The Hydrocarbon Occurrence Conditions And The Pool-forming Characteristics In Chuxiong Reformed Basin

Chuxiong basin is a reformed Mesozoic-Cenozoic basin, which locates in the Southern China. Due to strong post-sedimentary alternation and structural deformation, the pool-forming conditions and history became very complicated and oil and gas distribution regularity is varied. So the research about the occurrence condition and pool-forming characteristics is necessary for the further petroleum exploration of Chuxiong basin.In this study, according to the features of multi-period migration accumulation and destruction in the superimposed basins, the analysis principles of the "Integrated, Dynamic, Comprehensive" have been used. On the basis of the analysis of oil and gas pool-forming condition, the evolution of fluid dynamic is considered as the main research thread and the stage of oil and gas accumulation and leakage is discussed, especially the oil and gas accumulation in the latest stage. At last, the dominating pool formation actors are comprehensively analyzed and the reservoir-forming features are summarized.The research on the hydrocarbon occurrence condition shows there are so many kinds of source rock in Chuxiong basin. Major hydrocarbon rock lies in the upper-Triassic with high organic thermal maturation. The Xishelu-Pupeng and Chuxiong-Shuangbai area is the center of hydrocarbon generation. The upper-Triassic sandstone with great thickness and vast distribution is the main reservoir as well. However, the pore and permeability of the reservoir sandstone is so poor that they cannot be regarded as available reservoir. By the study of sandstone diagenesis, it is included that some pore may be held because the early charged of oil and gas could restrain further compaction. In addition, the structural fracture can improve the reservoir properties during the course of the late oil and gas accumulation. The regional and local cap-rock own not only perfect macroscopic feature, but also strong microcosmic sealing ability. But abundant fracture is developed in most of the local cap and some of the regional cap because of strong diagenesis, which reduce the sealing ability. The gypsum and halite cap in the northern and eastern of the basin provide the best sealing conditions. There are various kinds of traps in the basin such as lithologic and stratigraphic traps, cap-rock detached fold traps, fault-bended fold traps, fault-propagated fold trap and so on. However, the structural trap that has been reformed violently during the Himalayan cycle is the leading type.It is indicated that geo-thermal gradient is low but the heat flow is high, and the geo-pressure belong to normal or subnormal pressure from the well survey date of the temperature and the pressure. But the research of restoring pressure by means of the compaction and fluid inclusion shows that Yuncanl well has low range overpressure. The over-compaction is developed in Wulongl and Chucanl well may relate to compaction once more after overpressures have been released.By means of basin modeling technique, ancient fluid potentials and pressure during different geological period could be restored. It is discovered that the Palaeo-fluid-dynamic evolution is very complicated and manifests evident diversity in different area and stage. During the successive sedimentary period it seems that the oil and gas potentials and potential gradient are accumulated step by step, while reduced in the tectonic movement period, which shows the oil and gas migration have happened in a large scale.According to the distribution of oil and gas potential, considering synthetically hydrocarbon generation, reservoir and traps-forming, the basin is divided into several migration and accumulation systems in each evolution stage. On the basis of analysis of the distribution and evolution of transport system.it is considered that Shazi-Maojie, R35 well area, Pingchuan-Midian area, Guangtong- Yipnglang area, R92 well-R98 well in the west of basin and R132 well area, R146 well-Gaoqiao area, R128 well -Wande area are the successive areas which are pointed to by oil and gas migration...