鄂尔多斯盆地是我国陆上最主要的油气盆地之一,三叠系延长组是该盆地的主要含油层位.通过对延长组典型露头的考察与研究,结合古生物及岩性岩相资料,取得了3点新认识:(1)恢复了延长组沉积时期的古气候环境,认为其具有三分性,其中早期拉丁期为干旱环境;中期受卡尼期梅雨事件(CPE)影响气候发生突变,转变为温暖潮湿气候环境;晚期诺利-瑞替期再次转变为半干旱-半湿润气候环境.(2)CPE事件改变了延长组沉积物搬运与沉积方式,其中CPE事件之前与事件之后的干旱环境时期,主要发育暴雨洪水引发的季节性河流、决口扇、决口河道沉积;CPE事件当中及卡尼中期,陆源碎屑物质主要通过异重流、浊流及砂质碎屑流等多种途径搬运至水下环境,形成富砂质重力流事件沉积,同时受CPE事件控制,在深水环境还发育了黑色富有机质页岩事件沉积.(3)建立了延长组干旱与潮湿两种环境沉积模式,干旱环境湖泊水域面积较小,主要沉积单元为洪泛平原、季节性河道及决口扇,主要沉积方式为填平补齐、加积式沉积,不发育前积沉积现象;潮湿环境湖泊水域面积较大,发育完整的陆相河流-三角洲-湖泊-重力流沉积体系,由于具有稳定的长流水,河道相对固定,加之受湖平面变化控制,其沉积方式以前积作用为主.该认识不仅对于深入探讨鄂尔多斯延长组大型坳陷湖盆形成演化机理、沉积层序充填演化及指导油气勘探实践有积极意义,而且对揭示晚三叠世全球极端气候事件在内陆湖盆的沉积学记录有积极意义,可以填补CPE事件在古特提斯东缘泛大陆内部沉积响应研究的空白.

This study reports a comprehensive geochemical analysis of several samples of the solid bitumen recently discovered in the Cambrian reservoirs in drillings and outcrops in the Ordos Basin. The results show that the solid bitumen in the reservoir features intergranular pores and micro-fractures, with mineral particle surfaces of dolomite and limestone, and relatively clear and flat boundaries. The D and G peaks in the laser Raman spectrum were prominent. According to distributions of shapes of the D and G peaks and the relevant parameters of the laser Raman spectrum, the vitrinite equivalent reflectance (Roeq) values were from 2.12% to 3.46% in the solid bitumen. This indicates that the solid bitumen in the reservoirs had undergone significant thermal evolution and was mainly composed of pyrobitumen. Moreover, it mainly consisted of four types of atoms, C, O, Ca, and Mg, which confirms the hypothesis of the significant thermal evolution of the samples. In addition, the analysis of the origin of the Cambrian natural gas and the correlation between the solid bitumen and the potential source rocks show that the solid bitumen in the Cambrian reservoirs of the Southern Basin had features similar to those of the Lower Cambrian source rocks, except for the samples from well T59. All evidence suggests that the high-abundance source rocks of the Lower Cambrian have made considerable contributions to the Cambrian natural gas and the solid bitumen in the Cambrian reservoirs of the Southern Basin. The work here provides a new scientific basis for exploring natural gas in the Cambrian reservoirs and deep strata of the Ordos Basin.

The hydrocarbon source rocks of the marine carbonates of the Ordovician Majiagou Formation in the Ordos Basin are generally in the high-overmature stage and are, therefore, not suitable for hydrocarbon thermal simulation experiments. Their hydrocarbon generation potential and hydrocarbon generation characteristics are not clearly understood. Meanwhile, Nordic Cambrian carbonates are similar in lithology, parent material type, and sedimentary age, and are in the low evolution stage, which is suitable for hydrocarbon thermal simulation experiments. Therefore, in this study, we selected the Nordic carbonates for the gold tube thermal simulation experiment to analyze the content and geochemical characteristics of the thermal simulation products. The experimental results are also compared and analyzed with the characteristics of thermal simulation products of Pingliang Formation mud shale (contemporaneous with the Majiagou Formation) and Shanxi Formation coal (in the upper part of the Majiagou Formation), which are similar to the Majiagou Formation in the Ordos Basin. The results showed that the Nordic carbonate has different hydrocarbon production characteristics from the mud shale of the Pingliang Formation of the same parent material type, and although the hydrocarbon production yields of the two are not very different, the carbonate still produces methane at 600 °C. The hydrocarbon production yield of the Nordic carbonates is almost equivalent to that of type-II2 kerogen, indicating that the hydrocarbon production yield is not related to lithology and only to the organic matter type; however, the Nordic carbonate can produce a large amount of H2S. The alkane carbon isotope changes are mainly controlled by the degree of thermal evolution, showing gradual heaviness with increasing temperature. No carbon isotope sequence reversal occurred during the thermal simulation, and its distribution range is roughly the same as that of the alkane carbon isotope composition of the mud shale of the Pingliang Formation. The ethane carbon isotope composition is as heavy as −21.2‰ at the high-temperature stage, showing similar coal-type gas characteristics. The addition of calcium sulphate (CaSO4) causes the TSR reaction to occur, which has a significant impact on the methane content under high maturity conditions, reducing its content by more than 50% at 600 °C. However, the addition of CaSO4 increases the yield of heavy hydrocarbon gases, such as ethane, and promotes the production of C6-14 hydrocarbons and C14+ hydrocarbons at high-temperature stages, and the addition of CaSO4 substantially increases the yield of H2, CO2, and H2S. The thermal simulation results have implications for the hydrocarbon formation mechanism of the early Paleozoic marine carbonate formation system in the stacked basins of the Ordos Basin and the Tarim Basin in China.

鄂尔多斯盆地是我国陆上最主要的油气盆地之一,三叠系延长组是该盆地的主要含油层位.本文通过大量野外露头及钻井岩芯观察与实测,结合室内鉴定分析,系统研究了延长组沉积时的古气候环境及沉积特征,取得了如下认识:①延长组沉积时期,气候具有三分性:早期为干旱环境;中期转变为温暖潮湿气候环境,生物繁盛,是烃源岩发育的最有利时期;晚期再次转变为半干旱—半湿润气候环境;②受干旱气候控制,延长组早期与晚期无大面积汇水区存在,洪水事件主导了盆地中心地区大规模砂体的形成与分布,尤其洪水的接力搬运与多次分选可能是造成延长组砂岩粒级普遍较细的主因;③延长组发育干旱与潮湿两种环境沉积模式,前者以低位域河流扇体系为特征,后者以湖侵期河流-三角洲-湖泊-重力流体系为特色;④干旱环境低位域河流扇砂体与潮湿环境水进域富含有机质泥岩相匹配,形成了延长组"满盆含砂、满凹含油"的特征.该研究发展了大型坳陷湖盆的沉积模式,对丰富陆相盆地沉积理论认识及指导油气勘探实践均有积极意义.

The Carnian Pluvial Episode（CPE） in the Triassic was one of the most abrupt known climatic events in the Earth’s history. It strongly influenced sediment deposition in inland lakes. The case considered here（the Yanchang Formation in the Ordos Basin） is the most important terrestrial petroliferous basin in China. A comprehensive review of research progress in China and elsewhere was carried out for global paleoclimate, event sedimentation, source rock development mechanisms and xenoconformity in terrestrial basins. Rethinking and investigating some of the sedimentation and accumulation questions related to the Yanchang Formation has revealed the following three points.（1） The Yanchang Formation, which developed during the Carnian stage at the beginning of the Upper Triassic, is redefined and its sedimentary depositional response to the CPE is clarified. The upper boundary is equivalent to the stratigraphic boundary between the Chang 4 + 5 members and the Chang 3 member. The CPE roughly corresponds to the deposition of the so-called “Chang 7 member black shale event”.（2） During the Carnian and CPE, the Yanchang Formation sedimentary lake basin underwent rapid transgression and oscillating slow retreat, very conducive to the development of high-quality hydrocarbon source rocks.（3） Due to the paleoclimatic conditions and CPE, upper and lower xenoconformities were formed in response to the abrupt climatic and environmental changes. These both significantly influenced the distribution of oil and gas. This study is of positive significance for in-depth discussion of the formation and evolution mechanisms of the Yanchang Formation lake basin, as well as sedimentary sequence filling and evolution, and as a guide for oil and gas exploration.

A significant amount of natural gas resources has been discovered in the Ordovician reservoirs under a thick layer of gypsum-salt strata as a result of ongoing research into deep natural gas in China’s Ordos Basin, however, the genetic type and source of the Ordovician sub-salt natural gas remain contentious. These limits understanding how the geochemical properties of the natural gas in Ordos Basin have evolved and how to best guide future exploration and development. Based on the components, carbon and hydrogen isotopic ratios of natural gas from the latest exploration wells, combined with the geological background, this study systematically analyzed the genetic types and sources of sub-salt natural gas of the central and eastern Ordos Basin. The results show that the Ordovician natural gas is mainly composed of hydrocarbon gases with low content of heavy hydrocarbons and dryness (CCH4/CCH4+) above 0.95, belonging to typical dry gas. Non-hydrocarbon gases mainly include N2 and CO2, and some natural gas samples contained H2S. The Ordovician sub-salt natural gas is primarily a self-generating and self-preserving oil-cracking gas with relatively high maturity (Ro ranging from 1.5% to 2.1%) mixed with coal-derived gas generated from upper-Paleozoic coal with relatively low maturity (Ro ranging from 1.1% to 1.5%). Due to the dual-source hydrocarbon supply, the Ordovician sub-salt reservoirs provide favorable gas accumulation conditions and development prospects. This study offers a reasonable explanation for the anomalous geochemical characteristics of the Ordovician sub-salt reservoirs in the Ordos Basin, and also may serve as a guide for future exploration of natural gas in the carbonate gypsum-salt sedimentary system in other basins.

Deep-lacustrine systems are considerably less studied than their marine counterparts, mostly due to the low number of large and continuous outcrops worldwide. This study details outcrops and cores from Chang 7, Ordos Basin, China, which are composed dominantly of fine-grained deposits interbedded with amalgamated sandstones. Thick sandstone deposits, previously described as massive sandstones and interpreted as sandy debrites, are here re-interpreted as amalgamated sandstones, deposited by high-density turbidity currents associated with deep-lacustrine slope channels. Two outcrops composed of these deposits, which form intervals ranging from 6 to 20 m thick, laterally ranging from 600 to 1200 m, preserving evidence of sediment bypass such as erosional features and abundant trough cross-bedding, have been interpreted as lacustrine slope channels. Deposits composed dominantly of interbedded thin-bedded normal-graded sandstone and mudstone, with common occurrences of ripple cross-lamination (>70 % of the beds), interbedded with sporadic amalgamated medium-bedded sandstones have been interpreted as levee deposits. These deposits outcrop laterally to slope channel deposits, supporting the interpretation they are genetically and architecturally related. Similar deposits are also described in core, overlying channelised sand-prone deposits. Interbedded thin- to medium-bedded normal-graded sandstones and mudstones, which are not associated with a confining surface (non-channelised), nor an adjacent slope channel, have been interpreted as terminal splays. The re-interpretation of the sandstone-prone deposits of the Yanchang Formation as slope channel-levees to terminal splays provides a different approach to lateral and temporal distribution of architectural elements in intracratonic lacustrine basins, and therefore hydrocarbon exploration and production.

为了明确鄂尔多斯盆地南部三叠系延长组长7油层组细粒沉积特征及沉积模式,以衣食村、瑶曲等典型野外剖面为研究对象,在野外踏勘和测量的基础上,分析其岩相及岩相组合特征,探讨沉积相类型及特征,并建立了细粒沉积中不同岩相的演化模式.结果表明:铜川地区延长组中下部野外露头主要发育叠覆冲刷正粒序粉砂—细砂岩相、块状层理粉砂—细砂岩相、软沉积变形砂泥混杂岩相、块状泥岩相、水平纹层泥页岩相、凝灰岩相共6种岩相类型.铜川地区长7油层组发育背景泥质沉积、凝灰岩与重力流沉积的垂向组合、滑动滑塌与背景泥岩互层叠置、重力流沉积砂岩、泥岩垂向叠置.衣食村剖面下部长73亚油层组以块状层理碎屑流沉积和滑塌沉积为主;长72亚油层组以深水原地沉积为主,岩性从粉砂岩—粉砂质泥岩过渡到水平纹层泥岩再到页理极其发育的黑色页岩;瑶曲剖面长71亚油层组发育丰富的软沉积变形构造,如液化砂岩脉、块状砂岩内具有泥质条带以及火焰状构造等.研究区延长组长73亚油层组沉积期,主要为三角洲前缘沉积物垮塌再搬运形成的相对厚层滑动滑塌沉积;长72亚油层组沉积期以深水页岩沉积为主,夹杂火山灰和少量的低密度浊流薄层粉砂岩沉积;至长71亚油层组沉积期,部分三角洲垮塌再搬运形成砂质碎屑流沉积和低密度浊流沉积;整体指示了长7油层组沉积时期湖平面先升高后降低的周期性变化特征.湖平面的升降变化控制了细粒沉积物的搬运方式与沉积模式,该研究对于明确细粒沉积物的搬运机制与分布规律具有重要的指导意义.

为明确新近在鄂尔多斯盆地西缘YT2井羊虎沟组发现的油砂地球化学特征及其油气来源,利用气相色谱-质谱联用技术(GC/MS)和同位素质谱技术对YT2井油砂中饱和烃生物标志物和抽提物及族组分的碳同位素进行了分析.分析结果表明:YT2井油砂中正构烷烃系列化合物呈前峰型,主峰碳为nC17;Pr/Ph、Pr/nC17和Ph/nC18值分别为0.90、0.30和0.46,指示了其源岩形成于偏还原的沉积环境;萜烷系列化合物中,三环萜烷系列相对含量丰富,以C23三环萜烷为主峰,呈近似正态分布特征;甾烷系列化合物以C27规则甾烷为优势;具有低的藿烷/甾烷比值,反映其有机质来源以低等生物藻类为主;饱和烃和芳烃馏分的碳同位素分别为-31.5‰和-30.5‰.生物标志化合物和稳定碳同位素分析表明YT2井羊虎沟组油砂具有明显的海相原油特征,意味着在鄂尔多斯盆地西缘首次发现了海相成因原油.通过与奥陶系平凉组、石炭系羊虎沟组、三叠系延长组和侏罗系延安组烃源岩生物标志物和碳同位素特征的系统对比分析,认为该油砂可能来源于平凉组海相烃源岩.

Abstract Based on natural gas compositions, carbon isotope ratios, and geological analysis, the genesis and origin of gases in the Lower Paleozoic of Ordos basin are discussed. Due to differences in distribution and genesis, the gases in Lower Paleozoic were divided into five types, namely western margin gas, weathered crust gas, pre-salt gas, Ordovician deep gas, and Cambrian gas. The results show that the δ 13C1 and δ 13C2 of western margin gas range from −35.6 to −38.9‰ and from −27.2 to −35.9‰, respectively, indicating oil-type gas and mainly from the O1k and O2w marine source rocks. The δ 13C1 of weathered crust gas varies from −31.2 to −37.8‰, but δ 13C2 is mostly around −25.0‰, which indicates weathered crust gas originates from the Carboniferous–Permian coal-measure source rocks. In contrast, δ 13C1 and δ 13C2 in the pre-salt strata are mostly less than −30.0‰. Yet its distribution of Δ(δ 13C2–δ 13C1) is from −1.7 to 13.6‰, and C1/C2 + C3 is of 6.68–4372.50. These indicate that the pre-salt gas is mainly high-over mature oil cracking gas from the O1m marine source rock. The δ 13C1 of Ordovician deep gas is averaging −39.4‰, and δ 13C2 varies from −25.4 to −33.0‰, which imply coexistence of oil-type and coal-type gas. It is presumed that the C–P coal-type gas may migrate into and accumulate at Ordovician deep reservoirs through unconformity and fault. The δ 13C2 and Δ(δ 13C2–δ 13C1) of Cambrian gas are both the most negative, respectively, averaging −34.9‰ and averaging −3.2‰, indicating over-mature oil-type gas. Formation and evolution of the Qingyang paleo-uplift result in that the Cambrian gas mainly comes from the Cambrian or Ordovician marine source rocks in the southern basin.

The high mature to over-mature bitumen from the Cambrian reservoir in the Ordos basin, Northern China, is classified into three types (Type I, II, and III bitumens) and the sources of different types of bitumen are investigated using cluster, neural-network, and cross-plot analyses of major, trace elements and carbon isotopic composition. Type I bitumen is hosted in the fractures and pores of dolomite distributed in the southwestern part of the Ordos basin, and originates mainly from the Lower Cambrian source rocks containing abundant organic matter. Type II bitumen is hosted in the fractures of oolitic limestone distributed in the eastern and southeastern part of the Ordos basin, and also stems from the Lower Cambrian source rocks. Type III bitumen is hosted in the pores of sandstone distributed in the interior of the Ordos basin, might originate from Mesoproterozoic Changchengian source rocks. Cluster and neural-network analyses of major and trace elements are proved to be highly effective tools for determining different types and origin of reservoir bitumen. The study findings provide guidance in the exploration of hydrocarbons in the Palaeozoic and deeper strata of the Ordos basin and may contribute to further breakthroughs in deep hydrocarbon exploration.

鄂尔多斯盆地南缘洛南和周家河地区发育下寒武统高丰度海相烃源岩,岩性主要为页岩,局部发生了动力变质作用,为泥板岩.有机地球化学分析结果表明,该套烃源岩厚度约为0～80 m,有机碳含量(TOC)介于0.10％～13.75％之间,均值为3.32％,其中91％的样品TOC含量大于1％,52％的样品TOC含量大于2％.有机质类型以II1型为主,部分为I型.烃源岩总体达到了较高的热演化程度,沥青等效镜质体反射率介于2.25％～2.71％之间,甲基菲比值F1为0.46～0.60,评价为优质气源岩.尽管鄂尔多斯盆地寒武系—奥陶系时期,受到加里东和怀远运动的影响而遭受抬升剥蚀,但庆阳古隆起及以南地区寒武系—奥陶系的地层产状总体保持向南倾斜,故北秦岭—洛南地区发育的下寒武统海相烃源岩生成的油气能向庆阳古隆起方向运聚成藏.鄂尔多斯盆地南部寒武系天然气与四川盆地高磨地区寒武系油型气在同一区域,为反序列油型气.寒武系天然气中乙烷碳同位素值在鄂尔多斯盆地下古生界天然气中最低,甲烷碳同位素值与下寒武统烃源岩干酪根碳同位素值分布相似,这为揭示下寒武统烃源岩对鄂尔多斯盆地南部天然气的成藏的贡献提供了直接证据.其次,盆地南部发现的寒武系储层沥青与下寒武统烃源岩的亲缘关系则为寒武系天然气成藏的间接证据.

The dark shales of the Lower Cambrian Dongpo Formation, along the southern margins of the Ordos Basin, were researched based on biomarkers and carbon isotope analyses of outcrop samples to reveal their hydrocarbon potential, organism composition, and depositional environment. Similar to the Yangtze and Tarim blocks, the Lower Cambrian in the southern margin of Ordos Basin, which is a part of North China block, also deposited high abundance marine source rocks. The shales displayed good to excellent total organic carbon (TOC) content (up to 13.75%). The crossplot of phytane/nC(18) vs. pristane/nC(17) and organic carbon isotopes indicate the kerogen to be primarily type I-II. The low Hydrogen index values, and high pyrobitumen reflectance (>3.0%) indicate that the Dongpo shales are currently in over-mature stage. The Dongpo shales thus exhibit high hydrocarbon generation potential and might have produced and discharged massive amounts of hydrocarbons during their geological history. The G/C30H ratios (0.17-0.29) and extended tricyclic terpanes Ratio (ETR) values (0.54-0.61) suggest sedimentary environments of stratified water and relatively moderate salinity. In addition, the Dongpo shales display low Pr/Ph (<0.63), low C-30*/C29Ts (<0.44), high C-35 22 S/C-34 22 S (>0.47), and relatively abundant elemental sulfur. These parameters indicate that Dongpo shales were formed in anoxic waters. The abundant steranes and hopanes in the Dongpo shales suggest the diversity of organisms, including eukaryotes and prokaryotes. The composition of eukaryotes (planktonic algae) is consistent with that of the Yangtze and Tarim blocks, but there are obvious differences with Oman, reflecting the heterogeneity in the global distribution of eukaryotes during the Early Cambrian. In addition, compared with the Yangtze and Tarim, the relatively contribution of prokaryote to Dongpo shale is low, which may also be an important reason for the obvious enriched of C-13 in kerogen. The positive relationship between TOC and Pr/Ph and C-27 St (%) suggests that high primary productivity in the paleoenvironment probably attributed to red algae. The Pr/Ph, C-35/C-34 values and others indexes are related to anoxic conditions, which is good for preserving deposited organic matter.

基于对青海湖滩坝砂体形成和保存条件研究的认识,应用"将今论古"的研究方法,从物源供给、湖盆底形、风动力-水动力、湖岸线形态及湖平面变化(层序演化)等方面,对现代青海湖与鄂尔多斯盆地滨浅湖滩坝沉积进行了对比研究.认为鄂尔多斯湖盆在上三叠统延长组沉积期间,长9—长82—长7沉积期既处于二级层序的早期,同时又位于三级层序湖侵体系域,十分有利于陆源碎屑滩坝的保存.建立了延长组滨浅湖滩坝砂体分布的预测模型,指出盆地南部(包括西南部与东南部)是长9—长82—长7期滩坝砂体发育与保存的有利地区,也是未来寻找滩坝型油气藏的有利地区.

In order to clarify the hydrocarbon accumulation significance and exploration prospect of the unconformity caused by the Huaiyuan movement in the Ordos Basin, this paper studies the spatial distribution and structural plane characteristics of this unconformity and its relationships with hydrocarbon accumulation by observing field outcrops and cores and analyzing logging data, based on the previous research results and the interpretation results of 2D and new 3D seismic data. And the following research results are obtained. First, the unconformity was mainly formed in the Floian Age of Early Ordovician and widely occurs at the bottom of the Jiawang Formation and the top of the Sanshanzi Formation and the related tectonism lasts 30 Myr. Second, basal conglomerate and sandstone less than 1 m in thickness are developed above the unconformity at the edge of the basin, while thin mudstone, argillaceous dolomite (limestone) and marl are developed above the unconformity in the central part of the basin. Third, the unconformity structurally consists of three layers, including a basal conglomerate layer, a paleosoil layer and a fully–semi weathered carbonate layer from top to bottom, among which, the last one is 20–90 m in thickness with developed dissolution fractures and pores to form a quality reservoir. Fourth, the unconformity results in the development of a series of large valleys landforms, which incise the Lower Ordovician–Upper Cambrian. Fifth, the unconformity can act as a good channel for hydrocarbon migration, and it connects with the unconformity caused by the Caledonian movement within the paleo-uplift of the Ordos Basin, which is favorable for the the hydrocarbon of different sources in the west side of the basin eastwards to migrate, accumulate and form a gas reservoir. In conclusion, the deep Lower Paleozoic related to the Huaiyuan unconformity is expected to be an important natural gas exploration field in the Ordos Basin.

通过野外踏勘和岩心观察,在鄂尔多斯盆地下古生界—中元古界发现了大量储层固体沥青,其中寒武系储层固体沥青为首次发现.对储层固体沥青分布含量、显微特征、成熟度、成因及资源潜力进行研究,结果表明:奥陶系沥青含量为0.15％ ～2.38％,寒武系沥青含量最高为7.62％,蓟县系沥青含量为2.21％;平面分布上,盆地南部沥青含量较高,向北逐渐降低,推测其来源可能与盆地南部下古生界—元古界的海相烃源岩有关;显微镜下,除个别发微弱荧光外,大部分储层固体沥青样品几乎不发荧光,且有一定的外观形态,边界清晰.根据激光拉曼相关参数转换,得到储层固体沥青等效镜质体反射率为2.32％ ～2.80％,表明已达到过成熟演化阶段.综合储层固体沥青的地质特征,认为下古生界—中元古界储层固体沥青主要为原油裂解形成的焦沥青.伴随焦沥青的形成,必然会生成大量的原油裂解气,估算下古生界—中元古界古油藏生气总量约1.207×1013～2.559×1013 m3.下古生界—中元古界储层固体沥青的大量发现及油气特征研究为寻找鄂尔多斯盆地深部大型油气田提供了重要的科学依据.

Water-soluble organic acids (WSOAs) are closely related to the formation of secondary pores, however, it's little-known for the distributions of WSOAs in sedimentary rocks at deep-ultradeep zone and high-over mature stage. In the present study, 22 sedimentary rocks, involving diverse sedimentary rocks, thermal maturities and buried depths. Using deionized water to extract sedimentary rocks selected was conducted, and then WSOAs in extracts were quantitatively characterized using 940 Ion Chromatography (Metrohm AG). Meanwhile, key factors affecting WSOA distributions in sedimentary rocks were also discussed. Results show that besides at shallow zone and before mature stage, sedimentary rocks at the deep-ultradeep zone and high-over mature stage involve a certain amount of WSOAs. WSOA distributions for diverse sedimentary rocks, on the whole, are similar, concentration is higher for monocarboxylate than dicarboxylate, moreover, monocarboxylate and dicarboxylate are dominated by formate and acetate, and oxalate, respectively. Formation pathway and occurrence state of WSOAs are the same on the basis of Pearson correlation coefficient among the concentrations of different types of WSOAs. TOC-normalized WSOA concentrations correlate positively with oxygen index (IO). With increasing buried depth, total WSOA concentrations tend to decrease. Total WSOA concentrations are greater at Tmax less than 435 °C for type-III organic matter (OM) such as coal due to greater oxygen content, while almost comparable for diverse OMs at Tmax more than 435 °C. Moreover, as thermal maturation rises, type-III OM possesses high proportional of formate while type-I and -II OMs involve great percentage of acetate.

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.

怀远运动不整合面是华北地台上一个重要的区域性不整合面.在对华北地台怀远运动表现形式与地质特征调研分析的基础上,基于大量的露头、岩心观察和地震资料解释工作,对鄂尔多斯盆地怀远运动不整合面存在的证据、特征及其与储层和油气成藏的关系进行了深入分析,并取得了新认识.研究认为:①鄂尔多斯盆地奥陶系深层存在由怀远运动形成的区域不整合面,并可能发育大型喀斯特岩溶沟谷地貌体系;②该区域不整合面及相关沟谷地貌体系为上覆马家沟组中-下组合(马四段—马一段)沉积提供了古地貌背景,并控制了其沉积格局与有利储集相带展布,同时也控制下伏下奥陶统—寒武系—长城系白云岩化与风化壳储层发育;③该区域不整合面为不同来源天然气的区域性横向运移提供了有利通道,是油气运移的"高速公路",同时也为油气聚集提供了有利场所,其中不整合面附近的上、下层位有利于天然气的大规模聚集与成藏,可能是继奥陶系顶面风化壳领域后又一勘探新领域,值得重视.目前对盆地内部怀远运动不整合面的认识还比较薄弱,建议加强三维地震勘探部署,以推动鄂尔多斯盆地的地质认识创新和勘探新发现.

华北板块鄂尔多斯盆地寒武系具有较大勘探潜力.通过对华北板块构造-古地理格局和烃源岩分布特征、生烃能力、生排烃期次与发育模式的研究,明确了鄂尔多斯盆地深层寒武系的勘探潜力并指明下一步有利勘探方向.研究结果表明:①鄂尔多斯盆地南缘下寒武统沉积了一套高丰度优质烃源岩,最厚达80 m,主要为泥页岩,有机碳含量平均值为3.14％,最高达9.19％;干酪根类型以Ⅱ型为主,少量为Ⅰ型;等效镜质组反射率大于2％,处于高—过成熟阶段.②下寒武统烃源岩的发育受构造背景、陆缘斜坡及深水海湾欠补偿环境的共同控制:一方面,早期形成的古地貌背景和深水海湾共同控制着烃源岩的发育规模,使得烃源岩在古凹槽或断陷区、深水海湾区较为发育;另一方面,强还原环境使得烃源岩具有较高的有机质丰度和生烃潜力.③下寒武统烃源岩具有两期生排烃特征,早期大规模生排烃发生于二叠纪末期—中三叠世,此时秦岭尚未大幅度隆升,盆地南缘为一向南倾斜的斜坡;晚期发生于中生代晚期、新生代,在构造活动较弱的富平—洛川海湾和新生代渭河盆地发生了二次生烃.鄂尔多斯盆地南缘庆阳古隆起、富平—洛川海湾两侧的隆起区为油气运移的指向区,具有较大勘探潜力.