Borehole


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borehole

[′bȯr‚hōl]
(engineering)

Borehole

 

(well), a circular mining excavation more than 5 m deep and usually between 75 and 300 mm in diameter, made by a drilling rig. Boreholes are drilled from the earth’s surface and from underground mining excavations at any angle relative to the horizon. Three parts are distinguished: the head (mouth), bottom (face), and shaft. Borehole depths range from a few to 9 km and more. During exploratory drilling for solid minerals, borehole diameters are usually 59 and 76 mm, whereas petroleum and gas wells range from 100 to 400 mm in diameter.

Depending on their purpose, boreholes are classified as exploratory boreholes, operating wells, auxiliary wells, special-purpose boreholes, and shot holes. Exploratory boreholes are used for geological purposes, geological-engineering and hydrologic surveying, the study of structures, geophysical work, and exploration and analysis of useful minerals. Operating wells are used to extract petroleum and gas, subterranean water, and mineral salts. Auxiliary wells include pressure, observation, piezometric, ventilation, water-removal, and de-gasification wells. Special purpose boreholes are used for refrigeration, plugging, and drainage, and shot holes are used for the placement of explosive charges.

Boreholes are made by drilling and removal of the drilled rock and, where necessary, reinforcement of the borehole walls against caving. The drilled rock is removed by a flushing liquid, gas, or mechanical devices. Exploratory boreholes drilled through unstable upper rocks are cased with thin piping; in stable rocks, no reinforcement is used. In heavily fissured rocks and absorption zones, quick-setting mixtures are used for plugging. Operational wells and deep exploratory boreholes are reinforced with metal casing and cemented. The casing is screwed or welded together; in shallow water wells, plastic, asbestos cement, and other types of piping are used.

Reinforcing a petroleum and gas well involves setting the first casing column, usually up to 20 m in length and called a guide, into the mouth of the well. A second column of casing, which is called the conductor and ranges from dozens to hundreds of meters in length, is sunk both to ensure that the subsequent shaft of the well is vertical or has the proper inclination and to seal out gas and water flows. A cement solution is pumped through the conductor into the open space between the walls of the well and the conductor by means of a flushing or special fluid. After drilling has reached the planned depth and geophysical work to determine the presence of petroleum, gas, and other producing horizons has been completed, the operating column of casing is lowered into the well. The well space outside the operating column is also filled with a cement solution to prevent oil or gas seepage into overlying horizons and to keep water out of producing strata. Under complex geological conditions (water-bearing, absorbent horizons), when it is impossible to drill the well without additional reinforcement, an intermediate column is lowered between the conductor and the operating column. If only an operating column is sunk after the conductor, the well is called a single-column well; when there are one or two intermediate columns, the well design is called two- or three-column.

There are different methods of opening and rigging up the face to extract liquid or gas minerals from the strata. In most cases a series of holes is shot in the wall of the casing and in the cement shell in the lower cemented part of the operating column, which is in the producing stratum. In stable rocks, the well zone near the face is equipped with various types of filters and not cemented or the casting is lowered to the roof of the producing stratum; the stratum is drilled and worked without reinforcement of the well shaft. Depending on its purpose, the well head may have various kinds of fittings, such as a column head, shutoff valves, or crosses.

REFERENCES

Burenie neftianykh i gazovykh skvazhin. Moscow, 1961.
Kulichikhin, N. I., and B. I. Vozdvizhenskii. Razvedochnoe burenie, 2nd ed. Moscow, 1973.

S. N. UDIANSKII

boring, borehole

A hole drilled in the ground to obtain soil samples for evaluation and to obtain information about the strata.
References in periodicals archive ?
The diameter of the charge is normally around 50% of the borehole diameter and the length of the charge should be around four to six times the diameter.
After the detailed study and observations, the borehole logs were prepared for each borehole which has the detailed information about the water table, strata lithology, joints, weathering, permeability, fractures, angle of joints, infilling, water loss, core recovery, rock quality dissemination and other information.
This is convenient because the effective ground thermal resistances do not depend on borehole length.
Developments concerning the borehole at the former Scottish & Newcastle brewery site have been watched keenly by scientists around the world since drilling began three years ago.
Profiles, logs of boreholes, seams correlation and collar co-ordinates completed;
It was necessary to install this type of solar panel to eliminate the risk of the panels being stolen for those purposes, which happens with most community type boreholes fitted with solar pumps," says Uschi Ramakhutla, executive officer of the Meatco Foundation.
Regarding coaxial designs, Hellstrom (2002) mentioned an annular open BHE system, where the fluid travels in direct contact with the rock in the annular channel, having almost no thermal resistance to the borehole wall.
The borehole is part of a pounds 1million project to tap into 80C water in rocks two kilometres underground and use that water for environmentally-friendly heating.
This volume is a guide to the safety standards related to borehole disposal facilities of radioactive waste.
Furthermore, a simple way to evaluate the equivalent borehole thermal resistance, based on the work of Hellstrom (4) is proposed.
The Government cash will be used to drill a second borehole to work alongside the 995m deep exploration borehole which was originally drilled three years ago.