Borehole

Did You Know?

• Drillers may sink a borehole using a drilling rig or a hand-operated rig.
• For offshore drilling, floating units or platforms supported by the seafloor are used.
• The technique of seasonal thermal energy storage can use media ranging from gravel to bedrock.

Importance

A water well borehole is typically completed with a vertical casing and well screen to prevent collapse and block surface contaminants, also protecting pumps from sand and sediment. Oil and natural gas wells use a similar but more complex completion. Borehole temperature measurements at various depths can be mathematically inverted to estimate historic surface temperatures. Clusters of small-diameter boreholes with plastic PEX heat exchangers enable seasonal thermal energy storage in native rock, with depths ranging from 150 to 1000 ft.

History

Borehole drilling dates back to at least the Han dynasty (202 BC – 220 AD), when the Chinese used deep drilling for mining. Sites could reach 600 m deep, with a method involving a team jumping on and off a beam to impact the bit while buffalo and oxen rotated the tool—the same technique used for California petroleum in the 1860s. A Western Han bronze foundry in Xinglong, Hebei had mining shafts 100 m deep with timber frames, ladders, and iron tools. By the first century BC, Chinese craftsmen cast iron drill bits and drilled boreholes up to 1500 m deep. By the eleventh century AD, depths reached 3000 ft. Drilling a single well could last nearly a decade. Europe and the West did not rival this technology until the 19th century. The world's longest borehole was the Kola Superdeep Borehole in Russia; from 2011 to August 2012, the Sakhalin-I Odoptu OP-11 Well held the record at 12345 m. The Chayvo Z-44 extended-reach well, with a total measured depth of 12376 m, took the title on 27 August 2012. In July 2023, China began drilling deep boreholes: one at the Sichuan Basin expected to reach 10520 m, and another at the Tarim Basin planned for 11100 m.

Hand digging

In many developing countries, boreholes are still dug by hand using shovels, picks, and crowbars. Workers excavate soil layer by layer in a circular motion, lining the hole with bricks, stones, or concrete rings to prevent collapse and contamination. A concrete platform or slab may be installed at the bottom to block sediment, and the top is capped for protection.

Rural Africa expansion trends

Since the late twentieth century, boreholes have become a major source of improved drinking water in rural Africa. Government, stakeholders, international agencies, and non-governmental organizations have invested heavily in borehole drilling projects to address water scarcity and improve water quality. Population growth, international development goals, and increasing recognition of groundwater as a fresh water source have driven this expansion.