Hi Claudia,
Within OpendTect Pro, we have the PetrelDirect Link which is capable of transferring data objects and surveys between the two softwares.
But for this to happen, you need to have the PetrelDirect Link installed on the OpendTect Pro side, and the OpendTect Pro plugin for Petrel installed in Petrel on the other side.
Both of these softwares must be installed (each with an up-to-date license) and running simultaneously on the same machine.
If I understand your question correctly as, 'I only have OpendTect and want to open a Petrel project' - that is not possible.
I hope this clarifies things for you... get back to us if you have any other questions.
Kind regards,
Mark