BP might be able to keep its blown out Macondo well shut despite a day of test results that weren't as good as hoped, a top company official said Friday. Since Thursday afternoon, when engineers remotely closed a final line that stopped the oil from flowing into the Gulf for the first time since late April, the well's pressure has risen - a positive sign that may indicate few if any leaks below the wellhead. The well runs from the seafloor almost a mile beneath the Gulf's surface to a reservoir under 14,000 feet of subsea rock. Well pressure continued to rise very slowly Friday evening - about 2 pounds per square inch every hour - and was 6,720 psi by early evening, BP Senior Vice President Kent Wells said in a conference call. That's lower than the 7,500-plus psi figure BP and government officials initially said would be a sure sign the well was sound. But there are a number of possible explanations. The well's initial pressure may be depleted after nearly three months of unobstructed well flow. The oil and gas bearing formation might have partially collapsed and restricted flow under the increased pressure when the last valve was closed. Or, in the worst scenario, there could be small leaks in the well casing - the piping that runs from the wellhead to the reservoir. Concern that the casing might be compromised caused BP to abandon an earlier attempt to plug the well through a procedure called a top kill. Barring any obvious signs of a leak, the company plans to continue monitoring at least until early Saturday afternoon, 48 hours after it shut the well in. At that point keeping the well closed 'is a possibility,' Wells said, as is reopening it and sending oil and gas to the surface until a nearly complete relief well can kill the well for good near its source. Monitoring of the seafloor for leaks with remote controlled submarines and acoustic devices has increased, while a science vessel able to detect small volumes of methane that may leak from the well is being moved into place. Wells sounded cautiously optimistic. 'The pressure building up we are seeing is consistent with models of reservoir depletion and full well integrity,' Wells said. subhed Before shutting the well in Thursday, BP had been collecting or burning about 25,000 barrels a day at the surface since early last month - well below the 35,000 to 60,000 barrels a day the government says has been pouring from the well. But the capping stack of valves and lines attached to the wellhead Monday, and used Thursday to stop the flow, could capture all the oil and send it to surface vessels with capacity of 80,000 barrels a day. That would mean, if the 60,000 barrel maximum is correct, that no oil would flow into the Gulf. Don Van Nieuwenhuise, director of geosciences programs at the University of Houston, agreed with the possible explanations for the lower pressure readings given by BP and federal officials on Friday. If there is a leak in the casing it would more likely be thousands of feet below the wellhead, far from the seafloor. At that depth it would be less likely the oil and gas would appear in the water in the near future. 'If there is a leak they should be able to see it with seismic runs,' Van Nieuwenhuise said. Seismic data gathered earlier on Friday showed no signs of leaks but the company says it will run more seismic tests. Greg McCormack, director of the Petroleum Extension Service at the University of Texas, said he expects the ambiguous pressure readings will lead the company and the government to opt for reopening the well and continuing to produce the oil using the new collection equipment. 'The fact that the pressure is still going up is a good sign, but the safest thing to do would be to go back to producing,' McCormack said. If there is even a small breach in the casing, he said, keeping the well shut in could make it worse. Eric Smith, associate director of Tulane University's Energy Institute in New Orleans, thinks BP may go the other direction, however. 'If the pressure stabilizes and they see no oil leaking (after 48 hours), they don't need to produce the oil,' Smith said. Relief well operations had been halted at the beginning of the test but they resumed on Friday. Wells said the Discovery Driller III soon will drill down another 30 feet and install casing. This keeps the relief well on target to intercept the failed well as early as the end of July, and begin the bottom kill by pumping in mud and cement. Brett Clanton and Sharon Hong contributed to this story. tom.fowler@chron.com XXX - End of Story3D 