.
Against:
▪ If though petroleum should be accompained with all volcanoes
1. Cosmic Theory
2. Alkali Metal
3. Carbide Theory
4. Volcanic Emanation
INTRODUCTION

Factors which support the organic origin:
▪ Petroleum contains nitrogen (N) which found in plants and animal.
▪ Green coloring matter in plants.
▪ Petroleum consists mainly of (H & C) which found by processes of plants and animals.
▪ The ash content of algae similar to that of crude oil.
▪ Found a wide Varity of organic remains in petroleum.
▪ 99% of oil fields found in marine sediments.
5. ORGANIC THEORY
Transformation of organics into petroleum:
▪ Heat and pressure: needs long time of heating (200 c) with aid of pressure.
▪ Effect of catalysts: they are substances that aid or accelerate the reactions.
▪ Radioactivity: decay of POTASSIUM, URANIUM, THORIUM (in marine shale) emit high temperature.
▪ Bacterial action: Splitting Oxygen, Nitrogen, Sulfur and phosphorous from various organic compounds.
INTRODUCTION

INTRODUCTION
The origin of petroleum and petroleum generating processes
- Hydrocarbons are composed of only two elements, hydrogen and carbon.
- Because of the ability of the carbon atom to bond itself to other carbon atoms, there are a
large number of hydrocarbon compounds, the molecules of which can contain 1 to over
50 carbon atoms.
- They range from gases through liquids to solids.
- Chemically they can be divided into four main groups by the nature of the carbon bonds
and the arrangement of the carbon atoms in the molecule. These groups are the
aromatics, the naphthenic, the branched-alkanes and the normal alkanes.
- The original source material from which petroleum is formed is organic matter
deposited in sediments.
- There are two main sources:
(a) Aquatic organisms, principally algae and other phytoplankton.
(b) The remains of terrestrial plants carried into the site of deposition.

INTRODUCTION
PETROLEUM ELEMENTS
(PETROLEUM SYSTEM)
1. Source
rock
2. Reservoir
3. trapping
4. Sealing
5. Migration

1. SOURCE ROCK ELEMENT
INTRODUCTION
PETROLEUM ELEMENTS

Rocks from which hydrocarbons have been generated or are capable of being generated.
They are organic rich sediments that may have been deposited in (deep water marine, lacustrine and deltaic).
Organic particles are usually fine-grained, and will settle out most easily in quiet-water environments.
Therefore, source rocks are fine-grained rocks, particularly shales.
Other potential sources are fine-
grained carbonates (lime mud),
mud-carbonate
mixtures (marl), or coal.
What is the Source rock?
INTRODUCTION
Fig. 5: The Ratio of possibility for rocks to formed source rock of oil and national gas.

What is the Source rock?
INTRODUCTION

1. Thermal maturity determines whether an organic-'rich rock will become a source rock or no.
2. Preservation of organic matter is usually hard.
3. Most organic accumulations are rapidly destroyed through oxidation and biological activity.
4. This occurs most commonly in restricted marine environments, where a basin is prevented from easy
communication with the open ocean.
RESULTS IN VARIOUS HYDROCARBONS:
(organic compounds with mostly Hydrogen and Carbon).
These can be solid, liquid, or gas.
petroleum system term:
1. understanding of the generation of oil and gas within a source rock.
2. Interested in expulsion, migration, entrapment, and survival to the present day.
3. The Petroleum System (i.e. sedimentary basin) consists of: a mature source rock, migration
pathway, reservoir rock, trap and seal.
TIMING:
Appropriate relative timing of formation of these elements and the processes of generation, migration
and accumulation are necessary for hydrocarbons to be accumulated and preserved.
Factors controlling hydrocarbon formation:
Source rock as an element in Petroleum system:
INTRODUCTION

▪ Pressure and the presence of
bacteria and catalysts also
affect generation.
hydrocarbon generation is the formation of hydrocarbon to accumulate as oil or gas.
▪ The presence of organic matter rich enough to yield hydrocarbons.
▪ Adequate temperature.
▪ Sufficient time to bring the source
rock to maturity.
Generation of the source rock:
INTRODUCTION
Generation depends on four main factors
Fig. 6: The hydrocarbon formation stages from immature to over mature source rock.

▪ Direct generation of hydrocarbons from kerogen
stops at approximately 225 degrees C; methane,
however, can form from the cracking of previously
formed oil up to315 degrees C.
▪ Major oil generation begins when source rocks are heated above 60 degrees C.
▪ These low-temperature oils, formed at relatively shallow depths.
▪ tend to be heavy and laden with non-saturated oil (NSO) compounds.
▪ Oils become lighter at greater depths and higher
temperatures.
▪ Oil generation peaks at temperatures in the vicinity of
100 degrees C, beyond which oil generation declines
and condensates form.
▪ The boundary between oil and gas windows occurs at
approximately 175 degrees C.
INTRODUCTION
Fig. 7: The hydrocarbon formation stages from heavy to light
oil and from light to condensate and gas in source rock.
EFFECTS OF (DEPTH & TEMPERATURE & TIME)

▪ The local geothermal gradient, kerogen type and burial history affect generation depths for
particular types of source rocks.
▪ The gas window ranges from 3 to about 4 km, and
corresponds to the stage of late catagenes is during
which predominantly gas forms.
▪ Below this zone, source rocks are over-mature
and only methane gas is formed.
Fig. 8: Shows the average maximum and minimum generation depths.
▪ At very shallow depths, only biogenic methane is generated during diagenes is by the action of
anaerobic bacteria.
▪ At depths of 1 to 2 km, catagenesis begins.
▪ The principal zone of oil formation during the
early stage of catagenes is - the oil window -
begins at depths of 1 to 2 km and continues to a
depth of approximately 3 km.
▪ Petroleum generation is related to the burial depths of source rocks.
INTRODUCTION

▪ by deposition of later, overlying sediments, the increasing heat and pressure turns the
soft sediments into hard rock strata.
▪ When temperatures of source rock 1200 C (2500 F) the organic remains begin to be
"cooked" and oil land natural gas are formed and expelled from the source rock. If the
organic materials mostly wood fragments, maturation gives natural gas.
▪ If the organic materials are mostly algae or the soft parts of land plants, then both oil and
natural gas are formed.
▪ above 1500 C (3000 F) any oil remaining in source or reservoir will be broken down
Into natural gas.
Source rocks and hydrocarbon
generation
▪ Source rocks are comprised of very small mineral fragments with remains of organic
material (algae, small wood fragments, pieces of the soft parts of land paints).
INTRODUCTION

1-Effective source rocks:
Are sedimentary rocks that have actually
generated hydrocarbons.
2-Possible source rocks:
Are sedimentary rocks about which we don't
yet have enough data and whose source
potential has not yet evaluated but considered
to have generated hydrocarbons.
3-Potential source rocks:
Are organically rich immature sedimentary
rocks known to be capable of generating
hydrocarbons if the level of thermal maturity
was higher.
Classification of source rocks
INTRODUCTION
Fig.9: The shape of source rock exposure.
1- Effective source rocks (Wells)
2- Possible source rocks (seismic)
3- Potential source rocks(magnetic)

PETROLEUM ELEMENTS
INTRODUCTION
2. RESERVOIR ROCK ELEMENT

Reservoir
A reservoir is a subsurface volume of porous and permeable rock that has both storage
capacity and the ability to allow flowing through it. Hydrocarbons migrate upward through
porous and permeable rock until they form surface seepage or become trapped below the
surface by a non-permeable cap rock. Porosity and permeability are influenced by:
the depositional pore-geometries of the reservoir sediments. the post-depositional
(diagenetic) changes that take in place
physical characters of reservoir (Porosity)
It is simply a measurement of the pore or void spaces in rock. Porosity in reservoir
rocks is normally between 10% and 20%, but some excellent reservoirs may have
porosities of 30% or _more. Accumulations in reservoirs with less than 5% are usually
not commercial.
INTRODUCTION
physical characters of reservoir (Permeability): is a measure of a rock's ability to
conduct fluids. The unit of permeability is the Darcy

INTRODUCTION
Types of reservoir
Fig.10: The different types of reservoir rocks as one of the petroleum elements.

1- Sandstone reservoirs:
The term sand implies a range of grain size (between 2 to 116 mm) , and not a particular composition.
Sand stone reservoirs form ~ 60% of all reservoirs in the world They have average porosity =15 %.
Environments of sandstone:
A - Aeolian ( dune ) sandstone reservoirs: exceedingly well sorted , have adequate porosity to provide
good reservoirs, but a source of hydrocarbons is less likely to be available.
B - Glacial sandstone reservoirs : fundamentally an argillaceous greywacke, un stratified and essentially
structure less.. It contains randomly scattered fragments without uniformity of size or composition, but
tending to have angular or tabular shapes resulting from glacial abrasion.
C - Fluvial sandstone reservoirs: Fluvial ( alluvial ) sands deposited by rivers, necessarily occur within
non-marine successions. Commonly rest on erosional surface relief, easily recognized strafigraphically and
seismically.
D - Deltaic sandstone reservoirs: Beach and barrier bars , bar fingers , distributary channels , etc.
E- Coastal marine environment : Coastal clastic depositional environments occur in significant variety.
F- Deep - water sandstone reservoirs: were deposited in waters deeper than 200 , (possibly very much
deeper), commonly associated with shales bearing pelagic fossils and other evidence of deposition far
below wave-base.
INTRODUCTION

Most carbonate rocks begin as skeletal assemblages and animal remains.
-
- They are produced locally.
- They subject to more post-depositional digenesis ranging from simple cementation of the
original particles to complete recrystallization or replacement by dolomite or chert.
INTRODUCTION
:
carbonate reservoir rocks
Fig.11: The carbonate
reservoir rocks as one of the
reservoir types.

The most important four kinds of carbonate reservoirs are:
(1) Shell fragments, called "BIO".
(2) Fragments of previously deposited limestone called "INTRACLASTS".
(3) Small round PELLETS - the excreta of worms.
(4) OOLITHS- spheres formed by rolling lime particles along the bottom.
Effect of lime mud
1 - lime mud important in the development of porosity because it may be easly dolomitized
and may also leached out more than the grains due to the larger surface area.
2- Good porosity in carbonate reservoirs is usually due to dolomitization, a volume loss of
12 to 13 % due to dolomitization.
Lime mud
Clay-sized particles as a material between the grains: (grain-supported rock), or the grains
may be "floating" in lime mud: {mud-supported rock).
INTRODUCTION

processes that may occur in sediments after they have been deposited.
The environment can also involve subsequent alterations of the rock such as: Chemical
changes.
Digenesis: is the chemical alteration of a rock after burial. An example is there placement
of some of the calcium atoms in limestone by magnesium to form dolomite.
Diagnosis:
INTRODUCTION
Mg + Ca Co3
Mg
Mg Ca (Co3)2
Mg
Fig.12: The carbonate reservoir rocks digenesis feature as one of the reservoir types.

Fractured reservoir
Are caused by brittle failure, usually due to such factors as:
(a) Folding.
(b) Faulting.
(c) Fluid pressure.
(d) Release of lithostatic pressure
(e) Pressure solution.
(f) Dehydration.
(g) Weathering.
(h) Cooling.
(i) Impact craters
- Particularly common in carbonates.
- Fractures range in size from hair-size
to several millimeters in aperture.
- The fracture system-generally
contains only a small fraction of the
reservoir pore space, while it contain the
bulk of the reservoir flow capacity.
INTRODUCTION
Carbonate reservoir rocks
Fig.13: The carbonate fractured reservoir rocks as one of
the carbonate reservoir types.

- Conventional reservoirs
Hydrocarbon reservoirs are classified as conventional or nonconventional:
▪ Conventional are characterized by high permeability with the hydrocarbon stored in sand
or carbonate formations in pore spaces that are interconnected.
INTRODUCTION
▪ Hydrocarbon resource is generally considered
conventional if it does not require a large
stimulation treatment to be able to produce oil and
gas at economic flow rates.
▪ A conventional reservoir is essentially a high- to
medium permeability reservoir in which one can
drill a vertical well, perforate the pay interval, and
then produce the well at commercial flow rates
and recover economic volumes of oil and gas. fig.14: The resource triangle of both the
conventional and unconventional resources.

▪ An unconventional reservoir can be denned as, reservoir that cannot be produced at economic
flow rates or in economic volumes unless the well is stimulated by a large hydraulic fracture
treatment, a horizontal wellbore, or multilateral wellbores (Holditch, 2006).
▪ Unlike conventional reservoirs, which are small in volume but easy to develop.
▪ unconventional reservoirs are large in volume but difficult to develop.
▪ Increasing price and the improved technology are the key to their development and the future.
▪ Unconventional resources are probably very large, but their character and distribution are not
yet well understood.
▪ It is known to exist in large quantity but does not flow easily toward existing wells for
economic recovery.
▪ Unconventional gas formations are "continuous" deposited over large areas rather than in
discrete traps.
▪ The geological setting of unconventional gas is several order complex than conventional gas.
INTRODUCTION
- Unconventional reservoirs:

INTRODUCTION
Fig. 15: Schematic cross-section showing the general setting of basin centered/low permeability regional gas accumulations
Conventional and unconventional reservoirs :

PETROLEUM ELEMENTS
3. TAPPING ELEMENT
4. SEALING ELEMENT
INTRODUCTION

The term (trap) was first applied to a hydrocarbon accumulation by Orton (1889).
OLevorsen, (1967) “Trap = place where oil and gas are barred from further movement"
Crest or culmination: is the highest point of the trap.
Spill point: is the lowest point at which hydrocarbons may be contained in the trap; this lies
on a horizontal contour (with a horizontal plane).
Closure: is the vertical distance from crest to spill point.
The Pay: productive reservoir Within the trap.
gross pay: vertical distance from the top
of reservoir to the petroleum/water contact. This
thickness may vary from only 1 or 2 m to several
hundreds meters.
Seals and cap rocks: Is the fundamental part of the
trap, which prevents the petroleum from migrating
onward through the rock. The most common
lithology that forms a petroleum seal is Murdock,
But evaporites are the most effective.
PETROLEUM TRAPS
INTRODUCTION

Fig. 16: shows the accumulation to occur atrap must exist either before or coincident with the time of
migration.
INTRODUCTION
PETROLEUM TRAPS

A - Anticlinal Traps:
- Adjacent to, subductive where there is a net shortening of the
Earth's crust.
- Fields in such traps are found within, and adjacent to,
mountain chains in many parts of the world.
- Compressional anticlines are also a common feature within
both transpressional and transtensional strike - slip basins.
B –Fault Traps:
- Fault implies fracturing of rock and relative
motion across the fracture surface.
- This upward migration will continue until it
trapped by the impermeable shale (seal).
Classification of Traps
1. Structural Traps:
The oil trapping due to structure
INTRODUCTION

C- DIAPIRIC TRAPS:
- Produced by the upward movement of sediments that are less dense than those overlying them.
- Generally caused by the upward movement of salt or, less frequently, over pressured clay.
- Formed by lateral and vertical
lithological variations (channels,
reefs, and bars, truncations).
- About 13o/o of the world's
reserves.
2.1. Primary stratigraphic traps:
- Result from variations in facies that
developed during sedimentation.
These include features such as lenses,
pinch-outs, and appropriate facies
changes.
INTRODUCTION
2. Stratigraphic Traps:
The oil trapping due to stratigraphy
Fig. 17: shows the diapiric trap caused by the upward movement of
salt.

:
SAND BODIES
Channels (shoestring sands),
Coastal barrier bars or Lenses.
Usually surrounded by shales,
which may act both source rock
and seal.
:
B) UP-DIP PINCH OUT
Primary pinch out of strata, e.g., strata that
pinch out up-dip in less permeable rocks
such as shale.
INTRODUCTION

C) DIAGENITMANGES:
- differential solution or cementation
have caused the rock type to vary
laterally.
D) CARBONATE REEFS:
- Porous reefs that are surrounded by
shale, etc.
- They often occur along shelf margins,
adjacent to deeper basins where source
rocks can accumulate.
INTRODUCTION

2.2. Secondary stratigraphic traps:
result from variations that developed after
sedimentation, mainly because of
digenesis. These include variations due to
porosity enhancement by dissolution or loss by
cementation.
UNCONFORMITIES (TRUNCATION)
Due to lateral and vertical changes in
rock type.
HYDRODYNAMIC TRA PS
Uncommon and caused by differences in
water pressures associated with water flow,
which creates tilt on the contacts between
hydrocarbons and water.
The downward movement of water
prevents the upward movement of oil
INTRODUCTION

3- Combination traps
▪ Formed by a combination of two or more of the previously defined genetic processes.
▪ Contains about 9o/o of the world's petroleum reserves.
▪ Most of these traps are a combination of structural and strati graphical processes.
INTRODUCTION

PETROLEUM ELEMENTS
5. MIGRATION ELEMENT
INTRODUCTION

MIGRATION
INTRODUCTION
Fig. 18: Migration pass way from source rock to reservoir and trapped by structure and stratigraphy.

INTRODUCTION
- MIGRATION CAN BE DEFINED AS:
- a step of petroleum history located between its origin and accumulation.
- It could be explained by
- steps of expulsion of petroleum from the source rock then the journey from source rock to trap
or leakage at the Earth's surface.
HOW MIGRATION OCCURS
After generation, the weight of the overlying rocks provides the driving force necessary to expel
the dispersed hydrocarbons in the fine-grained source beds throughout the more porous beds or
fractures to regions of lower pressure.
MIGRATION:

Migration Evidence: Oil Seepages
INTRODUCTION
Oil seepages can be seen from satellite images with SAR. Left: Santa Monica Bay, California. Above:
Caspian Sea, Azerbaijan.
Fig. 19: Shows the migration Evidence Oil Seepages feature

a) Burial
1- The source rock is buried deeper in the Earth.
2- Compaction by the weight of the overlying beds.
3- Increasing pressure provides the driving mechanism to expel the hydrocarbons.
b)Increase in volume
The maturation of a liquid or gas from a solid, causes an enormous increase in volume which may
cause fracturing of the source rock, therefore, escape upwards through such fractures.
c) Separation
Gravity separation of gas, oil and water in reservoir rocks make petroleum is forever trying to rise
until it is trapped or escape at the earth's surface.
STAGE OF MIGRATION
INTRODUCTION

Traditionally (Illing, 1933):
The process of petroleum migration is divided into two parts:
1- primary migration within the low-permeability source rocks
2- secondary migration in permeable carrier beds and reservoir rocks.
It is now recognized that fractured source rocks can also act as carrier beds and reservoir rocks so
more modern definitions are:
Primary migration:
Movement within the fine-grained portion of the mature source rock.
Secondary migration:
Any movement in carrier rocks or reservoir rocks outside the source rock or movement through
fractures within the source rock.
The main driving force is the buoyancy of hydrocarbons.
Tertiary migration:
Movement of a previously formed oil and gas accumulation.
INTRODUCTION

Concerns the expulsion of petroleum from source rock to the
permeable rock.
Takes place across bedding surfaces ,Relatively slower than
secondary migration.
Takes place during the compaction of source rocks.
The obvious transporting medium is the interstitial liquid in
the clay.
petroleum is finely disseminated through the very small
pore spaces seems to exclude transportation in a separate
liquid phase.
Concerns the movement of petroleum through permeable rocks
until it accumulates in a trap.
The main driving force is the buoyancy of hydrocarbons.
PRIMARY MIGRATION
SECONDARYMIGRATION
INTRODUCTION
TERTIARY MIGRATION:
Includes leakage, seepage, and moving from trap to another.
The products of such processes, might be useful as direct petroleum indicators in a poorly understood
basin.

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