Drilling deep into Earth’s crust and sedimentary basins, whether for resource exploration or scientific investigation, has been one of the most technological achievements of modern times – thanks to the oil industry.
Recently, some companies have developed ambitions to drill even deeper. Earlier this year, Ecopetrol and Occidental Petroleum planned to drill the Komodo-1 well in Colombia’s Caribbean waters to a depth of 3,900 meters below sea level, but the project has been delayed due to political conflicts.
Houston-based Quaise Energy also recently announced plans to use a gyrotron to surpass the current record for deepest hole ever dug. It will drill into sediments using conventional drilling, then switch to using the gyrotron, which vaporizes basement rock at 11.2 miles per hour. The company’s goal is to reach crustal temperatures of 500 degrees Celsius for geothermal power.
Let’s look at which projects hold the current records for the deepest holes ever drilled, and the history leading up to the innovative pursuits of today.
Ultradeepwater Drilling
Angola’s offshore well Ondjaba-1, drilled in 2021 to 3,627 meters, is the deepest oil well by water depth ever drilled for petroleum exploration. In terms of vertical rock depth below the sea floor, BP’s Deepwater Horizon (Macondo) drilled in the Tiber field in 2009 holds the record at 10,685 meters. Incidentally, 2009 also marked the 150th anniversary of the Drake Well in Titusville, which hit oil at a depth of 21 meters and ushered in the modern oil industry in North America. Edwin Drake could not imagine how much the petroleum industry has accomplished, tapping deep fuels and revealing the hidden geology of Earth.
Ocean Floor Drilling
Other records can be classified based on the type of rock drilled. The race to drill into the mantle began between the United States and the former Soviet Union in the late 1950s. The United States’ Project Mohole in 1961 drilled through the Pacific Ocean floor off the island of Gudalupe. The well penetrated 183 meters of sea floor in a water depth of 3,600 meters. Objecting to the rising costs, Congress ceased funding five years later.
In 1968, the U.S. National Science Foundation launched the Deep Sea Drilling Project. DSDP’s drillship, the Glomar Challenger, drilled Hole 504B in the Eastern Pacific Panama Basin in 1979. The well penetrated 2,111 meters below the sea floor at 3,460 meters of water depth and cored pillow lava underlain by sheeted magmatic dikes. It remains the deepest ocean floor well drilled by the International Ocean Discovery Program.
The longest mantle core ever recovered during IODP expedition 399 was in 2023, when the JOIDES Resolution drillship cored 1,268 meters of serpentinized peridotite and gabbroic intrusions from a hole drilled at water depths of 850 meters atop the Mid-Atlantic Ridge at 30 degrees North..
Continental Crust Drilling
The former Soviet Union began drilling into the Precambrian granitic gneiss on the Kola Peninsula near the Norwegian border in 1970. The Kola Superdeep Borehole SG-3 reached a vertical depth of 12,262 meters in 1989 and remains the deepest well drilled vertically into Earth. The project was discontinued in 1994.
Although the well did not reach the crust-mantle boundary, it penetrated the 2.7-billion-year-old Archean rocks under the Baltic Shield and found water-saturated fractured rocks, high levels of hydrogen gas and even plankton fossils at great crustal depths.
Onshore Petroleum Wells
In 1953, the Ohio Oil Co. drilled KCL-A 72-4 to a depth of 6,657 meters in California’s Paloma Field. It was the world’s deepest well at the time and remains California’s deepest.
Twenty-six years later, the Bertha Rogers natural gas well in Oklahoma reached a depth of 9,583 meters, where it struck molten sulfur. It was the world’s deepest well drilled until 1979 when Kola SG-3 surpassed it.
In recent years, the Chinese have drilled ultradeep onshore wells in the Tarim Basin – oil and gas reservoirs of more than 6,000 meters.This year, CNOOC completed drilling the Shendi Take 1 to a vertical depth of 10,910 meters—the deepest onshore petroleum well.
Horizontal and Extended Reach Wells
Directional wells have shallow vertical depths but longer lateral length. Extended reach wells are directional wells often drilled at high angles into conventional offshore reservoirs, while horizontal stimulated wells are drilled into tight reservoirs.
Big Lake Oil Co. drilled the first directional well (without stimulation) in 1929 near Texon in Texas. During the 2010s, the offshore Sakhalin Chayvo Field in the Sea of Okhotsk held the record for the longest extended reach wells: 15,000 meters drilled from the Orlan platform in 2017. Five years later, Abu Dhabi National Oil Co. drilled an extended reach well of 15,240 meters from the artificial island Umm Al Anbar to the Upper Zakum Field, surpassing the record.
Today, four-mile-long “super lateral” horizontal wells are not uncommon in tight plays. Several wells in the Big Bend field of the Bakken exceed five miles long. In 2022, Axis Energy and Ascent Resources announced drilling the “largest lateral in North America” with a horizontal well of 10,347 meters into Utica Shale in Ohio. In the same year, ConocoPhillips beat that record, completing a horizontal drill of 10,828 meters in the Alpine field in Alaska’s North Slope.
Offshore Wells
Offshore well depths can be measured from sea level (water depth) or sea floor (rock depth). Subduction trenches have the deepest water depths. In 2021, the Japanese research vessel Kaimei drilled a hole for earthquake studies in the Japan Trench at a water depth of 8,023 meters.
Across drilling types, these deep wells have provided influential scientific knowledge about the Earth’s crust, mantle, sea floors and subsurface formations and resources. Novel technological advancements may soon extend record depths – and the depths of researchers’ knowledge – even further.