Deep-earth drilling projects

Deep-earth drilling projects represent one of the most ambitious attempts by earth scientists to investigate the origins, structure, and nature of planet Earth. Scientists believe that these projects can reveal information concerning the planet that is unobtainable by other methods.

Origins of Scientific Drilling Projects

The idea of drilling deep holes in the earth's crust so as to determine its nature and history originated with nineteenth century geologists and naturalists. Charles Darwin was among the first scientists to call for a deep drilling project for purely scientific purposes. In 1881, Darwin proposed that a shaft be sunk to a depth of 150-180 meters on a Pacific atoll to test his theory concerning the origins and growth of coral islands.

Eighteen years later, the Royal Society of London financed the drilling of a 348-meter-deep hole on one of the Ellice Islands (Tuvalu) in the South Pacific to test Darwin's theories. That was perhaps the first deep-earth drilling project ever undertaken for purely scientific purposes.

The Mohole Project

Many earth scientists have proposed deep-earth drilling projects to advance scientific knowledge of the earth's interior. Many proposals have been met with indifference because of the great expense and the technological problems involved. In the 1950s, a number of well-known geologists, geophysicists, and oceanographers from several countries began corresponding with one another about deep-drilling projects. A major topic of their correspondence was whether they might be able to capture the imagination of the public with a deep-drilling project and consequently claim a larger share of research funds from government agencies. These scientists believed the public to be over-focused on space research. They eventually formed an unofficial organization they called the American Miscellaneous Society (AMSOC), which held informal meetings during official scientific conferences at which they discussed the desirability of a deep-drilling project that would penetrate the Mohorovičić (Moho) discontinuity in the earth's mantle. Ideally, they agreed, there would be two deep-drilling projects, one on land and one on the ocean bottom.

In 1958, the members of AMSOC became the Deep Drilling Committee (DDC) of the National Academy of Sciences (NAS). The NAS is a private organization that was chartered by US President Abraham Lincoln in 1865 to act as an adviser to the federal government on scientific matters.

The NAS, on the recommendation of the DDC, proposed in 1958 that the federal government fund a deep-drilling project to penetrate the Moho. Rumors that the Soviet Union was about to begin a similar project may have provided a catalyst for the recommendation. It was feared that the Soviets might learn the secrets of the earth's interior before the United States just as the Soviet Union had begun to learn the secrets of outer space before the United States with the launch of Sputnik in 1957.

The original proposal envisioned a hole to be drilled on land to a depth of perhaps 10,500 meters as a training project to develop the technology necessary to penetrate the Moho at the ocean's bottom, where the crust is thinner. The DDC subsequently scrapped the ground-hole idea when it received a grant of $15,000 for a feasibility study of the deep-sea drilling project. A DDC member summarized the result of the feasibility study in an article in Scientific American (April 1959) entitled “The Mohole,” which stirred immediate industrial and public interest.

The Mohole project became a source of considerable international embarrassment for the American scientific community. It failed to meet most of its objectives, cost considerably more than originally estimated, and discredited the idea of deep drilling in the minds of the public and many members of Congress. It was not until 1968 that oceanographers were able to convince Congress to finance another deep-sea drilling project. Another decade passed before federal funds were forthcoming for continental deep-drilling projects.

The Kola Project

Although rumors concerning a Soviet deep-drilling project were at least partially responsible for the urgency with which the US scientific community and government embraced the ill-fated Mohole project, historical evidence would later reveal that these rumors were unfounded. Scientists in the Soviet Union did not begin a deep-drilling project until twelve years after Mohole. In 1970, Soviet geophysicists launched a project on Kola Peninsula near Murmansk, 240 kilometers north of the Arctic Circle. The project reached a depth of more than 12,000 meters, almost twice the depth of any preceding hole. Under the direction of a Soviet government agency called the Interdepartmental Council for the Study of the Earth's Interior and Superdeep Drilling (formed in 1962), the Kola project became the first of several proposed deep holes meant to explore the structure of the earth's crust and mantle.

The Kola drillers penetrated through almost 3 billion years of earth's geologic history, into rock from the Archean eon. Along the way, they discovered large quantities of hot, highly mineralized water at greater depths than geophysicists and geologists had previously thought possible. Scientists at the Kola project concluded from this and other unexpected findings that enormous mineral deposits may be located at great depths, waiting for humankind to reach them. Soviet scientists expected that as they developed a better understanding of the deeper layers of the earth's crust from the Kola project, they would concurrently find ways to discover and exploit available supplies of petroleum, gas, and minerals located at great depths. However, temperature increases beyond 12,000 meters made the project unfeasible, and drilling was stopped in 1992, about a third of the way through the Baltic continental crust. Lack of funding stopped the project in 2005 and the site was abandoned in 2008.

The Appalachian Project

Spurred in large part by Soviet Union's successes in deep continental drilling and the related propaganda created by the Soviet government, scientists and government agencies in several Western nations began developing similar programs in the 1970s. The US Geodynamics Committee of NAS held a workshop on deep continental drilling near Los Alamos, New Mexico, in 1978. The members of the workshop convinced NAS to form its own permanent Continental Drilling Committee (CDC) that same year. The members of the CDC identified a number of geophysical objectives that could be addressed through deep-earth drilling projects, including those related to crust structure, geothermal systems, mineral resources, and earthquake research. The CDC also solicited proposals from US geologists and geophysicists for specific projects that would address those objectives. After examining the many proposals received, the CDC assigned highest priority to two of them: a project to drill a hole 3.7 kilometers deep through the highly mineralized area near Creede, Colorado, and a core hole in the southern Appalachian region 8-10 kilometers deep.

At its 1983 meeting, the CDC unanimously endorsed the Appalachian project as the most promising for America's first deep continental drilling project. It also endorsed two other drilling projects in Creede and at Cajon Pass in California. The following year, the CDC convened a workshop in New York to consider exactly how the project should be approached. After the workshop, the committee organized the Continental Scientific Drilling Program, established with the aid of a grant from the National Science Foundation (NSF). NSF gave the grant to a management group called Direct Observation and Sampling of the Earth's Continental Crust (DOSECC). DOSECC, coordinating its activities with the US Geological Survey and the Department of Energy, prioritized deep-drilling projects and issued contracts for drilling deep continental holes for scientific purposes. In 1985, the White House's Office of Science and Technology Policy (OSTP) recommended to the NSF that it appropriate $2 million for preliminary studies of the Appalachian project. OSTP also recommended that by 1990 the various deep-earth drilling projects be funded at a level of $20 million per year. In 1988, the Cajon Pass project, overseen by DOSECC, got underway; within two years it reached its targeted depth of 4,875 meters. DOSECC began the Appalachian project in the northwest corner of South Carolina in 1989. Its goal was a continuously cored hole 15,250 meters deep.

The DOSECC undertook the Snake River Scientific Drilling Project in September 2010 to explore the interaction between the earth's mantle and crust. In addition, the Dead Sea drilling project using the Deep Lake Drilling System (DLDS) began in November 2010 to explore climate history from core samples at depth.

Quest for Petroleum

The technology employed in deep-earth drilling projects is directly derived from the petroleum industry. The modern origins of that industry date back to the middle of the nineteenth century, when petroleum fields were discovered and exploited in regions all over the world, including Romania, Myanmar, Sumatra, Iran, the Caucasus, and the United States. The oil wells in those areas were initially shallow and drilled with tools designed to drill water wells.

As the petroleum industry grew in economic significance, the search for petroleum went deeper and deeper into the earth and required ever more sophisticated drilling machinery. In addition, oil companies began to employ geologists and geophysicists in their quest to meet the skyrocketing demand for petroleum of an increasingly industrialized society. These earth scientists, in part to become more efficient in their effort to locate significant quantities of petroleum and in part as a by-product of that endeavor, began to learn more and more about the nature and history of the earth's crust from the drilling process itself. This new knowledge led to the modern deep-earth drilling projects that seek to drill deep and superdeep holes to learn more about the earth. Such project are not necessarily undertaken to locate mineral resources, although the discovery of such resources is often a by-product of the undertaking.

The quest for petroleum in the twentieth century caused earth scientists to penetrate ever deeper into the earth's crust. By the latter part of the century, wells in the US were producing oil from depths of more than 6,000 meters (the record being a well in Louisiana, producing oil at a depth of 6,527 meters).

China broke ground on a deep-drilling megaproject to find oil and natural gas and learn more about Earth's deep interior. China used its 15,000-meter ultradeep intelligent drilling rig. Prior to the megaproject, China's deepest oil well extended 11,000 meters into the earth.

Drilling Methods

There are two basic methods of drilling deep wells: cable-tool and rotary. Cable-tool drilling utilizes a heavy drill bit and drill that are suspended by a cable and raised about a meter above the bottom of the hole, then dropped. Workers add mud and water to the hole to hold the rock chips produced by the concussion in suspension. Periodically, drilling crews extract the tools from the hole and pump out the mud, water, and rock chips. Cable-tool drilling is slow and has been largely superseded by the rotary drill, which has proven to be much more effective in deep-earth drilling.

Rotary drilling, though much faster than the cable-tool method, is also more expensive. The rotary drilling method requires hundreds and often thousands of meters of drill pipe and well casing, a derrick, drill bits of several kinds (depending on the type of rock being drilled through), drilling muds and chemicals, a power source (usually one or more diesel engines), and a sizable crew of workers. In rotary drilling, workers attach a drill bit to a string of drill pipe that has at its top a square cross-section called the kelly. The kelly passes through a square hole in a powered turntable, which rotates the drill pipe and bit. Workers add new sections of drill pipe just below the kelly as the bit progresses downward. The rock cut by the rotating drill bit is removed by pumping chemically treated mud down the drill pipe through the drill bit, then back up through the space outside the pipe (the pipe being somewhat smaller in circumference than the hole in which it rests) to a settling pit on the surface.

One drill bit developed for the rotary process, the hollow or core bit, is of particular importance for deep-earth drilling projects. Because petroleum is often found in readily identified geological formations, companies exploring for oil found it expedient to bring to the surface intact samples of the rock being drilled through for examination by geologists. To extract the samples, technicians developed a hollow bit that would allow a cylindrical section of the rock, called a core, to be extracted from the hole without otherwise damaging it. These cores allow geologists to determine not only the petroleum potential of the rock, but also the geological history of the earth in the area of the hole. Core drilling has become an integral part of all deep-earth drilling projects.

Modification of Methods

In the years following their inception, deep-earth drilling projects have required considerable modifications as they have become more focused on uncovering sources of petroleum. Soviet scientists at the Kola project learned that at depths exceeding 9,000 meters, conventional rotary drilling methods encounter virtually insurmountable problems. The rotary method uses a power source to turn the drill bit by rotating the entire string of pipe connected to it and to the kelly. At 9,000 meters, the pipe weighs in excess of 800 metric tons, the rotation of which creates enormous stress at the kelly-power source interface and multiplies the friction resistance of the rock through which the scientists are drilling. The Soviets overcame this problem by developing a bottom-hole turbine to rotate the drilling bit, driven by the flow of the drilling mud being injected into the hole. The necessity of rotating the pipe was thus completely eliminated.

To reduce the weight of the huge lengths of drill pipe necessary for deep-earth drilling, Soviet scientists at Kola began to utilize a high-strength aluminum alloy pipe weighing only about half as much as conventional drill pipe. This innovation considerably reduced the burden on the derrick and the power required to lift the pipe periodically to replace the drill bits and remove the core samples.

The process of core sampling also underwent modification at Kola. In conventional wells, core samples several centimeters in diameter enter the hollow drill tube as the bit cuts a ring of rock at the bottom of the hole. The core remains in the tube until it is brought to the surface and removed. At depths of more than 2,100 meters, however, the rock is under such tremendous pressure that it bursts when the drill bit relieves the compression of overlying rock strata. Soviet drillers developed a new core-sampling device that diverted some of the mud into the core tube and caught the pieces of burst rock, then carried them to the surface in a special chamber. This technique also offered the advantage of clearing the tube for new core samples without the necessity of bringing the tube to the surface.

It is likely that other modifications in drilling technology will be necessary as continental deep-drilling projects proceed to great depths. Thus far, technological innovations have solved the problems encountered by adequately funded deep-earth drilling projects.

Exploiting Earth's Energy Resources

The mineral and fossil fuel resources of the earth are finite. They are non-replaceable commodities. As industrialization continues to spread to developing countries and continues to intensify in countries with developed economies, the demand for irreplaceable and limited commodities continues to increase. Sometime in the twenty-first century, the presently known reserves of fossil fuels may be exhausted. If modern lifestyles are to be maintained in industrialized regions of the world and living standards raised for burgeoning populations in India and China, new reserves of fossil fuels and sources of minerals must be discovered and exploited and new sources of energy must be developed. Deep-earth drilling projects represent one approach to both these necessities.

Strong evidence exists that significant quantities of fossil fuels, both petroleum and natural gas, might be found at depths that are currently unreachable, necessitating projects that are economically unfeasible. However, developing technology in the deep-earth drilling program has the potential to put those resources at the disposal of humankind.

Deep-earth drilling projects under way in the United States and elsewhere in the world are exploring the possibility of exploiting on a large scale a relatively new way of producing energy by utilizing the earth's internal heat. The temperature of the earth increases by about 1 degree Celsius per hundred meters to a depth of 3 kilometers and, as shown at Kola, by 2.5 degrees Celsius thereafter. At 15 kilometers beneath the surface, the earth's temperature is more than 300 degrees Celsius. The US Department of Energy has concentrated efforts in deep-drilling projects aimed at investigating the possibility of commercially exploiting this source of virtually inexhaustible energy.

Disposing of Toxic Wastes

Some scientists suggest that deep-earth drilling might also offer a solution to the problem of toxic waste disposal. The safe disposal of the wastes produced by modern industry and by the production of atomic energy is a major concern of contemporary scientists. Before industries and atomic energy plants inject these materials into the deep crust of the planet, however, extensive studies must be conducted into the potential ecological consequences of such an action. Nevertheless, it is possible that deep-earth drilling can help to solve the problem of toxic waste disposal.

Principal Terms

core drilling: a method of extracting samples of the materials being drilled through in a deep-drilling project

crust: the outer layer of the earth, averaging 35 kilometers in thickness on land and 5 kilometers on the ocean bottoms

mantle: the area of basaltic rocks separating the earth's crust from its core; it is estimated to be about 2,900 kilometers thick

Mohorovičić discontinuity (Moho) discontinuity: an area of undetermined composition and depth between the earth's crust and mantle

rotary drilling: a method of drilling holes to great depths using a rotating drill bit

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