Identifying oil migration through tectonic fractures in stable cratons is always challenging due to limited technical approaches. Here, we provide a case study showing that combined geochemical and geological analyses are a robust tool for identifying oil vertical migration through tectonic fractures. The core samples and crude oils from the Mesozoic petroleum system in the Zhijing area were investigated by an integrated analysis including petrography, biomarkers, nitrogen compounds, and spatial distribution. The tectonic fractures in the Yanchang Formation (YcF) are more developed compared to the Yan’an Formation (YaF), influencing oil migration patterns and reservoir distribution. Eighty-one percent of the tectonic fractures are filled with calcite cement, while only two percent of the tectonic fractures contain solid bitumen. The YaF and YcF oils originating from the same oil source are at the same maturity level. However, the YaF oils exhibit disordered nC18- distribution and “mismatches” at n-undecane and a decrease in toluene/n-heptane ratios, which resulted from the phase fractionation caused by the vertical migration through tectonic fractures. The spatial distributions of 1/4-MC, 1,8/2,7-DMC, and Ts/Tm values in the YaF oils are irregular. Furthermore, the areas occupied by the YaF oil reservoirs exhibit an absence of YcFs, and vice versa. These distribution patterns can be explained by oil vertical migration through tectonic fractures. A series of pieces of evidence indicates that the oils migrated vertically through tectonic fractures to the YaF. This study offers new insights into the oil migration process within the Mesozoic petroleum system of the central Ordos Basin and serves as guidance for identifying oil migration through tectonic fractures in stable cratons.

开展有效厚度下限研究,对研究区储层精细评价、储量计算参数的确定和油田开发具有重要的意义.本文利用 9 口井岩心资料综合分析确定海子塌区长 6 储层岩性下限为细砂岩;利用 11口井 126 个试油试采数据综合确定长 6 油层含油性下限为油迹级.利用自然伽马与组合参数构建交会图技术有效地识别出油层、水层和干层.用经验统计法、压汞参数法和类比法对 72 口井 440 个分析化验数据综合分析确定长 6 油层组常规油层孔隙度下限为 7.5％,渗透率下限为 0.20×10-3μm2;声波时差下限为 215μs/m,深感应电阻率下限为 14.5Ω?m,自然伽马 68API～110API;长 6 低阻油层孔隙度下限为 8.5％,渗透率下限为 0.25×10-3μm2;声波时差下限为 220μs/m,深感应电阻率为6Ω?m～18Ω?m,自然伽马下限为 98API.这些参数值为该区块储集层评价和开发生产提供了依据.

使用全烃气相色谱和饱和烃色谱质谱技术对志(丹)靖(边)地区延长组长6以浅的原油开展地化研究.结果发现,这些原油的生源指标相近,均揭示了混合有机质输入的生油母质以及弱氧化-弱还原、水体分层性差的源岩沉积环境.它们的成熟度指标也相近,揭示原油均已成熟.但是,延安组和延长组石油的正构烷烃分布特征和相分馏指标明显不同:前者C18以下的正构烷烃分布凌乱并在C11处出现"错位",甲苯/正庚烷普遍小于0.2;后者正构烷烃分布相对规律,甲苯/正庚烷普遍大于0.2.在延安组内,古河道附近原油的成熟度普遍小于远离古河道的原油,原油成熟度在平面上的分布也无规律.研究认为,研究区长6以浅的原油同源同期,均来自湖盆中心的长7烃源岩.延安组石油异常的正构烷烃分布与石油沿断裂/裂缝垂向运移过程中发生的轻重组分分离、混合有关:源自长7的石油先在延长组内沿砂体发生北东向侧向运移,然后沿断裂/裂缝垂向运移注入延安组.导油断裂/裂缝的展布控制了延安组油藏的分布,是导致延安组油藏在远离古河道的区域仍然发育的原因.

针对安塞坪桥区长9油层组致密油储层难以预测、勘探开发有利区不明确、严重制约勘探开发进程等问题,笔者通过对典型取心井岩相、测井相研究,在确定砂岩沉积微相类型及其空间演化的基础上,对砂岩进行横向追踪对比,准确获取单砂体厚度数据,刻画出单砂体展布特征,并结合生产动态情况,优选出致密油勘探开发有利目标区.研究结果表明,研究区致密油主要分布在长9油层组上部,自上而下可以分为3套砂体.其中,上部1号砂体属于小范围水下分流河道沉积,砂体厚度为1～3 m,油藏分布局限,开发潜力小;下部3号砂体属于水下分流河道沉积,砂体厚度为6～12 m.预测研究区中部P149-6井区、南部H87-19井区和W328-8井区是致密油开发的有利区,其中研究区中部P149-6井区油层分布稳定,对油藏认识程度较高,能够作为水平井开发先导试验靶区.研究成果有效解决了坪桥区致密储层预测难的问题,可以为具有相似地质特征的储层预测提供参考.

鄂尔多斯盆地延长组下组合普遍发育致密储层,寻找其中相对高孔渗层段是当前延长组致密油勘探开发的重点工作之一.以志丹地区长9油层组致密油储层为例,综合运用测井、岩心测试等资料,借助阴极发光、扫描电镜等手段,对储层岩石学特征、孔隙类型及物性进行了研究.从宏观和微观两方面分析了控制储层物性的因素,在此基础上对储层进行综合分类,并指出了相对高孔渗层段.研究结果表明,长9油层组储层以岩屑砂岩、长石-岩屑砂岩和岩屑-长石砂岩为主;孔隙以粒间孔隙和长石溶孔为主;沉积微相是其发育的宏观控制因素,其中河口坝中上部和水下分流河道中部物性最好;砂岩粒度、盐酸盐岩含量、岩屑含量及长石含量是储层发育的微观控制因素.细-中砂岩储层物性较好;碳酸盐含量小于10％有利于储层物性发育;岩屑含量越高,储层物性越差;长石含量越高,储层物性越好.综合考虑储层发育的多种控制因素,可以将储层分为5种类型,其中粒度较粗、岩屑含量较低、长石含量较高及碳酸盐岩含量小于10％条件的I类和Ⅱ类储层较好,是勘探有利目标区;Ⅲ类储层中等,Ⅳ类储层物性差-致密,V类属于致密层.研究成果对延长组致密油勘探开发有一定的借鉴意义.

本文通过对定边-安塞地区生、储、成藏配置与油藏关系的分析,揭示鄂尔多斯盆地延长组的石油聚集规律,明确不同层位的成藏特点,为后期的勘探工作提供地质依据.研究结果表明,定边-安塞地区油藏分布范围主要受控于烃源岩,在生烃中心附近,延长组油藏具有纵向上含油层系多,且叠合分布的特点;距离生烃中心较远的区域,纵向上含油层系相对单一,且叠合区相对较少.区内主要发育三角洲前缘水下分流河道、河口坝和深湖相的浊积砂储集体,其中三角洲前缘水下分流河道是最优质的储集体,绝大部分的石油分布在该类沉积相带内.成藏组合有下生上储、自生自储、上生下储型岩性油藏,以下生上储油藏为主.

在加蓬海岸盆地最新油气田相关数据与油气地质资料基础上,以储层为核心将盆地划分了盐上、盐下两类共6个油气成藏组合,其中位于盐下有贝利阿斯阶砂岩成藏组合、阿普特阶砂岩成藏组合,盐下油气成藏组合特征为:陆相储层、盐岩上覆遮挡封盖、断裂带运移;而位于盐上有阿尔布阶—赛诺曼阶砂岩成藏组合、马斯特里赫特阶碎屑岩成藏组合、康尼亚克阶—坎潘阶浊积岩成藏组合、始新统—渐新统河道砂岩成藏组合,盐上油气成藏组合特征为:海相储层、盐构造控藏、盐运动沟通源储。以蒙特卡洛模拟为计算方法,以成藏组合为单元进行油气资源评价,计算出加蓬海岸盆地未来30年待发现资源量为6895×10~6bbl,其中石油资源量为5893×10~6bbl,天然气资源量为6005×10~9ft3;凝析油资源量为34×10~6bbl。结合加蓬海岸盆地成藏组合特征分析与资源评价结果,认为阿普特阶砂岩成藏组合为最有利勘探区。

借助丰富的岩心物性分析、铸体薄片、压汞、扫描电镜、阴极发光等资料,对研究区的储层特征进行了分析,长8油层组储层主要以长石砂岩为主,其次为岩屑质长石砂岩.砂岩碎屑成分以长石为主,其次为云母、石英以及各类岩屑和少量的重矿物,分选较好.胶结物以碳酸盐胶结物为主,其次是粘土胶结、以及少量的硅质和铁质胶结.研究区长8油层组为特低孔、特低渗储层,次生孔隙较为发育.沉积作用是研究区储层物性的主要因素.此外成岩作用对储层物性也有一定的影响.研究区储层有利的成岩作用主要有溶蚀作用,而胶结作用、压实作用等会使储层的孔隙降低,储层物性变差.

鄂尔多斯盆地延长组长10油源一直存在争议,以志丹地区为例,试图通过对志丹地区可能为长10供烃的3套烃源岩的发育情况、长10原油族组成情况.、生物标志化合物等特征的分析,开展油-源对比综合研究,探讨长10石油来源,为后期勘探提供科学依据.志丹地区长10原油样品具有饱和烃含量最高,芳烃次之,非烃和沥青质含量最低的特点.长10原油生物标志化合物显示出生油母质为低等水生生物和高等植物混合成因,原油具有成熟度高的特点.通过对该地区长7,长9,长10等3套烃源岩的分析,认为该区长7烃源岩厚度最厚,长9次之,长10发育程度较低;生物标志化合物方面3套烃源岩在正构烷烃、萜烷分布上表现出一定的相似性,主要差异体现在长7-长10,Pr/Ph有增高趋势,ααα20R构型的C27,C28和C29规则甾烷具有从“L”型为主到“V”型和反“L”型增加的趋势.综合分析认为,长10原油主要为长9烃源岩贡献,长10烃源岩有一定贡献.

Turbidity was important reservoir of Yanchang formation in Ordos basin. Research of turbidite was focus on Chang 6 and Chang7 formation now. But there was no specific report about turbidite in Chang9 formation. Through analyzing the multiple perspectives of characteristics about cores,well logging data,grain size analysis and so on,the results showed that the upper strata of Chang9 reservoir group in Zhouchang area was turbidite deposit. Existence of turbidite with northern provenance was confirmed in Chang 9 formation of central basin for the first time. Through detailed discussion about rock combination,structure,sand body section and so on,slump turbidite fan was confirmed in Chang9 formation. Three subfacies of the inner fan,middle fan and three microfacies that con-tained main channel,branch channel,and inter-channel were identified. Tight oil geological significance of slump turbidite fan of Chang9 formation in Zhouchang area was ascertained from the oil source condition,trap,reservoir and so on.

根据普通薄片、铸体薄片、扫描电镜和岩心分析等资料,对定边—安塞地区(包括定边、吴起、志丹、安塞4个地区)储层岩石学特征、物性特征及影响因素进行了分析.结果表明:吴起与安塞地区为单物源沉积,岩石类型主要为长石砂岩,定边与志丹地区为多物源沉积,岩石类型多样,主要为长石砂岩和岩屑长石砂岩;储层以原生粒间孔和次生溶孔为主,具有低—特低孔隙度和低—超低渗透率特征;受沉积微相和成岩作用的影响,在平面上吴起与定边地区物性最好,志丹地区物性次之,安塞地区物性较差,纵向上长10物性最好,长9物性次之,长7和长8物性均较差.

The main reservoirs in the Mesozoic of Xizichuan oilfield are distributed in Chang 6,Chang 2,Chang 4+5 of Triassic Yanchang formation,especially enrichment in Chang 6 and Chang 2.With the development of exploration,Chang 9,Chang 8 reservoirs continue to be discovered,which is subtle,small sized and harder to discover.The present study shows that they are cont rolled by multiple factors.The distribution of reservoirs is mainly cont rolled by sedimentary faces,nose-shaped uplift is important for oil enrichment.

According to the comprehensive analysis on the logging data,well logging data,and well cores testing data of 120 wells and the seismic facies of 25000 kilometers long two-dimensional seismic sections of Tabei Area at the same time,the following conclusions are able to draw from.Six sedimentary facies have developed in Jurassic in Tabei Area;they are alluvial fan,braid river,braid river delta,fan delta,littoral-shallow lake,and half-deep lake.Among of them,the braid river delta and fan delta have most widely developed.The braid river deltas have mainly distributed in the area of Yingmaili,Donghetang,Yuenan,western of Lungu,Hadexun,and the southern area of Caohu and Juema.The fan deltas have mainly distributed in the areas of Lunnan and Caohu.The braid rivers have mainly distributed in the areas of Mana 1-Mana 3-Yingmai 3-Yuenan 1-Hade well blocks,Yingmai 6 well block,and southeast of Tabei Area.Littoral-shallow lake and half-deep lake have mainly distributed in Qunkeer Area.The alluvial fan has mainly distributed in the west part of Mana 3 well block and mountain front zones of Kuqa depression.According to the analysis,the aquatic bifurcating channels and subquatic distributary channels of the braid river delta,the bifurcating channels of the fan delta plain,braid river channel sandbody,and the turbinate sandbody located in eastern part of the Tabei Area are the prospective objects for finding lithologic trap.

A suit of high-quality source rock of semi-deep to deep lacustrine facies developed during the age of the seventh member of yanchang formation(Chang7) at late triassic in Ordos basin,which is the most important source rock in Ordos basin.Through using organic geochemistry and organic petrology,the source rocks of Chang 7 in the middle of Ordos basin were systematically studied.The source rocks of Chang7 in the middle of Ordos basin are widespread,whose thickness is in the range of 3～85 m,generally in the range of 10～50 m,and has the trend of gradually thinning from southwest to north and east on the whole.The organic matter abundance of the source rocks of Chang7 in the middle of the Ordos Basin is higher,and its content of TOC generally exceeds 1.0%,and hydrocarbon generation potential generally exceeds 6.0 mg/g,and chloroform bitumen"A" generally exceeds 0.1%,so it belongs to better hydrocarbon source rocks.The organic matter of the source rocks of the Chang 7 member in the middle of the Ordos basin is mainly typeⅠandⅡ1 and small amount is type Ⅱ2 and Ⅲ.The vitrinite reflectance Ro of the source rocks of the Chang 7 member in the middle of Ordos basin is in the range of 0.54%～0.92%,and their highest pyrolysis peak temperature Tmax is in the range of 411～456 ℃,and most of the organic matter has been in maturation hydrocarbon generation stage.

According to the logging data and well logging data of 120 wells,the authors analyze the seismic facies of 25 000 kilometers two dimensional seismic sections and analyze seismic attributes of the three dimensional seismic data of the northern Tarim area,using the seismic amplitude attributes,coherence and seismic facies as the main research techniques.Six sedimentary facies developed in the Triassic: meandering river,braided river,delta,littoral-shallow lake,half-deep lake and deep lake.With the comprehensive analysis of oil and gas accumulation and the sedimentary evolution history,the sandbodys of the meandering river channel,braided river channel,aquatic bifurcating channels and subquatic distributary channel in the Triassic are considered to be favorable lithological-prospecting objects.

The reservoir sandstones from the Chang6 and Chang4+5 oil formations of Zhaotai in Shaanbei is mainly gray fine feldspathic sandstones. The maturaty of components is generally low and that of the texture is fine. Through the analysis of thin sections, cathode light, stereo scanning and diagenetic properties, it showed that there were diversity diagenesis, the most important diagenetic properties which influenced porosities development were mechanical-chemical compaction, cementation and dissolution. The diagenetic stage here was a period of later diagenesis. During the porosities development, compaction and cementation contributed to the massive loss of porosity and caused bad physical property. Constructive diagenesis, such as dissolution and hydrocarbon emplacement improved the physical property of reservoir.

The Shanxi Formation of Lower Permian in the eastern Ordos Basin is the main purpose stratum of gas exploration in the eastern Ordos Basin. The degree of exploration is low in southeast Ordos Basin.The paper analyses the regional geology milieu,the sedimentary type,the sedimentary system and the distribution characteristics of Shanxi Formation.This area is the collection area of the north and south Provenance,mainly grows the littoral-shallow lake facie and the delta front facies.The north and south area grows the delta front facies which submarine distributary channel is the main reservoir.The paper analyses reservoir's characteristic of rock mineral characteristic,physical characteristic,pore configuration as well as analyses the influence reservoir performance's factor.Shanxi Formation sandstone types are mainly quartzose sandstones,the next are debris-quartz sand-stones and debris sandstones.The sandstone reservoir is a close sand reservoir with low porosity and permeability.The leading roles that control reservoirs are deposition and diagenesis.

The Mesozoic Ordos Basin developed the special oil pool sequence,which contains lithologic oil pool,lithologic-structural combination oil pool and structural oil pool from down to up.The comprehensive analyses on the different type of reservoir-forming condition and exploration status showed that the formation of oil pool sequence was controlled by many factors including source rock,oil-gas migration,and reservoir-cap rock combination.The source rock is the main controlling factor for generation of oil pool sequence.The vertical distance between trap and source rock is the vital index,which determines oil source condition.The quality of cap rock has significance for oil pool sequence.

The degree of exploration is low in Yanchang area,SE Ordos Basin.The paper analyses its paleogeographic format,sedimentary facies and their distribution characteristics,rock characteristics,and reservoir conditions,and forecasts the exploration prospect for gas in the lower Shihezi and Shanxi Formations.The conditions of gas source and cap rock are favorable in the area,where develop the main gas productive reservoirs of the lower Shihezi and Shanxi Formations located on the delta front facies,delta plain facies and littoral-shallow lake facies.Quartzose sandstones and litharenites are the primary and secondary reservoirs respectively,and are of low porosity and permeability.Based on rock characteristics,physical property and pore configuration,the reservoirs are divided into four types.Industrial gas is formed in types Ⅰ to Ⅲ,and type Ⅳ doesn't contain industrial gas.The low production rate results from the dispersed distribution of reservoirs.The area of Zichang-Yanchuan-Yanchang,which has multiple-phase channel deposits and thick sandstones,is a promising gas exploration area.