Saudi Aramco is looking for further investment opportunities in Indonesia's downstream refining and petrochemicals industry, the company's CEO said on Thursday, after initiating a $5.5 billion project to upgrade the country's largest refinery.

The Saudi Aramco CEO's comments are positive for Indonesian President Joko Widodo's efforts to attract investment after a clean-up of the country's oil and gas sector that followed a series of scandals.

"Indonesia is an important country for Saudi Arabia, a rising global economy, we would like to be a part of the growth of Indonesia," Saudi Aramco CEO Amin H Al-Nasser said at the signing of the initial agreement to upgrade the Cilacap refinery in Indonesia's Central Java province.

Indonesia will rejoin Opec as its 13th member nation next month.

The project is expected to increase the refinery's crude processing capacity to 370,000 barrels per day (bpd) from 348,000 bpd at present, and is also likely to include an agreement to import crude from Saudi Arabia, the world's top crude exporter.

The upgrade will include a new hydro cracker unit, as well as units to increase production of paraxylene and polypropylene production, according to a Pertamina statement.

"It's a great opportunity for growth in a global market," Nasser said. "We're hoping this is the start."

Aramco was also expected to join a tender to develop a greenfield refinery project in East Java, Wiratmaja Puja, Indonesia's director general of oil and gas, said.

Further details on a strategic partnership between Aramco and Indonesia's state energy company Pertamina have yet to be finalised, including how a joint venture between the two will be shared.

Indonesia broke off talks on building two refineries with Aramco and Kuwait Petroleum in 2014 due to a disagreement over taxes and fiscal terms.

Brent crude trading at $45 a barrel may have helped restore investor interest in Indonesia's downstream sector as Saudi Arabia and other oil companies move to secure markets.

Saudi Arabia, Opec's top producer, has rebuffed calls to cut output in an effort to support prices, and is instead focused on defending market share.

Nasser said Aramco would meet its customers' demands.  - Reuters