Explanation of Horizontal Directional Drilling
Technological developments in directional drilling in recent decades have helped lessen the environmental impact of many necessary activities and improved the restoration of contaminated areas. A technology created in part because of alleged abuses and oil theft, directional drilling has migrated from slanted oil wells to horizontal water wells, horizontal drilling under pavements for utility installations, and horizontal wells for soil and groundwater remediation. Does this Spark an idea?
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History
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Oil wells have never been drilled perfectly plumb, and the variance from vertical was emphasized by numerous lawsuits in the early decades of the 20th century. These suits alleged that some wells had crossed property boundaries and taken oil from the wrong reservoirs. Efforts to measure the exact position of well shafts followed, and those efforts produced a measuring technology that measured a well's depth, its inclination and its location under the surface. Visualizing their shafts' routes through the earth help oil men realize there were advantages to slanted well shafts, and the development of directional drilling technology began. Today horizontal directional drilling (HDD) is used for several, widely different purposes.
Horizontal Water Wells
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HDD can be used to dig horizontal wells alongside a beach or river that are capable of supplying a large amount of water with low solids content. Wells drilled horizontally along lateral conductive zones such as sand and gravel layers are also able to deliver large volumes of water through the bigger pore spaces. Horizontal wells are also useful for accessing shallow aquifers with large cross sections.
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Trenchless Utility Installation
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One very important use of HDD today is trenchless utility installation. The ability to accurately steer and track the drill from the surface enables utilities to drill under streets, highways, parking lots, and even buildings without damaging existing utilities. A pilot hole is drilled downward at a shallow angle until the desired depth is reached and the angle is changed to the horizontal. The pilot hole is reamed out by pulling reaming heads back through it to the rig. Once the hole is 1.5 times the diameter of the pipe or cable, the pipe or cable is pulled through with the final reaming pass.
Soil Remediation
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HDD is often used to remediate contaminated soil. HDD is also used for drilling horizontal shafts through areas of contaminated soils. These shafts are used to extract volatile and semivolatile organic compounds from the soil by vacuum, a technique called soil-vapor extraction. Horizontal wells have more area of contact with the affected layer of soil than vertical wells, and are therefore much more effective. These horizontal wells are also well-suited for biosparging or soil venting (the slow aeration of the soil and/or groundwater), techniques which are often used in conjunction with soil-vapor extraction.
Recovery of Dense, Non-Aqueous Phase Liquids (DNAPLs)
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DNAPLs are liquids that are denser than water but that do not readily mix with water. They can be long-term sources of dissolved contaminants if left in the subsurface of contaminated sites. Horizontal wells drilled using HDD can be located at the optimum depth for removing DNAPLs from the soil.
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References
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- Photo Credit oil well image by michael langley from Fotolia.com pollution 1 image by Nathalie P from Fotolia.com
