by Mickey Horn
The first oil was found simply by looking at an oil seep on the surface of the earth. Today, oil prospectors have extensive knowledge of the earth's geology and can see where oil might be located underground. The first underground oil was extracted by accident while drilling for water in West Virginia during the beginning of the nineteenth century. Since then, we have learned to look for geological features, such as buckles and domes, which suggest there may be oil pushing up against the layers of earth.
Prospectors also know that oil is most likely to be found in sedimentary rock basins. What used to be a never-ending exploration from the ground is now a technologically advanced operation consisting of satellite scans and radar images. Once a likely place is found, a geophysical analysis is conducted. These surveys can give us clues as to where the oil might be. Clues encompass things like gravitational fields and the earth's magnetism that may be created or altered by the presence of oil beneath the surface.
A seismic survey is another way that we can try to predict where an oil trap may be. Vibrations are sent into the ground. Different frequencies reflect differently from each unique type of rock. This data is used to draw a computer model of what the layers of earth look like beneath the ground being surveyed. Traps and bubbles can usually be seen and some of these actually contain oil and gas. The only way to really know is to drill down and see if there is anything there. Seismic survey is a lot like an ultra-sound of the earth's surface.
Seismic surveys are conducted by setting off vibrations from explosive charges or by special trucks designed to shake the ground by hitting it with a giant hydraulic pad. The hydraulic pad hits the ground with tremendous force and speed sending vibrations very deep into the ground. Geophones record and amplify the sounds that are reflected back to the earth's surface. These recordings are translated into pictures that we can see and analyze.
We can also hunt for oil under the sea by using seismic surveys. Powerful air guns are towed on cables behind the boat. The air gun releases a blast of compressed air towards the sea floor. Echoes come back and are collected by sound-detecting hydrophones. This gives us a clear picture of what the surface of the sea bed looks like. We use many tow lines behind multiple boats to collect enough data to give us a three dimensional view of the bottom of the sea. Then oil prospectors can analyze the data, compare it to similar features found on the surface of the earth and determine where oil might be found. We used to use dynamite to create the seismic sound, but the use of air guns has greatly reduced the amount of pollution and marine-life death that the dynamite once caused. Specific guidelines are followed to keep the disturbance of marine animals to a minimum.
0 Comments