Drilling technology is older than we think.
For most of us, drilling and the exploitation of hydrocarbons date back to the mid-19th century. However, sophisticated drilling techniques were first developed in the ancient salt producing industry in China’s Sichuan Province. As detailed by Mark Kurlansky in his book, Salt: A World History, the drilling technology used to produce brine and natural gas in this region far pre-dates western efforts.
Sichuan Province, one of China’s richest regions, has undergone an intense period of human development. The Yangtze River flows along the southern edge of the basin, and numerous tributaries drain south through the rich agricultural lands and into the Yangtze. With its fertile, well-watered soil and mild climate, Sichuan is one of China’s most productive farming regions. Since ancient times, this region has held attractive conditions for human habitation and has been occupied by humans since the dawn of our existence. Many of China’s ancient technical accomplishments came from this region, including sophisticated irrigation techniques and their drilling technology.
Approximately 5,000 years ago Chinese coastal people were boiling sea water to produce salt. As high density human settlement penetrated further and further inland and increasingly relied on farming, salt — critical to human survival as a vital food supplement and preservative — became a valuable commodity. The first recorded salt well in China was dug in Sichuan Province, around 2,250 years ago. This was the first time water well technology was applied successfully to the exploitation of salt and 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, essentially ground water with a salinity of more than 50 g/l. The water is then evaporated using a heat source, leaving the salt behind.
About 2,000 years ago the technology began to evolve. The inhabitants began to dig wells with percussive drilling systems instead of digging them by hand with shovels. By the beginning of the third century AD, wells were being drilled up to 459 ft (140 m) deep. Rural farmers in China still use this drilling technique for water wells today. The drill bit is made of iron, the pipe bamboo. The rig is constructed from bamboo; one or more men stands on a wooden plank lever, much like a seesaw, and this lifts up the drill stem about 3.3 ft (1 m) or so. The pipe is allowed to drop, and the drill bit crashes down into the rock, pulverizing it. Inch by inch, drilling slowly progresses.
It has been speculated that percussive drilling was derived from the pounding of rice into rice flour. While it may seem that this was a fairly crude technology, the methods became quite sophisticated over time. Eventually, these ancient drillers had developed most of the tools and techniques one might see on a modern drilling rig, albeit on a smaller scale and without the benefits of modern machining methods.
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.
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, and the many different drilling requirements. For example, opening the hole at the wellhead required a large heavy bit — 9.8 ft (3 m) long weighing 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, light 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 Shenghai 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 Sichuan salt producing industry was centered in the city of Zigong, and early photographs show hundreds of producing derricks, salt stove operations, and the Fuxi River jammed with salt trading boats. Brine and natural gas were transported through extensive networks of bamboo pipelines.
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. At some point in the 16th century, techniques were developed to harness the natural gas encountered during drilling for brine. Natural gas was burned beneath the big salt pans. The introduction of natural gas and its coexistence with brine pushed Zigong’s salt production into the industrial scale.
Once wells were drilled down to 2,297 to 2,625 ft (700 to 800 m), they could 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. The salt industry was a huge economic driver, and many large cities in Sichuan were established and flourished,because of the 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 be produced simultaneously, and efficiently separated. One bamboo pipeline would take away the brine and others the gas.
The 2,000 year-old Sichuan salt industry has drilled approximately 130,000 brine and gas wells, with 10% of those in the immediate Zigong area. Zigong has a cumulative gas production over this period of over 1.06 Tcf. The area continues to be a major salt producer, and many of the historical wells are still in production.
This article was originally published in the journal of the Canadian Society of Exploration Geophysicists RECORDER, June 2004, pp. 34-43. For a full version of Ancient Chinese Drilling visit www.cseg.ca/ publications/recorder/2004/06jun/06jun-ancient-chinese-drilling.pdf