Oil
...rocks. They take samples if the site is a probable oilfield. The tests reveal how the various rock layers lie and if the spaces between the rock particles are big enough to hold oil. Geophysicists use sensitive instruments called magnetometers and gravitometers that show the type and hardness of the rocks’ position below. Patterns of the various layers are shown by seismographs. A seismograph is done by setting off a series off small explosions. Shocks waves then bounce back from the earths crust and then are recorded. Geophones record these vibrations. This is a very expensive process but to many companies it is worth it for oil is growing more valuable. (c)Before a well can be drilled, government approval must be obtained. Drilling must then conform to statutory conditions and further operations are covered by industry codes of practice. Drilling oil out of the sea needs special offshore drilling rigs. They either sit on floating tanks or stand on the sea bed supported by long spindly legs but these rigs do not pump it up. On every oil rig is a drilling derrick. While the drill is cutting through thousands of metres of earth a derrick supports its weight. Roustabouts and roughnecks hurry to finish the well without delay but even so, it can take up many months to sink a well. The first stage of drilling is called "spudding" and drilling starts when the drill bit is lowered into the seabed. Men must screw on a new ten-metre lengths of drill pipe. The drill bit is attached to drill pipe (or a drill string) and rotated by a turntable on...