Based on multiple testing data from the casting slice, cathodoluminescence, scanning electron microscopy, X-ray diffraction, HPMI, reservoir physical property, and fluid inclusion thermometry, systematic research was conducted to investigate the petrologic features, reservoir properties, diagenetic porosity evolution, and temporal relations between the densification and oil charging process of the Chang 8 sandstone reservoirs of the Upper Triassic Yanchang Formation in Tiebiancheng area of Jiyuan Oilfield, Ordos Basin. The results show that the Chang 8 reservoirs in the study area are mainly composed of fine-grained lithic feldspar sandstones with low maturity of composition and texture, featuring unconventional tight reservoirs with an average porosity of 7.34% and permeability of 0.112×10-3μm2, which generally reach the middle diagenetic stage A. The diagenetic porosity evolution of the Chang 8 reservoirs mainly experienced three stages: porosity reduction by compaction and cementation in early diagenetic stage A-B, porosity increase by dissolution and reduction by cementation in middle diagenetic stage A1, and porosity reduction to densification by cementation in middle diagenetic stage A2 to B1. Until the end of the Early Cretaceous, all the occurred compaction and cementation made the reservoir porosity decrements approach 21.14% and 14%, respectively, while the porosity increment by dissolution was only about 1.76%. At the beginning of two episodic large-scale oil charging events that occurred at 125 and 105 Ma during the middle to late period of the Early Cretaceous, the porosity of the Chang 8 sandstone reservoirs decreased to 7.82% under the influence of late cementation. It became a typical ultra-low porosity and ultra-low permeability tight sandstone reservoir, thus most likely indicating that the densification of the Chang 8 reservoirs occurred earlier than the hydrocarbon accumulation in this study.

通过铁边城地区长9砂岩储层流体包裹体特征的研究,结合埋藏史-古地温综合分析研究区的油气成藏期次.烃类包裹体的镜下观察及其相伴生的盐水包裹体测温数据统计表明研究区长9砂岩储层存在三期烃类包裹体:第一期烃类包裹体相对偏少,在单偏光下多呈浅褐色,相伴生的盐水包裹体均一温度为75～90℃;第二期油气包裹体数量较多,多为浅褐色呈带状分布的液烃(或气液烃)包裹体,与其相伴生的盐水包裹体均一温度为95～115℃;第三期油气包裹体数量最多,烃类包裹体中液烃在单偏光下呈褐色或淡黄色,荧光下显示多为浅蓝色,与其相伴生的盐水包裹体均一温度为115～130℃.结合埋藏史-古地温综合分析认为研究区长9储层存在三期油气充注成藏:第一期为侏罗纪末期(155～150Ma)发生的小规模的油气充注;第二期为早白垩世中期(128～120Ma)发生的大规模油气充注和成藏;第三期发生早白垩世末期(110～103Ma),是受到早白垩世中晚期发生的构造热事件影响而导致的大规模油气充注成藏.

The southern margin of the Ordos Block (S-OB) is located in the western part of the southern region of the North China Craton (S-NCC), and has been involved in multiple orogenic episodes that uplifted the North Qinling Orogenic Belt (NQB). Determining whether the S-OB deposits and sources were controlled by late Precambrian or Ordovician tectonic sedimentation is extremely important for understanding the paleo-tectonic evolution of the S-NCC and its relationship with the North Qinling Terrane (NQT). In this study, the depositional age and trace of the source area of the Tangwangling Group (TWL) were constrained using detrital zircon U-Pb isotopic analyses. Six sandstone samples collected from the TWL Group yielded similar detrital zircon age patterns, with four distinct clusters at 2588-2305 Ma, 2100-1600 Ma, 1251-1005 Ma 995-744Ma which correspond to peak ages of 2.45 Ga, 1.80 Ga, 1.10 Ga, and 0.82 Ga, respectively. The youngest zircon ages that peak at 0.82 Ga suggest that the depositional age of the TWL Group is the closest to the late Neoproterozoic, based on comparisons with geochronological data from late Precambrian and Ordovician successions that outcrop in the OB. The detrital zircon age ranges of the TWL Group, in comparison with those of the NCC and NQT, also indicate that clastic grains deposited in the TWL Group were mainly sourced from NCC basement rocks and less so from the late Precambrian NQT complex, which was coincident with a Grenvillian-aged tectonomagmatic event. Thus, we conclude that the NQT had accreted onto the S-NCC before the TWL Group were deposited during the late Neoproterozoic, implying that the S-NCC or the S-OB may have experienced or was at least influenced by the assembly and breakup of Rodinia.

油源对比是油气地质研究中必不可少的一种技术,本文对油源对比方法进行了简单介绍,其中生物标志化合物对比法是最常使用的方法.近年来鄂尔多斯盆地延长组中下组合油藏的发现使其成为勘探开发的热点话题.通过对鄂尔多斯盆地长9烃源岩发育范围、生烃潜力以及长9油层组原油地球化学特征的研究,发现鄂尔多斯盆地志丹南部地区长9油层组发育有较好的烃源岩,生烃潜力高,最大厚度可达20 m以上,通过对比发现志丹地区长9油层组的原油与长9暗色泥岩烃源岩生物标志化合物组成相似,有较近的亲缘关系;其它地区长9油层组的原油与长7油层组烃源岩具有较近的亲缘关系.因此,鄂尔多斯盆地志丹及其邻近地区长9油层组的原油有长9油层组的烃源岩贡献,其它地区绝大部分为长7油层组的烃源岩贡献,与鄂尔多斯盆地延长组长9油层组烃源岩分布是一致的.

运用LA-ICP-MS锆石U-Pb年代学方法,分析探讨了鄂尔多斯盆地南缘南曹德组和庄河沟组的沉积时代、物源特征及其所处的华北(鄂尔多斯地块)与北秦岭地体之间的构造演化关系.结果表明:两件砂岩样品的碎屑锆石年龄谱基本一致,测年数据集中分布在820～995 Ma(n=13)、1041～1203 Ma(n=23)、1223～1451 Ma(n=36)、1458～1650Ma(n=24)、1659～1935 Ma(n=39)、2017～2445Ma(n=7)6个区间,对应的峰值年龄分别接近832Ma、1120Ma、1330Ma、1590Ma、1856Ma和2090Ma.这与邻区经典的震旦系正目观组和罗圈组具有相似的碎屑锆石年龄谱特征,年轻主峰年龄832Ma,包含有4个820～834Ma的年轻单颗粒锆石年龄,显著有别于以往认为与之可比的研究区近邻剖面锆石U-Pb高频主峰年龄主要集中在454Ma的奥陶系平凉组,由此认为南曹德组和庄河沟组应属于新元古代晚期832Ma之后或震旦纪的沉积岩石单元.锆石U-Pb年龄谱的区域对比进一步揭示,南曹德组和庄河沟组的滨浅海沉积碎屑物源明显具有来自华北(鄂尔多斯)陆块与北秦岭(杂岩)地体的双向混合物源特征,表明华北陆块与北秦岭地体至少在832Ma之前的格林威尔晚期已经碰撞拼合为一体,随后在新元古代晚期拼合大陆边缘接受了大致与Rodinia超大陆裂解事件相当的陆缘海相碎屑岩沉积.