Reasons to Close an Oil Well

• There are two reasons oil wells are shut down. The first is that oil reserves pumped from the well have run dry -- meaning the well no longer produces any oil. More commonly, however, oil wells are shut down even though plenty of oil remains. This is because oil companies calculate the cost of recovering the oil and compare it to the price the oil sells at. If the projected profit does not justify the continued expense, the company shuts the well down -- often permanently, but sometimes just temporarily until the price of oil increases again.
  
  

Permanantly Closing an Oil Well

• Oil wells are simply long tunnels, bored hundred or thousands of feet into the earth until they puncture a reserve of oil underground. Then, like sucking up a milkshake through a straw, the oil is sucked out. When an oil well ceases to become profitable, the bored well hole is plugged up with a rubber stopper, almost like a bottle cork, and then sealed in place with concrete. The rubber stopper prevents leakage, while the concrete prevents the pressure of any unpumped oil from popping the cork out.
  
  

Temporarily Closing an Oil Well

• When oil prices fluctuate, it is sometimes profitable to start pumping oil from a previously abandoned well. Alternatively, unprofitable wells can be used to boost production from another well by pumping air or seawater into the oil bore hole and "pushing" underground oil reserves towards another pump. For this reason, oil companies will often seal oil pipelines temporarily with a safety valve cap. This cap has a valve that can allow pressure to escape, preventing pressure from popping the cap off. Because this cap can be removed, however, it occasionally leaks and there is a danger of it bursting.
  
  

Reopening a Shut Oil Well

• Oil wells that still have oil reserves within them might be opened under two sets of circumstances: when oil prices increase to the point that pumping the oil out becomes profitable again or when new technology makes it more affordable -- and therefore profitable -- to restart pumping. A 21st-century development that makes old oil wells more profitable involves pumping byproduct carbon dioxide into underground oil reserves to increase the pressure of the remaining oil and multiply the amount that can be extracted by many times. This method makes many old oil wells profitable once again.