EXPLORATION FOR OIL
Petroleum, or oil, is the world’s most important source of energy. It is produced in more than sixty countries throughout the world, but there are mainly six important petroleum producing regions in the world. The problem is: how can we determine the possible regions for oil?
Drilling a well is a difficult and expensive operation. Therefore, an oil company first looks for good indications, or signs, of oil in an area. The aim of this exploration is to discover the best areas for drilling. There are four stages in the process of exploration: aerial surveys, a geological survey, a geophysical survey and exploration drilling.
In an aerial survey, a survey of the area is made from an aeroplane. There are two different types of aerial survey: the photographic and the magnetic. During the former, photographs are taken from an aeroplane, showing the most important geological features on the earth’s surface. Maps are made from these photographs.
During the magnetic survey, the earth’s magnetism is recorded. Rock formations under the earth’s surface differ from place to place. As a result, the intensity of the earth’s magnetism and the thickness of the rocks are not the same everywhere. The measurements are analysed and in this way information is obtained about the rock formations. The geologists then look for signs of oil in these formations.
If the indications are good, exploration continues. A geological survey is the next stage. Certain rock formations are visited. By examining these structures, geologists learn about the shape and direction of the rock formations under the surface. Samples of rock are taken to the laboratory and analysed. If the samples contain fossils, these will indicate the age of the rock.
Fossils of marine animals show that there may be oil in the area. Geophysical surveys are used to confirm the results of geological surveys. During a geophysical survey, an explosion is made on the earth’s surface. The rocks under the earth vibrate. These vibrations, called seismic waves, travel down into the earth. Some of them, however, are reflected by rock layers under the surface and ‘heard’ by special equipment.
The waves are recorded on a seismogram. Analysis of this information shows the depth and type of rock formations. All these surveys can help to locate structures under the earth’s surface. But still there may be no oil. There is only one way to be sure, and that is to drill a well. The first wells are called exploration wells or wildcats. A wildcat without any oil is called a dry hole. A discovery well is wildcat with some oil. When oil is discovered, several more wells are drilled in the same field. These are known as production wells.
Exploration for oil is a long, difficult and expensive process. However, it reduces drilling, which saves money.
1. What is the third stage in the process of exploration for oil?
2. What is a discovery well?
3. What is the only one way to be sure that there is oil under the earth’s surface?
4. Why are seismic waves recorded on a seismogram during the geophysical survey?
5. Why are certain rock formations visited during a geological survey?
6. Why are the intensity of the earth’s magnetism and the thickness of the rocks not the same everywhere?