The use of one precious fluid - water - to recover another - oil - chafes in dry country. Rivers and groundwater are receding in Texas for lack of rain and over-pumping just when the demand for water in new oil and gasfields is growing.
Now one production company in San Antonio is fracturing its wells mostly without water, using gas liquids instead, in a practice that's beginning to spread. Fracturing, or fracking, refers to using fluid and chemicals under pressure to create fissures to extract oil and gas from rock.
BlackBrush Oil & Gas is using a butane-rich mix for fracking after being confounded by many of the same obstacles other energy companies face in buying, moving and disposing of large amounts of water.
"Ranchers don't want to give up their water," BlackBrush production manager Jasen Walshak said.
Gas liquids refer to three fluids - propane, butane and pentane - that occur together with natural gas. They're extracted from natural gas and sold, mostly as fuels.
Switching to gas liquids also seems to reduce controversy for BlackBrush. "People don't see water transfer lines all over the place," Mr Walshak said, referring to the kilometres of pipe that move water from rural wells to oilfield tanks and rig trucks.
In the US, oil and gas fracturing is done almost entirely with water-based fluids, said Mukul Sharma, a professor of petroleum engineering at the University of Texas.
Much less water is drawn for oil and gas than for agriculture or residential use, but the amounts are still significant, and they often come from places where every drop of water is already spoken for. It takes about 22 million litres to fracture a well in the Eagle Ford shale, about 10 million in the Barnett shale, and less still in some other Texas fields.
BlackBrush contracts with the Canadian company that developed the method, GasFrac Energy Services. BlackBrush and GasFrac initially used propane purchased on the retail market. That was expensive, but had immediate advantages, nearly doubling initial production. They were able to use less propane, by volume, than they had water. And fracturing the formation with propane didn't damage the formation the way water did.
On the negative side, gas liquids are less forgiving than water, and can be more expensive. Any problem that occurs during fracking requires the site to shut down.
Mr Walshak said the company had done 20 jobs so far with the liquids. On concerns over the idea of using flammable compounds to recover other flammable compounds, he said, "It is safe." No volatile hydrocarbons are exposed to the atmosphere. A truck on site holds nitrogen to clean gas lines and send the fluids to a flare where they are burned off. An employee is detailed full-time to a thermal camera, checking for leaks.
They have experimented with a range of mixes. They tried 50-50 butane and pentane. Managers now prefer a hybrid, 60-70 per cent butane and 30-40 per cent "frac oil". Frac oil can refer to a controversial oil that contains compounds harmful to people, including benzene and toluene.
Forcing fuel down-well could revive the controversy over diesel fuel. Energy companies have denied using diesel as a frac fluid, but a congressional investigation found they used 35 million litres of straight diesel between 2005 and 2009. BlackBrush and GasFrac recover their oil-butane mix and sell it as oil. Instead of paying to dispose of polluted water, they have an end product they can sell.
From a climate change perspective, using butane instead of water will not have significant impact, said Barry Lefer of the University of Houston. "Propane, butane and pentane are not greenhouse gases and have relatively short atmospheric lifetimes," he said.