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reminder to attach Xerox printer driver - PROCEDURE: DONT FORGET TO CHANGE FOOTER!!
File / Print / Printer
click on Xerox
click on set as default printer
click on close and close again - now delete this text box - sdone! (Topcon styles)
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TABLE OF CONTENTS
Page
Preliminary Pages 3-i to v
SECTION 1 INTRODUCTION TO PETROLEUM 3-1-1
1.1 DEFINITION OF PETROLEUM 3-1-3
1.2 THE OIL AND GAS INDUSTRY 3-1-3
EXERCISES RELATING TO SECTION 1 3-1-5
SECTION 2 BASIC GEOLOGY 3-2-1
2.1 TYPES OF ROCK 3-2-3
2.1.1 General 3-2-3
2.1.2 Igneous Rock 3-2-3
2.1.3 Sedimentary Rock 3-2-3
2.1.4 Metamorphic Rock 3-2-5
2.1.5 The Cycle of Rocks 3-2-52.2 ROCK STRUCTURE 3-2-5
2.2.1 General 3-2-5
2.2.2 Folds 3-2-7
2.2.3 Faults 3-2-7
EXERCISES RELATING TO SECTION 2 3-2-9
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Page
SECTION 3 ORIGINS OF HYDROCARBON DEPOSITS 3-3-1
EXERCISES RELATING TO SECTION 3 3-3-5
SECTION 4 SEDIMENTARY ROCK 3-4-1
4.1 GENERAL 3-4-3
4.2 POROSITY AND PERMEABILITY 3-4-34.2.1 General 3-4-3
4.2.2 Porosity 3-4-3
4.2.3 Permeability 3-4-3
4.2.4 Cementation 3-4-4
4.3 TYPES OF SEDIMENTARY ROCK 3-4-4
4.3.1 General 3-4-4
4.3.2 Sandstone 3-4-54.3.3 Shale 3-4-5
4.3.4 Limestone 3-4-5
4.3.5 Evaporites 3-4-5
EXERCISES RELATING TO SECTION 4 3-4-7
SECTION 5 RESERVOIR FORMATION 3-5-1
EXERCISES RELATING TO SECTION 5 3-5-7
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TABLE OF CONTENTS
Page
SECTION 6 EXPLORATION 3-6-1
6.1 EXPLORATION METHODS 3-6-3
6.2 DRILLING PROPOSAL 3-6-3
EXERCISES RELATING TO SECTION 6 3-6-5
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TABLE OF CONTENTS
ILLUSTRATIONS
FIGURE NO. DESCRIPTION
1-1 Global Energy Supply
2-1 Sediment Formation
2-2 Cycle of Rocks
2-3 Types of Fold
2-4 Typical Fault
5-1 Oil Seeps
5-2 Anticlinal Trap
5-3 Migration of Petroleum
5-4 Salt Dome Formation
6-1 Seismic Surveying
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SECTION 1
INTRODUCTION TO PETROLEUM
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Figure 1-1 Global Energy Supply
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1 INTRODUCTION TO PETROLEUM
1.1 DEFINITION OF PETROLEUM
The word petroleum comes from the Greek/Latin words petra, meaning rock,
and oleium, meaning oil. Rock oil, or crude oil, is an oily flammable liquid,
varying from almost colourless to black. It comprises a complex mixture of
hydrocarbons (i.e. basically chemically organic material) with small quantities
of other materials, existing at many places in the upper strata of the earth.
It can vary from black, tarry asphalts to light oils which can be used almost
directly as motor fuel. In between are oils of all colours varying through red,
reddish brown, dark brown to black, and some fluorescent green or purple in
reflected light. In odour some smell sweet, some smell like turpentine, and
others have an odour like rotten eggs due to the presence of sulphur
compounds. Wax occurs in some oils; others have none.
In addition to liquid hydrocarbons, large quantities of hydrocarbon gas are
usually present in the wellhead product, often exceeding the liquid content.
1.2 THE OIL AND GAS INDUSTRY
Refer to Figure 1-1.
Petroleum has been used for thousands of years. Seepages from cracks in
the ground were collected and used for lamp fuel and medicine in the Middle
East and China over 3000 years ago. Dried out oil seeps, in the form of
bitumen lakes, have for centuries provided material to keep ships watertight,
build roads and even as mortar for house building (by the ancient Greeks).
The petroleum industry as it is known today began in the USA. The first well
to be drilled for oil was in 1859, the oil produced being used to make kerosene
for oil lamps.
The invention of the gasoline engine, around 1900, increased the demand for
oil. Kerosene had to be refined to produce the lighter grade of petroleum
(gasoline) needed for automobile fuel. This requirement generated the growth
of the refinery industry. Demand further increased when ships changed from
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coal to oil for fuel. Since those days, the uses for oil and gas have steadily
increased.
The petrochemical industry uses petroleum to produce many products such
as soap, detergents, cosmetics, perfumes, plastics and medicines. Many newproducts have been developed by the industry to improve living standards.
Today the economy of the world depends upon the petroleum industry.
More recently, governments and industry have come to appreciate that
petroleum is a scarce and valuable resource. They have adopted
conservation policies designed to prevent waste.
In the past, produced gas was flared as there was no means to harness or
use it for fuel. Today, gas is transported along pipelines for industrial and
domestic distribution and consumption. It may also be liquefied for shipment
to distant users. If there is no immediate requirement for gas, it may be
reinjected into the reservoir to provide gas lift or simply as a means of
conserving it for future use.
Over the years the world demand for petroleum has increased considerably.
This demand will continue to increase as more nations become industrialized.
The following figures illustrate this growth:
1900 100 million (100 000 000) barrels per year
1981 20 billion (20 000 000 000) barrels per year
1990 80 billion (80 000 000 000) barrels per year.
These figures only account for liquid oil products. Liquefied gas levels also
show increases as more gas becomes available. Liquefied Natural Gas
(LNG) is being used in more and more domestic and industrial applications.
For these reasons, exploration and prospecting for new hydrocarbon fields is
an ongoing and ever important aspect of the oil and gas industry. To
appreciate how this is carried out, some understanding of the geology
involved is essential and is covered in this training module.
This module also provides information which will help in the understanding of
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the composition, characteristics and behaviour of wellhead fluids.
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EXERCISES RELATING TO SECTION 1
1 Crude oil can appear at the wellhead in various colours. List 4 of them.
2 What causes crude oil to smell like rotten eggs?
3 Name 3 historical uses for bitumen.
4 In which country did the modern petroleum industry begin?
5 Name 4 products derived from petroleum produced by the petrochemical
industry.
6 Produced gas is sold for domestic and industrial use. Name 1 other use.
7 What was the approximate worldwide demand
for petroleum in 1990 (in barrels per year)?
(a) 10 million
(b) 20 billion
(c) 80 billion
(d) 120 billion
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SECTION 2
BASIC GEOLOGY
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Figure 2-1 Sediment Formation
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2 BASIC GEOLOGY
2.1 TYPES OF ROCK
Refer to Figure 2-1.
2.1.1 General
All the rocks of the Earth can be divided into three basic types:
igneous
sedimentary
metamorphic.
Of these three, it is sedimentary rock which is of particular interest
to the petroleum geologist as this is where hydrocarbons are
formed and trapped.
2.1.2 Igneous Rock
In the centre of the Earth is a hot molten mass of rock known as
magma. Magma is released at the surface when volcanoes erupt.
The released molten rock quickly cools and solidifies into igneous
rock. Magma can also cool and solidify without breaking out onto
the surface.
2.1.3 Sedimentary Rock
The forces of nature in the form of wind, rain, temperature changes,
tides and gravity begin to attack igneous rock as soon as it has
cooled. Over millions of years, this erosion process is considerable
and is extreme enough to wear away whole mountain ranges given
sufficiently long time scales. The eroded rock does not, however,
simply lay on the surface but is carried away by the action of wind,
rain and river flow, eventually to be deposited in the sea. The
layers thus deposited are known as sediments.
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K I O - 4 - 0 1 5 8 . C D R
M E T A M O R P H I C
R O C K S
M A G M A
S E D I M E N T A R Y
R O C K SS E D I M E N T S
I G N E O U
R O C K S
P R E S S U R E
C E M E N T A T I O N
E R O S I O N
H E A TC O O L I N G
Figure 2-2 Cycle of Rocks
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As these sediment layers build up, the overall weight increases, as
does the pressure on the lowest levels. As a result, the lower
layers become increasingly compacted until they become new rock
formations known as sedimentary rocks.
Some types of sedimentary rock can be formed by the deposition
over millions of years of the skeletal material of billions of sea
creatures, e.g. vertebrate skeletons, invertebrate shells and corals.
2.1.4 Metamorphic Rock
the Earth's crust is not a fixed stable surface. The continents are
constantly in motion, albeit extremely slowly, floating on the molten
magma below. This activity causes both sedimentary and igneous
rock to be subjected to enormous forces of heat, pressure and
friction, resulting in a third type of rock known as metamorphic rock.
2.1.5 The Cycle of Rocks
Refer to Figure 2-2.
Over millions of years, the process of formation of igneous,
sedimentary and metamorphic rocks, including mountain building
and erosion, are continuously repeated throughout the life of the
planet. This is known as the cycle of rocks.
2.2 ROCK STRUCTURES
2.2.1 General
As discussed in Section 2.1.4 above, the Earth's crust is continually
in motion. Among other effects, this movement results in
realignment of the strata, known as folds and faults.
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Figure 2-3 Types of Fold
Figure 2-4 Typical Fault
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2.2.2 Folds
Refer to Figure 2-3.
When layers of sedimentary rock are upfolded into an arch-likeform, the structure is called an anticline. When the beds are
downfolded into a trough-like structure they are called synclines. If
an anticlinal structure is vertical so that it plunges in all directions it
is known as a dome. If a synclinal structure has a vertical axis such
that it dips inwards in all directions it is known as a basin.
2.2.3 Faults
Refer to Figure 2-4.
Faults are formed when the compression or tension forces acting
on rock strata cause the layers to fracture. The rock on either side
of the fracture is then free to move up or down, displacing the strata
from their original positions. Faults range in size from just a few
centimetres to many hundreds of kilometres along the break line
(fault plane).
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EXERCISES RELATING TO SECTION 2
1 Name the 3 basic types of rock.
2 Which of the above is of particular interest to the petroleum geologist?
3 What is the name of the molten rock at the centre
of the Earth?
(a) Sedimentary
(b) Mud
(c) Petroleum
(d) Magma
4 Name 4 forces of nature responsible for the erosion of igenous rock.
5 Fill in the missing words in the following sentence:
Movement of the Earth's crust results in realignment of the strata, known
as ........... and ........... .
a b c d
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6 Name 2 types of fold.
7 Consider each of the following sentences and state if true or false:
(a) The smallest faults found are in the order of one kilometre.
(b) The largest faults found are in the order of 100 metres.
(c) Faults range from a few centimetres to many hundreds of kilometres.
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SECTION 3
ORIGINS OF HYDROCARBON DEPOSITS
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3 ORIGINS OF HYDROCARBON DEPOSITS
Hydrocarbons, also known as fossil fuels, are organic substances formed from the
remains of plants and animals deposited millions of years ago over long periods of
time.
Although traces of hydrocarbons have been found in rocks more than 1 billion
(1 000 000 000) years old, it is considered that most petroleum was formed less than
500 million (500 000 000) years ago. Some deposits may have been formed as
recently as 10 million (10 000 000) years ago.
Hydrogen Hydrocarbon deposits are almost exclusively found in the sedimentary
beds deposited in ancient seas. These seas once covered much of the present day
land surfaces.
The process of converting buried organic matter to oil, gas or coal requires two main
factors: time and temperature, with pressure playing a subsidiary role.
The term cooking time is used to describe how long (millions of years) the buried
matter has been at sufficient temperature to undergo conversion to oil or gas. The
rate at which the conversion takes place doubles with every 10C rise in
temperature above 60C (the critical temperature below which conversion will not
take place).
Above a temperature of 120C the conversion process breaks down the organic
matter and any oil is formed into gas. The term oil window is applied to zones of
buried sediments that lie between 60C and 120C. Above 120C to 325C lies
the gas window. Both these zones are sometimes referred to as the kitchen as it is
within this area that oil and gas are formed, provided the cooking time is right.
Above 325C, hydrocarbons are destroyed and reduced to carbon or coke.
Sediments experience a rise in temperature as they are buried increasingly deeper
below the surface with the passage of time. Typically a 1C rise in temperature is
experienced for every 30 m of burial. The rate of increase in temperature with depth
is known as the geothermal gradient and varies from basin to basin.
Knowledge of the geothermal gradient is important as it determines the location in
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depth terms of the kitchen in which oil and gas will have been produced from the
original organic matter. Knowledge of earth movements is important as it determines
the length of time that the sediments have remained in the kitchen.
The longer a sediment has been buried, the lower the threshold temperaturerequired to convert its organic matter to oil. Jurassic sediment needs only 60C
threshold as it has had over 150 million years in which to cook. Tertiary sediment
needs a threshold of 80C to 100C as it may have had fewer than 60 million years
in which to cook.
Marsh gas is produced by degradation of organic matter at or near the surface and
at normal temperatures. While significant volumes are created in this way, it is rarely
trapped in geological structures to form an economic accumulation of natural gas.
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EXERCISES RELATING TO SECTION 3
1 From what are hydrocarbons formed?
(a) Sulphur
(b) Coal
(c) Plant and animal remains
(d) Eroded igneous rock
2 Consider each of the following sentences and state if rue or false:
(a) Hydrocarbons have been found in rocks more than 1 000 000 000
years old.
(b) Hydrocarbons have been found in rocks more than 3 000 000 000
years old.
(c) Some hydrocarbon deposits may have formed as recently as 1 000
years ago.
(d) Some hydrocarbon deposits may have formed as recently as
10 000 000 years ago.
3 What are the 2 main factors in the process of converting buried organic matter
into oil, gas or coal?
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4 What is the critical temperature below which
conversion will not take place?
(a) 60C
(b) 120C
(c) 180C
(d) 325C
5 In the conversion process, what happens above 325C?
6 What is a zone of buried organic matter, at the
correct temperature for conversion to oil and/or
gas, known as?
(a) Gas cooker
(b) Sink
(c) Kitchen
(d) Cellar
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SECTION 4
SEDIMENTARY ROCK
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44 SEDIMENTARY ROCK
4.1 GENERAL
When considering new areas for hydrocarbon exploration, the geologist first
considers areas with sedimentary rock formation as it is in this type of rock
that petroleum is primarily found.
4.2 POROSITY AND PERMEABILITY
4.2.1 General
There are two basic rock properties to be considered in the searchfor hydrocarbons:
porosity
permeability.
4.2.2 Porosity
Porosity is the ability of a rock to hold fluids and is directly related to
the amount of space between the grain particles comprising the
rock. Porosity is quoted as a percentage.
4.2.3 Permeability
Permeability is the ability of a rock to allow fluid to flow through it.
Permeability is measured in millidarcies.
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4.2.4 Cementation
If silica (present in most sands) is present in the deposit it will
dissolve in any water contained in the deposit. Due to the effects of
heat, this silica solution will recrystallize between the rock particles.
If the deposit is sufficiently permeable, flow of water through the
particles may occur. Any carbonates dissolved in the water will also
be precipitated due to the higher temperature. These two
processes, silica recrystallization and carbonate precipitation, are
referred to as cementation as they act to bind the individual grains
together. In general, the deeper a rock has been beneath the
surface of the earth (which is not necessarily the depth at which it is
found) the greater will be the degree of cementation. This process
of pressure increase, temperature increase, and cementation, is
known as diagenisis. The greater the degree of cementation the
lower the porosity and the permeability.
4.3 TYPES OF SEDIMENTARY ROCK
4.3.1 General
There are four main types of sedimentary rock:
sandstone
shale
limestone
evaporites.
Sandstone and shale are known as clastics or rocks formed from
fragments of other rock. Limestone and evaporites are known as
chemical deposits as they are formed by chemical precipitation from
seawater.
Sandstone reservoirs are usually more porous than those of
limestone. The least consolidated, younger sandstones are more
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porous than the more tightly compacted, older or more deeply
buried formations.
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4.3.2 Sandstone
Sandstone consists of sand-sized grains composed predominantly
of quartz. Often cemented by a silica or carbonate cement. It is the
typical oil reservoir rock.
The degree of porosity in sandstone depends on grain size, grain
shape, the degree of sorting and the amount of cement. The
permeability of a rock does not always correlate directly with its
porosity but it is usually good in a clean porous sandstone.
4.3.3 Shale
Shale, including mudstone, claystone and siltstone, is composed of
silt-sized grains and smaller. Clay particles make up a large
percentage of the rock. It usually displays laminations parallel to
the bedding plane. Whilst the porosity of shale may often appear to
be as high as that of good sandstone, the pores are so small and
the pore throats so restricted that effective porosity is zero. The
rock is usually impermeable, unless it is fractured when it allows
flow or storage of hydrocarbons.
4.3.4 Limestone
Limestone is a general term for rocks containing at least 80% by
volume calcium or magnesium carbonates. It often occurs as a
bedded and distinctly jointed rock which is the consolidated
equivalent of limy mud, calcareous sand or shell fragments, or all
three in combination.
Usually it has no primary (or intrinsic) porosity. In time, a secondary
porosity may develop as a result of joints and cracks being
developed and enlarged by ground water action.
4.3.5 Evaporites
Evaporites have no porosity or permeability. Their ability to flow
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plastically has very important implications for geologists and drilling
engineers.
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EXERCISES RELATING TO SECTION 4
1 Fill in the missing words in the following sentences:
(a) Porosity is the ability of a rock to .......... ..........
(b) Permeability is the ability of a rock to allow .......... to .......... through it.
2 What is the unit of measurement for permeability?
3 What are the 2 processes which together are referred to as cementation?
4 What are the 4 main types of sedimentary rock?
5 What are sandstone and shale known as?
(a) Clastics
(b) Elastics
(c) Clays
(d) Evaporites
6 What are the porosity and permeability properties
of evaporites?
(a) High
(b) Average
(c) Low
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(d) Zero
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SECTION 5
RESERVOIR FORMATION
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Figure 5-1 Oil Seeps
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Figure 5-2 Anticlinal Trap
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5 RESERVOIR FORMATION
As sediments are buried beneath the sea, their pore spaces fill with salt water. With
increasing depth, the muddy organic-rich rocks move into hydrocarbon generation.
Oil and gas is formed and is squeezed out of these source rocks, migrating by
various pathways, along fault planes, through permeable beds until it seeps to the
surface (refer to Figure 5-1) or it is trapped by an overlying impervious cap rock
(refer to Figure 5-2) so that it accumulates below it. The rock in which the
hydrocarbon accumulates is always permeable and porous. This is the reservoir
rock. Five essential requirements can be identified for the development of a
hydrocarbon reservoir:
mature source rock
migration route
impervious cap rock
permeable reservoir rock
trapping structure.
The hydrocarbon fluid displaces the salt water or brine in the pore spaces as it flowsupwards to fill the reservoir rock under the trap. Because the reservoir is originally
saturated with salt water, the petroleum migrating into it displaces some water,
leaving a film of water around the sand grains and leaving the smaller pores full of
water.
The operating force is capillary pressure so the smaller the opening, the more
difficult it is to displace water from the water-wet rock. Assuming a liquid
hydrocarbon with its gas phase in solution, if the initial porosity is 25%, the pores willtypically contain 80% hydrocarbon and 20% water.
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Figure 5-3 Migration of Petroleum
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In attempting to recover the oil, the same capillary forces work in reverse and often
only 30% of the oil in place can be recovered to the surface, the rest being trapped in
the smaller pore spaces (refer to Figure 5-3).
There are several different geological situations that can give rise to suitable traps.
Traps can be formed by folding rock into an anticline (refer to Section 2.2.2). The
formation of salt domes (refer to Figure 5-4) is another mechanism, as is faulting. A
trap may result from a change in the type of sediment being laid down (known as a
stratigraphic trap).
There is almost an infinite variety of geological conditions that can combine to form a
trap. When studying a trap, the geologist attempts to find out what geological
conditions had to develop for it to form.
Commercial hydrocarbon deposits are classified as accumulations, fields and
provinces. The simplest unit of commercial occurrence is the accumulation. It is
defined as the body of oil or gas, or both, occurring in a separate reservoir and under
a single pressure system. An accumulation may be small, underlying only a few
hectares, or it may extend for many square kilometres. Its content may be entirely
gas, or it may be entirely or mainly oil.
When several accumulations are related to a single geological feature, either
structural or stratigraphic, the group of accumulations is termed a field. The
individual accumulations in a field may occur at various depths, one above another,
or they may be distributed laterally throughout the geological feature.
The petroleum reservoir is the part of the rock that contains the accumulation of oil.
The location of every oil and gas accumulation may be said to be the result of
complex or interrelated geological conditions. Each reservoir is unique in its details.
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Figure 5-4 Salt Dome Formation
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EXERCISES RELATING TO SECTION 5
1 What are the 5 essential requirements for the development of a hydrocarbon
reservoir?
2 If the initial porosity of a reservoir rock is 25%,
what would be a typical ratio of hydrocarbon to water?
(a) 50 : 50%
(b) 70 : 30%
(c) 80 : 20%
(d) 90 : 10%
3 Name a geological condition which could result in the formation of a trap.
4 Fill in the missing words in the following sentence:
Commercial hydrocarbon deposits are classified as .........., .......... and
..........
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5 Consider the following sentences and state if true or false:
(a) An accumulation may range in size from 10 square kilometres to
hundreds of square kilometres.
(b) An accumulation is usually less than 1 hectare in size.
(c) The content of an accumulation is always gas and oil in equal
proportions.
(d) An accumulation may range in size from a few hectares to many
square kilometres.
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SECTION 6
EXPLORATION
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Figure 6-1 Seismic Surveying
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6 EXPLORATION
6.1 EXPLORATION METHODS
By carefully plotting the landscape, the geologist can predict the type of
structure beneath which a reservoir may lie. Study of the surface rock
composition helps this prediction. Aerial survey can narrow down the search
by showing faults otherwise not noticeable at ground level, provided such
faults are exposed.
If geological and aerial surveys give strong indications, a seismic survey may
be carried out. The seismic survey team looks for the presence of cap rock
by measuring echoes. A charge of explosive is fired into the ground and the
time taken for the echo to return is noted (refer to Figure 6-1). If cap rock is
present, the echo returns quickly and sharply; the sooner the echo returns,
the nearer is the cap rock. There are other types of formation which return
echoes but the seismic team is able to differentiate between them by the
sharpness and timing of the echo.
By repeating these soundings over the area selected by the geologist, the
seismic team is able to draw an underground map and establish the presenceof caps and potential reservoirs. Exploration drilling is, however, the only
means of confirming (or denial) of the presence of a hydrocarbon reservoir.
6.2 DRILLING PROPOSAL
Before an oil company drills into a trap it must decide if that trap could contain
sufficient volume of hydrocarbons to make the venture worthwhile. This
requires a knowledge of the typical distribution of fluids in a reservoir.
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A detailed geophysical and geological prognosis of the prospective structure
must, therefore, be made and upon this is based an estimated chance of it
containing hydrocarbons. The likely volume of recoverable hydrocarbons isestimated as follows:
1 Estimate the volume of reservoir rock enclosed by the trap.
2 Assuming typical porosity and oil/gas saturation, estimate the total
oil/gas in place.
3 Apply an average recovery factor and allow for volume change in
bringing the oil/gas to surface temperature and pressure.
Armed with this estimated recoverable oil volume, the oil company is then in a
position to decide if the prospect is worthwhile drilling in terms of the likely
return on the investment.
6.3 TYPES OF WELL
6.3.1 Wildcat Wells
The geologist must decide where the first wells should be drilled, to
test if his assumptions are correct.
In a new basin or a previously undrilled area, this well is known as a
wildcat well or exploration well, its purpose being to give the
geologist access to the formation he would like to test for oil or gas
accumulation.
6.3.2 Appraisal Wells
If the wildcat well finds oil or gas, further wells may be required to
allow an accurate assessment of the volumes of oil or gas present.
These are known as appraisal wells or stepout wells.
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The following information is required before a decision can be made to
develop an accumulation:
(a) Level of the top of the oil-bearing formation.
(b) Level of the top of the gas zone (possibly the same as (a) above).
(c) Level of the bottom of the gas zone.
(d) Level of the top of the liquid zone, if present (possibly the same as
(c) above).
(e) Level of the bottom of the liquid zone.
(f) Level of the top of the water zone, if present (possibly the same as (e)above).
(g) Rock samples of producing zones from which porosity and permeability
can be determined.
Several appraisal wells may be required before the extent of the hydrocarbon
reservoir can be fully assessed.
The information from these appraisal wells allows maps to be producedshowing gas/oil evaluations and oil/water elevations (assuming the three-
phases exist in the reservoir). Thus, as reservoir porosity is already known,
an 'oil in place' volume can be calculated.
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In assessing the potential financial returns from a potential reservoir, it must
be remembered that a reservoir can rarely be made to produce more than
30% of its contents without pumping or other assistance. In some cases the
figure is much smaller. Even with assistance, a reservoir can rarely be made
to produce more than 50% to 60% of its contents. No method has yet been
devised to enable the final 30% or so to be extracted.
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EXERCISES RELATING TO SECTION 6
1 What is the purpose of aerial surveying?
2 Upon what principle is seismic surveying based?
(a) Echo returns
(b) X-rays
(c) Chromatography
(d) Photography
3 In which order are the following types of well drilled?
(a) Appraisal well
(b) Development well
(c) Exploration well
4 What is the name of the test used to establish (among other data) the gas/oil
ratio?
5 What percentage of a reservoir's content can be produced without pumping or
other assistance?
a b c d
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