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the bottom of the hole. When the tube was lifted, the weight of the
mud inside would keep the valve closed, and the contents could be
brought to the surface.
The drilling method on its own is impressive, especially
when considering that the rest of the world had nothing
comparable in the earlier centuries. But even more impressive are
all the techniques the Sichuan drillers developed to overcome
common drilling problems such as cave-ins, lost tools, deviated
wells, and so on. A huge variety of tools and techniques evolved to
handle well repair issues. Many different drill bits were also
developed, with different sizes, shapes and compositions, to deal
with the different rock types encountered. For example, opening
the hole at the wellhead required a large heavy bit — 9.8 ft (3 m)
long weighting 331 to 551 lb — called the “Fish Tail”; the “Silver
Ingot” drilled the well bore rapidly, but roughly; the “Horseshoe”
bit drilled slowly, but achieved round, smooth, high quality well
bores. Hollow logs were used in the near surface as casing.
A major breakthrough, which allowed for deeper wells, was
achieved around 1050 AD. Solid bamboo pipe was replaced by
thin, flexible bamboo “cable.” This dramatically lowered the
weight of the “drill string,” which made it easier to lift from the
surface. By the 1700s Sichuan wells were typically in the depth
range of 984 to 1,312 ft (300 to 400 m). In 1835 the Shаnghai well
was the first in the world to exceed a depth of 3,281 ft (1,000 m).
In comparison, the deepest wells in the United States at that time
were about 1,641 ft (500 m) deep. The salt producing industry was
centered in the city of Zigong, and early photographs show
hundreds of producing derricks, salt stove operations. Brine and
natural gas were transported through extensive networks.
Wood was initially the fuel used in the evaporation process,
but sources of wood became scarce before long due to the scale of
the salt production industry. Several energy saving techniques
were used during evaporation, but natural gas eventually replaced
wood in the brine evaporation process. Natural gas was burned

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