* Financial restrictions create heavy administrative burden
* Rules constructed to exempt Shah Deniz gas field
By Pete Harrison
BRUSSELS, Oct 29 (Reuters) - European sanctions on Iran are not intended to restrict Iranian imports or exports of oil, officials say, but the impact of wide-ranging financial restrictions on its oil flows remains unclear.
The EU sanctions became become law on Wednesday, putting extra pressure on Tehran to return to negotiations over its uranium enrichment programme.
"It is clear that the new rules are likely to mean more administrative burden for businesses as well as the authorities," said Georg Berrisch, a partner at the international law firm Covington & Burling in Brussels.
The rules block oil and gas investment in Iran and curtail Tehran's refining and natural gas capability, but they have been crafted in a way that reduces the impact on ordinary Iranian citizens.
"The restrictive measures should not affect the import or export of oil or gas to and from Iran, including the fulfilment of payment obligations in connection with such import or export," reads the legal document.
But financial transfers of 40,000 euros ($55,520) or more require authorisation, and it remains unclear whether the bureaucracy involved and other wide-ranging financial restrictions will continue to deter banks from extending credit for oil deals.
"In particular the obligations to notify payments, but also the possibility to apply for exemptions from certain export prohibitions, will put a heavy burden on the national export control authorities," said Berrisch.
"One can only hope that they will be able to commit sufficient resources -- otherwise chaos is likely," he added.
The measures have also been crafted to exclude Azerbaijan's Shah Deniz gas project, in which Iranian state energy firm NIOC has a stake.
Europe views the gas field as a big potential source of supply that could reduce its reliance on Russia, and any sanctions might damage its future energy security.
Shah Deniz is not mentioned by name in the text of the sanctions, but EU lawyers have carefully constructed an exemption with the gas field in mind.
"Any body, entity or holder of rights derived from an original award before the entry into force of this regulation by a sovereign government other than Iran, of a production-sharing agreement shall not be considered an Iranian person, entity or body," reads the complex legal text, which EU sources say refers to Shah Deniz.
(Reporting by Pete Harrison and Juliane von Reppert-Bismarck, editing by Jane Baird)