Fundamentals of Petroleum Geology

1. Fundamentals of Petroleum Geology
July 02, 2020
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DEPARTMENT OF PETROLEUM AND MINING
ENGINEERING
SHAHJALAL UNIVERSITY OF SCIENCE AND
TECHNOLOGY, SYLHET
Course: PME 241
Course Title: Petroleum Geology
Md. Shofiqul Islam, PhD
Professor
Dept. of PME, SUST

2. Rationale
• Petroleum geology course is the basic course for
petroleum engineering programs world-wide.
• This course aims to develop an understanding of
processes and prerequisites required for the formation
of a complete petroleum system (i.e. how petroleum
reservoirs form).
• The module additionally provides the overview of
regional petroleum exploration and production and
reservoir characteristics.
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3. Objectives
• To summarize the fundamentals of Geology
that need to be understood and integrated with
Engineering data to effectively and optimally
manage petroleum reservoirs.
• To understand the variety of geologic data that
are integrated together to describe the
geometry of a reservoir.
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4. Course Layout
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Lecture No. Topic Lecture No. Topic
Lecture 1-3 Fundamentals of PG Lecture 15 Reservoir Rocks
Lecture 4 The subsurface
environment
Lecture 16 Reservoir Rocks
Lecture 5 Subsurface Temperature Lecture 17 Reservoir Rocks
Lecture 5 Subsurface Pressure Lecture 18-19 Petroleum migration
Lecture 6-8 Fluid Dynamics Lecture 20-22 Traps and seals
Lecture 9-10 Generation of petroleum Lecture 23-27 Sedimentary Basins and
Petroleum Systems
Lecture 11-12 Formation of Kerogen Lecture 28-32 Petroleum System of
Bangladesh
Lecture 13-14 Source and Reservoir
Rocks
Lecture 33-36 Review Classes

5. Reference Books
• ELEMENTS OF PETROLEUM GEOLOGY by Richard C. Selley
• PETROLEUM GEOSCIENCE by Jon Gluyas and Richard Swarbrick
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6. • Petroleum
• Comes from Latin: 'petra' (rock) + Latin: oleum (oil) or crude oil is a naturally
occurring flammable liquid consisting of a complex mixture
of hydrocarbons of various molecular weights and other liquid organic
compounds, that are found in geologic formations beneath the Earth's surface.
• By definition
• Petroleum is a mixture of hydrocarbon molecules and lesser quantities of
organic molecules containing sulfur, oxygen, nitrogen, and some metals. The
term includes both oil and hydrocarbon gas.
• Petroleum geology
• Petroleum geology is the application of geology to the exploration for and
production of oil and gas.

7. Relation with other branches

8. Fundamental Elements of a
Petroleum system
Gluyas and Swarbrick, 2006

9. Physical Chemical Properties
Our general concerned with the search for oil or gas
Hydrocarbon
Grades from gases, via liquids and plastic substances, to solid
Gases, dry (methene)
and wet (ethene,
propane, butene etc.)
Condensates are
HCs that are
gases in
subsurface but
condensed to
liquid when they
are cooled at
surface
Liquid HCs are oil,
crude oil
Plastic HCs
include asphalt and
related substance
Solid HCs are
coal and kerogen

10. Natural Gas
A mixture of hydrocarbons and varying quantities of
nonhydrocarbons that exists either in the gaseous phase or in
solution with crude oil in natural underground reservoirs.
Adopted by API, AAPG and SPE
Dissolved gas
Is in solution in
crude oil in the
reservoir
Associated gas
Known as gas cap
gas, overlies and is
in contact with
crude oil in the
reservoir.
Nonassociated gas
Is in reservoirs that do
not contain significant
quantities of crude oil.

11. Natural gases and their dominants modes of formation

12. Significant data of the paraffin series

13. Molecular
structures
of the more
common
HC gases.

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Element Percent range
Carbon 83 to 87%
Hydrogen 10 to 14%
Nitrogen 0.1 to 2%
Oxygen 0.05 to 1.5%
Sulfur 0.05 to 6.0%
Metals < 0.1%
Hydrocarbon Average Range
Paraffins 30% 15 to 60%
Naphthenes 49% 30 to 60%
Aromatics 15% 3 to 30%
Asphaltics 6% Remainder
Chemical Composition
Composition by weight
Composition by weight

15. Crude oil
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“a mixture of hydrocarbons that existed
in the liquid phase in natural underground
reservoirs and remains liquid at atmospheric
pressure after passing through surface
separating facilities" (joint API, AAPG,
and SPE definition).
In appearance crude oils vary from straw
yellow, green, and brown to dark brown or
black in color. Oils are naturally oily in texture
and have widely varying viscosities.
Oils on the surface tend to be more viscous
than oils in warm subsurface reservoirs.
Surface viscosity values range from 1.4 to
19,400
centistokes and vary not only with temperature
but also with the age and depth of the oil.

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18. Methane Hydrates
• ???
• Shale gas
• ??
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19. Gas hydrates
• Gas hydrates are a crystalline solid formed of water and gas. It
looks and acts much like ice, but it contains huge amounts of
methane
• It is known to occur on every continent; and it exists in huge
quantities in marine sediments in a layer several hundred
meters thick directly below the sea floor and in association
with permafrost in the Arctic.
• It is not stable at normal sea-level pressures and temperatures
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20. Gas hydrates are important for three reasons:
• They may contain a major energy resource
• It may be a significant hazard because it alters sea floor
sediment stability, influencing collapse and landsliding
• The hydrate reservoir may have strong influence on the
environment and climate, because methane is a significant
greenhouse gas.
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Gas hydrates

21. • What are gas hydrates used for?
• Hydrate deposits are important for a variety of reasons:
– Gas hydrate deposits may contain roughly twice the carbon contained
in all reserves of coal, oil, and conventional natural gas combined,
making them a potentially valuable energy resource.
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Gas hydrates

22. • What is the main gas found in gas hydrates?
• Gas hydrates occur abundantly in nature, both in Arctic
regions and in marine sediments. Gas hydrate is a crystalline
solid consisting of gas molecules, usually methane, each
surrounded by a cage of water molecules. It looks very much
like ice.
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Gas hydrates

23. • How Gas hydrates are formed?
• Gas hydrates are ice-like crystalline minerals that form when
low molecular weight gas (such as methane, ethane, or carbon
dioxide) combines with water and freezes into a solid under
low temperature and moderate pressure conditions.
• Is methane hydrates renewable or nonrenewable?
• Methane hydrate is a non-renewable resource. This is because
the methane trapped in the ice is a fossil fuel, created over
millions of years of heat..
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Gas hydrates

24. • What temperature do hydrates form?
• The temperature at which hydrates form at 6.8 MPa (1,000
psia). The highest gas gravity without hydrate formation, when
the pressure is 4.76 MPa (700 psia) and the temperature is 289
K (60°F).
• How do you extract gas from hydrates?
Methane hydrate can be dissociated by pumping in hot water
– (a) or by reducing the pressure in the well using pumps
– (b). If carbon dioxide is injected into the hydrate
– (c), the carbon dioxide molecule replaces the methane.
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Gas hydrates

25. • What physical conditions are necessary for the formation and
stability of methane hydrates?
• Methane hydrates are only stable under pressures in excess
of 35 bar and at the low temperatures of the bottom waters of
the oceans and the deep seabed, which almost uniformly range
from 0 to 4°C. Below a water depth of about 350 m, the
pressure is sufficient to stabilize the hydrates.
• Why methane hydrate is called Fire Ice?
• Methane hydrate is often called “fiery ice.”
• Methane hydrate looks like an ice, and starts burning when
an open flame is brought close to it; hence the name. Only
water is left after combustion. It is a strange substance.
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Gas hydrates

26. • Gas hydrate is a crystalline solid consisting of gas molecules,
usually methane, each surrounded by a cage of water
molecules.
• Thus it is similar to ice, except that the crystalline structure is
stabilized by the guest gas molecule within the cage of water
molecules. Gas hydrates are gas concentrators.
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Structure of Gas hydrates

27. • Three hydrate structures have been confirmed in these natural gas hydrate
samples: the cubic structures I (sI) and II (sII) and the hexagonal structure
H (sH). Structures I and II were already described in 1951 and 1952 by von
Stackelberg and Müller, whereas structure H was identified 35 years later
by Ripmeester and co-workers (von Stackelberg and Müller 1951; Müller
and von Stackelberg 1952; Ripmeester et al. 1987). All structures are
composed of various kinds of cages as shown in Table 1.
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Gas hydrates

28. • In structure I, two small pentagonal dodecahedrons (512) are combined with six
tetrakaidecahedrons (51262) into a unit cell. The pentagonal dodecahedron consists
of 20 water molecules forming a 12-sided cavity which has pentagonal faces with
equal angles and edge length. It is the smallest cavity type with an average radius of
0.39 nm and part of all hydrate structures. The tetrakaidecahedron combines 12
pentagons with 2 hexagons, and, therefore, the radius of these cavities increases to
0.433 nm (McMullan and Jeffrey 1965; Sloan 1998).
• A unit cell of structure II consists of 16 pentagonal dodecahedrons (512) and 8
hexakaidecahedrons (51264). The latter cage combines 12 pentagonal faces with 4
hexagonal faces and has a radius of about 0.473 nm (Mak and McMullan 1965;
Sloan 1998) (see also Fig. 1).
• Structure H is the only structure containing a cavity with three square faces in
addition to pentagonal and hexagonal faces (435663). The combination of three
pentagonal dodecahedrons (512), two irregular dodecahedrons (435663), and one
icosahedron 51268, which is the largest cavity (average radius 0.579 nm), forms the
characteristic unit cell of structure H (Ripmeester et al. 1987; Sloan 1998).
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30. • All three structures have been confirmed on natural hydrate samples (Sloan and
Koh 2008, and literature within).
• Structure I CH4 hydrates with very little amounts of additional gases such as CO2
or H2S are the most common species. In 2007, oceanic gas hydrates on the
Cascadian margin
• more complex hydrate, composed of coexisting structure II and structure H hydrate,
has been identified in a sample from the Barkley Canyon on the northern Cascadian
margin.
– Surprisingly, the samples contain, besides methane and other lighter hydrocarbons, some
molecules which were not known as hydrate formers before, such as n-pentane and
nhexane.
• X-ray diffraction measurements on the recovered gas hydrate indicated the
coexistence of a structure I CH4-C2H6 hydrate in addition to a complex structure II
hydrate containing C2 through C4 hydrocarbons besides CH4
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Gas hydrates

31. • The typical methane clathrate hydrate composition is usually
represented as (CH4)4(H2O)23 or 1 mol of methane for every
5.75 mol of water, corresponding to 13.4% w/w, but the actual
composition is dependent on the number of methane
molecules that can be accommodated by the various cage
structures of the water lattice.
• When brought to the earth's surface, one cubic meter of gas
hydrate releases 164 cubic meters of natural gas.
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Gas hydrates

32. • Reserve
• Gas hydrates are now thought to occur in vast volumes and to
include 250,000–700,000 trillion cubic feet of methane and the
formation thickness can be several hundred meters thick.
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Gas hydrates

33. Assignment 01
• Tasks
• 1. world wide distribution of Gas hydrates
• 2. Mechanism of the extraction process of gas hydrates
• 3. Problems and prospect of gas hydrates
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34. Thank you