THE CHARACTERISTICS AND SOURCES OF NATURAL GASES FROM ORDOVICIAN WEATHERED CRUST GAS RESERVOIRS IN THE CENTRAL GAS FIELD IN ORDOS BASIN

摘要

The central gas field, located in the northern part of central paleo-uplift zone around the Jingbian and Hengshan areas in the Ordos Basin, is a famous large-sized gas field in Onshore China. Many scholars at home and abroad have done a lot of research work, but there has still been controversy on the origin of Ordovician weathered crust gases in the central gas field. In General, the gas spurce of this gas field is a mixture of Carboniferous-Permian (C-P) coal-related gases and Ordovician oil-type gases. Thus, the main gas source is the key problem involved in natural gas exploration and development in this region. There are two different hypotheses concerning the main source of Ordovician weathering crust natural gases. One holds that Ordovician natural gases in the central gas field were mainly derived from C-P coal-bearing strata, i.e., coal-derived gases (e.g. Guan Deshi et al., 1993; Yang Junjie et al., 1991, 1996; Dai Jinxing et al., 1997, 1999; Zhang Wenzheng et al., 1997; Xia Xinyu, 2000). The other suggests that natural gases in the central gas field were mainly derived from Ordovician carbonate rocks and belongs to the oil-type gases (e.g. Chen Anding, 1994, 2002; Huang Difan et al., 1996; Xu Yongchang et al., 1994; Jiang Zhusheng et al., 1999; Li Jian et al., 2001; Li Xianqing et al., 2001, 2003). On the basis of these researches, the authors try to further discuss geochemical characteristics and gas sources of Ordovician weathered crust gas reservoirs in the central gas field.