Borehole

Lore & Background

Borehole drilling has a long history. By at least the Han dynasty (202 BC – 220 AD), the Chinese used deep borehole drilling for mining and other projects. The British sinologist and historian Michael Loewe states that borehole sites could reach as deep as 600 metres (2,000 ft). K.S. Tom describes the drilling process: 'The Chinese method of deep drilling was accomplished by a team of men jumping on and off a beam to impact the drilling bit while the boring tool was rotated by buffalo and oxen.' This was the same method used for extracting petroleum in California during the 1860s (i.e. 'kicking her down'). A Western Han dynasty bronze foundry discovered in Xinglong, Hebei had nearby mining shafts which reached depths of 100 metres (330 ft) with spacious mining areas; the shafts and rooms were complete with a timber frame, ladders and iron tools. By the first century BC, Chinese craftsmen cast iron drill bits and drillers were able to drill boreholes up to 1,500 metres (4,900 ft) deep. By the eleventh century AD, the Chinese were able to drill boreholes up to 900 metres (3,000 ft) in depth. Drilling for boreholes was time-consuming and long. As the depth of the holes varied, the drilling of a single well could last nearly one full decade. It was not up until the 19th century that Europe and the West would catch up and rival ancient Chinese borehole drilling technology.

Reader's Guide

Boreholes are significant as a fundamental technology for accessing subsurface resources and information. Engineers and environmental consultants use the term borehole to collectively describe all of the various types of holes drilled as part of a geotechnical investigation or environmental site assessment (a so-called Phase II ESA). This includes holes advanced to collect soil samples, water samples or rock cores, to advance in situ sampling equipment, or to install monitoring wells or piezometers. Samples collected from boreholes are often tested in a laboratory to determine their physical properties, or to assess levels of various chemical constituents or contaminants. Borehole temperature measurements at a series of different depths can be effectively 'inverted' to help estimate historic surface temperatures. Clusters of small-diameter boreholes equipped with heat exchangers made of plastic PEX pipe can be used to store heat or cold between opposing seasons in a mass of native rock, a technique called seasonal thermal energy storage. Since the late twentieth century, in Africa borehole has become one of the major sources of improved drinking water in rural areas, driven by population growth, efforts to achieve international development goals, and increasing recognition of groundwater as a source of fresh water.

Did You Know?

• By the first century BC, Chinese craftsmen cast iron drill bits and were able to drill boreholes up to 1,500 metres (4,900 ft) deep.
• The world's longest borehole as of August 2012 is the Chayvo Z-44 extended-reach well, with a total measured depth of 12,376 metres (40,604 ft).
• Clusters of small-diameter boreholes with PEX pipe heat exchangers can be used for seasonal thermal energy storage, with depths ranging from 50 to 300 metres (150 to 1,000 ft).
• In July 2023, China began drilling deep boreholes in the Sichuan Basin (planned 10,520 metres) and the Tarim Basin (planned 11,100 metres).