The Study Of Sedimentary And Sequence Stratigraphy Characteristics For Permian Qixia Formation Of The Mid-south Part Of Sichuan Province

The study area is located in the mid-south part of Sichuan province, the target layer is Middle Permian Qixia formation. The south area of central Sichuan Basin has found a good reservoir and get industrial gas flow in the early Middle Permian drilling, showing the great potential of exploration and development. However, there is a lack of in-depth understanding of the sequence stratigraphy and sedimentary facies of Qixia formation in this area, which restricts the development and distribution of reservoir and the overall understanding of the gas bearing properties in Qixia formation. This paper according to the current status of exploration and application of tectonics, sedimentology, sequence stratigraphy and seismic stratigraphy theory as the guidance, aims to the further study of Sichuan basin area in Qixia formation of Permian rock strata, sedimentary facies and sequence stratigraphy. By logging, seismic, slice data established Permian tertiary sequence stratigraphic framework to analysis the sequence strata sedimentary characteristics and tectonic significance of key interface. Finally, based on the integrated sequence stratigraphy, sedimentary facies distribution and the identification of the reservoir, using system as a unit of Qixia formation of Permian sedimentary facies.Sichuan basin is a marine deposit in the Paleozoic, until late Triassic began extensive continental deposit, Based on the tectonic and sedimentary evolution characteristics,, often divided its evolution into pre-Sinian, Sinian Period-Middle Triassic,late Triassic-early Cretaceous,late Cretaceous- Quaternary Period. Liujiang movement, Yunnan movement and Dongwu movement(middle Permian-late Permian) control sedimentary tectonic movement in mid-south part of Sichuan basin. Liujiang movement and Yunnan movement formed the Liangshan formation and the underlying strata angular unconformity, Dongwu movement formation of Maokou Formation and the overlying Longtan group parallel unconformity. Liujiang movement and the Yunnan movement made Liangshan and its underlying strata angle disconformity,Dongwu movement made Maokou and its overlying formation parallel unconformity.According to sedimentary facies flag, such as lithology, sedimentary characteristics, logging and seismic, study the sedimentary facies during the middle Permian of study area. Study area Permian Qixia mainly developed sedimentary facies carbonate gentle slope, It can be broken down into three categories subfacies, Including shallow gentle slope platform, intra-platform shoal, Deep Water gentle slope platform. Developed a deep water gentle platform deposition in the section 1-B of Qixia formation,and developed the shallow gentle slope platform, intra-platform shoal in the section 1-A of Qixia formation to section 2 of Qixia formation.Comprehensive regional tectonic and sedimentary facies analysis movement, carried out the seismic sequence boundaries Calibration, Identify, track and contrast three sequences and its system domain interface, Established the regional integration in third-Permian sequence stratigraphic framework, the middle Permian is divided into one second-order sequences SSQ1( Liangshan formation to Maokou formation,280~260 Ma);the Qixia formation is divided into one third-order sequences SQ1(Liangshan formation to Qixia formation). Identified sequence interface includes orogenic angular disconformity, erosional unconformity. Based on the maximum flooding surface mfs1, internally divided SQ1 into LST(SQ1-LST), transgressive systems tract(SQ1-TST) and highstand system tract(SQ1-HST).Based on thestudy of the maily Over well profile, according seismic facies characterization and single well sedimentary facies constraint and converted to sedimentary facies, prepared the s edimentary facies plan, Revealed sedimentary facies law. According to sea-level variation, summed up the three kinds of depositional model. Tectonics, sea level is the main controlling factor of the middle Permian in two, three stratigraphic sequences and the formation of internal systems tract. Orogenic tectonic movement formed bottom of Liangshan formation angle unconformity and top Maokou parallel unconformity uplift. Eustatic control of the third-order sequence succession cycle, thereby controlling the three internal sequences of sedimentary facies.