Sedimentary Evolution Of The Carboniferous Huanglong Formation In The Eastern Sichuan Basin

After30years of exploration and development, East Sichuan’s carboniferous system has become an important exploration area of the natural gas’s main pay zone and reserve. Along with the in-depth exploration and development of East Sichuan’s natural gas, gas deposit get more complex and exploration and development get more difficult. In order to satisfy the need of exploration, make further research of East Sichuan’s carboniferous system exploration and seek potential and beneficial exploration block or new prospecting types, it needs to conduct a new study on some essential issues, like its stratigraphic distribution and sediment reservoir, in the expectation of expanding the exploration field of non-structural gas reservoir and providing theoretical guidance for East Sichuan’s carboniferous system exploration.Guided by the previous research results and latest research progress abroad and at home and using the method of combining sequence stratigraphy, petrology, well drilling, mud logging, well logging and2D seismic exploration, this study is primarily conducted in the following aspects:regional geological research, division and correlation of the strata, types of sedimentary facies, sedimentary facies analysis and sedimentation evolution. In term of regional geological research, this study focuses on analyzing regional stratigraphic characteristics and regional tectonic evolution process. In term of division and correlation of the strata, the study makes division and identification of third grade sequence units and an analysis of single well and wells sequence to establish the stratigraphic framework. As for sedimentary facies analysis, distribution characteristics of sedimentary system in the sequence stratigraphic framework will be expounded by the analysis of single well facies, wells facies and in-plane phasing. In the aspect of types of sedimentary facies, it concludes and summarizes Huanglong formation sediments’generating environment, conditions and features and identifies tidal-flat facies, subfacies and microfacies growing in this section. The research of sedimentation evolution characteristics makes a detailed account of sedimentary facies in each section and its evolution features by analyzing all kinds of single factor maps and drawing out maps of sedimentary facies in each section.We think that the HuangLong Formation of Carboniferous can be divided into1third-order sequences and four section by our deepen research, then a new opinion was put forward, the lowstand systems tract and short-term local regression common led to the high-gamma in Carboniferous carbonatite. The distribution of Eastern Sichuan Basin is "west high east low",and the distribution area occurred twice transformation from a small angle to larger in Late carboniferous. The intensely tectonic movement between Early Carboniferous and Late Carboniferous not only made "west high east low" into "east high west low", but also continued into the last stage of Last Carboniferous. According to study, the Eastern Sichuan Basin was developed carbonatite deposition of tidal flat depositional system in Late carboniferous, two transgression channels were developed in southeast of Yunyang and northwest of Dazhou in the area, two tidal-flat depositional systems in Chongqing-Wanzhou and southeast of Dazhou respectively were formed, and a suit of complete third-order sequence composed of lowstand systems tract (C2h1), early transgressive systems tract (C2h1), late transgressive systems tract (C2h3) and early highstand systems tract (C2h4) was developed. The upper carboniferous is a suit of complete thied-order sequence, but it could been divided into two evolutionary phase. The one phase is that the restricted saline lake, the supratidal-dolomitic flat was developing in tidal flat environments of lowstand systems tract, and the syndeposit rubble beach, the dolarenite beach was developing in early transgressive systems tract; the another phase is that the wide intertidal dolomite-limestone flat, the restricted syndeposit rubble beach and dolarenite beach was developing in late transgressive systems tract, and the intertidal-dolomite-limestone flat, the subtidal-limestone flat, the restricted bioclast beach and the ooid beach in early highstand systems tract.