SAO PAULO, Oct 21 (Reuters) - Brazilian oil company 3R Petroleum (RRRP3.SA) is planning to launch a share offering to fund acquisitions and investments in assets, it said in a securities filing on Thursday. The company said the value and date of the issue has not been decided yet, but financial website Brazil Journal reported earlier on Thursday that it would be of up to 1.5 billion reais ($265.07 million). The company plans to use the proceeds to pay for assets recently acquired from Petroleo Brasileiro SA (PETR4.SA), the journal said. Shares in 3R were down 5.8%, trading at 35.80 reais. The share offering will be managed by Banco Itau BBA, as the lead coordinator, Banco BTG Pactual, XP Investimentos and Banco Safra, among other financial institutions, the filing said.The issue will depend on market conditions in Brazil and abroad, and regulatory approvals, the company said. ($1 = 5.6588 reais)