The rock is drilled with a rotating drill bit, in a similar way to using an electric drill and bit to make a hole in a plank of wood. The sharp end of the drill, the drill head, is attached to steel pipes and as the drill goes into the ground additional pipes are put on the end to extend the drill head. Each steel pipe that is used to extend the drill head is normally 9 metres long and is put into position by the large structure on the drilling platform called a derrick. The derrick must be very strong as it lifts the new pipes into position and supports all the pipes that are in the ground and the drill head itself. The derrick also regulates the load that the drill head is working under by supporting the drill head and all the pipes. In addition, and because of the heat generated by drilling the drilling process, and particularly the drill head, must be lubricated and cooled. A special drilling mud is used to lubricate and cool the drill head and the steel pipes. he mud is pumped down the inside of the steel pipes to the drill head and then returns to the top of the hole between the rock and the outside of the pipes. As the mud moves is also collects the rock debris, so providing the geologists with more rock samples to prove what rock types are being drilled through. The mud also prevents any oil found from escaping through the drilling hole by sealing the hole. As the oil is often held under pressure in the ground a set of valves, called a Christmas Tree, is also fitted to the well head to stop, and control the release of any oil. If a test drilling finds oil then other areas close by are drilled to determine the area of the oil reservoir.
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modern day floating oil rig
