Stratigraphic Distribution And Geological Significance Of The Middle Permian In The Sichuan Basin

Qixia and Maokou formation is an important marine carbonate gas reservoir in Sichuan basin of middle Permian. But limit to the investment in the exploration work and the stratigraphic division of the Permian is not unified, result in an unclear understanding of the strata preservation or deletion even the specific distribution, which seriously restricted the oil and gas exploration work thorough development of Middle Permian. This paper through the system finishing of Sichuan Basin and its surrounding408drilling well, logging data and204district profile data, based on the new three division scheme of Permian of Sichuan Basin, By the guidance of the relative sea level change sedimentary cycle, combined with the lithology, electrical property and the profile observation, promoted the new wok of the stratigraphic division and correlation of Middle Permian in Sichuan Basin, established several well profile for stratigraphic correlation which can cover the whole basin, then calculated each small layer (residual) formation thickness. In view of the above, compiled the layers of the group of Qixia and Maokou every (residual) formation thickness isoline map and the paleo-geological map before Longtan Formation sedimented of upper Permian. By the analysis of the specific distribution and the sedimentary filling evolution of the (residual) formation of Qixia and Maokou group, Combined with the characteristics of seismic profile, three North East paleo-uplift exst in the Permian Sichuan Basin, as Leshan-Longnvsi paleo-uplifit、 Luzhou paleo-uplift and Kaijiang paleo-uplift, these paleo-uplift topographic relief is less than200m, the landscape gently stretched as a whole, with a characteristic of succession of development. There into, the development of Kaijiang paleo-uplift may be affected by the impact of Leshan-longnvsi paleo-uplift and maybe there is some relationship between the two paleo-uplift systems. But with the Luzhou paleo-uplift, they are more likely two independent palaeo-uplift system since they are departed by some lowlands. In the period of Qixia, the Stratigraphic pattern is west thin and east thick, but Maokou period is just the opposite, with the characteristics of east is thin and west is thick, analysis of that this is controlled by the Emei taphrogenesis. This movement lifted the upper Yangtze region as a whole and also strengthened the paleo-landform pattern of uplift and depression due to it’s specific property of that tectonic uplift process is not a balanced block movement and it’s special evolution of tectonic movement of temporal characteristic. The transition of tectonic compression and extensional environment caused by the movement and interaction between the Yangtze plate and it’s adjacent tectonic plate, these kind of elements jointly led to the paleo-landforms of Sichuan Basin occurred the "seesaw" conversion and the development of paleo-uplift. High-energy shoal facies which associated with quality reservoir often developed in the high position of paleo-uplift, in the Late Middle Permian the Dongwu movement caused by crustal uplift, under the influence of weathering and leaching of exposure the weathering crust karst reservoir developed, so to understand the characteristics of the paleo-uplift helps to further regional oil and gas exploration of Middle Permian.