TOKYO/DUBAI (Reuters) -Saudi Aramco will buy from Japan's Sumitomo Chemical a 22.5% stake in their petrochemical joint venture Petro Rabigh for $702 million, the companies said on Wednesday, as part of a turnaround plan for the loss-making venture. Under the deal, Aramco and Sumitomo Chemical will each provide $702 million in funding to Petro Rabigh and waive loans worth a total $1.5 billion, they said. Petro Rabigh had racked up 8.871 billion riyals ($2.36 billion) of accumulated losses by the end of June, equivalent to over 53% of its share capital, it said on Wednesday.