求翻译：今年5月，中石油集团总经理蒋洁敏宣布，中石油已制定600亿美元的海外投资计划，以确保规划期内海外油气年产量达2亿吨的目标。而在2020年前后，国内石油和天然气的年需求将达6亿吨，中石油将贡献4亿吨，其中一半来自海外油气作业区。是什么意思？

In May of this year, announced CNPC general manager Jiang Jiemin, CNPC has developed a $ 60 billion overseas investment program to ensure that the planning period of overseas oil and gas annual production of 200 million tons. In 2020, the annual demand of domestic oil and natural gas will reach 600