鄂尔多斯盆地东缘可容纳空间变化控制的C-P煤系沉积特征

鄂尔多斯盆地东缘是国内煤系非常规天然气勘探开发的重点地区,区域范围广,沉积环境多变。结合野外露头、钻井岩芯、单井和连井剖面刻画了研究区构造隆降、海水进退、多向物源影响下的层序地层格架和沉积环境演变。结果表明:在统一研究区典型标志层的基础上,可将太原组分为4个和山西组3个III级层序;太原组主煤层顶面是区域范围内的构造转换面,南北地势近乎水平,之后中间地势进一步沉降;北部物源在太原期初始即发生影响,但南部物源到山西期才产生明显影响;研究区大致以北纬38°构造带为南北隆降支点,控制地层的厚度和岩性变化,影响厚煤带的迁移;太原期的汇水中心由南部逐渐向中部过渡,即由延川南(Sq1)到大宁—吉县(Sq2)到柳林石楼地区(Sq4),在Sq3沉积时期,海侵范围相对最大。相关成果对认识研究区含煤地层发育规律,开展煤系非常规天然气勘探开发具有支撑作用。

Sedimentary features of C-P coal bearing strata controlled by variation of accommodation spaces in east margin of Ordos Basin

The east margin of Ordos Basin is an important area for unconventional natural gases exploration and development in coal bearing strata,with extended study areas and complex sedimentary environment.The field outcrops,cores observation,and the cross sections of single and multiple wells were used to describe the tectonic movement,transgression and regressions,multiple direction sedimentary sources and their influence on the sequence stratigraphy and sedimentation evolution.The results show that the strata of Taiyuan Formation can be classified into four sequences and the Shanxi Formation of three sequences,based on the uniform of marked layers in different areas.The roof of the main coal seam in Taiyuan Formation is the tectonic transformation surface of the study areas,with the north and south areas being relatively leveled,and the subsidence continues in the middle areas consequently.The source rocks from the north influenced at the beginning of the Taiyuan Stage,while the obvious source rock supply was seen until Shanxi Stage.The 38° tectonic belt served as the fulcrum of the tectonic movement,also controlled the thickness and lithology variations in the coal forming strata,with a control on thick coal seams deposition.During the Taiyuan Stage,the water center of the transgression showed a transition from south to north,which varied from Yanchuannan area in Sequence (Sq1) to Daning-Jixian area in Sq2,and then to Liulin and Shilou areas in Sq4,and the Sq3 was relatively of the largest transgression.The results would be benefitial for a clear understanding of the coal development rules in the study areas and also lay a foundation for unconventional natural gases exploration.