Residues from the oil and gas industry often contain radium and its daughters. The sulfate scale from an oil well can be very radium rich. The water inside an oil field is often very rich in strontium, barium and radium, while seawater is very rich in sulfate : so if water from an oil well is discharged into the sea or mixed with seawater, the radium is likely to be brought out of solution by the barium/strontium sulfate which acts as a carrier precipitate.