Genesis of green sandstone/mudstone from Middle Jurassic Zhiluo Formation in the Dongsheng Uranium Orefield, Ordos Basin and its enlightenment for uranium mineralization

The middle Jurassic Zhiluo Formation in the Dongsheng is comprised of a big set of green sandstone/mudstone with most of uranium orebodies occurring in close proximity to its footwall.By synthesizing field observations,region analysis,data collected from previous coal and uranium borehole,a regional north-south geological profile across the entire orefield is conducted.Experiments on sandstone/mudstone including rock mineral identification,clastic micromorphology and element geochemistry were carried out.Information from the geological profile indicates that green sandstone/mudstone is widely present in a stable horizon with clear boundaries to the country rock.Microscopic observations and geochemical data on sandstone/mudstone exhibit similar mineral composition with almost identical slightly flat,minor Eu enriched,Ce depleted chondrite-normalized REE patterns.Furthermore,the green clay membrane of the clasts has a complex composition containing chlorite/smectite,green smectite,chlorite,and green kaolinite,with elements including Fe,Mg,Si,and Al.These above results indicate that the green sandstone/mudstone underwent resemble sedimentary diagenetic processes as the country rock without transformation by large-scale regional fluid,while the existence of Fe2+-rich membrane is the main factor to the green sandstone/mudstone.Further concentration of the pre-enrichment uranium during diagenetic process led to the final formation for uranium deposits.The above studies are conducive to enrich the metallogenic mechanism of sandstone type uranium deposits and could provide certain reference for uranium exploration and deployment.

Insights into the Tectonic Fractures in the Yanchang Formation Interbedded Sandstone-Mudstone of the Ordos Basin Based on Core Data and Geomechanical Models

The distribution and intensity of tectonic fractures within geologic units are important to hydrocarbon exploration and development. Taken the Upper Triassic Yanchang Formation interbedded sandstone-mudstone in the Ordos Basin as an example, this study used the finite element method（FEM） based on geomechanical models to study the development of tectonic fractures. The results show that the sandstones tend to generate tectonic fractures more easily than mudstones with the same layer thickness, and the highest degree of tectonic fractures will be developed when the sandstone-mudstone thickness ratio is about 5.0. A possible explanation is proposed for the tectonic fracture development based on two important factors of rock brittleness and mechanical layer thickness. Generally, larger rock brittleness and thinner layer thickness will generate more tectonic fractures. In interbedded sandstone-mudstone formations, the rock brittleness increases with the increasing mechanical layer thickness, hence, these two factors will achieve a balance for the development of tectonic fractures when the sandstone-mudstone thickness ratio reaches a specific value, and the development degree of tectonic fractures is the highest at this value.

Mudstone Lithofacies in the Cretaceous Qingshankou Formation from SK-1,Songliao Basin,Northeastern China

Located at Songliao Basin in the Northeastern China, SK-1 is the first Cretaceous terrestrial scientific drilling in the world.This program recovered the Middle to Upper Cretaceous strata of Songliao Basin which includes,from bottom to top,the Quantou, Qingshankou,Yaojia,Nenjiang,Mingshui and Sifangtai Formations.Lithofacies analysis has been undertaken on the core of Qingshankou Formation by a combination

Sedimentary environment controls on the accumulation of organic matter in the Upper Ordovician Wufeng–Lower Silurian Longmaxi mudstones in the Southeastern Sichuan Basin of China

The Upper Ordovician–Lower Silurian mudstones(including the Wufeng, Guanyinqiao and Longmaxi Formations) in the Sichuan Basin are some of the most important shale gas plays in China. In order to enhance our understanding of the process of formation of organic carbon up to 10%, optical, microscopy and geochemical methods have been used to investigate the petrographic and geochemical characteristics of the formation. Firstly, three mudstone lithofacies were identified based on a wide variety of mudstone laminations. These are:(a) indistinctly laminated mudstone;(b) parallellaminated mudstone; and(c) nonparallel-laminated mudstone. Then, combining with the evidence from depocenter migration, Th/U ratios and total organic carbon, the abundant organo-minerallic fabrics suggest that organic carbon was preferentially deposited and preserved in anoxic, low energy and stagnant water conditions during deposition of the Wufeng and Longmaxi Formations. On the contrary, the Guanyinqiao Formation with poor organic carbon was deposited in oxic and high-energy water conditions.

Gas Generation from Coal and Coal-Measure Mudstone Source Rocks of the Xujiahe Formation in the Western Sichuan Depression,Sichuan Basin

The Triassic and Jurassic tight sandstone gas in the western Sichuan depression,Sichuan Basin has attracted much attention in recent years,and the Upper Triassic coal-bearing Xujiahe Formation is believed to be the major source rock.However,there are relatively few studies on the carbon isotopic heterogeneity of methane generated from coal-measure source rocks and the origin of the natural gases in Xinchang Gas Field is still controversial.In this study,one coal-measure mudstone sample and one coal sample of the Xujiahe Formation in western Sichuan Basin were selected for gold tube pyrolysis experiment to determine their gas generation characteristics.Geological extrapolation of gas generation and methane carbon isotope fractionation parameters reveals that the main gas generation stage of Xujiahe Formation ranges from Late Jurassic to Cretaceous in the Xinchang Gas Field.The natural gas in the 5th member of Xujiahe Formation in Xinchang Gas Field is mainly derived from the 5th member of Xujiahe Formation itself,i.e.,self-generation and self-reservoir,however,the gas in the Jurassic gas pools is mainly derived from the source rocks of the 3rd member of Xujiahe Formation rather than the 5th member of Xujiahe Formation.

Water-sensitive characterization and its controlling factors in clastic reservoir:A case study of Jurassic Ahe Formation in Northern tectonic zone of Kuqa depression

Water-sensitivity is a factor that must be paid attention to in the reservoir development stage of oil and gas fields.As a clastic reservoir,the water effect of Ahe formation in the northern structural belt of Kuqa is strong as a whole,but the mechanism analysis of medium and strong water-sensitivity effect is restricted by the evaluation method with permeability damage rate as the main parameter.Taking the shape of water-sensitivity test curve as the starting point,combined with the analysis of microscopic pore throat and clay minerals,the difference of permeability change rate measured by samples is characterized.The strong to medium water-sensitivity effects in the study layer are divided into three types:The permeability gradually decreases in the early stage-the rapid decrease in the late stage,the continuous decrease in the permeability,and the rapid decrease in the early stage-the slow decrease in the later stage.As awidely developed reservoir space in the study section,the micropore not only has the characteristics of fine pore size and easy blockage,but also serves as the occurrence space of the main water-sensitive mineral illite-smectite mixed layer.Therefore,the change types of the above different water sensitivity test curves are mainly controlled by the difference of micropore content.When the micropore content is low,the permeability decreases slowly in the early stage and decreases rapidly in the later stage(type Ⅰ),while when the micropore content is high,the permeability decreases rapidly in the early stage and slowly decreases in the later stage(type Ⅱ),while when the micropore content is medium,the permeability decreases continuously,and there is no obvious rate change(type Ⅲ)before and after the micropore content.The results show that the structural characteristics and relative content differences of micropores in the samples are the internal mechanism of the difference of water sensitivity effect types.

准噶尔盆地盆1井西凹陷石炭系火山岩凝析气藏的发现与勘探启示

准噶尔盆地石炭系火山岩油气藏是油气勘探的重点领域之一。根据录测井资料、地球化学分析数据及岩石薄片鉴定资料,结合地球物理方法,厘清了准噶尔盆地盆1井西凹陷石炭系火山岩油气成藏的主控因素,总结出深层火山岩气藏富集规律,明确了有利勘探方向。研究结果表明:(1)准噶尔盆地盆1井西凹陷风城组烃源岩厚度为100~300 m,面积约为5 400 km2,整体进入生凝析油—干气阶段,生气强度大于20×108m3/km2,为凹陷提供了丰富的天然气源。(2)研究区石炭系火山岩岩性复杂,爆发作用形成的安山质火山角砾岩受到风化淋滤作用,可形成物性较好的风化壳型储层。石炭系—二叠系大型不整合面和广泛发育的深大断裂是重要的输导体系,二叠系上乌尔禾组泥岩作为区域盖层,为凝析气成藏提供了保存条件,油藏主要分布在高部位,气藏分布于低部位。(3)通过“两宽一高”(宽方位、宽频带、高密度)技术,提高地震成像精度,联合时-频电磁技术(TFEM),实现了石炭系火山岩的精细刻画,为深层油气藏的勘探提供了有力支撑。石西16井的重大突破,证实了盆1井西凹陷石炭系火山岩具有巨大的勘探潜力。

准噶尔盆地环东道海子凹陷侏罗系煤层气成藏条件及勘探方向

为了明确准噶尔盆地环东道海子凹陷侏罗系煤层气勘探方向,开展了煤层连井对比、井-震标定和地震资料解释以及煤层测、录井资料分析。研究结果表明:①准噶尔盆地侏罗系西山窑组和八道湾组煤层发育,厚度较大,分布稳定,其中西山窑组发育2~3层煤层,累计最大厚度为20 m,八道湾组发育2~4层煤层,累计最大厚度为29 m。煤岩含气性好,录井气测异常明显。②环东道海子凹陷内中下侏罗统煤系烃源岩为中等—好烃源岩,Ro为0.6%~0.8%,处于低成熟—成熟阶段,具有较好的生气能力;天然气碳同位素分析结果显示,煤层气亦可来源于深部高成熟腐殖型有机质。③研究区西山窑组煤岩为中—低孔、低渗储层,孔隙度为7.0%~20.8%,渗透率为0.32~8.67 mD;八道湾组煤岩为低孔、中—低渗储层,孔隙度为5.6%~7.8%,渗透率为2.30~13.83 mD;煤层夹于泥岩之间且煤层之上区域性泥岩盖层分布广泛,封盖保存条件好。④研究区存在凹陷区源内煤层气富集成藏和凸起区深部外源气富集成藏等2种模式。环东道海子凹陷煤层气勘探潜力较大,特别是凹陷北东方向斜坡区和凹陷北部斜坡—滴南凸起区。

露天矿排土场土-泥岩混合体渗透特性研究

泥岩作为一种露天矿常见的岩石类型可作为排土场地层重构的隔水材料,利用自制土柱装置,按照正交实验设计原理,开展以土-泥岩混合体中的泥岩掺杂比例、泥岩颗粒度、土柱压实度、灌水量为可变因素的土柱渗透试验,通过观测湿润锋、土柱液面及烧杯积水高度的变化规律,探索土-泥岩混合体渗透速率及涵水率的渗透特性。结果表明,泥岩掺杂比例越高颗粒度越小,压实度越高,整体渗透速率越低,而灌水量越高混合体涵水率越高,此结果对露天矿排土场表层地层重构具有重要的参考价值。

泥岩进水诱发地层滑移条件下的套变影响因素分析

吉林大情字油田注水开发过程中由于泥岩进水诱发地层上抬从而导致弱结构面滑移,进一步使油水井发生严重套变现象。为实现对油水井注水开发后套变情况的预测,基于有限元建立数值模型,结合油田现场资料,对泥岩进水滑移导致套变的影响因素进行分析。研究结果表明,泥岩层未进水时,套管壁厚增大到10.54 mm,或将套管钢级提升为TP140V时,能够有效避免套管失效;进水后,套管壁厚需增到14.27 mm,而套管钢级仍然选用TP140V才能避免套管失效;对于注CO_(2)的井,当泥岩层未进流体,套管屈服强度降至458 MPa时,套变量增大了82%;流体进入后,套管屈服强度降低到458 MPa时,套变量增大了125%。该研究结果对油田预防套变具有一定的指导意义。

巴东组泥岩大断面隧道开挖面大变形滑塌失稳机制与防治措施研究

隧道穿越富水软弱地层时易发生开挖面滑塌失稳破坏,为此,本文以郑万高铁巴东隧道为工程依托、以巴东组紫红泥岩为研究对象,开展系列室内试验,揭示泥岩遇水软化的力学特征。综合考虑围岩节理发育及施工扰动等因素的影响,基于Hoek-Brown强度准则将室内试验获取的完整岩体的强度参数转化为现场岩体参数,并采用两相单质点流固耦合物质点法(MPM)对隧道开挖面滑塌失稳大变形全过程进行模拟,并结合现场评价超前帷幕注浆预加固措施的有效性。研究结果表明:开挖面滑塌失稳过程可大致分为开挖面隆起变形、开挖面局部失稳及滑塌体加速运动、滑塌体稳定这3个主要阶段。随着开挖面前方滑塌体的加速运动,围岩的渗流场发生明显的变化,渗水形态呈“漏斗状”,水流向开挖面“缺口”汇集;滑塌体稳定后呈锥体状堆积,滑塌体坡脚与开挖面的距离约25 m,与现场滑塌体最终形态较吻合。采取超前帷幕注浆预加固措施后围岩稳定性较好,确保了隧道施工安全顺利推进。流固耦合物质点法可动态再现地下水渗流作用下软弱地层隧道滑塌失稳破坏全过程,可为类似工程研究提供参考。

铜车坝水库泥岩石渣坝复合土工膜与振冲碎石桩地基中混凝土防渗墙综合防渗体系的应力变形特性

铜车坝水库泥岩石渣坝综合防渗体系具有振冲碎石桩地基中设置混凝土防渗墙、柔性复合土工膜联结混凝土防渗墙等关键因素,为确保大坝防渗体系的安全性,采用大型三轴试验获得了坝料的邓肯模型参数,建立了准三维有限元模型,在土工膜与上、下垫层料接触部位均设置接触单元,反映土工膜与垫层料之间的接触特性,数值模拟了大坝施工与蓄水过程,阐明了复合土工膜与防渗墙综合防渗体系的应力变形特性。结果表明,泥岩石渣料属于低压缩性土,但其具有较为明显的强度非线性特性;防渗墙各时期的位移变形模式不同,围堰挡水期防渗墙水平位移偏向下游,竣工期逐渐向上游偏移,而蓄水期防渗墙在水压力作用下向下游发展,因此防渗墙上、下表面均存在一定的拉应力区域;土工膜的拉应变主要集中在防渗墙与土工膜的连接处,这是由于该地区刚度差异较大变形非协调所致。研究成果可为设计与施工提供重要的理论与技术支撑。

水-岩软化作用下巴东组泥岩隧道大断面开挖掌子面稳定性研究

为明确软弱围岩条件下高速铁路隧道大断面机械化施工过程中的掌子面稳定性特征,以郑万铁路巴东隧道穿越巴东组紫红泥岩段为工程背景,对隧道揭露的巴东组紫红泥岩开展不同含水率下的三轴试验,揭示巴东隧道紫红泥岩的水-岩软化特征;在考虑水-岩软化特征的Hoek-Brown强度准则下,构建考虑水-岩软化作用的隧道穿越巴东紫红泥岩地层流-固耦合数值模型,揭示不同地层水位下巴东组紫红泥岩隧道大断面施工掌子面稳定性特征;最终提出“掌子面喷混凝土+掌子面超前锚杆+超前管棚”的组合式超前加固方案。经过试验和模拟计算,结果表明:1)随含水量的增加,巴东隧道紫红泥岩的刚度与抗剪强度显著降低,与既有研究揭示的浅表地层紫红泥岩相比,巴东隧道紫红泥岩具有更高的抗剪强度;2)掌子面后方拱顶沉降、掌子面前方拱顶预收敛、掌子面挤出变形的最大值均随历史水位的升高而增大;3)根据不同地层历史水位条件下开挖面支护力与挤出变形之间的关系,巴东隧道紫红泥岩掌子面稳定性可以分为A(稳定)、B(短期稳定)以及C(不稳定)3类,对于C类掌子面,采用“掌子面喷混凝土+掌子面超前锚杆+超前管棚”的组合式超前加固措施后,掌子面前后方各项变形最大值可以减小60%~90%。

贵州金沙煤矿东部晚二叠世龙潭组底部铝土质泥岩中镓富集规律及找矿前景

研究区位于金沙县东部,龙潭组底部铝土质泥岩中镓含量为24.7269.38 ug/g,平均43.87 ug/g。通过相关关系法,分析了Ga与SiO_(2)、Al_(2)O_(3)、Fe_(2)O_(3)、TiO_(2)的相关关系,其中Ga与SiO_(2)呈中负相关,与Al_(2)O_(3)+Fe_(2)O_(3)+TiO_(2)呈强正相关,表明镓在风化、搬运和沉积过程中更容易追随Al与Ti,主要以离子吸附态或以氢氧化物胶体方式赋存。根据含镓岩系岩性、沉积构造及化石特征,富铝粘土岩系沉积时期由下至上古水深为深-浅-深,氧化还原环境为还原-弱氧化-还原环境,风化作用相对弱-强-相对弱的变化规律。结合大地构造背景,镓的富集有利区为滨海平原及低洼地带,主要经历源岩风化-搬运-再风化淋滤过程。研究区北东部田湾煤矿-沙土-中心一带含矿品位高,为找矿前景区。

西湖凹陷平湖斜坡北段平湖组薄煤层与泥岩的微观岩石学特征及其沉积学意义

西湖凹陷平湖斜坡北段平湖组受河流与潮汐作用共同影响,水动力条件复杂,分支流水道砂体与潮汐水道砂体的成因存在争议。通过煤层与泥岩的微观岩石学特征分析,探讨其岩石结构与矿物组成、泥岩中碎屑颗粒排列方式、水动力条件与水介质环境,进而划分岩性相类型,展开砂-泥岩一体化的微相划分与水动力分析。其中,薄煤层可分为封闭洼地含草莓状黄铁矿煤层、分支流间湾沼泽纯煤层与天然堤粉砂质纹层煤层;泥岩可分为封闭洼地水平纹层状菱铁矿、分支流间湾含结核状菱铁矿,以及砂岩中交错纹层状菱铁矿。泥岩中广泛发育的菱铁矿指示平湖组沉积时期,发育富铁的局限潟湖环境;泥岩中黏土矿物以高岭石与伊利石混合的黏土为主,指示淡水-海水混层的沉积水介质环境。泥岩中微古生物与煤的显微组分指示其互层的箱形、钟形砂体为三角洲背景下的水道沉积,砂体为多期水道叠置的复合体。薄煤层与碳质泥岩及相关砂岩的微观岩石学分析表明,平湖斜坡北部平湖组具有典型的缓坡局限浅水沉积背景,陆源有机质供给丰富,泥岩中普遍富含碳质,砂体以单向水流沉积作用为主。薄煤层与泥岩岩相分析为薄煤层与砂岩成因分析提供了新的沉积学信息,为砂体预测评价提供了新的依据。

桂东南泥盆系莲花山组泥岩膨胀性研究

泥岩的膨胀性对边坡稳定性及其他岩土工程有重要影响。桂东南中部岑溪市区一带发育泥盆系莲花山组泥岩,主要呈小范围分布于剥蚀-溶蚀垄丘谷地地貌区低丘地带。为查明该区泥岩是否具膨胀性,对出露于山坡地带的泥岩开展了常规调查、钻探、野外试验、室内土工试验、X射线衍射等研究,厘定了泥岩的宏观特征和物理力学性质;采用宏观初判—物理力学指标定量初判—高斯过程定量详判的综合评价方法对泥岩膨胀性进行研究,选取的物理力学指标为效蒙脱石含量、<2μm的胶粒成分含量、液限、塑限指数和胀缩总率,并给出了泥岩膨胀性定量判别标准。研究区泥岩的这5个指标值分别为22%~33%、20%~33%、46.8%~78.0%、24.1~42.9、1.3%~5.2%,经综合判断,该泥岩具中等—强膨胀性。

涠西南凹陷流二段油页岩与泥岩形成环境及生烃特征差异性

始新统流沙港组二段(流二段)油页岩和泥岩是涠西南凹陷古近系的主力烃源岩,二者形成环境和生烃特征差异研究对北部湾盆地新区优质烃源岩预测和凹陷评价意义重大。本文根据有机地球化学、元素地球化学及有机岩石学的原理和方法,基于烃源岩地球化学特征综合分析和实验室模拟研究,对比了两类烃源岩形成环境和生烃特征的差异。结果表明,涠西南凹陷流二段油页岩有机质丰度高、类型好,为很好烃源岩;泥岩有机质丰度较低、类型较差,为好烃源岩。油页岩与泥岩地球化学特征及有机质富集程度的差异是由母岩性质、生源构成、古生产力和有机质保存条件等因素共同作用的结果。油页岩沉积时期湖盆古生产力高、藻类勃发,主要形成于还原环境,有利于有机质的保存;泥岩沉积时期弱还原的水体环境、较快的沉积速率和陆源物质的大量输入不利于有机质的保存。有机质类型和生源构成的差别造成两类烃源岩生烃动力学特征和生烃演化模式存在较大差异,其中油页岩活化能分布相对集中,而泥岩活化能分布相对分散;油页岩的生油高峰早于泥岩,且生油高峰期油页岩的生油率明显高于泥岩。

西湖凹陷上部杂色泥岩井壁失稳研究和钻井液优化

东海西湖凹陷部分区块在Φ311.15 mm井段钻遇龙井组、花港组杂色泥岩地层时,频繁发生起下钻阻卡、倒划眼困难等复杂情况,严重影响井下安全和作业时效。室内采用X射线衍射、扫描电镜、压汞法、抗压强度测试等方法对地层岩性组构特征、力学特性以及其他物理化学性能进行试验,研究井壁岩石失稳机理,表明杂色泥岩本身极具失稳特性。模拟现场条件,试验研究现场油基钻井液封堵和井壁稳定能力、钻井液润湿性能对岩屑井壁黏附和润滑性的影响,发现影响杂色泥岩起下钻遇阻的主控因素是钻井液胶结封堵稳定井壁能力和钻井液润湿性能不够。针对地层特性和钻井液性能不足,制定油基钻井液稳定井壁优化对策,强化钻井液封堵固壁性,提高地层承压能力;优选钻井液乳化剂,提高体系高温稳定性和润湿性。优化后的油基钻井液体系能够有效封堵泥岩微纳米孔缝,提高井壁稳定性,提高泥饼润滑性,可降低起下钻阻卡风险。现场应用表明,钻井过程中井壁稳定,起下钻、下套管等均顺利,与邻井相比起下钻效率提升96%~353%,取得了良好的应用效果,有效解决了西湖凹陷上部杂色泥岩地层井壁失稳问题。

苏里格气田多层理泥岩井壁坍塌机理分析

井壁失稳是制约苏里格气田泥岩地层低成本钻进长井段水平井的首要技术难题。在评价泥岩矿物组分、层理发育及力学特性的基础上,综合理论分析、实验评价以及数值仿真模拟等手段,研究了多层理泥岩在流体作用下的力学行为及破坏失稳特征。由于苏里格气田山西组泥岩层理和微裂缝的存在,岩石在钻井液侵入后将会发生强度劣化。泥岩弱面的导流能力远高于岩石基质,钻井液沿弱面渗透到地层中,会直接导致泥岩结构面强度的下降,易发生井壁坍塌。对苏里格气田实钻过程中的泥岩地层坍塌压力进行了计算,将井斜角、方位角和钻井液浸泡时间分别代入岩石力学参数劣化模型,给出了目的层段安全钻井液密度,对实现苏里格气田多层理泥岩井壁稳定和安全钻井具有重要的指导意义。

贵州织金文家坝地区铝土质泥岩成因分析

该文以贵州织金文家坝龙潭组下段铝土质泥岩为研究对象,结合沉积学、岩石学、地层学、矿床学、地球化学等理论和方法,划分了区域内龙潭组沉积相类型,认为铝土质泥岩为峨眉山玄武岩风化产物,经历了三个阶段的铝富集,但因峨眉山玄武岩风化作用不彻底,风化物中铝含量少,成岩后没有受构造运动抬升地表经受风化淋滤而未形成铝土矿。