Sequence Stratigraphy And Reservoir Sand-bodies Of Xiashihezi Formation In The Northeast Of Ordos Basin

Oidos Basin is a large multicycle craton superimposed basin,in the middle tectonic strip of sedimentary basin of china,an important basin with strong potential for natural Gas exploration, and one of the backbone resource bases for "West to East Gas Pipeline Project".The research of Gas Reservoirs of the northeast of Ordos Basin confronts with the those difficulties that could be expressed as how the formation and evolution of basin controls the natural gas transferring, the reservoir-forming and the enrichment rule of the lothological reservoir.Based on sedimentology,this thesis studied the field outcrop,well core,well logging data and sample testing result of the Xishihezi formation in the northeast of Ordos Basin,and discussed the controlling factor of the natural gas reservoir-forming.Firstly,this thesis reseached the high-resolution sequence stratigraphy of the Xishihezi formation in the northeast of Ordos Basin, summarized the sound markers of stratigraphic division and correlation,and built the high resolution sequence stratigraphic framework of Xishihezi formation.Consequently, one Super Long-term Sequence Cycle(SLSC) was indentified, and then,subdivided into five Long-term Sequence Cycle(LSC) and 10 Middle-term Sequence Cycle(MSC) respectively.Furthermore,it went to study the characteristics and genesis of sequence boundary, systems tracts and sequences.Based on the sequence stratigraphic framework above,Xiashihezi formation was indentified as the Continental sedimentary system including alluvial depositional systems,lacustrine-delta depositional system and lacustrine depositional system,in terms of sedimentary pattern and Characteristic.Obviously,two river-delta systerms developed in the east and west respectively. The sedimentary system evolved from braided channel dalta(LSC1,LSC2) and meandering channel talta(LSC3,LSC4)to anastomosed channel dalta(LSC5) which was recognized for the first time. Some other important work is as following: drawing the maps of sequence-based lithofacies paleogeography,isoline of sand thickness and ratio between sand and mud within the long-term and middle-term sequence cycle;analysing the genesis,shape and distribution of the sand-body in different sedimentary environment;expounding the evolution of the depositional system and the sequence-based lithofaeies paleogeography;creating the 3D model and the Line Section reflecting the channel transfer and the river shape;inllustrating the relationship between the accumulation and provenance supply. Furthermore,the analysis of elastic composition,debris,cathodoluminescence,heavy minerals,paleocurrent and Dickinson triplot of elastic component of the sandstone shows that the provenance is the north Yinshan paleoland,or the recycled orogen.Finally,this thesis discussed the controlling factors of subtle oil/gas reservoir,such as the sequence stratigraphy,the sedimentary system, the sand-body characteristic and the basin evolution.All the Analyses indicate that the reservoir bodies locate in the microfacies of the distributary channel of delta plain,Xiashihezi Formation is a lithologic gas reservoir with low-porosity and Low Permeability,and the early period of the super-long-term cycle of Xiashehezi is related with the super-long-term base level cycles,a period with active regional tectonism and abundant provenance supply.