Transcript 1. Source Rocks – THE INGREDIENTS FOR OIL & GAS These

The Oil & Gas Industry
4. Seismic Survey
1. Where does Oil and Gas come from?
Oil and gas are hydrocarbons that were formed from the remains of plants and other organisms between layers of sediment around
300 million years ago. These liquid hydrocarbons gradually seeped through porous rock until they reached an impervious layer and
became trapped, forming an oil or gas field. Oil in different parts of the world contains different proportions of the various
hydrocarbons.
1. Source Rocks – THE INGREDIENTS FOR OIL & GAS
These contain organic material from plants or algae. They are buried and cooked below the
earth’s surface for millions of years.
2. Migration
Once the oil is formed, it is forced by gravity to move out of the source rock and upwards
towards the surface. This is a very slow process travelling only a few kilometres over millions
of years.
Our activities in Uganda
What
6. How
happens
does a drilling
if we make
rig work?
a discovery?
A land seismic survey involves firing pulses of sound energy down
through the layers of rock beneath the Earth and recording the energy
that is bounced back by the rock layers below the surface. The way in
which the sound energy travels back depends on the kinds of rocks
and the structures they form.
Signal emitted to
vibrator truck
Data transmitted to a
recording truck
Think of it as a hand drill . . but 10,000 times bigger!
The well is started by rotating the bit into the ground Drilling can continue to depths of several miles
into the earth.
Well Log
Land
Rig
Drill ship
Seismic data acquisition on land
Reflected waves received
by geophones
3. Reservoir
The oil or gas will flow until it collects in a reservoir rock, which has pores (holes) that acts like
a sponge.
4. Trap
To trap the oil and gas the reservoir rock needs to have an impermeable rock, called a
‘caprock’ above it and around it. This caprock will not allow oil or gas to travel through it. If
there is no caprock the oil and gas will reach the surface as an oil or gas seep.
2. How do we know where the Oil and Gas is?
EHS
How do we know if we have found oil or gas?
Once the well reaches its target depth, electric
logging tools are lowered down the hole on a
cable.
These logs can tell us about the quality of the
rocks and the reservoir fluids.
To do a seismic survey at sea, a survey ship fires blasts of
compressed air into the water. A long cable with receivers called
hydrophones, which are sensitive listening devices, like microphones,
is towed behind the ship to detect the echoes from the layers of rocks
beneath the seabed.
If the well finds oil or gas - it can be tested to
estimate the production rate.
The fluid in the reservoir is at a high pressure
and will flow naturally to surface through tubing
set in the wellbore.
Seismic survey at sea
How does the search begin?
Rock structures that contain oil or gas are hidden from view by the sea or other rock
layers but we can't just go around drilling lots of holes and hoping to strike lucky. We
have to be more precise and start by doing a full survey of the area. This is where
geologists and geophysicists, the scientists who study rocks and their formations, are
really valuable.
A geologist looks at the makeup of rocks - where they are and the formations they make.
A geophysicist, as the name implies, uses the physical characteristics of rocks - their
magnetic and gravitational properties, and very importantly, how sound waves travel
through different kinds of rocks - to help understand the structures below the Earth's
surface.
Offshore rig
If the well test is successful then a production
platform will be installed to develop the field.
7. The Crude Oil cycle
An Oil Refinery
Source Rock
An oil refinery is an industrial processing plant where crude oil is processed and refined into more useful
petroleum products such as Gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied
petroleum gas. Oil refineries are typically large sprawling industrial complexes with extensive piping
running throughout, carrying streams of fluids between large chemical processing units.
Different surveying techniques can be used to locate the particular rock formations that
might contain trapped oil. Geologists and geophysicists can build up a detailed picture
of the rock structures, even though these are often many hundreds of metres beneath
the Earth's surface using the results from these techniques.
Transporting Petroleum
to Refinery
Transporting
Petroleum
Seismic Vessel
General survey techniques cover large areas quite quickly and easily and help to build
a broad picture of the underlying rock structures. If the results are encouraging, and a
promising area located, a second stage of exploration is undertaken and a more
detailed seismic survey is carried out.
Seismic section for interpretation
Offshore
Platform
Oil Field
3. Why do we carry out an EIA Assessment?
Tanker
Oil Field
An Environmental Impact Assessment (EIA) is an assessment of the possible impact-positive or negative - that a proposed project may
have on the environment; considering natural, social and economic aspects.
The International Association for Impact Assessment (IAIA) defines an environmental impact assessment as "the process of
identifying, predicting, evaluating and mitigating the biophysical, social, and other relevant effects of development proposals prior to
major decisions being taken and commitments made."
The purpose of the assessment is to ensure that those proposing to undertake certain projects must show that their projects will not
significantly affect the environment.
Drilling
The result of an EIA is assembled in a document known as an Environmental Impact Statement (EIS) which looks at all the positive and
negative effects of a particular project on the environment.
This isGeology
just one component
of the information required to aid decision makers in making their ultimate choices about a project.
The
team
A computer is used to measure and record the echoes, or pulses, that
are reflected back to the surface. The geophysicists then have to
interpret the data, which is displayed as a series of wavy lines, to build
up a detailed picture of the rock formations. Seismic data can now be
shown as a three dimensional picture using the latest computer
technology.
Pipeline
Refinery
Pipeline
Consumers
Tank truckTruck
Tank
Local
Distributor
Railroad Tank Cars
Railroad Tank cars
Mobil
Mobil
5. If we make a discovery?
Once the environmental and seismic surveys are completed, and if the
results look good, drilling an exploratory well is considered.
If large deposits of crude oil and gas are found, the company must
apply to the Government to develop the oil field and bring it into
production. The average time between discovering an oil field and
piping oil ashore is four to five years. During that time various stages
before production are gone through.
Industrial
Customers
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Crude oil is brought to a refinery by either tanker or pipeline. The refined products are then stored
before local distribution by truck or flowlines to industrial users
8. Usage of oil and gas
Crude oil is separated by a heat process into many substances that we rely on for our normal daily
lives.
For example road surfaces, coatings for medicines in the pharmaceutical industry, petrol for boats and
cars and the building industry for roofing and piping.