The Characteristics Of Sediment-Diagenesis Of Yanchang Series In Trias In The Western Edge Of Ordos Basin

The Ordos basin is a multi-gyration,oil-gas bearing basin, whose subsidence is stable, depression is various and twist is distinct. The basin is a large terrestrial lake during the late Trias. The western edge of basin, the main area of the lake at that time, has many multi-series of source rock, reservoir bed and caprock, so the perspective of containing oil and gas is splendid. However, the process of sediment and diagenesis is complex, lithology of reservoir is compact, physical characterization is bad, pervasion of hole is low, throat is abundant in pore and unhomogeneity is strong, so description and forecast for reservoir bed are difficult.Through particular observation on character of sediment, characteristics of sequence compages and signs of sedimentary facies in outcrop, and using rationale and method of modern sedimentarism analysising type of sedimentary face and character of sedimentary system, the model of sedimentary face were founded and lithofacies palaeogeo graphic during Yanchang Formation sedimentary period were reconstructed. Also through observation of microcosmic character on typical core with microscope and statistics and analysis on a great deal of physical characterization data, diagenesis of Yanchang Formation were studied systematically. On the basis of study for these two aspects (including sediment and diagenesis), sketched advantaged sediment and diagenesis facies belt, namely relative high pervasion district in low pervasion region, accordingly roped main target district of oil and gas exploration in the western edge region of the Ordos basin.fruit and cognition we have attained are following:1. There was a terrestrial facies lake basin in study area and mainly developed clastic rock during the late Trias. Alluvial fan , river, delta , delta fan and turbidite are all developed.2 Yanchang lake come through: during changlO age, began to sedimentation; chang9-8 age, accelerated expanding; chang7 age, reached the biggest; chang6-3 age, it's shrinking age and chang2-l age, died out. All this composed a integrated sedimentary evolution process (including birth, development and death). At the same time, Rujigou area located in the northwest of basin appeared the character of lake facies sediment.3 Chang2- Chang8 sandstone of Yanchang formation rifely endured mid-high compaction,so cementation was complicated and multiple, solution was developed, chlorite clay film form and hydrocarbon infusion often appeared, also obviously affected physical characterization of sandstone.4, Delta plain distributary channel secondary solution opening facies, Delta plain distributary channel chlorite clay film cementation secondary solution opening facies, delta front chlorite clay film cementation primary facies and delta front secondary solution opening facies, are advantaged sediment and diagenesis facies.5 We concluded that Xing'anbian-Wuqi-Ansai and Chongxin-Xifeng-Qingyang oil enrichment belt are the most favorable exploration regions, along with Dingbian-Youfangzhuang-Jiyuan and zhenyuan-Maling belt are much favorable exploration regions.