MOBILE, Alabama -- Oil is once again fouling the Gulf of Mexico around the Deepwater Horizon well, which was capped a little over a year ago.

Tuesday afternoon, hundreds of small, circular patches of oily sheen dotted the surface within a mile of the wellhead. With just a bare sheen present over about a quarter-mile, the scene was a far cry from the massive slick that covered the Gulf last summer.

Floating in a boat near the well site, Press-Register reporters watched blobs of oil rise to the surface and bloom into iridescent yellow patches. Those patches quickly expanded into rainbow sheens 4 to 5 feet across.

Each expanding bloom released a pronounced and pungent petroleum smell. Most of the oil was located in a patch about 50 yards wide and a quarter of a mile long.

The source of the oil was unclear, but a chemical analysis by Louisiana State University scientists confirmed that it was a sweet Louisiana crude, and could possibly be from BP PLC’s well.

The oil could be flowing from a natural seep on the seafloor near the wellhead, experts said. Other possibilities include oil trapped within the wreckage of the Deepwater Horizon drilling rig, or oil deposited on the bottom during the spill that is slowly working its way to the surface.

The most troubling possibility, according to petroleum engineers, is that oil is leaking up through the seafloor surrounding the sealed well pipe.

Last week, in response to Internet postings by lawyers and environmental groups describing a leak, BP issued a blanket denial, stating, “None of this is true.”

Subsequently, the Gulf Restoration Network and Bonny Schumaker with On Wings of Care took aerial photographs of circles of oil floating in the area Friday. The group filed a report with the National Response Center, the federal clearinghouse for pollution incidents.

“We stand by what we said last week, neither BP nor the Coast Guard has seen any scientific evidence that oil is leaking from the Macondo well, which was permanently sealed almost a year ago,” BP spokesman Justin Saia wrote in an emailed statement Wednesday. “We welcome the opportunity to test any hydrocarbon sheens detected in the area of the well.”

U.S. Coast Guard officials said Wednesday that the earlier reports were investigated by flying over the site.

The Coast Guard determined that the reported sheens resulted from “natural seeps” and permitted pollution releases at other oil drilling sites. Coast Guard officials did not elaborate when asked how those determinations were made, and said that no boats had visited the well location since the reports were filed.

“I think the primary source with high probability is associated with the Macondo well,” said Robert Bea, an internationally prominent petroleum engineer and professor emeritus at the Berkeley campus of the University of California. Bea responded to Press-Register questions via email after examining photographs taken by the newspaper.

“Perhaps connections that developed between the well annulus (outside the casing), the reservoir sands about 17,000 feet below the seafloor, and the natural seep fault features” could provide a pathway for oil to move from deep underground to the seafloor, Bea said.

“Looks suspicious. The point of surfacing about 1 mile from the well is about the point that the oil should show up, given the seafloor at 5,000 feet ... natural circulation currents would cause the drift,” Bea said. “A Remote Operated Vehicle (ROV) could be used to ‘back track’ the oil that is rising to the surface to determine the source. This should be a first order of business to confirm the source.”

Oil analysis

Samples collected by the newspaper Tuesday were provided to Scott Miles, a chemist at LSU. Together with oil chemist Ed Overton, Miles conducted the chemical analysis that federal officials used to fingerprint the Deepwater Horizon oil — known as MC252.

“Looking at the fingerprinting, the samples were low concentration, so it is not giving a real good picture. It is possible it could be MC252. It’s south Louisiana crude for sure,” said Miles. “You can’t say 100 percent that it is from the spill itself, but they do need to get somebody out there to investigate further.”

Miles said he could smell the oil in the samples as soon as he opened the jars.

“The fact that it is right over the Macondo well site is pretty tantalizing,” said Overton, who was one of the first people contacted by the National Oceanic and Atmospheric Administration after the spill began in April 2010.

“There is no way to say for sure whether the well is leaking, based on what is on the surface,” he said. “Of course it is suspicious.”

Overton noted that a number of natural seeps had been found within 12 miles of the well, and that those nearest the well would bear a similar chemical signature.

Phillip Johnson, author of the Standard Handbook of Petroleum and Natural Gas Engineering and a professor at the University of Alabama, said that photographs from the site were intriguing, but it appeared that a fairly small amount of oil was reaching the surface.

“There are two broad categories you would consider. One is leakage, and two is residual oil. I’d say leakage is pretty unlikely. That would imply that the seal on that well — which is about 5,000 feet of cement — failed. That’s unlikely,” Johnson said. “Then you think of residual oil that might be present in the 5,000 feet of riser pipe that wound up on the bottom. Large amounts of the platform ended up on the bottom. Those things could have oil in them that is slowly working its way to the high points and floating out.”

Riser pipe connected the well to the Deepwater Horizon rig on the surface. Neither the pipe nor the rig has been salvaged.

Johnson also suggested that heavier fractions of oil may have settled to the bottom during the spill. Over time, as bacteria degrade oil on the seafloor, the lighter fractions might be released and float to the surface, he said.

The Press-Register reporters located the area where the oil was rising to the surface by going to a point directly over the Macondo well and then moving in the direction of the prevailing surface current. The first blobs of oil seen on the surface were detected about a half-mile from the well. The frequency of the sightings increased gradually over the next half-mile.

In the Olympic swimming pool-sized area where the oil was rising most frequently, new sheens were erupting every few seconds on all sides of the 36-foot boat.

Marcus Kennedy, who piloted his fishing boat, the Kwazar, 115 miles from Dauphin Island to the well site, said he was stunned by the heavy petroleum scent in the air. A nearby data buoy recorded winds of less than 2 mph at the time.

Mahi-mahi and blue runners were schooling in the area. In the distance, yellowfin and blackfin tuna could be seen churning the water to a froth as they attacked bait. A 40-foot whale shark also surfaced in the area.

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Jeff Dute contributed to this report.