Exploring oil or gas deposits is an ongoing global pursuit to respond to increasing demand for energies in developed and developing countries. However, exploration only commences after costs and benefits have been assessed and once the proper type of oil and gas agreement or contract has been determined. Nonetheless, there are three general classifications or types of methods and strategies used in oil and gas exploration. These are surface methods, gravity and magnetic surveys, and seismographic methods.
Three main types of oil and gas exploration methods
1. Surface methods: Oil and gas exploration using surface methods are based on either one of the two principles. The first is to survey the geological feature of the surface to determine sedimentary rock formations and repeated folds and faults or salt domes in subsurface rock formation. Note that the rocks that contain oil and gas are all sedimentary rocks.
The second is to determine hydrocarbon seepage on the surface of the earth. Oil seeps in low areas as tarlike deposits that can be easily observed visually and confirmed using lab analysis. Large deposits of oil underground do not leak however. On the other hand, gas is not visible but its concentration in the air or seawater can be detected using special instruments.
2. Gravity and magnetic surveys: Small differences in gravitational force can be picked by an instrument known as gravimeter and can serve further as a basis for assessing the presence of oil or gas deposits. Remember that gravitational force is slightly greater on surfaces close to dense rock formation and it is slightly weaker on surfaces with slat domes underneath.
Using an instrument called magnetometers that can also be attached to an aircraft or sea vessel, properties of rock and rock formation or anomalies can be assessed and mapped based on response to magnetic field measurements and electrical resistivity.
3. Seismographic methods: Both surface methods and gravity or magnetic surveys can map out large geologic anomalies such as faults and folds, salt domes, and anticlines. However, the problem with these methods is that they cannot produce detailed images of smaller and inconspicuous areas.
Seismographic methods use sound waves to produce detailed images of underground rock formations. These methods can involve invasive and destructive techniques however, especially when drilling shallow holes on the surface to place microphones or listening devices to reflect and transmit sound signals.
A note on oil and gas exploration methods
The aforementioned methods and strategies do not guarantee the presence of oil or gas deposits. Results from using either one or more of these methods merely indicate the presence or absence of favorable underground formations or geographic features and characteristics that are conducive for the accumulation of hydrocarbons. It is also important to stress the difference between resources and reserves, especially in classifying the viability of the suspected or proven oil and/or gas deposits in a particular area.