HOW THEY DRILL FOR OIL

http://www.youtube.com/watch?v=M22pgJ_ztEY

Forming Oil

Oil comes from the remains of tiny plants and animals (plankton) that died in ancient seas between 10 million and 600 million years ago. After the organisms died, they sank into the sand and mud at the bottom of the sea.

Over the years, the organisms decayed in the sedimentary layers. In these layers, there was little or no oxygen present. So microorganisms broke the remains into carbon-rich compounds that formed organic layers. The organic material mixed with the sediments, forming fine-grained shale, or source rock. As new sedimentary layers were deposited, they exerted intense pressure and heat on the source rock. The heat and pressure distilled the organic material into crude oil and natural gas. The oil flowed from the source rock and accumulated in thicker, more porous limestone or sandstone, called reservoir rock. Movements in theEarth trapped the oil and natural gas in the reservoir rocks between layers of impermeable rock, or cap rock, such as granite or marble.

These movements of the Earth include:

Folding - Horizontal movements press inward and move the rock layers upward into a fold or anticline.

Faulting - The layers of rock crack, and one side shifts upward or downward.

Pinching out - A layer of impermeable rock is squeezed upward into the reservoir rock.

Locating Oil

Whether employed directly by an oil company or under contract from a private firm, geologists are the ones responsible for finding oil. Their task is to find the right conditions for an oil trap -- the right source rock, reservoir rock and entrapment. Many years ago, geologists interpreted surface features, surface rock and soil types, and perhaps some small core samples obtained by shallow drilling. Modern oil geologists also examine surface rocks and terrain, with the additional help of satellite images. However, they also use a variety of other methods to find oil. They can use sensitive gravity meters to measure tiny changes in the Earth's gravitational field that could indicate flowing oil, as well as sensitive magnetometers to measure tiny changes in the Earth's magnetic field caused by flowing oil. They can detect the smell of hydrocarbons using sensitive electronic noses called sniffers. Finally, and most commonly, they use seismology, creating shock waves that pass through hidden rock layers and interpreting the waves that are reflected back to the surface.

In seismic surveys, a shock wave is created by the following:

• Compressed-air gun - shoots pulses of air into the water (for exploration over water)
• Thumper truck - slams heavy plates into the ground (for exploration over land)
• Explosives - detonated after being drilled into the ground (for exploration over land) or thrown overboard (for exploration over water)

The shock waves travel beneath the surface of the Earth and are reflected back by the various rock layers. The reflections travel at different speeds depending upon the type or density of rock layers through which they must pass. Sensitive microphones or vibration detectors detect the reflections of the shock waves -- hydrophones over water, seismometers over land. Seismologists interpret the readings for signs of oil and gas traps.

Once geologists find a prospective oil strike, they mark the location using GPS coordinates on land or by marker buoys on water.