The deepest borehole ever drilled (on mainland)

There is a book, a wonderful book, that I warmly recommend you, it's
A short history of (nearly) everything by Bill Bryson.
It's one of the best book on science I have ever read!
Written by a journalist, who at a certain point in his life, decided to learn more about our planet and about about science in general and full of anecdotes.
Today I want to tell you about the deepest borehole, one of the stories Bill Bryson tells in his book.


By the 1960s scientists had grown sufficiently frustrated by how little they understood of
the Earth’s interior that they decided to try to do something about it. Specifically, they got the
idea to drill through the ocean floor (the continental crust was too thick) to the Moho
discontinuity and to extract a piece of the Earth’s mantle for examination at leisure. The
thinking was that if they could understand the nature of the rocks inside the Earth, they might
begin to understand how they interacted, and thus possibly be able to predict earthquakes and
other unwelcome events.

The project became known, all but inevitably, as the Mohole and it was pretty well
disastrous. The hope was to lower a drill through 14,000 feet  (4267.2 meters) of Pacific Ocean water off the
coast of Mexico and drill some 17,000 feet (5181.6 meters) through relatively thin crustal rock. Drilling from
a ship in open waters is, in the words of one oceanographer, “like trying to drill a hole in the
sidewalks of New York from atop the Empire State Building using a strand of spaghetti.”
Every attempt ended in failure. The deepest they penetrated was only about 600 feet (182.88 meters). The Mohole became known as the No Hole. In 1966, exasperated with ever-rising costs and no
results, Congress killed the project.

Four years later, Soviet scientists decided to try their luck on dry land. They chose a spot on
Russia’s Kola Peninsula, near the Finnish border, and set to work with the hope of drilling to
a depth of fifteen kilometers, Google Maps Link 
The work proved harder than expected, but the Soviets were
commendably persistent. When at last they gave up, nineteen years later, they had drilled to a
depth of 12,262 meters, or about 7.6 miles. Bearing in mind that the crust of the Earth
represents only about 0.3 percent of the planet’s volume and that the Kola hole had not cut
even one-third of the way through the crust, we can hardly claim to have conquered the
interior. 

(Kola Superdeep Borehole, commemorated on the 1987 USSR stamp, wikipedia)

The hole reached 12,262 m (40,230 feet) in 1989. In that year the hole depth was expected to reach 13,500 m (44,300 feet) by the end of 1990 and 15,000 m (49,000 feet) by 1993. However, because of higher-than-expected temperatures at this depth and location, 180 °C (356 °F) instead of expected 100 °C (212 °F), drilling deeper was deemed unfeasible and the drilling was stopped in 1992.
Accoding to wikipedia, the project was closed down in late 2005 because of lack of funding. All the drilling and research equipment was scrapped and the site has been abandoned since 2008.



As Bill Bryson says:
Interestingly, even though the hole was modest, nearly everything about it was surprising.
Seismic wave studies had led the scientists to predict, and pretty confidently, that they would
encounter sedimentary rock to a depth of 4,700 meters, followed by granite for the next 2,300
meters and basalt from there on down. In the event, the sedimentary layer was 50 percent
deeper than expected and the basaltic layer was never found at all. Moreover, the world down
there was far warmer than anyone had expected, with a temperature at 10,000 meters of 180
degrees centigrade, nearly twice the forecasted level. Most surprising of all was that the rock
at that depth was saturated with water—something that had not been thought possible.


The record of the Superdeep borehole was set in 1989, how is the situation today?
Citing Wikipedia:

The Kola Superdeep Borehole was the deepest and longest borehole in the world for nearly 20 years. However, in May 2008, a new record for borehole length was established by the extended-reach drilling (ERD) well BD-04A, which was drilled by Transocean for Maersk Oil in the Al Shaheen oil field in Qatar. It was drilled to 12,289 m (40,318 ft), with a record horizontal reach of 10,902 m (35,768 ft), in only 36 days.

On 28 January 2011, Exxon Neftegas Ltd., operator of the Sakhalin-I project, drilled the world's longest extended-reach well offshore on the Russian island of Sakhalin. It has surpassed the length of both the Al Shaheen well and the Kola borehole. The Odoptu OP-11 well reached a measured total depth of 12,345 m (40,502 ft) and a horizontal displacement of 11,475 m (37,648 ft). Exxon Neftegas completed the well in 60 days.



As a bonus trivia, I read on Wisegeek that
The Kola Superdeep Borehole was the source of a tabloid rumor, started by a Finnish newspaper, that Russian researchers had burrowed through to Hell. The story was reproduced by several American tabloids. It stated that 9 miles (14.4 km) down into the Earth's crust (1.4 miles (2.25 km) deeper than the real depth), the scientists reached a pocket of air with a temperature of 2,000°F (1,093°C). Intrigued, they sent down a heat-tolerant microphone, which picked up the screams of the damned. The rumor was exacerbated when recordings of the alleged screams popped up on the Internet shortly thereafter.

References:
A Short History Nearly Everything (Amazon link)
Wisegeek
Wikipedia