Long before the first commercial oil wells appeared in North America, Chinese engineers had already mastered the art of drilling deep into the earth. In the salt-producing region of Zigong in China's Sichuan Province, workers were sinking wells hundreds of meters deep using techniques that would not become common in the West until many centuries later. These remarkable salt wells not only transformed the economy of inland China but also helped inspire the drilling methods that fuelled the 19th-century oil boom in the United States.
A salt drilling field near Zigong, Sichuan, in 1929. Credit: South China Morning Post
Salt has always been one of humanity's most valuable commodities. Essential for preserving food before refrigeration, it was often as important as precious metals to ancient economies. While many civilizations obtained salt by evaporating seawater or mining rock salt, the people of Sichuan faced a different challenge. The province lay far from the coast but sat atop underground brine deposits.
As early as the first millennium BCE, Chinese well-drillers began extracting salty water from beneath the earth. Over centuries, they developed increasingly sophisticated techniques to reach deeper reserves. By the Tang Dynasty (618–907 CE) and especially during the Song Dynasty (960–1279 CE), Chinese drilling technology had reached a level unmatched anywhere else in the world.
The center of this industry eventually became Zigong, a city located in the south of Sichuan Province.
The salt wells of Zigong were astonishing feats of engineering. Instead of digging broad shafts, Chinese drillers employed a method known as percussion drilling. A heavy iron drill bit was repeatedly lifted and dropped, gradually pulverizing the rock below. The drilling apparatus was powered by teams of workers and animals, and later by elaborate systems of bamboo ropes and wooden derricks.
The drilling technique is still employed in rural China where it is used to drill water wells. A bamboo and wood rig is constructed, upon which one or more men stand. A wooden plank lever is connected to a long bamboo pole which functions as the pipe. At the end of the pipe is a heavy iron drill. The wooden lever can be raised and lowered like a seesaw. The lever is worked by the men, which lifts up the drill stem a meter or so. The pipe is then allowed to drop, and the drill bit crashes down into the rock, pulverizing it. Inch by inch, month by month, the drilling slowly progresses.
A modern recreation of drilling technique from the North Song Dynasty (960-1127 AD). Credit: Oliver Kuhn
A typical day’s labour may drill anywhere from four inches to more than a foot. Sometimes it may take several days to drill even one inch, and several years of drilling to reach the brine aquifers.
Despite the apparent crudeness of this technology, Chinese drillers achieved truly remarkable depth. While most European wells of the period were relatively shallow, the Chinese routinely reached depths of several hundred meters. By the 19th century, some wells exceeded 1,000 meters (3,280 feet).
Among the most famous was the Shenhai Well, completed in 1835 near Zigong. Reaching a depth of approximately 1,001 meters (3,284 feet), it is often regarded as the world's first well to surpass the one-kilometer mark.
Achieving such depth with pre-industrial technology required extraordinary skill and perseverance. Sichuan drillers invented an assortment of drill bits of different size, shape and composition to deal with the different rock types encountered, and the many different drilling requirements. For example, opening the hole at the wellhead required a large heavy bit called the “Fish Tail” which weighed anywhere between 150 to 250 kg; the “Silver Ingot” drilled the well bore rapidly, but roughly; the “Horseshoe” bit drilled slowly, but achieved round, smooth, high quality well bores.
Various drill bits. Credit: Li Jung
They also developed an impressive variety of techniques to overcome common drilling problems such as cave ins, lost tools, deviated wells, and so on.
The innovations of Zigong's salt industry extended far beyond drilling. Workers discovered that many deep salt wells also released natural gas. Rather than allowing this gas to escape, Chinese engineers devised methods to capture and transport it through pipelines made from hollow bamboo sections sealed together. The gas was then used as fuel to boil brine and produce salt.
This system represented one of the earliest known industrial uses of natural gas anywhere in the world. With a forest of wooden derricks and miles of bamboo pipelines, the landscape resembled an industrial oil field long before the age of petroleum. In fact, it was pictures of these ancient Chinese derricks that inspired George Bissell, considered the father of the American oil industry, to conceive of the idea of drilling for oil in Pennsylvania in the 19th century.
Gravity driven bamboo pipelines. Credit: Oliver Kuhn
The coexistence of brine and gas pushed Zigong’s salt production into the industrial scale. Salt became an engine of commerce and wealth for Zigong. There were cheaper methods for salt production, as to start a borehole well cost 3,000 pieces of silver, but transportation cost into the Sichuan valley negated the cheaper production methods. Zigong became a significant supplier of salt to the Sichuan province up until the 1930s.
In 1946, the first modern well was drilled in Zigong with a rotary drillbit. Ancient percussion drilling methods became obsolete and most of the drilling rigs were torn down due to decay. Only one traditional salt well still exists, the aforementioned Shenhai Well, as a tribute to the workers and industry. The Shenhai Well still operates using the older manual methods of pumping and boiling. The salt is used for pickling or canning, and makes an important ingredient to Sichuan style pickles. Today, Zigong is a primary source for natural gas, coal, and inorganic chemical production in addition to salt.
Brine being boiled down to produce salt at the Shenhai Well in Zigong, China. Credit: Wikimedia Commons
Sculpture of workers drilling for salt at Zigong Salt Museum. Credit: TitiFaitSonTour
References:
# Oliver Kuhn. Ancient Chinese Drilling
# Zigong. Wikipedia
# Li Jung, Lien-che Tu Fang. An Account of the Salt Industry at Tzu-liu-ching Tzu-liu-ching chi
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