New tool gives good vibrations

Natural gas companies looking for better ways to unclog the wells they use to withdraw gas from underground storage reservoirs may soon be getting good vibrations from a low-cost sonic cleaning tool.

A US Department of Energy-sponsored team of companies led by Furness-Newburge Inc. of Versailles, Kentucky, has produced a prototype of a system that uses sound waves to remove inorganic matter and other debris that clog the perforations of gas wells.

The technology is said to have the potential to significantly increase the efficiency at which natural gas is withdrawn from storage reservoirs.

Composed of an oscilloscope, a power supply, a wire line reel for the power cable, an acoustical transducer, a portable generator and waterproof connections, the device is approximately two feet in length, two inches in diameter, and weighs around ten pounds.

The tool is lowered into a well where it emits low frequency, high-intensity directed sound waves. After a short time, the sound waves reportedly force scale surrounding the well's opening to fall off.

The basis for this device stems from a process that Jim Furness, principle investigator and partner at Furness-Newburge, helped develop using acoustics to catalyse ozone and peroxide to prevent air pollution in foundries.

The technology is not ultra-sound; Furness points out, 'People can hear the sound used for the process.' The device is tuneable within the range of subsonic to 3kHz.

About two years of laboratory and bench-scale development yielded a prototype that reportedly achieved impressive results during testing last year at the Bashore No. 1 Observation Well, operated by Nicor Gas. More extensive field tests need to be performed along with additional laboratory work before the tool can be used commercially, but results so far are said to have been encouraging.

On average, more than 17,000 gas storage wells lose 5 percent of their ability to inject and withdraw gas from underground storage fields each year.

A US Department of Energy-Gas Research Institute study found that inorganic precipitate or scale was a leading cause of the problem. Inorganic matter such as calcium carbonate coats a well's openings from which gas is withdrawn. Over time, production can decline to the point where over half of the field's yield can be lost. The US gas industry spends between $60 million and $100 million a year trying to correct this problem.

Water analyses were conducted during the field tests and demonstrated the device's effectiveness in removing key constituents found in storage well deposits. Water samples collected after the sonication tool was used were compared with samples taken two months earlier. The water chemistry indicated a significant increase in mineral salts as well as increased levels of suspended matter.

The amount of calcium, magnesium, iron, and bicarbonate in solution increased by 100 percent, 60 percent, 60 percent, and 5,300 percent, respectively, after sonication. The amount of suspended solids also increased by 230 percent after sonication.