过渡型流体转换对洪水型重力流沉积研究的启示及地质意义

洪水型重力流是重力流沉积学的研究热点,以往研究认为洪水型重力流具有紊流支撑的流体性质,对于其流体性质转化及其沉积记录的识别不够深入。近年研究揭示重力流沉积过程中可形成多种过渡型流体,具有特殊流体转换机制和沉积特征。通过调研国内外最新文献,系统介绍了过渡型流体基本特征、沉积机制方面的研究进展,并讨论了其对洪水型重力流沉积研究的启示及地质意义。研究结果表明：在少量黏土矿物影响下,沉积物重力流流体的性质即可由紊流向层流转化,形成特殊的过渡型流体。转化过程主要取决于黏土矿物含量和类型控制的流体内聚力和流速控制的紊流应力二者之间的相互作用。过渡型流体可以产生大型流水沙纹(large current ripple)、砂质纹层—泥质纹层间互形成的低幅度沙波(low amplitude bed wave)等独特的底床类型。尽管实验研究揭示了过渡型流体可能形成的沉积底床特征,针对洪水型重力流沉积记录中过渡型流体的解释仍十分缺乏,尤其是过渡型流体转换机制及其沉积响应仍亟待深入探索。过渡型流体的沉积底形是研究洪水型重力流沉积动力机制的重要载体,可为深入理解洪水型重力流沉积过程提供新视角,同时可能具有更广泛的...     

浅议沉积学中的流体问题

笔者从流体的角度,对近年来有关流体沉积问题的研究成果进行整理、总结、归纳和诠释。从沉积学的角度总体上可将流体分为牵引流、过渡流和重力流3大类:其中牵引流是研究的基础,可进一步分为单向流、双向流和振荡流3种基本类型以及叠置流、复合流和叠加流3种复合类型,可按照流体力学的相关方法展开研究;过渡流和重力流沉积研究的关键在于各种重力流类型之间(浊流、液化沉积物流、颗粒流和碎屑流)及其和牵引流之间的相互转化。流体的沉积机制可分为垂直降落沉积(静水)、底床阻碍沉积(牵引流)和能量减弱沉积(重力流)3大类,各种流体的交互作用最终可形成丘状(洼状)交错层理的水动力条件。通过综述可以发现,从流体角度进行沉积学研究尽管困难,但仍然可行,特别是对于复杂水动力条件下的沉积学研究具有一定的意义。     

流体性质转换机制在重力流沉积体系分析中应用初探

自1950年Kuenen发表"浊流形成粒序层理"一文至今,深水重力流研究取得了长足发展。然而,目前很多学者不仅对浊流理论分歧很大,而且对浊流概念、术语的使用也有不同的观点,这严重制约了重力流的分类及重力流沉积体系的识别。本文在重力流沉积过程和流态研究的基础上,提出了基于"流体性质转换"理论的重力流沉积体系分析方法。研究认为,重力流在形成、发展和消亡过程中不仅存在多个流体阶段,而且存在着多种流态之间的转换。这种流体发育的最终阶段特征决定了重力流沉积体系的形态与类别,而流态共存与转换的特性造成了深水紊流成因的浊积岩与其他流体成因的岩相共存的沉积特征。根据这一理论对牵引流—碎屑流成因的扇三角洲体系、浊流成因的近岸水下扇体系和碎屑流成因的斜坡裙体系进行成因分析与特征对比,阐述了"流体性质转换"理论在沉积体系识别中的作用。     

基于沉积实验的重力流沉积体系砂体分布特征分析

重力流沉积体系砂体展布规律极为复杂,通过重力流流体实验,确定了重力流沉积不同岩相的成因及展布规律,并在此基础上,通过岩芯观察及测井、录井资料分析,在滨南油田古近纪沙三下亚段进行重力流砂体展布规律研究,研究结果表明:1)塑性流体在运动过程中被稀释,导致颗粒支撑机制发生复杂的变化,从而出现多种流态的流体,因此塑性流体被稀释到一定程度后会转换为液态流体; 2)重力流沉积层序的垂向演化及横向变化是流体性质演化的结果,即地质记录中的复杂重力流层序为流体性质转换后再沉积的结果; 3)重力流垂向层序与沉积模式的有机结合是进行砂体展布预测的关键。在该模式的指导下,明确了滨南油田沙三下亚段岩相的空间展布和变化规律。     

海相泥页岩沉积过程研究进展

随着全球页岩油气勘探开发的不断深入,海相泥页岩作为非常规油气沉积学的重要研究对象之一,其沉积特征及沉积过程日益引起学者们的关注,并在岩相分类、沉积过程解释及层序地层划分方面取得了显著进展。海相泥页岩的岩相划分已达到厘米—毫米尺度,其命名原则主要考虑结构（粒度）、层理及矿物成分等特征,结构方面着重参考砂级、粗泥级和细泥级的占比,层理描述注重纹层的连续性、形态和几何关系,矿物成分则比较黏土矿物、石英和碳酸盐岩矿物的相对含量。海相泥页岩的沉积过程多样,浅海陆棚环境下细粒沉积物（岩）的主要搬运与沉积过程包括风成输入、异轻流、重力流（前三角洲浊流、异重流和浪控沉积物重力流）及风暴流,而在平坦而广泛的陆表海则以季风或潮汐驱动下的远岸底流搬运沉积为主。重力流及风暴流沉积一般会形成特征相似但各具特色的粒序层理,而在远岸底流作用下则会形成纹层状泥页岩。沉积特征的精细描述推动了泥页岩层序地层格架的建立,三级层序界面的识别在于寻找可对比的主要侵蚀面,而层序内准层序的划分除了要寻找次要侵蚀面外,还需依靠对精细描述的沉积特征进行定量化统计与分析。上述研究表明,沉积特征的精细化描述与定量分析,并结合水槽模拟实验,是今后海相泥页岩沉积过程研究的主体发展方向。     

浅谈陆相湖盆深水重力流沉积研究中的几点认识

与海相盆地重力流沉积研究理论的快速发展相比,陆相湖盆重力流沉积的相关认识还存在着一定差距。综合国内、外重力流沉积相关研究成果,总结湖盆重力流沉积的相关认识,以明确湖盆重力流沉积研究中存在的不足。增强不同术语内涵及相互关系的理解、增加不同术语的解释说明,是减少术语混淆的有效途径;流体转化、流态转化和润滑作用是湖盆重力流搬运的主要动力学过程;受阻沉降、湍流抑制和牵引毯作用是湖盆重力流沉积物沉降的重要动力学过程。沉积物再搬运、洪水持续供给、漂浮羽流卸载是陆相湖盆重力流沉积主要的成因机制;重力流沉积相域类型、块状砂岩内部沉积特征和逆正粒序沉积特征精细解析可揭示重力流沉积成因。超临界浊流侵蚀作用形成重力流水道,盆地外部因素主控重力流物质成分和来源,盆地内部因素主控重力流分异效率,其综合表现形式即“源—汇”系统控制下的重力流砂体形成演化过程。洪水持续供给成因重力流沉积模式以重力流水道—堤岸沉积、水道—朵叶转换带和朵叶沉积依次过渡构成其典型沉积构型要素组合;沉积物再搬运成因沉积模式以三角洲前缘垮塌带、混杂沉积和朵叶沉积依次过渡构成其典型沉积构型要素组合。湖盆重力流沉积是非常规油气赋存的重要场所,流体转化成因的细粒沉积具有易于油气生成和富集,且易于压裂的先天优势,可能是页岩油气中的“甜点”区发育的优势沉积岩相组合类型。     

复合流沉积特征的谱系研究现状及其理论框架

复合流由单向流和振荡流叠加而成,属于不同流体相互作用范畴,其研究起源于水槽实验中对复合流波痕的观察,一开始便和沉积学结合在一起.复合流沉积对于复杂水动力条件下的沉积学研究具有非常重要的意义,是目前确定沉积岩沉积时流体相互作用的主要依据.以现有复合流文献为基础,从复合流底床形态与垂向序列谱系、沉积效应与层理构造谱系和泥质底床上的层面构造谱系等3个方面进行了总结.复合流沉积特征受单向流速度和振荡流速度的双重控制,各底床形态及相关的纹层构造均表现出从对称到不对称的连续变化,其不对称程度随单向流速度的增大而增加.垂向序列介于单向衰弱流悬浮沉积和双向振荡流悬浮沉积之间,鲍玛序列和风暴序列是其两个端元类型.复合流沉积虽然以粉砂和细砂颗粒为主,但是在较粗的颗粒中(如扁平砾屑)也可以形成特殊的颗粒组构.在层面构造中,由于单向流和振荡流速度的变化(包括大小和叠加方向)在泥质底床上也会形成不同的底痕谱系.因此,对复合流沉积的研究,将是注重振荡流与单向流相互作用的沉积过程研究,从而有别于传统沉积学在不同沉积环境下的模式研究.     

库鲁克塔格地区巷古勒塔格组瘤状灰岩及其沉积环境

新疆库鲁克塔格地区巷古勒塔格组发育瘤状灰岩,是一种深水沉积序列.本区瘤状灰岩形成于台缘斜坡带,滑塌重力流改造原岩形态,并分为富泥型、过渡型及富灰型3种类型.富泥型瘤状灰岩沉积在CCD线之下,受深度海水溶解作用改造.过渡型瘤状灰岩形成在CCD附近,受海底底流和深度海水溶解的双重作用改造.富灰型瘤状灰岩形成在CCD之上,受周期性的重力流作用的改造和海底底流的溶解作用.岩性组合表明,早奥陶世库鲁克塔格地区处于迅速海侵阶段.     

湖相重力流水道沉积特征与沉积模式: 以鄂尔多斯盆地瑶曲铁路桥剖面三叠系延长组为例

陆相深水重力流水道的类型细分及其沉积模式是制约其油气勘探开发的重要因素,但研究程度低。通过对鄂尔多斯盆地南缘瑶曲铁路桥剖面三叠系延长组实测、水道形态参数统计及岩相、粒度等分析,开展了湖相重力流水道的沉积特征、沉积过程及沉积模式研究。结果表明:(1)研究区内可识别出4期复合水道,主要为洪水重力流成因。根据其内部单一水道及单砂体形态特征、岩相组成,将其细分为沉积型和过渡型两类。(2)剖面下部2期复合水道为沉积型,以悬浮载荷成因岩相为主,常见块状净细砂岩、薄层泥岩岩相组合和鲍马序列岩相组合;上部2期复合水道为过渡型,岩相以底床载荷与悬浮载荷共存为特征,自下而上以交错层理细砂岩或叠瓦状泥砾细砂岩与含泥砾/泥岩撕裂屑块状细砂岩、平行层理粗粉砂岩及薄层泥岩的岩相组合为特征。(3)结合单一水道规模及其相互关系,建立了区内过渡、沉积型重力流水道的半定量沉积模式。过渡型水道内部侵蚀与沉积作用共存,单一水道宽度小、宽厚比低,呈透镜状,水道间切割性强,砂体横向稳定性较低,表现出不定向叠加、侧向拼接样式;沉积型水道内部由沉积作用主导,单一水道宽度较大、宽厚比较高,呈似板状—透镜状,砂体横向稳定性较高,表现出稳定的垂向加积样式。     

湖相重力流水道沉积特征与沉积模式:以鄂尔多斯盆地瑶曲铁路桥剖面三叠系延长组为例*

陆相深水重力流水道的类型细分及其沉积模式是制约其油气勘探开发的重要因素,但研究程度低。通过对鄂尔多斯盆地南缘瑶曲铁路桥剖面三叠系延长组实测、水道形态参数统计及岩相、粒度等分析,开展了湖相重力流水道的沉积特征、沉积过程及沉积模式研究。结果表明:(1)研究区内可识别出4期复合水道,主要为洪水重力流成因。根据其内部单一水道及单砂体形态特征、岩相组成,将其细分为沉积型和过渡型两类。(2)剖面下部2期复合水道为沉积型,以悬浮载荷成因岩相为主,常见块状净细砂岩、薄层泥岩岩相组合和鲍马序列岩相组合;上部2期复合水道为过渡型,岩相以底床载荷与悬浮载荷共存为特征,自下而上以交错层理细砂岩或叠瓦状泥砾细砂岩与含泥砾/泥岩撕裂屑块状细砂岩、平行层理粗粉砂岩及薄层泥岩的岩相组合为特征。(3)结合单一水道规模及其相互关系,建立了区内过渡、沉积型重力流水道的半定量沉积模式。过渡型水道内部侵蚀与沉积作用共存,单一水道宽度小、宽厚比低,呈透镜状,水道间切割性强,砂体横向稳定性较低,表现出不定向叠加、侧向拼接样式;沉积型水道内部由沉积作用主导,单一水道宽度较大、宽厚比较高,呈似板状—透镜状,砂体横向稳定性较高,表现出稳定的垂向加积样式。     

Status and Trends in Research on Deep-Water Gravity Flow Deposits

Deep-water gravity flows are one of the most important sediment transport mechanisms on Earth. After 60 years of study,significant achievements have been made in terms of classification schemes,genetic mechanisms,and depositional models of deep-water gravity flows. The research history of deep-water gravity flows can be divided into five stages: incipience of turbidity current theory; formation of turbidity current theory; development of deep-water gravity flow theory; improvement and perfection of deep-water gravity flow theory; and comprehensive development of deep-water gravity flow theory. Currently,three primary classification schemes based on the sediment support mechanism,the rheology and transportation process,and the integration of sediment support mechanisms,rheology,sedimentary characteristics,and flow state are commonly used.Different types of deep-water gravity flow events form different types of gravity flow deposits. Sediment slump retransportation mainly forms muddy debris flows,sandy debris flows,and surge-like turbidity currents. Resuspension of deposits by storms leads to quasi-steady hyperpycnal turbidity currents(hyperpycnal flows). Sustainable sediment supplies mainly generate muddy debris flows,sandy debris flows,and hyperpycnal flows. Deep-water fans,which are commonly controlled by debris flows and hyperpycnal flows,are triggered by sustainable sediment supply; in contrast,deep-water slope sedimentary deposits consist mainly of debris flows that are triggered by the retransportation of sediment slumps and deep-water fine-grained sedimentary deposits are derived primarily from finegrained hyperpycnal flows that are triggered by the resuspension of storm deposits. Harmonization of classification schemes,transformation between different types of gravity flow deposit,and monitoring and reproduction of the sedimentary processes of deep-water gravity flows as well as a source-to-sink approach to document the evolution and deposition of deep-water gravity flows are the most important research aspects for future studies of deep-water gravity flows study in the future.     

异重流沉积研究进展

在相关文献调研基础上,综述了异重流沉积研究现状,并结合中生代湖相异重岩研究实例,建立了“沟道-舌状体-朵状体”异重流沉积模式。异重流(hyperpycnal flow)是一种由洪水期河口直接注入、因密度大于汇水盆地水体密度而沿水体底部分层流动的持续型浊流。它呈牛顿流变性质、紊乱流动状态、湍流支撑机制,具有更高的发生频率和稳定的沉积物供给。异重流主要受地形、气候、密度差等因素控制,海洋和湖泊均有发生;水体密度小、近物源、地形高差大、中-小河流发育、构造活动强烈的陆相淡水湖泊更利于异重流的产生,但陆相湖盆异重流沉积并未引起足够的重视。异重流自近端向远端总体呈稀释趋势,依次对应于特定的沉积构造及序列;由异重流形成的沉积岩被称作异重岩(hyperpycnite),以发育由洪水增强-减弱所产生的逆粒序-正粒序组合、层内微侵蚀面、富含陆源有机质区别于其他浊积岩。深入研究异重流沉积,不仅有益于完善重力流沉积理论、分析沉积环境,而且有利于指导深水非常规油气勘探,具有重要的科学价值和现实意义。     

Depositional processes,bedform development and hybrid bed formation in rapidly decelerated cohesive (mud–sand) sediment flows

Flows with high suspended sediment concentrations are common in many sedimentary environments, and their flow properties may show a transitional behaviour between fully turbulent and quasi‐laminar plug flows. The characteristics of these transitional flows are known to be a function of both clay concentration and type, as well as the applied fluid stress, but so far the interaction of these transitional flows with a loose sediment bed has received little attention. Information on this type of interaction is essential for the recognition and prediction of sedimentary structures formed by cohesive transitional flows in, for example, fluvial, estuarine and deep‐marine deposits. This paper investigates the behaviour of rapidly decelerated to steady flows that contain a mixture of sand, silt and clay, and explores the effect of different clay (kaolin) concentrations on the dynamics of flow over a mobile bed, and the bedforms and stratification produced. Experiments were conducted in a recirculating slurry flume capable of transporting high clay concentrations. Ultrasonic Doppler velocity profiling was used to measure the flow velocity within these concentrated suspension flows. The development of current ripples under decelerated flows of differing kaolin concentration was documented and evolution of their height, wavelength and migration rate quantified. This work confirms past work over smooth, fixed beds which showed that, as clay concentration rises, a distinct sequence of flow types is generated: turbulent flow, turbulence‐enhanced transitional flow, lower transitional plug flow, upper transitional plug flow and a quasi‐laminar plug flow. Each of these flow types produces an initial flat bed upon rapid flow deceleration, followed by reworking of these deposits through the development of current ripples during the subsequent steady flow in turbulent flow, turbulence‐enhanced transitional flow and lower transitional plug flow. The initial flat beds are structureless, but have diagnostic textural properties, caused by differential settling of sand, silt and cohesive mud, which forms characteristic bipartite beds that initially consist of sand overlain by silt or clay. As clay concentration in the formative flow increases, ripples first increase in mean height and wavelength under turbulence‐enhanced transitional flow and lower transitional plug‐flow regimes, which is attributed to the additional turbulence generated under these flows that subsequently causes greater lee side erosion. As clay concentration increases further from a lower transitional plug flow, ripples cease to exist under the upper transitional plug flow and quasi‐laminar plug flow conditions investigated herein. This disappearance of ripples appears due to both turbulence suppression at higher clay concentrations, as well as the increasing shear strength of the bed sediment that becomes more difficult to erode as clay concentration increases. The stratification within the ripples formed after rapid deceleration of the transitional flows reflects the availability of sediment from the bipartite bed. The exact nature of the ripple cross‐stratification in these flows is a direct function of the duration of the formative flow and the texture of the initial flat bed, and ripples do not form in cohesive flows with a Reynolds number smaller than ca 12 000. Examples are given of how the unique properties of the current ripples and plane beds, developing below decelerated transitional flows, could aid in the interpretation of depositional processes in modern and ancient sediments. This interpretation includes a new model for hybrid beds that explains their formation in terms of a combination of vertical grain‐size segregation and longitudinal flow transformation.     

鄂尔多斯盆地南部三叠系延长组湖相重力流沉积细粒岩及其油气地质意义

随着页岩油气勘探开发和相关领域研究的不断深入,细粒沉积物的搬运和沉积已成为当前沉积学研究的热点问题之一,但中国中生代湖泊环境中的泥质重力流沉积尚未引起应有的关注。通过岩心观察、薄片鉴定等手段及综合研究,分析了鄂尔多斯盆地晚三叠世湖相泥质重力流沉积特征,探讨了其形成机制与成因分类。鄂尔多斯盆地三叠系延长组湖相泥页岩结构类型多样,发育泥质块体流沉积、泥质碎屑流沉积、泥质浊流沉积和泥质异重流沉积等多种重力流沉积类型。按照泥质含量将重力流划分为砂质重力流、泥质重力流和混合重力流3种亚类,并根据成因将重力流划分为滑塌体、碎屑流、浊流及异重流等4种亚类;结合成因和泥质含量,将重力流沉积共划分为12种类型。滑塌岩、碎屑岩分布于三角洲前缘斜坡脚附近;浊积岩、异重岩广泛分布于三角洲斜坡至沉积中心。认为泥质沉积物可以在强水动力条件下搬运-沉积;重力流沉积细粒物质在湖相沉积中占据很大的比例;泥质重力流对泥页岩中的碎屑物质、黏土矿物及有机质的搬运和沉积起到重要作用,因而对于页岩油气的生烃、储集性能和压裂工艺研究具有重要意义。     

鄂尔多斯晚三叠世湖盆异重流沉积新发现

水下重力流沉积作为重要的油气储层,已成为当前学术研究和油气工业共同关注的焦点.在鄂尔多斯盆地南部延长组长7~长6油层组深湖相沉积中,发现一种不同于砂质碎屑流沉积和滑塌浊积岩的重力流成因砂岩.其沉积特征为一系列向上变粗的单元(逆粒序层)和向上变细的单元(正粒序层)成对出现;每一个粒序层组合内部的泥质含量变化(高-低-高)与粒度变化一致;上部正粒序层与下部逆粒序层之间可见层内微侵蚀界面;砂岩与灰黑色纯泥岩、深灰色粉砂质泥岩互层;粉砂质泥岩层内也表现出类似的粒度变化特征.通过岩芯观察和薄片鉴定,认为该岩石组合形成于晚三叠世深湖背景下的异重流(hyperpycnal flow)沉积.其沉积产物--hyperpycnite(异重岩?)以发育逆粒序和层内微侵蚀面而区别于其它浊积岩,逆粒序代表洪水增强期的产物,上部的正粒序层为洪水衰退期的沉积,逆粒序-正粒序的成对出现代表一次洪水异重流事件沉积旋回;层内微侵蚀面是洪峰期流速足以对同期先沉淀的逆粒序沉积层侵蚀造成的.鄂尔多斯盆地延长组异重岩的发现,不仅为探索陆相湖盆环境下的异重流沉积提供了一个范例,而且对于深水砂体成因研究、储层预测和油气勘探具有理论和现实意义.     

The dynamics of turbulent, transitional and laminar clay-laden flow over a fixed current ripple

Most aqueous sedimentary environments contain varying concentrations of fine‐grained, often clay‐rich, sediment that is transported in suspension and may modify the properties of the flow and underlying mobile bed. This paper presents results from a series of laboratory experiments examining the mean and turbulent properties of clay‐laden (kaolinite) flows, of various volumetric sediment concentrations between 0·046% and 12·7%, moving over a fixed, idealized current ripple. As the kaolinite concentration was raised, with flow velocity and depth constant, four flow types were observed to occur: (i) turbulent flow, in which flow separation is dominant in the leeside of the ripple; (ii) turbulence‐enhanced transitional flow, in which turbulence in the leeside separation zone region is enhanced; (iii) turbulence‐attenuated transitional flow, in which turbulence along the separation zone shear layer and in the free flow above it becomes damped, eventually leading to a reduction in the size of the separation zone wake region; and (iv) laminar plug flow, in which turbulence is damped and flow is almost stagnant in the lee of the ripple. Such modulation of turbulence by increasing clay concentrations suggests that many paradigms of flow and bedform dynamics, which have been based on extensive past work in clear water flows, require revision. The present results highlight a need to fully characterize the boundary conditions for turbulence modulation as a function of clay type and applied flow conditions, and the effects of such flows on fully mobile cohesionless beds.     

中国湖相沉积物重力流研究的过去、现在与未来

深水重力流沉积领域是当前全球油气勘探与研究的热点,陆相盆地深水重力流沉积研究在我国已有50年历程,大致可以分为3个阶段,即浊流理论探索与发展阶段（1970—1980年）、浊流理论工业化应用阶段（1990—2000年）和砂质碎屑流研究阶段（2010年以后）。近10年来,随着国际深水沉积理论的发展与我国油气勘探技术的进步,湖盆深水沉积研究工作进展迅速,涌现出了大量的新成果、新认识,主要包括以下4个方面: 1）湖盆中央深水区至少存在浊流、异重流、砂质碎屑流及底流4种类型的重力流与牵引流沉积;2）湖盆中不同类型的流体在搬运与沉积过程中存在互相转化,形成混合事件层（Hybrid Event Bed）;3）建立了湖相砂质碎屑流搬运—沉积过程的鉴别标志—— “泥包砾”结构（Mud-coated intraclasts）;4）地震沉积学理论与技术方法在湖相重力流内部沉积单元解剖、湖盆深水沉积模式建立等方面取得巨大成功。展望未来,为适应油气工业勘探开发需求,湖盆深水沉积研究发展趋势主要有5个方面: 1）深水砂体成因类型划分、搬运—沉积过程及沉积模式的建立与完善;2）深水泥页岩（细粒沉积）成因机理、类型划分及其油气意义研究;3）深水沉积“源—汇”系统与地震响应及评价预测研究;4）深水沉积搬运—沉积过程实验模拟研究;5）新的深水沉积理论体系建立及其在油气勘探开发中的应用。