鄂尔多斯盆地子洲及邻区山西组二段高分辨率层序地层和煤沉积模式

High-resolution sequence stratigraphy and coal sedimentary modes of Member 2 of Shanxi Formation in Zizhou and its adjacent areas,the Ordos Basin

杨勇 雷卞军 冯永玖 孟堃 陈波 叶武

Yang Yong Lei Bianjun Feng Yongjiu Meng Kun Chen Bo Ye Wu

鄂尔多斯盆地山西组既有煤层又含天然气,是重要的能源勘探目标。山西组二段主要属于湖盆三角洲沉积体系,山亚段的三角洲分流河道砂体是子洲气田的主力储层。子洲及邻区山西组划分为2个长期、4个中期和8个短期基准面旋回,现已识别出5种短期基准面旋回结构。中-短期基准面旋回的划分,不仅采用了识别地层中层序界面、湖泛面和沉积旋回的方法,而且详细考虑了三角洲体系中煤层在高分辨率层序中的位置。文中运用了滨线轨迹分析法,将其与煤沉积模式研究紧密结合,精确地再现了研究区山亚段煤沉积环境的演变过程。山亚段是以间断性湖进-湖退为特征的三角洲环境沉积产物。山期发生了4次短期的湖进-湖退过程,在下三角洲平原沉积了4个煤层。其中,最后一次湖进-湖退的规模最大,下三角洲平原大面积沼泽泥炭化,形成了几乎覆盖全区的较厚的5煤层。

The Shanxi Formation of Ordos Basin is regarded as an exploratory target for it is rich in both coal and natural gas.The second member of the Formation (Shan-2) pertains to delta sedimentary system of a lake basin.The distributary channel sandbodies in the Shan-2 sub-member are the major pay zones of the Zizhou gas field.The Shanxi Formation in the gas field and its adjacent areas can be divided into 2 long-term basal level cycles;4 medium-term basal level cycles and 8 short-term basal level cycles.The structures of 5 short-term basal level cycles have been identified.During the division of medium-short term cycles,the writers not only employed identification methods of sequence boundary,lake flooding surface,and deposition cycles,but also took into conside-ration the positions of coal beds from delta sedimentary system in high-resolution sequence stratigraphy.Shoreline trajectory analysis was combined with research of coal sedimentary mode to exactly reconstruct the evolution of the coal deposition environment in the Shan-2 sub-member in the areas.The Shan-2 sub-member is the product of delta deposition environment with intermittent lake transgression-regression as the feature.There had been 4 short periods of lake transgression-regression and created environments for the deposition of 4 coal layers in the lower deltaic plain.Among the 4 short-term transgression-regression cycles,the last one is the most extensive and during the time the lower deltaic plain turned to swamp peat,forming the thick 5 coal-bed that is distributed almost in the whole study area.

10.11743/ogg20130108