Abstract:

The third Member of Feixianguan Formation (T₁f³) is the main gas producing formation of marine carbonate strata in western Hubei and eastern Chongqing area. Systematic research on natural gas accumulation stages and main controlling factors should be helpful for natural gas prospecting in this area. Based on natural gas composition and stable carbon isotope, kerogen carbon isotope, and homogeneous temperature of fluid inclusions data, this paper discussed the origin and source of the natural gas, hydrocarbon generating and petroleum charging history. Finally, gas accumulation stages and the main controlling factors of gas accumulation were analyzed according to the regional structure and local trap evolution histories. Following conclusions can be drawn. The natural gas of T₁f³ was mainly secondary cracking gas of the crude oil generated from the Permian source rock. Natural gas accumulation can be divided into three stages: oil accumulation of paleo-lithologic reservoir (190 Ma to 160 Ma), oil cracking and gas accumation of the paleo-lithologic reservoir (160 Ma to 140 Ma), and present structural-lithologic gas reservoir formed by the reaccumulation and adjustment of gas (140 Ma to present). The scale of the exposure shoal reservoir effects the scale of paleo-oil reservoir, and the reservation condition during the natural gas remigration and accumulation should be vital for the final gas accumulation of present gas reservoir.

Key words: western Hubei and eastern Chongqing, the third Member of Feixianguan Formation, natural gas, accumulation stage, main controlling factor