Geophysical Methods for Petroleum Exploration

Badhurahman Abie (2012-09525)

• Introduction • Geophysical Methods used in

Petroleum Exploration • Quick-a-Review

OUTLINE

INTRODUCTION

What’s Geophysical Exploration?

• Geophysical Exploration is an process/activity for searching natural resources (hydrocarbons, minerals, etc.) or other ‘anomalies’ which is used some methods that deal with physical properties of materials within earth sub-surfaces.

Why do we use Geophysical Methods on Petroleum’s Exploration? (1)

• Geophysical Exploration is somewhat cheaper than direct-prospecting by well-drilling.

• Information about occurrence and specific properties of petroleum should be gathered as much as possible and to be more detailed, but in a large area.

Why do we use Geophysical Methods on Petroleum’s Exploration? (2)

• But, this kind of prospecting anyway should be correlated and corrected with borehole data taken all the time.

• In exploration, it’s normally applying more than 1 method, so that each method could correspondence each other.

GEOPHYSICAL METHODS USED IN PETROLEUM

EXPLORATION

There are 3 Primary Geophysical Methods used in Petroleum Exploration

Passive Methods

• Gravity Method, and

• Magnetic Method

Active Method

• Seismic Method

Gravity Method

Gravity Methods

• This method measures variations in Earth’s gravitational field, caused by differences density of material sub-surfaced.

• In fact, it measures the variation in the acceleration due to gravity.

• It is expressed in so called gravity anomalies (in milligal, 10-5 ms-2), i.e. deviations from a predefined reference level, geoid (a surface over which the gravitational field has equal value).

• Gravity is a scalar.

Gravity Methods

Gravity Methods

Gravimeter

Gravimeter

Magnetic Method

• Magnetic surveying aims to investigate the subsurface geology by measuring the strength or intensity of the Earth’s magnetic field Lateral variation in magnetic susceptibility and remanenece give rise to spatial variations in the magnetic field

• It is expressed in so called magnetic anomalies, i.e. deviations from the Earth’s magnetic field.

Magnetic Method (1)

• The unit of measurement is the tesla (T) which is volts·s·m-2

• In magnetic surveying the nanotesla is used (1nT = 10-9 T)

• The magnetic field is a vector • Natural magnetic elements: iron, cobalt,

nickel, gadolinium • Ferromagnetic minerals: magnetite,

ilmenite, hematite, pyrrhotite

Magnetic Method (2)

Magnetic Method

Magnetometer

Seismic Method

• Seismic method using seismic waves that produced by artificial source that propagate through sub-surfaced rock layer and somehow travels back to the surface to be sensed by a receiver.

• There are 2 type of this method according to the way seismic waves travel back to surface:

1. Seismic Reflected Method 2. Seismic Refracted Method

Seismic Method

Seismic Refraction Method

Seismic Reflection Method

Waterborne Seismic Reflection Method

Geophones and Hydrophone

QUICK-REVIEW

• Geophysical Exploration is a kind of activity of exploring somewhat sub-surface through specifics physical properties of the rocks.

• Geophysical Exploration should be carried out with geological methods, so that interpretation could be correlated and corrected

• There are 3 main methods using in Petroleum Exploration, i.e. Seismic, Magnetic and Gravity methods

Quick-a-Review

Any Question stuck on your

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