It has become something of a old chestnut in the West that China will often claim to have achieved famous scientific advancements and inventions first, often hundreds of years before the West. The investigation of these sorts of disputes – and deciding who gets bragging rights – is probably best left to serious historical researchers, but there is firm evidence of many interesting early technical achievements from the Middle Kingdom. And, of course, there are also many instances of the same discovery at different times and in different places, such as Leibniz and Newton with calculus, and Wallace and Darwin with evolution. China developed large urban centers earlier than Europe, and no doubt the challenges presented by increasing population numbers and densities drove the development of technology just as it did some time later in Europe and the Middle East.
Ancient China’s development of deep drilling techniques predates similar advancements in the West by hundreds of years. Early Western drilling greats – such as Alekseev in Baku in1846 and Bissell and Drake in Titusville in 1859 – certainly were unaware of what had happened earlier in China, and their achievements are not diminished by it. It is remarkable how – just as seen with convergent evolution in nature, the methods and tools developed in the West closely resemble those of ancient China. Function does indeed dictate form.
Salt of the Earth
In ancient China, as was the case in most of the world, salt was a valuable commodity due to its use in cooking, food preservation and a wide array of other basic activities, such as bleaching, tanning and making soap. Areas far inland relied on salt traders from the coast. The first recorded salt well in China was hand-dug with shovels in Sichuan Province around 2,250 years ago, and it was here where ancient drilling techniques first emerged. It is only conjecture, but what probably happened was that in digging shallow wells for water, someone encountered a briny aquifer, and had the idea to boil off the water to produce salt. Perhaps others in the vicinity followed, and a nascent salt production industry emerged. This was the first time that water-well technology was applied successfully to the exploitation of salt, and it marked the beginning of Sichuan’s salt drilling industry. From that point on, wells in Sichuan have penetrated the earth to tap into brine aquifers (ground water with a salinity of over 50 grams per liter), and various evaporative techniques have been used to produce usable salt.
The Zigong Salt History Museum is the main source of information for this article. Zigong is a city in Sichuan Province, about a two-hour drive southeast of Chengdu. The museum is situated in the Xiqin Guildhall, built by salt merchants in the mid-1700s, and is well worth a visit.
Around 2,000 years ago, they made the leap from hand-dug to percussively drilled wells. By the beginning of the 3rd century AD, wells were being drilled up to 140 meters deep. This drilling technique can still be seen in China today, when rural farmers drill water wells. The drill bit is made of iron and the pipe of bamboo, as is the rig. One man (or more) stands on a wooden plank lever, much like a seesaw, and this lifts the drill stem a meter or so. The pipe is allowed to drop, and the drill bit crashes down into the rock, pulverizing it. Inch by inch, month by month, the drilling slowly progresses.
At regular intervals in the drilling, the crushed rock and mud at the bottom of the hole needed to be removed. The drill stem would be pulled from the hole using a large wheel, somewhat similar in appearance to that on a modern flexible cable downhole tool truck. A length of hollow bamboo with a leather foot valve would then be lowered to 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. Drilling would then recommence.
From this, more sophisticated drilling methods evolved, to the point where most of the tools and techniques one might see on a modern drilling rig had developed, albeit on a smaller scale and without the benefits of modern materials and machining methods.
Sichuan drillers developed techniques to deal with the different rock types and to overcome common drilling problems – cave-ins, lost tools, deviated wells and so on. The figure captioned “Well bore cave-in repair” shows the steps followed to fix a cave-in. They also deployed a broad variety of drill bits. For example, opening the hole at the wellhead required a large, heavy bit (3 meters long, 150-250 kilograms) 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 that allowed deeper wells was achieved around 1050 AD, when solid bamboo pipe was replaced by thin, light, flexible bamboo “cable.” This dramatically lowered the weight that needed to be lifted from the surface – a weight that obviously increased with the depth being drilled. By the 1700s, Sichuan wells were typically in the range of 300–400 meters deep, and in 1835 the Shenghai Well was the first well in the world to exceed 1,000 meters of depth. In comparison, the deepest wells in the United States at that time were about 500 meters deep. The Sichuan salt-producing industry was centerd around Zigong, and early photographs show hundreds of producing derricks known as “heaven carts,” salt stove operations, and the Fuxi River jammed with salt trading boats. Brine and natural gas were transported through hundreds of kilometers of bamboo pipeline.
Industrial Scale Efforts
The emergence of natural gas use is of particular interest. The fuel used throughout the earlier centuries in the evaporation process was of course wood. Eventually wood became scarce due to the scale of the salt production industry. First, some energy-saving techniques were used during evaporation: for example, spreading the brine on tree branches under the sun could increase the salt concentration before boiling, and several boiling pans could be put in the same chimney path to use residual heat. A big breakthrough occurred at some point in the 16th century with the development of techniques to harness the natural gas encountered during drilling for brine. This allowed natural gas to be burned beneath the big salt pans. One would have thought this would have resulted in the further development of a full-blown oil and gas industry, but that is not what happened, at least not initially. There are instances of oil and gas production and use in other parts of China going back as far as 61 BC, but it appears as if the salt and hydrocarbon industries were separate for a long time, and the use of gas in the Zigong area was largely limited to salt production.
It was the coexistence of brine and gas that pushed Zigong’s salt production into the industrial scale. Once wells reached depths of 700-800 meters, they were able to produce both brine and gas from the Jialingjiang group Triassic formations. Annual salt production in Zigong in the 1850s was about 150,000 tons. The Chinese population was about 450 million at that time, and Zigong exported salt widely. The salt industry was a huge economic driver, and many large cities in Sichuan were established, and flourished, because of this lucrative salt trade.
A key technological advance was the introduction of the “Kang Pen” drum at the end of the 18th century. This drum sat on top of the wellhead, and the pressure within the drum was controlled such that gas and brine could simultaneously be produced and efficiently separated. One bamboo pipeline would take away the brine, and others the gas.
The bamboo pipelines were made as follows. Each length of bamboo was cut in half, down its length. The segment walls were removed, and the insides of the bamboo further hollowed out to create a smooth inside surface of constant diameter. The two sections were then put back together and bonded with a glue made from a mixture of lime and tree seed oil. The pipe section was further bound together with twine inset into grooves in the outside surface of the bamboo, to prevent fraying, especially for downhole use where the hole’s rock walls would scrape against the exterior surface of the bamboo pipe as it was repeatedly lifted and lowered during drilling and production operations. Similar glue and twine techniques were used to link and splice pipeline sections together end-to-end in an airtight fashion. Conveniently, western Sichuan has extensive bamboo forests in the foothills of the Tibetan Plateau, home of the panda bear.
The more than 2,000-year-old Sichuan salt industry has drilled approximately 130,000 brine and gas wells, and 10 percent of those were in the immediate Zigong area. Zigong has a cumulative gas production over this period of more than 30 billion cubic meters. The area continues to be a major salt producer, and many of the historical wells are still in production. As recently as the 1950s, there was still more than 95 kilometers of bamboo pipeline in operation in the Zigong area. China’s ancient salt and gas industry represents a fascinating chapter in the human story of resource extraction, and a reminder that innovative technologies have been developed throughout our history, and in many different places.
For additional reading, see “Drilling and Gas Recovery Technology in Ancient China, by Jian, Z. C., Zhong, C. and Jian, H; and “Salt,” by Kurlansky, M.