In this image taken from video provided by BP on Monday, a remotely operated vehicle works around the containment stack at the site of the BP oil spill in the Gulf of Mexico. In this image taken from video provided by BP on Monday, a remotely operated vehicle works around the containment stack at the site of the BP oil spill in the Gulf of Mexico. (BP/Associated Press)

Seepage detected a few kilometres from BP's capped ruptured oil well is coming from another well, the official overseeing the U.S. government response to the Gulf of Mexico oil spill said Tuesday.

There are two wells within 3.2 kilometres of BP's blown-out well, known as Macondo. One has been abandoned and another is not in production.

"It's actually closer to … [the abandoned] facility than it is to the Macondo well," retired U.S. Coast Guard Adm. Thad Allen said at a Tuesday afternoon briefing.

The distance from the Macondo well and the fact that it's not uncommon to have seepage around abandoned wells is what convinced engineers that BP's well wasn't the source of the seepage, he said.

There are around 27,000 abandoned wells in the Gulf that are not checked for leaks, an investigation by the Associated Press has found.

Allen also said five leaks in and around the broken well are more like drips and don't mean the well is unstable. He has extended the testing period for the experimental cap that was placed on the well last week by another day.

Cap brings relief

The mechanical cap has stopped the oil flow since Thursday, but several leaks had caused mounting concern that the cap was displacing pressure and causing leaks deep underground.

A concrete pumper that has been converted into a water skimmer removes oil from the shores of St. Bernard, La., on Thursday. A concrete pumper that has been converted into a water skimmer removes oil from the shores of St. Bernard, La., on Thursday. (BP/Reuters)If oil is leaking through bedrock and mud, it could cause instability in the sea floor and make the environmental disaster even worse and harder to fix.

Beachgoers have reported less oil fouling the shore since the cap was closed on Thursday.

Bob Broadway, 41, of Huntsville, Ala., said his vacation spot in Orange Beach, Ala., had improved from a month ago.

Then, he said, the oil was thick "like chocolate" and the beach smelled like "an old mechanic's garage."

"The beach looks better now than before," he said Monday.

The spill began after a BP-leased oil rig exploded off the Louisiana coast on April 20, killing 11 workers.