陆相盆地深水沉积体系研究

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,老一辈沉积学家围绕湖相重力流理论及油气勘探实践方面开展了一系列创新性工作,相继建立了断陷型、坳陷型及前陆型湖盆浊流沉积模式,从而使陆相湖盆充填模式与沉积特征研究走在了世界前列。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,我国湖盆深水沉积研究工作再次呈现出勃勃生机,在湖盆深水搬运—沉积过程、沉积作用、沉积模式、地震响应及技术方法等方面涌现出大量令世人注目的成果,标志着我国陆相湖盆重力流研究进入了一个新的创新发展阶段。“陆相盆地深水沉积体系研究”专栏针对性地组织了一批相关文章,旨在对这些成果进行总结,进一步完善陆相盆地深水沉积理论认识,推动我国湖盆深水沉积油气勘探事业。专栏共收集论文5篇,主要内容如下:国际著名地质学家Henry W.Posamentier教授等人撰写的《深水浊流沉积综述》（An Overview of Deep-water Turbidite Deposition）一文,系统总结了层序地层格架下的海平面变化对深水浊流沉积体系的控制作用,对陆相盆地深水沉积体系研究具有重要启示作用。作者认为,浊流沉积体系一般可划分为三个区域:区域1位于上游近物源一端,包括陆棚边缘及支流供给峡谷,在这个区域沉积物重力流完全受峡谷壁的限制。区域2的显著特点是发育单一的供给水道复合体,其中的重力流不完全受水道壁的限制,常常形成与水道相伴生的天然堤沉积。当供给水道过渡为前缘分散体系或末端扇时就让位于区域3。区域3末端扇发育沟道化流体,但天然堤非常有限,因而经常发生决口,形成富砂的溢岸沉积。李相博等在对我国陆相盆地重力流沉积50年研究历程回顾的基础上,对近10年来湖盆深水沉积研究中涌现出的新成果、新认识进行了总结归纳,主要包括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 eventbed）;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。论文最后对湖盆深水沉积研究未来发展趋势进行了分析。以往关于砂级、泥级陆源碎屑与碳酸盐组分的混合沉积研究相对较多,而针对扇三角洲内砾级陆源碎屑与碳酸盐组分的混合沉积特征及模式研究较少,缺少典型实例。王越等以露头实测资料为基础,通过对新疆塔尔朗沟剖面中二叠统大河沿组、塔尔朗组扇三角洲的混合沉积特征的分析,结合前人在古气候方面的认识,建立了扇三角洲混合沉积模式。张国栋等对鄂尔多斯盆地南部旬邑地区上三叠统延长组露头剖面的解剖,通过岩石薄片观察和激光粒度分析,研究了块状砂岩的粒度组成、粒度参数及其垂向变化,认为属于洪水成因的异重流沉积。操应长等通过对准噶尔盆地玛湖凹陷夏子街地区百口泉组砂砾岩储层的研究,认为主要为重力流与牵引流共同控制的扇三角洲体系,并定量划分了扇三角洲体系的岩相—成岩相类型,分析了砂砾岩储层物性的控制因素。     

珠江口盆地荔湾井区珠江组深水扇沉积特征

珠江口盆地白云凹陷荔湾深水区为油气勘探有利区域,通过岩石学和古生物组合特征研究,认为该区珠江组下部属于典型的深水扇沉积,可划分为早期盆地扇和晚期斜坡扇两种类型,两类深水扇都以发育颗粒流、砂质碎屑流及低密度浊流等顺坡重力流沉积为主,同时夹有少量内波和等深流等深水牵引流改造沉积。砂质碎屑流为两类深水扇水道砂体的主要沉积类型,发育有逆-正粒序层理、平行层理和水平层理,粒序层内可见各种丰富的液化变形和生物逃逸构造,而水平层内发育有更多的生物钻孔和扰动现象。两类深水扇的沉积构造和古生物特征有明显差异,其中盆地扇水道砂岩中普遍含硅质小砾石,水道间泥岩中含有较多保存完好的抱球虫化石,斜坡扇水道砂岩以富含炭泥屑为典型特征,水道间泥岩含有更丰富的颗石藻和抱球虫化石,其中部分抱球虫和颗石具有遭受海底溶蚀作用的现象,指示斜坡扇相对盆地扇有更大的水体深度。平面上两类深水扇具有相似的重力流沉积的分带性,都具有自陆架坡折向盆地方向由颗粒流沉积逐渐向砂质碎屑流和近源高密度浊流、远源低密度浊流等单向演化的特点。     

水道加朵体型深水扇形成机制与模式:以白云凹陷荔湾3-1地区珠江组为例

深水扇储层的沉积特征是油气勘探开发中的一个热点问题。通过分析珠江口盆地白云凹陷荔湾3-1地区珠江组深水扇的沉积特征,明确了研究区具备深水扇形成的有利条件,受白云凹陷总体构造沉积背景影响,形成了富砂型的深水扇。本区深水扇是多种流体动力学机制共同作用的结果,碎屑流、浊流及底流相互作用与复合,形成了平面上具水道复合朵体的分布特征。在建立深水扇沉积模式的基础上,提出了水道加朵体型深水扇沉积微相划分方案,研究区储层以重力流水道、天然堤及滑塌朵体为主;而水道逐渐由相对近源的宽浅下切型变为远离物源的窄深型,其深度与天然堤宽度呈正比。     

西非被动大陆边缘盆地深水沉积体系特征

深水沉积砂岩储层是近年来全球油气勘探重点领域之一,对于深水沉积模式认识、沉积类型划分、储层分布规律及宏观演化规律能否实现系统深入的认知也成为制约全球油气勘探获得更多突破的关键问题之一。以典型深水沉积广泛发育的西非被动大陆边缘尼日尔三角洲盆地和刚果扇盆地为研究区,以地震资料为主,钻井资料为辅,开展针对性的深水沉积体系层序界面识别,明确研究区层序及体系域划分方案,建立深水沉积层序地层格架;综合2个研究区的深水沉积特征,探索建立了一套西非地区的深水沉积类型的划分方案,将其划分为陆坡峡谷、块体流、水道体、朵叶体、半深海泥5种亚相;将块体流细化为滑移体和滑塌碎屑流2种微相,将水道体进一步划分为高侵蚀充填型水道、低侵蚀过路加积型水道、过路高弯度水道、废弃水道、堤岸-漫溢5种微相,将朵叶体细分为末端朵叶和决口扇朵叶2种微相;同时系统总结解剖了各微相的岩性组合、地震反射及平面发育特征;深入分析了研究区深水沉积体系的宏观演化特征及展布规律,认识到尼日尔三角洲盆地深水沉积体系中水道体和朵叶体均有发育,自下向上,随着相对海平面先下降再上升的过程,早期主要发育朵叶体沉积,晚期则转变为以发育大型浊积水道为主。刚果扇盆地深水沉积则主要为水道体沉积,朵叶体较少发育,早期水道规模小,中期开始发育多支复合水道并呈退积趋势,水道发育程度逐渐降低,至晚期水道能量及侵蚀能力复又转强,甚至形成较大的陆坡峡谷及多支水道体。     

白云深水区东部重力流水道岩性圈闭特征分析

白云深水区东部在早中新世时期处于两种沉积相带的交汇处:古珠江三角洲物源体系深水重力流水道砂岩沉积和东沙隆起台地生物礁物源体系碳酸盐岩峡谷水道沉积。层序地层学、沉积学、构造学研究表明,在白云深水区东部21.0Ma陆架坡折带下方,早期低位体系域发育的条带状优质重力流水道砂岩可以作为岩性圈闭的主力储层;晚期海进体系域大型碳酸盐岩、泥岩充填的峡谷水道,切割了下部早期低位体系域的重力流水道砂体,起到了有效的侧封作用,从而形成了重力流水道岩性圈闭,实际钻井资料证实该岩性圈闭为工业油气藏。     

深水沉积层序与沉积演化模式典型实例——莺歌海盆地中深层黄流组

从莺歌海盆地东方气田中深层中新统黄流组深水沉积实例出发,利用多方资料揭示了一个从强制海退早期到海侵晚期的完整自旋回,以及每个时期深水沉积旋回的特征与发育规律。结合物源及地貌环境特征,将研究区分为三块,阐述了每块的特点。黄流组一段深水沉积属于多点供源、较富砂的沉积环境,且坡陡不大,海盆较小,为受沉积自旋回及地貌环境控制的较典型的深水沉积模式。研究区内的有利储层主要为强制海退晚期到低水位域正常海退和海侵早期的堤成水道及前缘决口扇复合沉积,而之后海侵早期的下切水道对于原有较连续的浊流砂体起到了分割作用,造成了现今的砂体展布格局。     

水下沉积物重力流与海底扇相模式研究进展

水下沉积物重力流将大量沉积物搬运至海底,形成了地球上最大的沉积体系——海底扇。综合前人研究成果,梳理水下沉积物重力流的基本概念、分类和识别标志,介绍了现代观测的重要结果和海底扇相模式的研究进展。浊流和碎屑流是重力流最主要的两类流体,浊流为逐层沉积,发育正粒序;碎屑流为整体沉积,垂向无序。由浊流转换为碎屑流的重力流称混合流,陆上洪水入海(湖)形成的浊流称异重流。现代观测的结果表明:浊流底部存在高密度层,横向结构并不都是涌浪型,浊流的持续时间可以长达1周。海底扇通常采用组构分析和层级分类进行研究,由水道、天然堤、朵体、远洋—半远洋沉积和块体搬运沉积组成。水道侧向延伸窄,发育侵蚀结构;天然堤由薄层泥—粉砂质浊积岩组成,横向呈楔形变薄;朵体侧向延伸宽,颗粒粒度集中,侵蚀结构较少。水道的层级从低到高依次为水道单元、水道复合体和水道复合体群。朵体的层级从低到高依次为层、朵体元素、朵体和朵体复合体。     

陆架坡折盆地强制海退及正常海退沉积——以珠江口盆地珠江组—韩江组为例

关于强制海退形成的沉积体对应层序中体系域的问题,一直是国内外争论的焦点。结合Exxon公司建立的层序地层沉积模型,将强制海退沉积体对应于早期低位体系域以及晚期高位体系域,正常海退沉积体对应于晚期低位域前积体、高位域早期前积体。以珠江口盆地坳陷期的珠江组—韩江组为例,将其划分为7个三级相对海平面变化旋回,对应7个三级层序。相对海平面变化是可容纳空间的外在响应。在陆架坡折之上产生的高位域晚期前积体和陆坡及以下地区发育的低位域早期低位扇体;在陆架坡折带及以下形成的低位前积楔、坡折带及以上形成的高位早期前积体,是有利的油气储集体。     

深水扇沉积研究现状和展望——以珠江口盆地白云凹陷珠江深水扇系统为例

与深水扇有关的储层将处于油气勘探和生产的最前沿。虽然深水扇沉积作用的研究已经取得了一定的进展,但目前国内外对其地质概念和沉积模式等方面的认识仍存在较大分歧。在国内外研究进展的基础上,结合我国南海北部珠江口盆地白云凹陷珠江深水扇系统的沉积特征,文中详细地描述了深水扇沉积体系中下切水道及其充填序列、水道、天然堤—溢岸及叶状体的沉积特征,具体地阐述了深水扇的层序发育特点及层序界面的识别标志。     

牛庄洼陷沙三中亚段低位域砂体沉积分布特征

依据录井、测井、岩芯和孢粉化石分析等,认为牛庄洼陷发育于原沙三下亚段上下两套油页岩之中的砂体应属于沙三中亚段低位体系域,为水下冲积扇和深水浊积扇;并阐明了其沉积分布特征,且进一步运用层序地层学原理研究认为研究区低位域砂体沉积相组合-层序及体系域叠置模式为低水位深水浊积扇-湖平上升初期的低水位水下冲积扇-后期的湖侵水道。     

Marine depositional events controlled by sediment supply and sea-level changes

Under conditions of high fluvial or coastal sediment supply, individual sandy storm layers (tempestites) and turbidites form after significantly shorter time intervals than Milankovitch cycles. To provide the material for mass flows of very high volume, large, mountainborne rivers require about ten thousand years. With little sediment supply, however, all event deposits become rare or are missing.Third-order sequences (about 1–4 Ma) vary considerably in thickness depending on the sedimentation rates in the basins. Thick and widely extended mud flows and megabreccias are preferentially triggered by sea level fall below the shelf edge. Mixed siliciclastics-carbonate systems along the foot of carbonate shelves generally become coarser grained and poorer in carbonates during lowstands. Turbidite successions also frequently occur in lowstand deposits, but may be present in the other systems tracts as well if a delta is prograding continually.The position of tempestites in third or higher order shallow water sequences is less clear. In studies on the migration of coastal sands in relation to falling and rising sea level, one should distinguish, apart from sediment supply, between settings with and without substantial wave scour. The generation of sandy tempestites appears to be favoured if coastal progradation and wave scour operate simultaneously for example during late highstand and early lowstand.     

Gravity Flow on Slope and Abyssal Systems in the Qiongdongnan Basin, Northern South China Sea

The study of new seismic data permits the identification of sediment gravity flows in terms of internal architecture and the distribution on shelf and abyssal setting in the Qiongdongnan Basin (QDNB). Six gravity flow types are recognized: (1) turbidite channels with a truncational basal and concordant overburden relationship along the shelf edge and slope, comprising laterally-shifting and vertically-aggrading channel complexes; (2) slides with a spoon-shaped morphology slip steps on the shelf-break and generated from the deformation of poorly-consolidated and high water content sediments; (3) slumps are limited on the shelf slope, triggered either by an anomalous slope gradient or by fault activity; (4) turbidite sheet complexes (TSC) were ascribed to the basin-floor fan and slope fan origin, occasionally feeding the deep marine deposits by turbidity currents; (5) sediment waves occurring in the lower slope-basin floor, and covering an area of approximately 400?km2, were generated beneath currents flowing across the sea bed; and (6) the central canyon in the deep water area represents an exceptive type of gravity flow composed of an association of debris flow, turbidite channels, and TSC. It presents planar multisegment and vertical multiphase characteristics. Turbidite associated with good petrophysical property in the canyon could be treated as a potential exploration target in the QDNB.     

库车前陆盆地白垩系亚格列木组浊流沉积特征与意义

通过对库车前陆盆地西部卡普沙良河剖面上侏罗统喀拉扎组-下白垩统亚格列木组沉积相垂向演化分析、砂泥岩X射线荧光光谱分析、储层微观特征研究,认为喀拉扎组-亚格列木组发育一套干旱气候背景下的陆上季节性辫状河-半深湖浊积扇-浅湖相的沉积演化序列。上侏罗统喀拉扎组主要以季节性辫状河沉积为主,下白垩统亚格列木组下部发育早晚两期浊积扇沉积,浊积扇水道砂体中见槽模、沟模以及重荷模,并发育典型的鲍玛序列,该沉积时期的古气候偏干冷;亚格列木组上部主要发育浅湖相泥岩与沙坝沉积,此沉积时期古气候由湿热变化至干冷。亚格列木组浊积扇水道砂体中石英含量较高,一般介于62%~70%之间,粒间溶孔与构造缝较发育;浅湖相沙坝砂体石英含量降低,一般为55%~58%,沙坝砂体中溶蚀孔较浊积扇中溶蚀孔多。亚格列木组中浊流沉积的发现,不但丰富了库车前陆盆地重力流沉积的研究成果,也表明在早白垩世库车西部发育较深水的沉积环境,为该地区湖相深水沉积的油气勘探奠定了基础。     

Hyperpycnal-fed turbidite lobe architecture and recent sedimentary processes: A case study from the Al Batha turbidite system, Oman margin

The main sediment depocenter along the Oman margin is the Al Batha turbidite system that develops in the Gulf of Oman basin. It is directly connected to the wadi Al Batha, and forms a typical sand and mud rich point source system that acts as regional sediment conduit and feeds a ~ 1000 km² sandy lobe.The Al Batha lobe depositional architecture has been investigated in detail using very high-resolution seismic, multibeam echosounder data and sediment cores. Several scales of depositional architecture can be observed. The Al Batha lobe is composed of several depositional units, made of stacked elementary sediment bodies (thinner than 5 m) that are each related to a single flow event. The lobe is connected to the feeder system through a channel-lobe transition zone (CLTZ) that extends on more than 25 km. The lobe can be divided into proximal, middle and distal lobe areas. The proximal lobe is an area of erosion and by-pass with small axial feeder channels that rapidly splay into several small distributaries. They disappear in the mid-lobe area where deposits consist of vertically stacked tabular to lens-shaped sediment bodies, with a lateral continuity that can exceed 10 km. The distal lobe fringe shows a classical facies transition towards thin-bedded basin plain deposits.Sub-surface deposits consist of sandy turbidites and hyperpycnites, interbedded with fine-grained deposits (thin turbidites, hyperpycnites, or hemipelagites). Although these distal deposits are mainly related to flow transformations and concentration evolution, they highlight the importance of flooding of the wadi Al Batha on the sediment transfer to the deep basin. The thick sandy hyperpycnites recovered in such a distal area are also possibly related to the initial properties of gravity flows, in relation to the flooding characteristics of mountainous desert streams.Finally, the Al Batha lobe depositional architecture is typical of sand-rich lobes found within “small”, sand and mud rich turbidite systems fed by mountainous “dirty” rivers. Turbidite sedimentation in the Al Batha system appears to be primarily controlled by the strong climatic and geomorphic forcing parameters (i.e. semi-arid environment with ephemeral, mountainous rivers subjected to flash-flooding).     

Lobe construction and sand/mud segregation by turbidity currents and debris flows on the western Nile deep-sea fan (Eastern Mediterranean)

Based on an unusual data set comprises bathymetric data, backscatter imagery, seismic-reflection and Chirp profiles, and sediment cores, the Late Quaternary lobe at the mouth of the youngest turbidite channel off the western Nile deep-sea fan was investigated. The large-scale construction of the lobe through time and space is mainly controlled by 1) a pre-existing topography inherited from the downslope movement of Messinian evaporites, and 2) the type and nature of gravity flows delivered to the basin floor. The margins of the lobe are defined by high-backscatter acoustic facies that contrasts strongly with the low-backscatter facies from the surrounding abyssal-plain deposits. Within the lobe, low-backscatter facies characterise the main channel-levee systems and lobate bodies immediately beyond the end of the channels. Cores reveal that the high-backscatter facies corresponds to a series of extensive but thin debris-flow deposits with a fingered margin. These debrites comprise a muddy-sand matrix and dispersed clasts with diameter of 5 to 10 cm. The lower backscatter facies at channel mouths corresponds to alternations of thin sandy turbidites and muddy hemipelagites. Extensive thin debris flows therefore traversed surprisingly low gradients to reach the distal fringes of the lobe complex but are never found in the lobate bodies just beyond the channel mouths. Although the Nile deep-sea fan is considered as a silt/mud-rich accumulation, sand-prone deposits exist within the lobe. This sand/mud segregation results either from the presence of channelized features in the lobe and/or from the hydrodynamic process of particle transport by debris flows and turbulent flows.     

滇东南法郎组含锰地层沉积相分析

滇东南中三叠统法郎组是重要的含锰地层,前人对其沉积环境的认识却存在着深水浊流沉积和浅水潮坪沉积的争议。本文通过对建水-开远地区典型剖面的研究,认为法郎组为浊积扇沉积。法郎组底部为碳酸盐滑塌沉积、碎眉流沉积与泥岩粉砂岩互层,中上部逐渐由外扇渐变为中扇辫状水道和辫状水道间沉积,顶部为内扇补给水道和溢岸沉积。相对海水深度总体表现为在拉丁早期逐渐加深,到拉丁中晚期有逐渐变浅。锰矿层主要发育在底部的碎屑流沉积中,其彤成可能与拉丁早期相对水深的增高有关。     

Seismic imaging of Pleistocene deep-sea cyclothems: implications for sequence stratigraphy

Plate collision along the New Zealand Alpine Fault since the late Miocene has resulted in an abundant supply of temgenous sediment to an adjacent starved late Cretaceous rift-basin, the Bounty Trough. During the late Neogene, alternating pulses of temgenous (glacial) and biogenic (interglacial) sediment were deposited in the trough in the form of deep-sea cyclothems, in sympathy with glacio-eustatic sea-level fluctuations. Individual cyclothems ranging up to 15 m in thickness have been directly imaged by both 3.5 kHz and single channel airgun profiling. They are particularly conspicuous on the continental slope and in areas of the trough under the influence of overbank turbidite deposition from the Bounty Channel. On the abyssal Bounty Fan, approximately 50 cyclothems have been deposited since the late Pliocene, i.e. each cyclothem corresponds to two contiguous oxygen isotope stages. Each cyclothem also corresponds to the offshore conformity of a single 5th or 6th order seismic sequence, with the lower, temgenous portion marking a lowstand systems tract, and the upper, biopelagic part representing the transgressive and highstand systems tracts. Therefore, as a single continental margin sequence is traced seawards it passes from unconformity-bounded shelf and shelf-margin cyclothems, to slope sediments which include thick conformity-bounded cyclothems or autocyclic canyon deposits, to thin conformity-bounded deep-sea cyclothems on the distal rise, and finally to cryptically cyclic biopelagic sediment andor red clay on the abyssal plain.     

Sedimentation of submarine fan deposits in the Pindos foreland basin,from late Eocene to early Oligocene,west Peloponnesus peninsula,SW Greece

Turbidite facies distribution and palaeocurrent analysis of submarine fan evolution in the Pindos foreland basin of west Peloponnesus peninsula (SW Greece) indicate that this part of the foreland was developed during Late Eocene to Early Oligocene in three linear sub‐basins (Tritea, Hrisovitsi and Finikounda). The basin fill conditions, with a multiple feeder system, which is characterized by axial transport of sediments and asymmetric stratigraphic thickness of the studied sediments, indicate that the Pindos Foreland Basin in this area was an underfilled foreland basin. Sediments are dominated by conglomerates, sandstones and mudstones. The flow types that controlled the depositional processes of the submarine fans were grain flows, debris flows and low‐ and high‐density turbidity currents. The sedimentary model that we propose for the depositional mechanisms and geometrical distribution of the turbidite units in the Tritea sub‐basin is a mixed sand‐mud submarine fan with a sequential interaction of progradation and retrogradation for the submarine fan development and shows a WNW main palaeocurrent direction. The Hrisovitsi sub‐basin turbidite system characterized by small‐scale channels was sediment starved, and the erosion during deposition was greater than the two other studied areas, indicating a more restricted basin topography with a NW main palaeocurrent direction. The Finikounda sub‐basin exhibits sand‐rich submarine fans, is characterized by the presence of distinct, small‐scale, thickening‐upward cycles and by the covering of a distal fan by a proximal fan. It was constructed under the simultaneous interaction of progradation and aggradation, where the main palaeocurrent direction was from NNW to SSE. Copyright © 2012 John Wiley & Sons, Ltd.     

Composite Sand Bodies Architecture of Deep-Water Turbidite Channels in the Niger Delta Basin

Abstract: Deep-water turbidite channels have attracted much attention as a focused issue in petroleum exploration and development. Extensive studies have been performed on the architecture of turbidite channels, and most researches have focused on their geometric shapes, sedimentary processes and controlling factors. However, little attention has been paid to the distribution patterns, distribution laws and quantitative studies of composite sand bodies of turbidite channels. Taken one slope area of the Niger Delta Basin as an example, this study conducted a semi-quantitative to quantitative analysis on architecture of composite sand bodies of turbidite channels based on cores, well logging and seismic surveys. It is shown that turbidite channel systems can be classified as confined and unconfined channel systems. For confined channel systems, the vertical evolution process involves four stages. The sinuosity of a channel system is controlled by slope, with a negative power function relationship between them. When slope gradient reaches four degrees, the channel system is nearly straight. Based on the migration direction and migration amount of single channels within channel complexes, channel composite patterns can be divided into four classes (the lateral composite, en-echelon composite, swing composite and vertical composite) and several subclasses. Various channel composite patterns show specific distribution laws spatially. For meandering channel complexes at the middle-late evolution stage of confined channel systems, the lateral migration amongst single channels shows the features of integrity and succession. The sinuosity of single channels in the late period is greater than that in the early period, and cut-offs may occur locally when the sinuosity is larger than five degrees. This study provides a better understanding for the geological theory of deep-water sedimentary, and also improves exploitation benefits of this type of reservoirs.