DRILLING for oil is unlikely ever to be good for the environment, but there could be way to make it a little greener. That鈥檚 the claim of scientists behind a new drilling fluid that they are hoping to test in offshore oil rigs in the South China Sea.
Drilling fluids cool and lubricate oil drills, and help to transport cuttings to the surface. But boreholes can be kilometres deep, and because pressure increases with depth, the fluid can be forced into tiny pores in the clay-rich rocks such as shale and mudstone through which boreholes pass. This destabilises the boreholes, triggering collapses that cost the oil industry an estimated $2 billion each year.
Some oil-based drilling fluids can prevent boreholes collapsing, in part because they penetrate the pores less. But the fluids persist in the environment and cleaning them up is expensive. There is increasing pressure to have some of the worst oil-based fluids banned, so the search is on for cleaner alternatives.
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鈥淕reen fluids should be particularly useful where there are stringent environmental regulations such as the North Sea or the Gulf of Mexico,鈥� says Chee Tan of the Australian research organisation CSIRO. Tan led the CSIRO team that developed the new fluid with Texas-based corporation Halliburton.
The green drilling fluid is a water-based, highly alkaline solution of silica-based chemicals called silanes. As long as the pH is high, the molecules in the fluid are small enough to enter the pores in the borehole wall, which may be only a few nanometres wide.
But when the drilling fluid mixes with water in the pores, the fall in alkalinity causes the molecules to join up to form a silicone-like polymer that plugs the pores.
In lab tests that modelled oil-drilling, the green fluid was as good as oil-based fluids at stabilising a clay borehole. It has also passed toxicity tests set by the US Environmental Protection Agency for fluids to be used when drilling in the Gulf of Mexico.
鈥淲ater-based fluids tend to be better because they don鈥檛 persist in the environment,鈥� says Mark McCallum, director of industry operations at the Australian Petroleum Production and Exploration Organisation in Canberra.
