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University of M’hamed Bougara - Boumerdes
Faculty of Hydrocarbons and Chemistry.
Lesson n 1: Geophysics
Group: STH20 1stsemester
What is geophysics? It is a subject of natural science concerned with the physical
properties of the earth and its surrounding space environment; and the use of quantitative
methods for their analysis. The term “geophysics” sometimes refers only to the geological
applications: Earth’s shape; its gravitational and magnetic fields; its dynamics and their
surface expression in plate tectonics; the generation of magma; volcanism and rock formation.
However, modern geophysics organizations use a broader definition that includes the water
cycle including snow and ice; fluid dynamics of the oceans and atmosphere; electricity and
magnetism and even problems associated with the moon and other planets.
The role of geophysics:
Geophysics is applied to societal needs such as mitigation of natural hazards and
environmental protection. Without this branch, we can explore earth only by direct
observations or drilling. Even drilling has reached a maximum depth of only 12 kms out of
6370 km of earth’s radius. Thus 99.9% of inside earth would have remained unexplored
without geophysics. It locates underground water; finds archaeological relics; determines the
thickness of glaciers and soil, exploration geophysics has helped us to find the energy sources,
also to analyze potential petroleum reservoirs and mineral deposits.
Find in the text words whose definitions as follow:
……….: a liquid mixture of hydrocarbons which is present in suitable rock and can be
extracted and refined to produce fuels including diesel oil …
………: are pure, solid, inorganic (nonliving) materials found in Earth's crust. They are
made of one or more elements that are the most basic, naturally occurring substances on
Earth and these elements cannot be broken down (except by radioactive decay).
………..: the study of remains of ancient buildings, etc
Insert the best word into the paragraph: physical, gravity, industries, seismic waves,
quality, seismic data, hydrocarbons.
Geophysicists study the … aspects of the earth using a range of methods, including …,
magnetic, electrical and seismic. They play a vital role in the oil and gas … by creating a
picture of what lies below the earth's surface. They do this by collecting data on…, which
move through and around the earth. Geophysicists are responsible for controlling the … of
the … collected and interpreting it in order to create maps of the build-up of…. They also
examine the physical properties of rocks, as well as gathering and evaluating well data in
order to build reservoir models.
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Branches of geophysics:
It has two main branches (1) solid earth geophysics which uses natural field source to
study the earth – their structural variation into crust, mantle and core and the geodynamics,
i.e., the plate tectonics. Seismology, Volcanology, geomagnetism… are important branches of
Solid Earth Geophysics. It provides the basis of the structure of the earth and the geodynamic
balance of the various layers of the earth. Around 8-10% of geophysicists work in this field.
The second branch makes use of artificial source and is called Exploration
Geophysics. This field was mainly developed for oil exploration and later extended to mineral
and ground water exploration. Application of exploration geophysics to oil and mineral
exploration made it the fastest developing branch of earth science – almost 90% of
geophysicists work in this field.
………….: A branch of science concerned with earthquakes and related phenomena.
How is solid earth geophysics different from exploration geophysics?
…………………………………………………………………………………………
…………………………………………………………………………………………
Who is the geophysicist?
A geophysicist is someone who studies the Earth using gravity, magnetic, electrical,
and seismic methods. Some geophysicists use these methods to find oil, iron, copper, and
many other minerals. Some evaluate earth properties for environmental hazards and evaluate
areas for dams or construction sites. Research geophysicists study the internal structure and
evolution of the earth, earthquakes, the ocean and other physical features using these methods.
Divisions of geophysics:
Geophysics covers a broad range of earth science and offers a variety of options. Here
are some, but not all, of the divisions of geophysics: Seismologists, Marine geophysicists,
Petroleum geophysicists, Mining geophysicists, Environmental geophysicists, Atmospheric
physicist, Gravity geophysicist, Magnetic geophysicist, Electromagnetic geophysicist,
Electrical geophysicist, Exploration geophysicists…
Petroleum geophysics:
The largest number of geophysicists find employment in the petroleum industry.
Petroleum geophysicists find oil and gas by building a clear picture of what is below the
Earth's surface. A seismic source is used to create shock waves that reflect off the rock layers.
The upcoming energy is received by the receivers, and the signal is transmitted through the
cable to the recording truck. The signal is digitally recorded and stored on disk. Petroleum
geophysicists usually specialize in the acquisition, processing or interpretation of seismic
data. Petroleum geophysicists can be divided into three categories: Acquisition Geophysicists
that
take 'pictures' of the subsurface; Processing Geophysicists that
develop and sharpen the 'picture' and Interpretation Geophysicists
that use the sharpened 'picture' to construct the shape of petroleum deposits. The most
common and effective method of obtaining a clear picture of the Earth's subsurface is the
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seismic method. In terms of cost management, however, gravity and magnetic data can
provide a cost-effective means to assist in interpreting basin to lease-scale structural geology
and depth to basement studies at the oil and gas exploration stage. At the reservoir scale,
geophysics, in particular, seismic data often provide the primary information on reservoir or
aquifer extent. High resolution 3D seismic survey has proven effective in reducing the risk of
dry holes and in predicting drilling hazards such as faults and overpressure.
1. Discuss the following questions:
A. What do geophysicists need in order to study the earth?
B. Count some of the geophysicists’ roles.
C. How are geophysicists affective in the oil and gas industry?
D. What do you know about the physical properties of the rocks?
E. Do you think that the largest number of geophysicists find employment in the
petroleum industry? Justify.
2. Fill in the gaps with the appropriate word: seismic data, physics, the seismic
method, the acquisition,
In the petroleum industry, the most common and effective method of obtaining a clear
picture of the Earth's subsurface is... This technique is based on principles of Earth…. Shock
waves set off at the surface penetrate the earth like sonar and the returning echo can be used
to tell what is below. Petroleum geophysicists usually specialize in…, processing or
interpretation of…. However, most will have a good knowledge of the other areas, as well as
geology and some engineering principles, as there is a high degree of collaboration between
the different groups.
3. Guess to what the following definitions refer:
A study of dynamic forces or processes within the earth.
The study of the earth, the materials of which it is made, the structure of those
materials and those processes. An important part of it is the study of how
earth’s materials, structures, processes and organisms have changed over time.
The general characteristics of sediments, rocks and rock types present in a
stratigraphic division of earth. In other words the study of rocks and their
formation.
4. Define/ explain briefly the following from your own background:
Earthquakes; marine geophysicists.
Good luck
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