Exploding bubbles detected by laser light

A revolutionary way of detecting the potentially dangerous gas bubbles in bore-holes that can lead to large explosions has been developed by researchers at the University of Reading.

The new technique could save the oil exploration industry millions of pounds by using laser light to detect tell-tale gas bubbles in the drilling slurry in oil bore-holes. The bubbles are an indication that the drill is about to enter a high-pressure gas pocket. Although experiments have so far only been carried out under laboratory conditions, Dr David Waterman says that this sort of technology could be developed for commercial use in under two years.

As the drill approaches the gas pocket it relieves the pressure close to the drill tip causing bubbles to form in the slurry, just as bubbles form when the top is removed from a bottle of lemonade. Detection of the bubbles tells operators at the surface to increase the pressure of the slurry at the drill bit to push against the imminent increase in pressure of the gas pocket and prevent a catastrophic blow out.

The proposed technique for detecting the bubbles illuminates the volume of slurry around the drill tip with sheets of laser light. As gas bubbles pass through the laser sheets they light up like dust passing through a cinema projector beam. Measurement of the time interval between bubbles lighting up in adjacent sheets of laser light enables the bubble size and speed to be determined.

However, the Reading technique goes beyond this and measures the amount by which light bends when passing through the gas bubbles. The amount of bending depends on the optical properties of the gas bubbles, so transparent bubbles can be discriminated from bits of rock in the slurry improving the reliability of the technique. The Reading team has used falling water droplets in the laboratory to mimic the behaviour of the gas bubbles in the slurry.

Their technique measures the size, speed and optical properties of the drops. It is envisaged that the technique could be applied in bore-holes within two years.