Shuwei Guan, Research Institute of Petroleum Exploration & Development, PetroChina, Beijing, China, John H Shaw, Harvard University, Earth and Planetary Sciences, Cambridge, MA, United States, Yanpeng Sun, Harvard University, Earth & Planetary Sciences, Cambridge, MA, United States and Yongshu Zhang, Petrochina Com. Lt., Beijing, China; Research Institute of Petroleum Exploration & Development, Qinghai Oilfield Company, Dunhuang, China