* CEO says BP report ignores key factor in oil spill
* CEO repeats criticism of BP's blown-out well
* Noble CEO blames human error, says BOP may not have failed
* Weatherford says mistake to rely on BOP
By Tom Bergin
LONDON, Oct 12 (Reuters) - The chief executive of Royal Dutch Shell Plc has criticised the investigation that rival BP Plc conducted into the causes of its Gulf of Mexico oil spill, and the design BP chose for its blown out well.
Peter Voser told the Oil and Money conference in London on Tuesday that to correctly investigate the accident one had to examine the thinking behind the particular well design BP used -- something BP's report did not consider.
The Macondo well design included a number of cheaper options, including the use of a single tube from the surface to the reservoir, rather than two overlapping tubes, and U.S. lawmakers said these choices reflected a tendency on BP's part to put profits before safety.
"Shell clearly would have drilled this well in a different way and would have had more options to prevent the accident," Voser said, referring to Shell's preference to include more barriers to hydrocarbon leaks in its well designs.
The chief executive of driller Noble Corp, who was speaking at the same conference, also challenged BP's claim that the blowout preventer (BOP) on the rig failed, and alleged that the failure to correctly read the well was the real cause of the accident.
The Deepwater Horizon drilling rig exploded in April after an uncontrolled surge of oil and gas went up the well. the sinking of the rig led to the worst oil spill in United States history.
BP has blamed the failure of the BOP, a stack of valves designed to cut off well flows in the event of a high-pressure surge, and human errors, largely on the part of its contractors, for the rig blast.
But Noble's chief executive David Williams said the cause of the blast was not the BOP.
"It was caused by a failure of the individuals involved to identify what the well was telling them," he told the conference, referring to the fact that rig staff did not shut in the well despite rising pressure and other warning signs.
He said the BOP may not have even failed at all, given speculation that pieces of piping were found inside the device. If this came from dislodged piping in the well, it could also call BP's well design into question.
REDUNDANT BOP
Bernard Duroc-Danner, chief executive of oil services company Weatherford said it was a mistake to rely on BOPs to avert disasters.
"BOPs should be, in many ways, redundant," he told the conference.
BP has come under fire from rivals who have suffered heavy losses due to the drilling ban imposed by President Barack Obama in the wake of the oil spill.
Nonetheless, Voser accepted that Shell and others had not invested enough in developing solutions to clean up spills.
"The industry was not prepared to handle this spill," he said.
Voser said he expected tighter regulation following the spill and that in future Shell would be more selective about who it would partner with on projects in the Gulf of Mexico.
IRAQ
Shell's CEO also said that his company was making progress in Iraq, where it won a contract to develop the Majnoon field last year.
Shell has raised output at the field to 70,000 barrels of oil per day from 45,000 bbls/day previously.
He also said Shell was abiding by United Nations sanctions against Iran but added:
"I have not given up my long term hope that we can actually develop sources in Iran." (Editing by Greg Mahlich)