致密砂岩储层孔隙结构成因机理分析及定量评价——以鄂尔多斯盆地姬塬地区长8油层组为例

利用普通薄片、铸体薄片、物性分析和压汞曲线等资料,对姬塬地区长8油层组储层的微观孔隙结构特征及其成因机理等进行了研究.结果表明沉积物在地质历史时期经历的压实、胶结、溶蚀和破裂等一系列成岩作用对储集岩孔喉特征影响显著,成岩作用的不均一性导致了储层宏观物性和微观孔隙结构的差异.通过视压实率、视胶结率、视溶蚀率和视微孔隙率等参数的计算阐明了压实、胶结、溶蚀等对排驱压力和分选系数等孔隙结构特征参数的定量控制.选取成岩综合系数作为成岩作用强度及其组合的定量表征参数,其与排驱压力、分选系数、储集层品质指数和分形维数等均具良好的统计相关关系,不同的孔隙结构类型具有不同的成岩作用组合特征以及成岩综合系数值,因此成岩综合系数可作为不同孔隙结构类型的定量表征参数.在对影响孔隙结构特征的成岩作用类型和强度组合深入剖析的基础上,通过成岩综合系数可实现储集岩孔隙结构的定性划分和定量评价.     

彭阳油田延长组长3段砂岩储层质量控制因素研究

彭阳油田位于鄂尔多斯盆地西南部,其上三叠统延长组长3段砂岩已发现商业油流,但是对其储层砂岩质量控制因素仍然缺乏了解。本文根据钻井、测井、岩心观察、铸体薄片、扫描电镜与岩心物性资料,研究了长3段层序格架与沉积相、砂岩成分与成岩作用特征及其对长3段砂岩储层质量的影响。长3段砂岩为发育在高位体系域早期的具有加积-进积准层序组特征的小型辫状河三角洲平原分流河道沉积,砂体孤立而不连续,成岩环境流体循环不畅而相对封闭,不利于早成岩期酸性大气水的普遍淋滤。长3段砂岩以长石岩屑砂岩和岩屑砂岩为主。高岩屑和长石含量使砂岩在早期成岩压实中损失了大量粒间孔,高白云岩岩屑含量促进了埋藏成岩期间硬石膏与铁白云石的大量胶结,进一步减少了粒间孔隙。三角洲平原环境促进了早期成岩过程中颗粒蒙脱石包膜的形成,并在埋藏成岩过程中转换为绿泥石包膜或伊利石,尤其是绿泥石包膜抑制了石英增生,使粒间孔得以保存。早成岩期的酸性大气水与埋藏成岩期的有机酸对长石、云母或岩屑的溶蚀对砂岩储层质量的贡献相对有限。长3段砂岩孔隙以残余粒间孔为主,这暗示长3段砂岩在晚三叠世末期剥蚀与侏罗纪末期-新生代的抬升（降低了长3段压实程度）以及埋藏成岩过程中绿泥石颗粒包膜的形成是长3段砂岩孔隙保存的最重要因素。成岩作用促进了长3段孤立砂体的致密化,加剧了该砂岩储层预测难度。     

Petrochemistry of sandstones from Neoproterozoic basins of the Bastar craton, Central Indian Shield: Implications for paleoweathering, provenance and tectonic history

Petrographic analysis and chemical analysis of major and trace elements including rare earth elements of the Neoproterozoic sandstones from the Chandarpur Group and the Tiratgarh Formation have been carried out to determine their provenance, tectonic setting and weathering conditions. All sandstone samples are highly enriched in quartz but very poor in feldspar and lithic fragments. Petrographically and geochemically these sandstones are classified as subarkose, sublitharenite and arenite. The Chemical Index of Alteration (CIA mean 68) and Th/U ratios (mean 4.2) for these sandstones suggest their moderate weathering nature. Generally, all sandstone samples are strongly depleted in major elements (except SiO₂), trace elements (except Zr) and REE in comparison with Post Archean Australian Shale (PAAS) and Upper Continental Crust (UCC). Their mineralogy and mean of elemental ratios suitable for determination of provenance and tectonic setting, e.g. Al₂O₃/SiO₂ (0.02), K₂O/Na₂O (10), Eu/Eu* (0.67), (La/Lu)n (10.4), La/Sc (3), Th/Sc (1.2), La/Co (0.22), Th/Co (0.08), and Cr/Th (7.2), support a felsic source and a passive margin tectonic setting for these sandstones. Also these key elemental ratios do not show much variation over a range of SiO₂. Thus we attest their significance in determining source rock characteristics of quartz rich sandstones. Chondrite‐normalized REE patterns with LREE enrichment and a strong negative Eu anomaly are also attributed to felsic source rock characteristics for these sandstones. The source rocks identified are granite and gneiss of the Bastar craton. Minor amounts may have been derived from older supracrustals of the Bastar craton. However, the major element data of the Paleoproterozoic Sakoli schists when compared with those of the Neoproterozoic sandstones indicate that the schists were derived from a mafic source and deposited in an active continental margin tectonic setting. There is, however, little difference in CIA values between the Paleoproterozoic Sakoli schists and Neoproterozoic sandstones, indicating prevailing of similar (moderate‐intense) weathering conditions throughout the Proterozoic in the Bastar craton. Our study also suggests a change in the provenance and tectonic setting of deposition of sediments from dominantly a mafic source and an active continental margin in the Paleoproterozoic to dominantly granite and gneiss (felsic source) and a passive continental margin in the Neoproterozoic in the Bastar craton.     

三轴应力下不同粒径破碎砂岩渗透特性试验

地下工程中破碎岩体往往处于三向应力状态,此类岩体具有孔隙率大、渗透性高等特点,在地应力与高水头作用下易发生渗流失稳破坏,诱发突水灾害。为研究三轴应力下破碎砂岩的渗透特性,运用自主研发的破碎岩石三轴渗流试验系统,采用稳态渗透法进行5种粒径破碎砂岩的渗流试验,得到了三轴应力下破碎砂岩渗透特性变化规律,推导了有效应力与渗流速度之间的关系。试验结果表明：三轴应力下破碎砂岩的有效应力与渗流速度呈线性关系,且轴向位移越大时,随有效应力的增加渗流速度减小的幅度越小;三轴应力下5种粒径破碎砂岩的孔压梯度与渗流速度服从Forchheimer关系,两者之间的相关系数达0.95以上;轴向位移恒定时,随着围压的增大,破碎砂岩渗透率k减小,非Darcy流β因子增大,各级轴向位移下,破碎砂岩的渗透率与围压之间呈指数函数关系;随着孔隙率的减小,5种粒径的破碎砂岩渗透率呈减小趋势,非Darcy流β因子整体增大,且渗透率量级为10-14～10-11 m2,非Darcy流β因子的量级为106～1012 m-1。     

西藏雄村铜金矿区侏罗系砂岩地球化学特征:对构造背景的约束

西藏雄村铜金矿区位于冈底斯造山带中段南缘,其南紧邻雅鲁藏布缝合带(IYS)和日喀则弧前盆地,北为谢通门始新世大岩基。通过对雄村矿区砂岩进行系统的镜下鉴定,主量、微量元素分析,揭示雄村组砂岩构造背景和物源属性。研究结果显示,雄村砂岩样品SiO_2含量53.27%~66.13%,平均含量58.27%,与古生代杂砂岩(66.1%)相近。Al_2O_3含量较高(14.53%~24.04%),平均20.12%,指示砂岩长石矿物较多且黏土化较强。综合微观特征,雄村砂岩为长石岩屑砂岩。主量元素中特征氧化物组合Fe2O3+MgO(7.3%~17.6%)、TiO_2(0.68%~1.25%)、Al_2O_3/SiO_2(0.22%~0.45%)与大洋岛弧成因砂岩值相似;微量元素蛛网图上雄村砂岩相对亏损Ta、Nb、P、Ti及HREE等高场强元素而富集K、Rb、U、REE等大离子亲石元素,REE球粒陨石标准化后具有轻稀土富集而重稀土元素较平坦的右倾分布模式。特征微量元素Th(2.5×10~(-6))、Zr(114×10~(-6))、Hf(3.6×10~(-6))、Ce(27.95×10~(-6))、Ti(0.54×10~(-6))含量及Th/U(2.9)、Zr/Th(46)、La/Sc(0.72)、Th/Sc(0.11)比值表明雄村砂岩具有大洋岛弧成因性质,La-Th-Sc、Th-Sc-Zr/10、Th-Co-Zr/10等判别图解显示砂岩形成源区可能位于大洋岛弧环境。稀土元素页岩标准化后具有弱负Ce异常及正Eu异常,指示砂岩受海水及深部热液双重影响,同样与大洋岛弧环境页岩标准化后特征相似。Co/Th-La/Sc和La/Th-Hf图解表明雄村砂岩物源区为长英质中酸性火山岩源区和安山质火山弧源区,结合他人对砂岩中碎屑锆石的年龄研究,认为雄村矿区砂岩没有早于晚三叠世的碎屑锆石,具有岛弧火山岩源区特点。     

Distribution of diagenetic alterations in glaciogenic sandstones within a depositional facies and sequence stratigraphic framework: Evidence from the Upper Ordovician of the Murzuq Basin, SW Libya

The spatial and temporal distribution of diagenetic alterations has been constrained in relationship to depositional facies and sequence stratigraphy of the Upper Ordovician glaciogenic quartzarenite sandstones in the Murzuq Basin, SW Libya, which were deposited during the Haritanian glaciation when the basin was laying along the continental margin of Gondwana. Eogenetic alterations encountered include: (i) replacement of detrital silicates, mud matrix and pseudomatrix by kaolinite in paraglacial, tide-dominated deltaic, in foreshore to shoreface (highstand systems tract; HST) and in post-glacial, Gilbert-type deltaic (lowstand systems tract; LST) sandstones, particularly below the sequence boundaries (SB). Kaolinite formation is attributed to the influx of meteoric water during relative sea level fall and basinward shift of the shoreline. (ii) Cementation by calcite (δ¹⁸O_VPDB = − 3.1‰ to + 1.1‰ and δ¹³C_VPDB = + 1.7‰ to + 3.5‰) and Mg-rich siderite in the paraglacial, tide-dominated deltaic and foreshore to shoreface HST sandstones, in the glacial, tide-dominated estuarine (transgressive systems tract; TST) sandstones and in the post-glacial, shoreface TST sandstones is interpreted to have occurred from marine pore-waters. (iii) Cementation by Mg-poor siderite, which occurs in the post-glacial, Gilbert-type deltaic LST sandstones and in the paraglacial, tide-dominated deltaic and foreshore to shoreface HST sandstones, is interpreted to have occurred from meteoric waters during relative sea level fall and basinward shift of the shoreline. (iv) Pervasive cementation by iron oxides has occurred in the glacial, shoreface–offshore TST sandstones and post-glacial, shoreface TST sandstones immediately below the maximum flooding surfaces (MFS), which was presumably enhanced by prolonged residence time of the sediments under oxic diagenetic conditions at the seafloor. (v) Formation of grain-coating infiltrated clays mainly in the glacial, fluvial incised-valley LST sandstones and in the post-glacial, Gilbert-type deltaic LST sandstones as well as, less commonly, in the paraglacial, foreshore to shoreface HST sandstones and in the tide-dominated deltaic HST sandstones below the SBs.

Mesogenetic alterations include mainly the formation of abundant quartz overgrowths in the glacial, fluvial incised-valley LST sandstones, post-glacial, Gilbert-type deltaic LST sandstones and glacial, shoreface TST sandstones, in which early carbonate cements are lacking. Illite, chlorite and albitized feldspars, which occur in small amounts, are most common in the glacial, tide-dominated estuarine TST sandstones and paraglacial, shoreface HST sandstones. This study demonstrates that the spatial and temporal distribution of diagenetic alterations and their impact on reservoir-quality evolution in glacial, paraglacial and post-glacial sandstones can be better elucidated when linked to the depositional facies and sequence stratigraphic framework.     

新疆伊犁盆地南缘水西沟群沉积体系演化与赋铀性研究

在分析伊犁盆地南缘水西沟群各地层岩石物性特征的基础上,结合盆地地形、地貌、沉积环境,建立和厘定了盆地水西沟群沉积体系,进而分析沉积体系的演化规律,指出在这一系列演化过程中砂体发育最好的是河流相及扇三角洲平原相至前缘相.结合层间氧化带砂岩型铀矿床成矿地质规律,分析了盆地铀成矿前景.     

成岩作用对河流-三角洲相砂岩储层物性演化的影响--以延长油区上三叠统延长组长2砂岩为例

延长油区上三叠统长 2地层河流相-三角洲相砂岩储层的物性明显受埋藏-成岩作用事件的影响。埋藏压实作用是导致砂岩孔隙丧失的主要原因,造成的平均孔隙度丧失为 17.8%。其中黑云母的早期成岩蚀变是造成原生孔隙丧失的一个重要原因。胶结作用造成的平均孔隙度丧失为 7.1%。其中碳酸盐胶结物和次生石英加大是造成砂岩物性降低的主要胶结物。碎屑颗粒周围绿泥石薄膜的存在阻止了一部分石英次生加大及碳酸盐胶结物的沉淀,使一部分原生粒间孔隙得以保存。晚期成岩阶段有机质分解形成的酸性流体及表生成岩作用阶段的大气降水是形成次生孔隙的主要原因,从而使长 2砂岩的物性得到改善     

山东东营凹陷东部深层浊积扇储层的微观特征及影响因素

东营凹陷东部深层浊积砂体以三角洲前缘的滑塌浊积砂体为主,储层岩性以长石细砂岩、岩屑细砂岩及粉砂岩为主,结构成熟度及成分成熟度均较低。储层微观特征研究表明,浊积砂体中主要发育剩余原生粒间孔、粘土矿物杂基内的微孔隙、粒间溶孔、粒内溶孔及微裂缝等储集空间类型;孔隙结构以低渗细喉型为主,为物性较差的中低孔、低渗型储层。通过对储层物性影响因素的研究得出,岩石组构、沉积微相、成岩作用和异常超压的形成与分布是影响本区浊积砂体储层物性的主要因素。其中成岩作用对浊积砂体物性的改造明显,压实和胶结作用是导致储层物性变差的主要原因;而溶蚀作用和成岩收缩作用则有利于储层孔渗性的改善。异常超压系统的存在、高的地温场及烃类的早期注入对该区浊积砂体储层物性起到了良好的保存和改善作用。     

Reservoir prediction of deep-water turbidite sandstones with seismic lithofacies control —A case study in the C block of lower Congo basin

Currently, conventional forecasting methods of well-to-seismic integration are unable to identify turbidite channel sandstones due to scarcity of well data in deepwater areas, small geophysical differences between sandstones and mudstones of turbidite channels and strong sandstones heterogeneity. The reservoir prediction of deep-water turbidite channels is still a difficult issue in deep-water research. On the basis of previous studies, we propose a new technology named “reservoir prediction of deep-water turbidite sandstones with seismic lithofacies control” in view of the characteristics of deep-water turbidite sandstones. This new technology improves the reservoir prediction of complex sedimentary systems after classifying seismic lithofacies and connecting lithofacies with rock-physics. Furthermore, it can accomplish the genetic classification statistics of rock-physics, improve conversion accuracy of seismic elastic parameters/reservoir parameters and achieve the quantitative reservoir prediction under the double control of seismic geomorphology and seismic lithofacies. The C block of Lower Congo Basin is characterized by few well data, complex lithology but high resolution-seismic. We use the technology to predict the reservoirs of this area and have achieved excellent results. This has great significance for the later exploration.