The Majiagou Formation of Lower Ordovician is an important gas-producing horizon of Lower Paleozoic in the Ordos Basin. So far,nearly trillions of cubic meters of natural gas geological reserves have been obtained in the field of Majiagou Formation supra-salt weathering crust. Moreover, the research results of supra-salt assemblage are rich and the understandings are accordant. However, the insufficient research and divergent understanding on the gas-bearing system of Majiagou Formation sub-salt assemblage seriously restrict the exploration of sub-salt natural gas in this area. Based on the geochemical characteristics of natural gas, this paper systematically researches the sub-salt gas bearing system by means of geology, geophysics and geochemistry. Then, the favorable accumulation conditions and enrichment zones of Majiagou Formation sub-salt natural gas reservoirs are determined by analyzing the sub-salt natural gas origin, the source rock scale and reservoir characteristics and by evaluating trap accumulation factors. And the following research results are obtained. First, the Majiagou Formation sub-salt natural gas is relatively light in carbon isotopes of methane and ethane, presenting the typical characteristics of oil-type gas. The hydrocarbon source rock may be acted by the thin marine source rock related to the high-frequency sequence of Majiagou Formation, which is lithologically dominated by dark argillaceous dolomite and microbial dolomite and has the capacity of large-scale hydrocarbon supply. Second,multiple sets of mound beach and mound flat powder crystal dolomite reservoirs are developed under the salt, and distributed along the low uplift in the platform in a large scale. The source-reservoir-cap assemblage reflects the hydrocarbon accumulation conditions of self-generation and self-storage under the salt, and the key factors of hydrocarbon accumulation are dredging faults and lateral sealing. Third, Yulin-Hengshan and Shenmu-Mizhi areas are favorable enrichment zones of sub-salt natural gas. In conclusion, the new understanding on the sub-salt gas bearing system and the natural gas enrichment zone of Majiagou Formation effectively supports the breakthrough in natural gas exploration in Well Mitan 1, which is of great significance to the further deep natural gas exploration in the Ordos Basin.

碳酸盐岩?膏盐岩组合蕴含了全球46％的碳酸盐岩油气储量,是重要的油气富集层位.鄂尔多斯盆地奥陶系马家沟组发育大套厚层碳酸盐岩?膏盐岩混合沉积,目前在盐上已发现了近万亿方探明储量.盐下和盐间有无勘探潜力?对该沉积体系的古环境恢复是关键.通过对盆内T112井400 m系统取芯进行描述,结合薄片鉴定、微量元素、稀土元素、碳、氧、锶同位素、岩石组分等分析,对马家沟组碳酸盐岩?膏盐岩沉积体系的沉积环境进行了恢复.根据海平面升降和水体氧化程度的变化,该体系可以划分为4个亚环境,分别是缺氧段、次氧化段、氧化段和硫化段.随着氧化程度加剧,U、Mo等微量元素含量降低,碳氧锶同位素逐渐正偏,但由于硫化段导致含氧量急剧降低,U、Mo和碳氧锶同位素急剧升高,并呈现随海平面频繁振荡分布.基于古环境与TOC和孔隙度的对比分析,硫化段和缺氧段是最有利的烃源岩发育层段,强烈蒸发作用导致水体分层及硫化,使有机质得到有效保存.氧化段和次氧化段是储层发育的有利层段,台内局部隆起沉积的丘滩体频繁暴露遭遇准同生溶蚀作用,发育大量溶蚀孔隙,经白云石化以后得到有效保存.硫化段的烃源岩与氧化段的白云岩储层纵向上呈层状频繁交互,平面上呈指状交叉,构成良好的源储配置关系.乌审旗隆起带上发育的立体型储集层网络是鄂尔多斯盆地奥陶系盐下勘探的有利区带.

A complete and continuous Cambrian system can be found in the Qinglongshan Profile and the Xiweikou Profile in the Ordos Basin. There are five strata in total, namely, the Lower Cambrian Mantou Formation and Maozhuang Formation, the Middle Cambrian Xuzhuang Formation and Zhangxia Formation, and the Upper Cambrian Sanshanzi Formation. The microbial mounds of the two profiles were developed in the Mantou Formation of the Lower Cambrian and the Xuzhuang Formation of the Middle Cambrian respectively. The columnar stromatolites formed by microbial mounds mainly developed in the high energy intertidal environment, which is indicative of the paleoenvironment. In this study, field observation, systematic sampling and measurement of the microbial mounds in the Qinglongshan and Xiweikou Profiles in the Ordos Basin were carried out. Moreover, the macroscopic and microscopic characteristics of stromatolites were systematically analyzed from the perspective of geobiology, based on the previous research results and combined with the sedimentological characteristics of the profile. The discovery of microbial carbonates in the Qinglongshan Profile and the Xiweikou Profile in the Ordos Basin provides important rock records for understanding the earth's microorganisms, paleoenvironment and paleoclimate in the Cambrian period.

近期,鄂尔多斯盆地中东部米探1井在奥陶系马家沟组四段(以下简称马四段)钻获高产工业气流,天然气勘探取得突破,引起科研人员对该层段颗粒滩储层的广泛关注.然而,现阶段对马四段颗粒滩的研究认识难以满足其勘探部署的需求.为此,在综合前人研究成果的基础上,利用野外露头、钻井岩心、微观薄片和测井等资料,结合马四段颗粒滩形成的地质背景,研究了马四段的颗粒滩类型与地质特征、滩体纵向叠置关系与横向分布规律,明确了颗粒滩发育的主控因素,并提出了下一步天然气勘探方向.研究结果表明:①鄂尔多斯盆地马四段发育由多期滩体叠置而成的台缘颗粒滩和台内颗粒滩,其中台缘颗粒滩单层厚度介于1.1～51.0m,累计厚度介于20.5～206.3 m;台内颗粒滩单层厚度介于1.1～4.5 m,累计厚度介于5.1～48.4 m.②颗粒滩的发育与海平面变化密切相关,马四期包含马四3期快速海侵、马四2期缓慢海退和马四1期振荡性缓慢海退共3个4级海平面变化旋回,纵向上颗粒滩主要发育于马四2亚段和马四1亚段;每个4级旋回又包括多个5级高频旋回,颗粒滩发育于高频旋回上部.③颗粒滩发育也受古地貌的控制,台缘颗粒滩分布于中央古隆起带,台内颗粒滩分布于神木—榆林—横山地区,古地貌低部位颗粒滩不发育.④颗粒滩是储层发育的基础,控制了有利储层的分布.结论认为,神木—榆林—横山有利区是下一步天然气勘探的有利方向,该研究成果为马四段勘探有利区评价和钻探目标优选提供了理论支持.

MT1井的战略突破揭示鄂尔多斯盆地马家沟组四段(简称马四段)具有良好的勘探前景,然而对马四段沉积期岩相古地理及储层认识的不足制约了天然气勘探与部署.利用地质与地球物理相结合的方法,对马四段沉积期岩相古地理进行恢复并开展岩相古地理对储层发育的控制研究,结果表明:(1)马四段沉积前鄂尔多斯盆地具有三隆一坳的古地理格局,三隆即伊盟古陆、中央古隆起和吕梁隆起,一坳即台内坳陷,又可进一步分为两凸两凹,即榆林—横山凸起、神木—米脂凸起、桃利庙凹陷和米脂凹陷.隆坳相间、坳中有凸的古地理格局控制了马四段储集相带的展布;(2)马四段沉积期由3个四级旋回组成,马四3亚段沉积期主体为海侵旋回,中央古隆起演化为弱镶边台地边缘,盆地东部整体表现为半局限台地,以石灰岩和云质石灰岩沉积为特点;马四2亚段沉积期为海退早期,随着台缘滩的加积和海平面下降,台缘滩障壁作用凸显,盆地东部表现为局限台地沉积特点,在凸起区开始发育丘滩并沉积薄层白云岩和硬石膏岩;马四1亚段沉积期为海退中期,台缘滩障壁作用加剧,盆地东部局限台地水体持续变浅,凸起以丘滩坪沉积为主,白云岩和硬石膏岩厚度增加、范围扩大.(3)岩相古地理控制了马四段储层发育的类型与分布,主要发育了颗粒白云岩储层、微生物白云岩储层和斑状(灰质)白云岩储层,颗粒白云岩储层和微生物白云岩储层受颗粒(丘)滩微相控制,沿古隆起和凸起区发育,而斑状(灰质)白云岩储层则分布于潟湖相.研究认为,榆林—横山凸起及神木—米脂凸起地区有利于马四段储层发育,是有利勘探区带.

鄂尔多斯盆地奥陶系白云岩是重要的天然气储集层,对其白云岩成因和储层发育规律的研究对于碳酸盐岩深层勘探理论的发展具有重要意义.文章基于大量岩心、薄片的观察,并结合稳定碳氧同位素、稀土元素、白云岩有序度、地层水、包裹体特征等地球化学分析,对盆地奥陶系存在的两种典型白云岩储层的发育特征和形成机理进行了详细研究.分析表明,含硬石膏结核或柱状晶的泥粉晶白云岩主要为潮坪蒸发环境的萨布哈成因,其规模储层的发育主要受到长时不整合面的控制,不整合面以下发育大量硬石膏结核和柱状晶溶模孔;颗粒滩白云岩主要为回流渗透成因,其储层孔隙的发育主要受到海平面高频升降的影响,发育多旋回的粒(晶)间孔隙型储层.虽然两种白云岩的白云石化流体都为浓缩海水,但由于白云石化的机制和速率不同,二者的原始孔隙类型和特征迥异.两种白云岩孔隙在后期的成岩改造和演变过程中,既有相同之处,又有明显的区别.这一认识也将对深层的白云岩储层勘探提供指导作用.

利用测井资料识别碳酸盐岩岩石结构组分,对于碳酸盐岩沉积相研究具有重要的实用意义.碳酸盐岩地层通常经历强烈的成岩作用,缝洞发育,如何利用常规测井资料较精确地识别其基于岩石结构组分分类的岩相一直是个难题.目前有效测井参数与机器学习方法结合已经成为提高岩相识别精度的有效手段,其中Lucia的视岩石结构数参数在国外碳酸盐岩地层中取得了很好的应用效果.然而,ARFN技术建立的条件为非裂缝和非水层,这使得其应用受到较大限制.以四川盆地GM地区寒武系龙王庙组为例,提出了改进的方法.首先,参考Lucia的岩石类型分类方案,将岩相划分为3大类:颗粒白云岩(包括砂屑白云岩和细晶白云岩)、粉晶白云岩和泥晶白云岩(包括泥晶白云岩和泥质泥晶白云岩).然后,通过岩-电关系分析优选出最敏感测井曲线,包括密度、声波时差和自然伽马.根据测井计算的孔隙度、含水饱和度及薄片鉴定资料,按照水层和非水层条件,对Lucia的视岩石结构数公式进行改进.计算结果表明,改进的ARFN曲线能够快速定量识别岩石结构组分,尤其对颗粒白云岩和泥晶白云岩的识别率很高.最后,将改进的ARFN作为输入测井参数之一,与K邻近分类算法(KNN)结合进一步提升岩相测井识别精度.取心井岩心资料验证表明,改进后的ARFN将平均识别符合率从74％提高到80％以上,有效推动了四川盆地GM地区龙王庙组碳酸盐岩沉积微相的精细研究工作.

To address the issue of non-unique interpretation of dolomite reservoir diagenetic and porosity evolution in the previous qualitative or semi-quantitative studies, we investigate two dolomite reservoir types, i.e. weathering-crust karstic reservoirs and mound-beach reservoirs, in the Ordovician Majiagou Formation, Ordos Basin by using in-situ laser ablation U-Pb dating as well as carbon and oxygen isotopic composition analysis. The results show that: (1) According to the dating of 8 reservoir samples, the Majiagou Formation experienced 5 diagenetic stages (Stage 1: deposition of matrix dolomite or penecontemporaneous dolomitization, in 444.0–494.0 Ma; Stage 2: dogtooth- or blade-shaped dolomite cementation, in 440.0–467.0 Ma; Stage 3: dolomitic silt filling, in 316.5–381.0 Ma; Stage 4: crystalline dolomite filling, in 354.0 Ma; Stage 5: crystalline calcite filling, in 292.7–319.0 Ma). (2) Supra-salt weathering-crust karstic dolomite reservoirs went through several diagenetic processes including penecontemporaneous dolomitization, compaction, weathering-crust karstification, packing, and rupturing in succession. Gypsum mold pores formed in the phase of hypergenic karstification and were filled with such minerals as dolomitic silts and calcites, and thus the porosity decreased from 10%–40% to 3%–8%. (3) Sub-salt mound-beach dolomite reservoirs went through the diagenetic processes including penecontemporaneous dolomitization, compaction, subsea cementation, penecontemporaneous corrosion, infiltration backflow dolomitization, packing, and rupturing. The porosity of reservoirs was originally 10%–30%, decreased to 0–6% due to seawater cementation, rose back to 5%–15% owing to penecontemporaneous corrosion, and finally declined to 2%–6% as a result of crystalline dolomites and calcites packing. The above methodology for the restoration of dolomitization and porosity evolution may be helpful for the restoration of porosity evolution in other basins or series of strata.

鄂尔多斯盆地寒武系深层具有良好的勘探潜力,中寒武统张夏组为寒武系勘探的重要目的层系.通过野外剖面详测和岩心、薄片观察及实验分析,对张夏组储层的特征、成因及主控因素进行了分析和研究,并预测了有利储层发育区.研究表明:①张夏组主要发育台缘鲕粒白云岩和台内鲕粒白云岩2类储层.②台缘带鲕粒滩累计厚度集中在50～300 m之间,鲕粒粒径平均为1.25 mm,鲕粒白云岩储集空间以溶蚀孔洞、粒间溶孔和晶间(溶)孔为主,平均测井孔隙度和渗透率分别为2.0％和0.038×10-3μm2.③台内鲕粒滩厚度在50～120 m之间,鲕粒粒径平均为0.85 mm,鲕粒白云岩储集空间以溶蚀孔洞、粒间溶孔为主,平均测井孔隙度和渗透率分别为3.3％和2.787×10-3μm2.④张夏组储层受鲕粒滩相、白云石化以及三级/四级层序界面控制,台缘规模有利储层发育在四级海退层序中上部的鲕粒白云岩地层中,台内规模有利储层发育在寒武系顶部不整合面之下的鲕粒白云岩地层中.预测台缘岐山—旬邑一带和台内陇东地区为两大规模有利储层发育区.

鄂尔多斯盆地奥陶系马家沟组四段(简称"马四段")是下古生界天然气风险勘探的重点层位.文中基于岩心、薄片观察,结合地层对比、沉积结构描述等,并运用岩石结构组分测井解释和井震结合古地貌恢复等手段,对鄂尔多斯盆地马四段沉积时期古地貌、沉积特征和储集层展布进行了详细分析.结果表明:(1 )受控于沉积期隆坳相间的古地貌格局,马四段发育大量台地内丘滩微相,其易于发生准同生溶蚀和白云石化作用,是储集层发育的有利相带;(2)马四段储集层以(藻)砂屑白云岩和粉—细晶白云岩为主,储集空间主要为粒间孔、晶间孔、溶蚀孔等;(3)纵向上,储集层主要分布于马四2 亚段和马四1 亚段;平面上,马四段储集层主要分布于台地内低凸起带和台缘带;(4)储集层的发育受控于3 个因素,其中古隆起部位发育的有效丘滩体是储集层形成的物质基础,高频层序控制的准同生溶蚀作用是储集层形成的关键,白云石化是储集层后期保存的重要因素.马四段沉积时期碳酸盐岩台地内隆坳相间的古地貌控制了丘滩相带和白云岩储集层的展布,这一新认识为鄂尔多斯盆地下古生界天然气勘探提供了有力支撑,也为碳酸盐岩台地沉积储集层的研究提供了新思路.

近期,米探1井的勘探突破表明鄂尔多斯盆地东部米脂地区奥陶系马家沟组四段(以下简称马四段)具有天然气勘探的巨大潜力,然而,对米脂地区马四段沉积相的认识还存在着争议,在一定程度上制约了该区天然气的勘探进程.为此,基于野外露头、钻井岩心、微观薄片、测井和碳/氧同位素等基础资料,系统开展了沉积相和有利储层方面的研究,确定了沉积演化模式,并预测了有利储层发育区.研究结果表明:①马四段发育灰质潟湖、台内丘和含云膏坪3种沉积微相,灰质潟湖微相中的石灰岩、灰质围岩δ13C、δ18O与同期海水相似;台内丘微相中的白云质围岩 δ13C、δ18O仍处于同期海水值范围,但较灰质潟湖沉积石灰岩偏正;含云膏坪微相中的白云质围岩 δ13C、δ18O较同期海水偏负.②马四段可识别出海侵体系域、高位体系域早期、高位体系域晚期3种沉积模式——海侵体系域期,水体最深,米脂地区为灰质潟湖沉积;高位体系域早期,水体变浅、咸化,凸起带发育台内丘,凹陷区发育灰质潟湖;高位体系域晚期,水体最浅,米脂地区整体演化为含云膏坪沉积.③台内丘内部沉积的微生物白云岩、斑状粉晶白云岩和斑状灰质白云岩发育晶间孔,物性相对较好,是有利沉积相带.结论认为,米脂地区的瑶镇—大保当、神木—米脂、绥德—碛口一带沉积期位于地势较高的凸起带上,且广泛发育台内丘,是下一步天然气勘探的重要方向.

A set of "special lithology" tight reservoirs related to volcanic activity developed widely in the lower submember of the first member of Cretaceous Tengger Formation (K1bt1x) in the A'nan Sag, Erlian Basin, which is the main target for tight oil exploration. Based on section observation, physical property analysis, scanning electron microscopy (SEM), mercury intrusion porosimetry, CT scanning and nuclear magnetic resonance (NMR), the characteristics and main controlling factors of "sweet spots" of tight oil reservoirs with different lithologies in the K1bt1x were studied. Tuffaceous rocks, sandstones, dolomites and mudstones developed in the K1bt1x, and tuffaceous rocks and sandstones are the favorable lithologies for the development of tight oil reservoirs. The reservoir space consists of dissolved pores, intercrystalline micropores, residual intergranular pores, drainage pores and microfractures. The main reservoir space of tuff includes devitrified intercrystalline pores and dissolution pores, whereas that of sandstone includes residual intergranular pores and dissolution pores. The reservoir pore structures can be divided into 3 types and 4 subtypes. The thin-layered tuff and fine sandstone with solution pores have better pore structures, but the sedimentary tuff and dolomite have poor pore structures. The reservoir has a strong oil content heterogeneity controlled by reservoir lithology, porosity and permeability. The development of "sweet spots" in tuffaceous tight reservoirs is mainly controlled by the volcaniclastic deposition, devitrification and dissolution, while the development of "sweet spots" in sandstone reservoirs is mainly controlled by sedimentary microfacies, rock structure and dissolution.

为了查明鄂尔多斯盆地奥陶系克里摩里组—乌拉力克组构造—沉积响应特征,为该区有利勘探区带预测与目标优选提供技术支撑,依据地震、测井、钻井岩心、微观薄片及野外剖面等资料,在构造控沉积思想指导下,对鄂尔多斯盆地西缘奥陶纪克里摩里期—乌拉力克期古构造格局及沉积特征进行了系统研究。结果表明:（1）克里摩里期—乌拉力克期古构造格局整体体现出"一陆一隆一坳、过渡带北东向凸—凹相间"的分异特征;（2）克里摩里期—乌拉力克期为镶边台地沉积模式,沉积相类型包括台地边缘、斜坡、深水陆棚和盆地;（3）古构造格局控制沉积相平面展布,台地边缘沿中央古隆起及隆坳过渡带上的北东向凸起分布;斜坡相主要沿隆坳过渡带上的北东向凹陷分布;深水陆棚相和盆地相主要沿西部坳陷分布。

为了查明鄂尔多斯盆地奥陶系克里摩里组—乌拉力克组构造—沉积响应特征,为该区有利勘探区带预测与目标优选提供技术支撑,依据地震、测井、钻井岩心、微观薄片及野外剖面等资料,在构造控沉积思想指导下,对鄂尔多斯盆地西缘奥陶纪克里摩里期—乌拉力克期古构造格局及沉积特征进行了系统研究.结果 表明:①克里摩里期—乌拉力克期古构造格局整体体现出"一陆一隆一坳、过渡带北东向凸—凹相间"的分异特征;②克里摩里期—乌拉力克期为镶边台地沉积模式,沉积相类型包括台地边缘、斜坡、深水陆棚和盆地;③古构造格局控制沉积相平面展布,台地边缘沿中央古隆起及隆坳过渡带上的北东向凸起分布;斜坡相主要沿隆坳过渡带上的北东向凹陷分布;深水陆棚相和盆地相主要沿西部坳陷分布.

多年来,海相碳酸盐岩构造—岩相古地理研究成果在鄂尔多斯盆地油气勘探部署工作中发挥了重要的作用,然而,限于资料和认识程度,原有的沉积相图难以满足该区深层海相碳酸盐岩油气藏勘探开发发展的需求.为此,在分析该盆地古地貌背景的基础上,运用新的钻井和地震资料,结合岩相识别技术,通过编制深层中寒武统张夏组和下奥陶统马家沟组构造—岩相古地理图,分析了张夏期和马家沟期的古地理特征,建立了两期沉积模式,研究了古地理对储层发育和分布的控制作用.研究结果表明:①张夏组沉积期具有“三隆四坳”古地理背景,隆坳背景受前震旦系裂陷的影响,呈北东向展布,坳陷区演化为深水海湾或台内洼地,隆起区演化为碳酸盐岩台地,隆坳转折带和古隆起周围发育鲕粒滩,构成张夏组有利的储集相带;②马家沟组沉积期具有“三隆两凹一凸”的古地理格局,主要呈南北向展布,古隆具有重要的障壁作用,海侵期沿古隆发育滩和坪、坳陷发育成渴湖,海退期古隆暴露、坳陷则演化为膏盐湖,膏云坪是有利的储集相带,潟湖成为盖层发育的重要场所;③构造—岩相古地理控制了储层沉积背景和物质基础,对早期白云石化和岩溶作用改造的范围和程度具有重要影响,从而控制有利储层宏观分布;④张夏组镶边台地沉积模式和马家沟组障壁台地沉积模式揭示张夏组存在着3种潜在的油气成藏组合、马家沟组存在着2种油气成藏组合.结论 认为,张夏组风化壳,以及马家沟组上组合风化壳、中下组合颗粒滩是该盆地有利的油气勘探方向.

台内碳酸盐岩是继台缘礁滩后值得关注的潜在勘探领域.基于露头、岩心、薄片观察及单井、地震、测试分析等资料,解剖四川盆地德阳-安岳晚震旦世—早寒武世台内裂陷石油地质特征及成因,类比塔里木盆地南华纪、鄂尔多斯盆地长城纪台内裂陷.结果表明:罗迪尼亚泛大陆裂解为德阳-安岳台内裂陷的发育提供了区域地质背景,张性或走滑断裂、差异沉降作用是台内裂陷形成的关键;德阳-安岳台内裂陷经历了灯二段侵蚀发育期—灯四段裂陷发育期—麦地坪组-沧浪铺组裂陷鼎盛-充填期—龙王庙组缓坡台地发育期的演化过程,其控制了筇竹寺组、麦地坪组两套烃源岩和灯四段、龙王庙组两套储集层的发育;烃源岩和储集层的空间配置构成"侧生侧储"和"下生上储"两类成藏组合;塔里木盆地南华纪、鄂尔多斯盆地长城纪台内裂陷与德阳-安岳台内裂陷具相似的地质特征,勘探潜力值得期待.上述认识使勘探领域由台缘拓展到台内,对中国古老小克拉通台地海相碳酸盐岩油气勘探具指导意义.

M54−1a is a new natural gas exploration target of the Ordovician in the Ordos Basin and is expected to have large-scale reserves and a production increasing area after M51 and M52 weathering crust gas reservoir. Based on the data of the drilling core, thin section, cathodoluminescence, physical properties, and geochemical characteristics, a study has been conducted about the genesis and distribution of the M54−1a reservoir in the central and eastern parts of the Ordos Basin. The study results showed the following: (1) The M54−1a reservoir is composed of fine-silt-crystalline dolomite containing anhydrite nodules in lithology. The reservoir storage space is mainly the moldic pores of anhydrite nodules with a small amount of anhydrite crystal moldic pores and micro-fractures. The average porosity is 5.54%, and the average permeability is 1.53 × 10−3μm2. (2) The reservoir pores have experienced anhydrite precipitation, atmospheric freshwater dissolution, mesocrystalline calcite filling, quartz filling, medium-coarse crystal dolomite filling, megacryst calcite filling, and cataclasis. (3) Differential dissolution and differential filling influenced by paleogeomorphology controlled the planar distribution of the reservoir. The results of the comprehensive analysis indicate that the superimposed area between the high part of sedimentary paleogeomorphology and the karst slope at the west of Yulin-Jingbian-Yanan as well as the Hongdunjie-Qingyangcha area are high-quality reservoir distribution areas with strong dissolution and low filling degree. The study results provide the theoretical basis for the next exploration and well deployment.

马五41a小层是鄂尔多斯盆地奥陶系天然气勘探新层系,有望成为继马五1+2风化壳气藏后又一个储量产量规模增长区.为此,依据钻井岩心、微观薄片、阴极发光、物性数据和地球化学特征等资料,研究鄂尔多斯盆地中东部奥陶系马五41a储层特征及成因.结果 表明:①马五41a储层岩性为含硬石膏细粉晶白云岩,储集空间主要为硬石膏结核溶模孔,含少量硬石膏晶体铸模孔和微裂缝,平均孔隙度为5.54％,平均渗透率为1.53×10-3 μm2;②储层孔隙经历了硬石膏沉淀,大气淡水溶蚀作用,中晶方解石、石英、中—粗晶白云石和巨晶方解石充填作用和破裂作用;③古地貌控制的差异溶蚀作用与差异充填作用控制了储层的平面分布.综合分析认为,榆林—靖边—延安以西的沉积古地貌高部位与岩溶斜坡叠合区域和红墩界—青阳岔地区储层溶蚀作用强,充填程度低,是优质储层的分布区,为下一步勘探部署提供了理论依据.

对于鄂尔多斯盆地海相碳酸盐岩储层宏观分布规律和有利区带的认识目前尚不十分清楚,难以满足区带评价和目标优选的需求.为此,利用野外露头、钻井和地球物理测井资料并结合实验分析数据,深入探讨了该盆地海相碳酸盐岩储层的特征、形成机制和分布规律,并指出了下一步天然气勘探的方向.研究结果表明:①鄂尔多斯盆地海相碳酸盐岩主要发育岩溶型和颗粒滩型两类白云岩储层,前者发育于蒸发台地的含膏云岩和膏质云岩坪微相,主要分布在下奥陶统马家沟组马五段上组合及马一段和马三段,后者主要发育于台地边缘颗粒滩和台内颗粒滩微相,分布在中寒武统张夏组、上寒武统三山子组、马四段和马五段中组合;②颗粒滩型储层岩性为鲕粒云岩、砂屑云岩、品粒云岩及微生物云岩,储集空间以残余粒间(溶)孔、微生物格架(溶)孔、晶间(溶)孔和溶洞为主,少量裂缝,孔隙度介于2.00％～18.03％,平均孔隙度为6.16％,机械沉积和微生物造丘是原生孔隙形成的重要机制,准同生溶蚀和裸露期风化壳岩溶作用是溶孔溶洞形成的主控因素,早期白云石化和封闭体系有利于孔隙的保持;③岩溶型储层岩性为(含)膏模孔细粉晶云岩和粉晶云岩,储集空间为膏模孔、溶洞及微裂缝,孔隙度介于2.00％～16.36％,平均孔隙度为5.98％,同生期层间岩溶和裸露期风化壳岩溶是膏模孔形成的主要机制,而膏模孔的保存受矿物充填和封闭体系两大因素的控制.结论 认为,有利储层主要分布在该盆地鄂托克前旗—定边—上韩、桃利庙—吴起和榆林—志丹一带,其中桃利庙—吴起和榆林—志丹一带是深层碳酸盐岩气藏勘探最有利的区带.