Deepwater drilling
Deepwater drilling, or deep well drilling, is the process of creating holes in the Earth's crust using a drilling rig for oil extraction under the deep sea. There are approximately 3400 deepwater wells in the Gulf of Mexico with depths greater than 150 meters. Deepwater drilling has not been technologically or economically feasible for many years, but with rising oil prices, more companies are investing in this sector. Major investors include Halliburton, Diamond Offshore, Transocean, Geoservices, and Schlumberger. The deepwater gas and oil market has been back on the rise since the 2010 "Deepwater Horizon" disaster, with  total expenditures of around US$35 billion per year in the market and total global capital expenditures of US$167 billion in the past four years. Industry analysis by business intelligence company Visiongain estimated in 2011 that total expenditures in global deepwater infrastructure would reach US$145 billion. A HowStuffWorks article explains how and why deepwater drilling is practiced: In the Deepwater Horizon oil spill of 2010, a large explosion occurred, killing workers and spilling oil into the Gulf of Mexico while a BP oil rig was drilling in deep waters. History. Some of the earliest evidence of water wells  are located in China. The Chinese discovered and made extensive use of deep drilled groundwater for drinking. The Chinese text "The Book of Changes", originally a divination text of the Western Zhou dynasty (1046 -771 BC), contains an entry describing how the ancient Chinese maintained their wells and protected their sources of water. Archaeological evidence and old Chinese documents reveal that the prehistoric and ancient Chinese had the aptitude and skills for digging deep water wells for drinking water as early as 6000 to 7000 years ago. A well excavated at the Hemedu excavation site was believed to have been  built during the Neolithic era. The well was cased by four rows of logs with a square frame attached to them at the top of the well. 60 additional tile wells southwest of Beijing are also believed to have been built around 600 BC for drinking and irrigation. Types of deepwater drilling facilities. Drilling in deep waters can be performed by two main types of mobile deepwater drilling rigs: semi-submersible drilling rigs and drillships. Drilling can also be performed from a fixed-position installation such as a fixed platform, or a floating platform, such as a spar platform, a  tension-leg platform, or a semi-submersible production platform. 2010 Gulf Oil Spill Disaster. On 20 April 2010, a BP deepwater oil rig (Deepwater Horizon) exploded, killing 11 and releasing 750,000 cubic meters (200 million gallons) of oil into the Gulf of Mexico. With those numbers, many scientists consider this disaster to be one of the worst environmental disasters in the history of the US. A large number of animal deaths have resulted from the release of the oil. A Center study estimates that over 82,000 birds, about 6,000 sea turtles, and nearly 26,000 marine mammals were killed from either  the initial explosion or the oil spill.