"We have made 15 arrests after reports of people gaining access to Navigator Terminals in Grays," the police said in a statement.
The statement also said that "the site has now been cleared of people," who have been "arrested on suspicion of aggravated trespass."
The detainees remain in custody, it added.
On 9 May, the UK introduced a new package of sanctions against Russia and Belarus targeting $2 billion worth of trade. The new restrictions became the third wave of trade sanctions that the UK imposed against Russia over its special military operation in Ukraine. Excluding gold and energy, about 96% of imports from Russia to the UK and over 60% of UK exports to Russia are now under restrictions.