Sedimentary characteristics and tectonic setting of sublacustrine fans in a half-graben rift depression,Beibuwan Basin,South China Sea

Drilling has shown that there is a large petroleum reserve in the Liushagang Formation of the Fushan Depression, South China Sea from reservoirs of the sublacustrine fans. To reduce the risk associated with exploration, the sedimentary characteristics of the sublacustrine fans should be identified and described. Analysis of the drilling cores, well data and 3D seismic data was conducted to identify and interpret the sublacustrine fans which formed in a lacustrine succession as the low-stand fan of the 2nd member of Liushagang Formation (SQEls2). The reservoirs were commonly associated with pebbly conglomerates, mudstone shivers, muddy debris, various deformation structures including micro-faults, liquified deformation structure, ball and pillow structure, slump and stress-release deformation. Further contrastive analysis of sedimentary characteristics and palaeogeomorphology between the western and eastern sublacustrine fans indicates that they belong to two different types of sublacustrine system in continental basins. More specifically, the western fan, controlled by the multi-level step-fault belt, is a typical gravel-rich sublacustrine system which is characterised by structurally controlled, high gradient (2.8–3.3°), admixtures of muddy debris and pebbly conglomerates and poor reservoir quality, while the eastern fan, controlled by the flexure slope-break belt, is a sand-rich sublacustrine system dominated by relatively low gradient (2.0–2.5°), general fining-upwards trend with good reservoir quality. Therefore, the development of future exploration should be conducted at different levels in the Fushan Depression.     

Controls on the development of valleys,canyons, and unconfined channel–levee complexes on the Pleistocene Slope of East Kalimantan,Indonesia

Shallow 3D seismic data show contrasting depositional patterns in Pleistocene deepwater slopes of offshore East Kalimantan, Indonesia. The northern East Kalimantan slope is dominated by valleys and canyons, while the central slope is dominated by unconfined channel–levee complexes. The Mahakam delta is immediately landward of the central slope and provided large amounts of sediments to the central slope during Pleistocene lowstands of sea level. In the central area, the upper slope contains relatively straight and deep channels. Sinuous channel–levee complexes occur on the middle and lower slope, where channels migrated laterally, then aggraded and avulsed. Younger channel–levee complexes avoided bathymetric highs created by previous channel–levee complexes. Levees decrease in thickness down slope. Relief between channels and levees also decreases down slope.North of the Mahakam delta, siliciclastic sediment supply was limited during the Pleistocene, and the slope is dominated by valleys and canyons. Late Pleistocene rivers and deltas were generally not present on the northern outer shelf. Only one lowstand delta was present on the northern shelf margin during the upper Pleistocene, and sediments from that lowstand delta filled a pre-existing slope valley complex and formed a basin-floor fan. Except for that basin-floor fan, the northern basin floor shows no evidence of sand-rich channels or fans, but contains broad areas with chaotic reflectors interpreted as mass transport complexes. This suggests that slope valleys and canyons formed by slope failures, not by erosion associated with turbidite sands from rivers or deltas. In summary, amount of sediment coming onto the slope determines slope morphology. Large, relatively steady input of sediment from the Pleistocene paleo-Mahakam delta apparently prevented large valleys and canyons from developing on the central slope. In contrast, deep valleys and canyons developed on the northern slope that was relatively “starved” for siliciclastic sediment.     

Sedimentary facies associations and sequence stratigraphy of source and reservoir rocks of the lacustrine Eocene Niubao Formation (Lunpola Basin,central Tibet)

The Eocene Niubao Formation of the Lunpola Basin, a large Cenozoic intermontane basin in central Tibet, is an important potential hydrocarbon source and reservoir unit. It represents ∼20 Myr of lacustrine sedimentation in a half-graben with a sharply fault-bounded northern margin and a low-angle flexural southern margin, resulting in a highly asymmetric distribution of depositional facies and sediment thicknesses along the N-S axis of the basin. An integrated investigation of well-logs, seismic data, cores and outcrops revealed three third-order sequences (SQ1 to SQ3), each representing a cycle of rising and falling lake levels yielding lowstand, transgressive, and highstand systems tracts. Lowstand systems tracts (LST) include delta and fan delta facies spread widely along the gentle southern margin and concentrated narrowly along the steep northern margin of the basin, with sublacustrine fan sand bodies extending into the basin center. Highstand systems tracts (HST) include expanded areas of basin-center shale deposition, with sublacustrine fans, deltas and fan deltas locally developed along the basin margins. Sequence development may reflect episodes of tectonic uplift and base-level changes. The southern margin of the basin exhibits two different structural styles that locally influenced sequence development, i.e., a multi-step fault belt in the south-central sector and a flexure belt in the southeastern sector. The sedimentary model and sequence stratigraphic framework developed in this study demonstrate that N2 (the middle member of Niubao Formation) exhibits superior hydrocarbon potential, characterized by thicker source rocks and a wider distribution of sand-body reservoirs, although N3 (the upper member of Niubao Formation) also has good potential. Fault-controlled lithologic traps are plentiful along the basin margins, representing attractive targets for future exploratory drilling for hydrocarbons.     

济阳坳陷博兴洼陷西部沙三段层序地层

选取以基准面为参照面的高分辨率层序地层学的理论与分析技术,对博兴洼陷西部沙三段开展层序地层分析工作。在博兴洼陷沙三段识别出5个层序界面和4个较大规模的洪泛面,由此将研究层段划分为4个长期基准面旋回(相当于3级层序),并通过长期旋回内部次级转换面的识别,细分出8个中期旋回(大致相当于4级层序)。通过对比建立了研究区的高分辨率层序地层格架,并分析了各层序的地层发育特征。以层序格架为基础,探讨了研究区各层序的沉积演化特征,建立了辫状三角洲—浊积扇层序发育模式,认为研究区辫状三角洲和浊积扇均具有加积作用特点;斜坡区为辫状三角洲发育区,而洼陷区为浊积扇发育区;中期基准面旋回下降期辫状三角洲发育,上升期浊积扇发育;浊积扇体的发育规模与湖泛规模相关。综合分析认为,浊积扇是形成岩性圈闭的主要储集砂体类型,其发育的有利层位是MSC8、MSC7、MSC6、MSC5旋回的上升半旋回,岩性圈闭发育的有利区是博兴南部斜坡坡折带之下的洼陷区。     

渤海湾盆地渤中凹陷古近系沉积体系演化及物源分析

综合运用地质、测井、地震及分析化验等资料,对渤海湾盆地渤中凹陷古近系沉积体系进行了较深入的研究,研究表明渤中凹陷古近系的沉积体系主要受构造升降和湖平面变化的控制,经历了3期裂陷和湖侵,发育5套沉积体系,其中沙河街组沉积时期为裂陷期,以扇三角洲、湖底扇沉积为主,并发育特征的滩坝及浅水台地相沉积;东营组沉积时期为湖侵期,主要发育大型湖泊三角洲沉积,并逐渐向辫状河相过渡。构造及沉积体系分析认为,沙三段沉积时期物源丰富,主要来自石臼坨凸起、渤南和庙西凸起,沙一、二段沉积时期物源有限,东三沉积期物源主要来自石臼坨和沙东南凸起,东二沉积期大面积的湖侵使得本区处于浅湖-半深湖环境,凹陷周边大量古水系将石臼坨凸起、沙垒田凸起的物源带入凹陷中沉积,使得大型三角洲叠覆体广泛发育。     

东营凹陷低渗透油藏分布规律及储层改造效果

东营凹陷2001年之前探明的低渗透油藏主要分布在洼陷带、中央背斜带及北部陡坡带,以沙三段深水浊积扇及沙四段滨浅湖相砂岩滩坝、扇三角洲前缘等沉积体系为主。油藏类型主要是岩性油藏,其次为构造—岩性复合型油藏。低渗透油藏以中深层、常压-超高压、低产、中产为特征,多为特小型、小型油藏,储量丰度为低丰度~特低丰度。低渗透油藏的探井试油过程中,经历了从酸化逐步到压裂的技术发展过程。统计探井的试油效果表明,沙四段碳酸盐含量较高的砂岩低渗透油藏,酸化效果较好;黏土含量较高的沙三段低渗透油藏,压裂效果较好。     

青东凹陷断裂特征及其对沉积的控制作用

通过对青东凹陷古近纪的断裂体系和主要同沉积断裂的活动和特征分析,表明区内主要发育NNE、EW、NW向三组断裂体系,NNE向的凹陷边界断裂青东1号断层和EW向的主要二级同沉积断层f1、f2控制了凹陷内次级构造单元的划分,凹陷由北向南依次划分为北部深洼、北部凸起、中部次洼、南部凸起、南部次洼、西南缘缓坡带以及东部陡坡带等7个次级构造单元。研究表明,凹陷内各洼陷的沉降中心在古近纪发生了明显的分异和迁移,这些变化受控于区内主要同沉积断裂的差异活动和演化,青东1号断裂和f3断裂在古近纪的持续活动共同控制了北部深洼的沉积充填,f1和f4断裂分别控制了中部次洼和南部次洼的发育;主要断裂的活动及其组合样式控制着湖底扇、扇三角洲、辫状河三角洲等粗碎屑沉积体系的发育。与生油洼陷相邻的主要同沉积断裂形成的断裂带具备形成砂岩油气藏的各种有利条件,其中东部盆缘断裂带是区内砂岩油气藏勘探最有利的区带。     

北黄海盆地东部坳陷东南部层序地层特征及沉积体系

以层序地层学为理论指导,通过对地震、钻井、测井及古生物等资料的研究,建立了北黄海盆地东部坳陷东南部的层序格架。研究区的中生界可分为1个一级层序、2个二级层序、5个三级层序,在此层序格架内进行了沉积相划分及沉积体系研究,厘定了扇三角洲、辫状河三角洲、浊积扇和湖泊沉积等4种沉积体系。断陷早期,JSQ1的西部与东部分别发育了中型的扇三角洲与辫状河三角洲沉积体系;断陷中期,西部的扇三角洲沉积体系逐步扩展并在其前端多发育小型浊积扇,东部的辫状河三角洲沉积体系亦持续扩张且在JSQ4沉积期规模达到最大;断陷晚期,KSQ1内仅发育盆缘的小型扇体和滨浅湖相沉积,东部、南部隆起区未接受沉积或沉积较薄并剥蚀殆尽。沉积体系的平面展布和纵向演化受古构造与古地貌的控制。     

造山带大陆斜坡沉积类型

造山带大陆斜坡可以划分出有扇与无扇大陆斜坡两种沉积类型。有扇大陆斜坡以近源浊积岩、碎屑流为特色;无扇大陆斜坡以远源浊积岩、等深岩、半远洋沉积为特色。因而大陆斜坡也是一个多种沉积作用活跃的场所。造山带深水沉积绝不是常人认为是单一的复理石、千篇一律的重力流,而是内容十分丰富的沉积作用非常活跃和堆积的场所。     

Slope and basin-floor reservoirs from the Miocene and Pliocene of the Veracruz Basin,southeastern Mexico

A regional study of the Veracruz Basin provided an excellent view of long-term deepwater sedimentation patterns from an evolving foreland-type basin. The regional seismic and well-log data set allows for an accurate reconstruction of slope and basin-floor depositional patterns, lithologic compositions, and paleogradients from a continuous succession of bathyal strata that span the Miocene to the lower Pliocene. Variations in Miocene and Pliocene deepwater reservoirs can be linked to prevailing slope characteristics. The Miocene basin had a high-gradient, tectonically generated slope, and the Pliocene basin had a low-gradient constructional slope. The Miocene basin owes its steep margin to the tectonic stacking of early Tertiary, Laramide-age thrust sheets. The Miocene margin shed a mixture of coarse elastic sediments (sands, gravels, and cobbles) and fines (silts and clays) that were transported into the deep basin via turbidity currents and debris flows. Channelized deposits dominate the Miocene slope, and reservoirs occur in long-lasting basement-confined canyons and shorter-lived shallower erosional gulleys. Thick and areally-extensive basin-floor fans exist outboard of the strongly channelized Miocene slope. Fan distribution is strongly controlled by synsedimentary contractional anticlines and synclines. In contrast, the latest Miocene to early Pliocene basin development was dominated by a strongly prograding wedge of shelf and slope deposits that was induced by volcanogenic uplift and increased sediment supply. During this phase, turbidite reservoirs are limited to narrow and sinuous deepwater channels that reside at the toe of the constructional clinoforms and areally limited, thinner basinal fans.     

海盆沉积“源-汇”系统分析:南海北部珠江海谷-西北次海盆第四纪深水浊积扇

运用近年来采集的高分辨率地震资料和多波束测深数据,在珠江海谷及西北次海盆深海平原区发现大规模发育的第四纪重力流沉积体系,该沉积体系沿珠江海谷以北西-南南东方向贯穿整个北部陆坡,进入西北次海盆后呈扇形展开,形成珠江海谷-西北次海盆大型深水浊积扇系统。据沉积体系空间展布特征差异,将珠江海谷划分为北、中、南三段,北段为过路侵蚀和水道下切,中段以水道充填和天然堤沉积为主,南段以水道-天然堤和朵叶体沉积共存为特征,揭示出北部陆坡珠江海谷是珠江口外陆缘物质输送海盆深海平原的主要通道;海盆区总体以朵叶体发育为特色,呈扇形展布。深水扇系统可分为三期次沉积体,其区域结构记录了重力流沉积物从侵蚀、卸载到南海海盆作为限制性盆地接收陆源沉积物的全过程,为“源-渠-汇”的研究构建了一个完美的范例。本文以珠江海谷-西北次海盆第四纪深水浊积扇沉积体系为例,完整地揭示了水道-扇体的组构和特征,清晰呈现了陆坡-海盆砂体展布的规律,可为建立南海北部新近纪早期深水扇形成模式提供参考,有助于指导南海深水油气勘探工作。     

Seismic stratigraphy and geomorphology of a tide or wave dominated shelf-edge delta (NW Australia): Process-based classification from 3D seismic attributes and implications for the prediction of deep-water sands

Shelf-edge deltas (SEDs) forming during periods of relative sea level fall and lowstand are generally efficient in transferring sediments to the slope and basins, and their identification in subsurface data is often considered a good indication of coeval development of slope and basin-floor turbidite reservoirs. This study investigates the seismic stratigraphic evolution of a forced-regressive and normal regressive shelf-edge delta (Bonaparte SED) that accumulated on the edge of the NW Australian margin during the late Quaternary. High resolution 2D and 3D reflection seismic data allow reconstruction of the main episodes of delta progradation and understanding of the extrinsic and intrinsic controls on their deposition. The lack of a significant turbidite system forming off the shelf-edge delta throughout the Quaternary is a striking feature of the Bonaparte SED. Instead, slope sedimentation is dominated by the accumulation of plume-derived mud belts and their reworking through mass-transport processes. Seismic geomorphology permits interpretation of the process regime of the youngest shelf-edge depocentre by applying a new process-based shallow-marine classification scheme to the 3D seismic attribute data. Results suggest either a tide or wave dominated delta with fluvial processes being of tertiary significance. A tide or wave-dominated, fluvial-affected shelf-edge delta classification is consistent with the paleogeographical reconstruction of the margin during the last glacial maximum (ca. 25 ka BP). The comparison of this mixed-process shelf-edge delta and starved slope system with a fluvial-dominated counterpart with significant sandy slope deposits emphasizes the potential of assessing the process regime of shelf-edge deltas as a rapid, first approach for predicting the presence or absence of coeval slope and basin-floor reservoirs.     

A seismic geomorphology study of the fluvial and lacustrine-delta facies of the Cretaceous Quantou-Nenjiang Formations in Songliao Basin,China

With the aid of seismic geomorphology method, depositional systems such as fluvial-delta and turbidity current of the Cretaceous Quantou-Nenjiang Formations in Sangliao Basin were studied in detail as well as the morphology, dimension, depositional structures and boundaries of these sedimentary bodies. A geological model of a point bar in a fluvial system and the method to identify paleocurrent direction were proposed. The delta of Yaojia Formation with a gentle slope less than 1.4‰ in trangressive system tract (TST) was controlled by lake waves. Subaqueous distributary channels were widely developed in large-scale delta front with a width more than 16 km. Fluvial-dominated deltas with leaf and bird's foot shapes were widespread in highstand system tract (HST) of Qinshankou and Nengjiang Formation with moderately high slope gradients of 4‰ and 6.7‰.The width of the leaf-like and bird's foot delta front ranges from 1 km to 4 km and 3 km–5 km respectively. The mouth bar were well preserved due to the poorly developed widely distributed subaqueous distributary channels and the delta plains having widths of 9 km–15 km, 16 km-25 km respectively. Many turbidity current systems were recognized in the TST of the first member of Nengjiang Formation and the distribution area is about 10,000 km². Fourteen sublacustrine fans with different dimension were formed by ten fluvial-delta systems extending 30 km–70 km toward the lake from the west and south. With the application of seismic geomorphology, the analysis of fluvial system, delta system and turbidity current system could switch from approximation to quantitative analysis. Sedimentary model proposed for point bars and the quantitative analysis of delta system could provide new technical support for exploration and drilling plan. The research on turbidity current systems will also be beneficial for new exploration targets.     

上新世——早更新世青藏高原北缘隆升的磁性地层学证据

对新疆叶城剖面西域砾岩及下伏第三纪地层的磁性地层学研究表明 ,西域砾岩的沉积时代为晚上新世至早更新世 ,磁性地层年龄为 3.5至 <1.8Ma。阿图什组沉积于早上新世 ,古地磁年龄为 4 .6～ 3.5 Ma。阿图什组以砂岩和粉砂岩为主夹薄层砾岩 ,为河流相及冲积扇前缘相。西域砾岩以厚层砾岩为主夹风成粉砂岩 ,为典型洪积—冲积扇堆积。西域砾岩的沉积反映了青藏高原北缘晚上新世至早更新世强烈的隆起和剥蚀     

Rhone Deep-Sea Fan: A review

The Rhone Fan is a large Plio-Pleistocene turbidite deposit in the western Mediterranean Sea. The fan is fed from the broad Rhone River delta, but only one canyon, the Petit-Rhone, has fed most of the major turbidite depositional sequences that have been mapped. Slumping of sediment from intercanyon areas on the delta slope also has provided much sediment for the fan. The lack of Recent turbidite deposition on the fan suggests that turbidite sedimentation dominates during glacial low stands of sea level, building major leveed valley sequences, while surficial slumping of the valley levee deposits and pelagic sedimentation seem to mark high stands of sea level during interglacial periods. Margin setting represents fan and/or source area     

渤海湾盆地沙南凹陷曹妃甸14-5区沙河街组砂体成因分析

西洼沙河街组沉积位于渤海湾盆地沙南凹陷,从Es3m到Es1,沙南凹陷经历四期裂陷幕,其间发育的不整合面T5使区域古地貌隆升,形成四期的三级层序变化旋回,并在西洼东—西向中央断裂带的控制下形成南、北物源和北部断裂坡折。双向物源和断裂坡折控制沙河街组沉积,形成多类型沉积,其中Es3m以半深湖—深湖、富泥质的湖底扇为特征,形成弱水动力沉积环境;Es3u以半深湖—深湖、富砂质的湖底扇和火山岩为特征,形成局部动荡的水动力沉积环境;Es12沉积较薄,形成独具特色的多样式、多类型沉积,包括半深湖—深湖、扇三角洲前缘、前缘斜坡扇、滑塌体、湖底扇及火山岩沉积,以及牵引流与重力流并存,以重力流为沉积主导。层段内的沉积序列及演化特征决定该区域形成南、北物源控制的4种成因砂体,南物源的晚期成砂机制,包括扇三角洲前缘砂、前缘斜坡扇砂,北物源的中晚期成砂机制,包括滑塌体砂和湖底扇砂。因此,西洼区域勘探以寻找岩性圈闭、构造—岩性圈闭为主,断裂与砂体的空间匹配关系决定了圈闭的有效性。     

Rhone Deep-Sea Fan: A review

The Rhone Fan is a large Plio-Pleistocene turbidite deposit in the western Mediterranean Sea. The fan is fed from the broad Rhone River delta, but only one canyon, the Petit-Rhone, has fed most of the major turbidite depositional sequences that have been mapped. Slumping of sediment from intercanyon areas on the delta slope also has provided much sediment for the fan. The lack of Recent turbidite deposition on the fan suggests that turbidite sedimentation dominates during glacial low stands of sea level, building major leveed valley sequences, while surficial slumping of the valley levee deposits and pelagic sedimentation seem to mark high stands of sea level during interglacial periods.     

Growth of a post-Little Ice Age submarine fan, Glacier Bay, Alaska

A small Holocene fan is forming where Queen Inlet, a hanging valley, enters West Arm fjord, Glacier Bay, Alaska. Queen fan formed in the last 80 years following retreat of the Little Ice Age glacier that filled Glacier Bay about 200 yr BP. It was built mainly by a turbidite system originating from Carroll Glacier delta, as the delta formed in the early 1900s at the head of Queen Inlet. The Late Holocene Queen fan is comparable to large Pleistocene fans that formed in the Gulf of Alaska and differs from trough-mouth fans formed by cooler climate glacier systems. Received: 7 January 1999 / Revision received: 3 June 1999     

辽河拗陷东部凹陷南部地区古近系沉积体系与储层评价

Detailed studies on a number of core sections,well logs and seismic date of the paleogene systems of the southern part of eastem sag in Liaohe Depression revealed theat six sedimentary systems,i,e.delta,lake,fan delta,braided river,delta,river and alluvial fan,were distinguished,The sedimentation in the studied area remarkably controlled reservoir and the variability of sedimentary facied caused the diversity of reservior sand bldies and the inhomogeneity of reservoir properties plane distribution;The best reservoir properties are the sand bodies of deltaic front and braided-river deltaic front;the better are the sand bodies of braided-river deltaic plain,deltaic front,braided river and meandering river;the medium reservoir properties are the sand bodies of delta plain,the fan-delta front,the alluvial-middle fan,beach-bar and turbidite fan;the wores are the sand bodies of upper fan and lower fan of alluvial fan,alluvial plain.The favorable sedimentary facies belt controlled the distribution of favorable reservoir and it was an important evidence for prediction favorable stratigraphiv reservoir.     

Tectono-sequence stratigraphic analysis of the Lower Cretaceous Abu Gabra Formation in the Fula Sub-basin,Muglad Basin,southern Sudan

The Fula Sub-basin of the Muglad Basin of southern Sudan is an active-fault bounded basin with an area of approximately 3300 km². The Lower Cretaceous Abu Gabra Formation formed during the first of three rifting cycles. It can be subdivided into five 3rd-order sequences named SQA∼SQE from bottom to top, indicating five stages of tectonostratigraphy and tectonosedimentary evolution. The spatial distribution and temporal evolution of clastic depositional systems are described in this paper based on integrated analysis of seismic, core and well logging data. In the Abu Gabra Formation of the Fula Sub-basin, a variety of depositional systems are recognized, namely, fan delta, braided delta, delta, sublacustrine fan and lacustrine system. The Fula Sub-basin has undergone a complex and phased rifting evolution, and a high abundance of transfer zones developed, causing the resulting distribution and architecture of both the sequence and depositional system to be controlled by various types of transfer zones. The following three types of sequence architectures from northern to southern part of the Fula Sub-basin have been identified: simple dustpan-shaped sequence architecture in the north, transfer-zone sequence stratigraphic architecture in the middle and graben-shaped sequence architecture in the south. The sequence architecture is under the control of the large-scale central transfer zone, and nine models are built to study the effect of at least three categories of small-scale transfer zones on the depositional systems in the Fula Sub-basin. The small-scale transfer zones play significant roles in basin fill, primarily in controlling of the positions of deposit-input points. This study provides valuable insights into tectonic control of depositional systems and sequence architectures in a continental rift basin such as the Fula Sub-basin.