Geophysical Methods of Hydrocarbon Exploration

1. GEOPHYSICAL METHODS
OF HYDROCARBON
EXPLORATION
M.T.H

2. What is Geophysical Exploration?
• The application of the principles of physics to the
study of the subsurface, in search of hydrocarbon
• Geophysical investigations of the interior of the
earth involves taking measurements at or near
earth’s surface that are influenced by the internal
distribution of physical properties.
• The objective of any exploration venture is to find
new volumes of hydrocarbons at a low cost and
in a short period of time.

3. Introduction
• The usual sequence of activities once an area has been
selected for exploration starts with the definition of a
basin.
• Petroleum exploration and production are concerned with
the geological interpretation of geophysical data,
especially in offshore areas.
• There are three main geophysical methods used in
petroleum exploration: Magnetic, gravity and seismic.
• The first two of these methods are used only in the
predrilling phase. Seismic surveying is used in both
exploration and development phases.

5. Gravity Surveying

9. Interpretation of gravity maps presents
many problems, the simplest of which
are caused by different subsurface
bodies producing the same anomaly on
the surface.
Example: distinguishing between a
small sphere of large density and a
large sphere of low density at similar
depths is impossible.
In some circumstances gravity maps may indicate drillable prospect by
locating salt domes and reefs (because of their low density.

12. Magnetics

17. Seismic Geophysical Survey
• The seismic methods are the most widely used of all
geophysical methods used in petroleum exploration.
• Seismic methods measure seismic velocity of rock layers to
detect both lateral and depth variations and the objective is to
determine the lithology and geometry of the layers.
• A seismic wave can be thought of as shock wave (elastic wave)
or vibration traveling through the ground.
• The rate of travel, or velocity, of the wave is related to the
density of the rock.
• There are two types of elastic waves produced: 1) P-waves,
which are primary or “compressional” waves, and 2) S-waves,
or shear waves

18. Sound as a Tool
Hydrophone
Streamers
Airgun
Sound Wave

19. Activity
Time = 0.7 seconds
Velocity = 1.4 km/second
V=D/T
where:
V = velocity
D = distance
T = time
Distance

20. Procedure
• The procedure used is to lay out a survey line with geophones set
at equal spacings along the line.
• A shock wave is produced at one of the stations by dropping a
heavy weight or detonating an explosion at a “shot point”.
• The shot point is the point on the surface directly above the zone
of interest.
• Ground motions caused by the explosion or impact are transmitted
in the form of P-waves and S-waves.
• A “seismic timer” is used to measure the travel time of the wave
from the instant it is generated until the time the wave reflection is
detected back at the surface.
• Times are measured for each of the successive stations along the
line. Either semi-graphical or computer methods are used to
determine the velocities.

30. Questions?