In a muddy clearing in southern Sumatra, a portable diesel power plant hammers away alongside a wellhead, struggling to extract crude from a depleted reservoir that lies below farmland and rubber plantations.

Oct. 22 (Bloomberg) — OAO Novatek, Russia’s second-biggest natural-gas producer, will supply the fuel in its liquefied form to China National Petroleum Corp. for 15 years, according to a preliminary...