Shell Oil reported the light sheen to the government’s National Response Center on Wednesday, but said in a statement that the company had “no current indication” that it originates from the firm’s nearby wells. The source of the rainbow sheen is unclear. It also is not clear whether the sheen is caused by oil or another substance.

The sheen is located between two existing oil production sites — the Mars and Ursa projects — about 130 miles southeast of New Orleans. Shell operates both projects, but BP has a working interest in the Mars field. BP, Exxon Mobil Corp., and ConocoPhillips each have working interests in the Ursa project.

Several oil companies also work in the surrounding waters, which are in the same federal leasing area as the failed BP Macondo well that launched the nation’s worst oil spill when it blew out almost two years ago. That area, known as Mississippi Canyon, includes active projects in widely ranging water depths up to at least 7,300 feet.

Shell said in its statement that it has mobilized an oil spill skimming ship — the Marine Spill Response Corp.’s Louisiana Responder –  “out of prudent caution.” That skimming vessel is expected to be on the site by Thursday morning, said Coast Guard Petty Officer 2nd Class Bill Colclough.