Coupling relationship and genetic mechanisms of shelf-edge delta and deep-water fan source-to-sink:A case study in Paleogene Zhuhai Formation in south subsag of Baiyun Sag,Pearl River Mouth Basin,China

The coupling relationship between shelf-edge deltas and deep-water fan sand bodies is a hot and cutting-edge field of international sedimentology and deep-water oil and gas exploration.Based on the newly acquired high-resolution 3D seismic,logging and core data of Pearl River Mouth Basin(PRMB),this paper dissected the shelf-edge delta to deep-water fan(SEDDF)depositional system in the Oligocene Zhuhai Formation of Paleogene in south subsag of Baiyun Sag,and revealed the complex coupling relationship from the continental shelf edge to deep-water fan sedimentation and its genetic mechanisms.The results show that during the deposition of the fourth to first members of the Zhuhai Formation,the scale of the SEDDF depositional system in the study area showed a pattern of first increasing and then decreasing,with deep-water fan developed in the third to first members and the largest plane distribution scale developed in the late stage of the second member.Based on the development of SEDDF depositional system along the source direction,three types of coupling relationships are divided,namely,deltas that are linked downdip to fans,deltas that lack downdip fans and fans that lack updip coeval deltas,with different depositional characteristics and genetic mechanisms.(1)Deltas that are linked downdip to fans:with the development of shelf-edge deltas in the shelf area and deep-water fans in the downdip slope area,and the strong source supply and relative sea level decline are the two key factors which control the development of this type of source-to-sink(S2S).The development of channels on the continental shelf edge is conducive to the formation of this type of S2S system even with weak source supply and high sea level.(2)Deltas that lack downdip fans:with the development of shelf edge deltas in shelf area,while deep water fans are not developed in the downdip slope area.The lack of“sources”and“channels”,and fluid transformation are the three main reasons for the formation of this type of S2S system.(3)Fans that lack updip coeval deltas:with the development of deep-water fans in continental slope area and the absence of updip coeval shelf edge deltas,which is jointly controlled by the coupling of fluid transformation at the shelf edge and the“channels”in the continental slope area.

Deep-water Fan Systems and Petroleum Resources on the Northern Slope of the South China Sea

The shallow shelf delta/strand arenaceous-pelitic deposit region in the north of the Pearl River mouth basin, sitting on the northern continental shelf of the South China Sea, has already become an important oil production base in China. Recent researched has revealed that a great deal of deep-water fans of great petroleum potentiality exist on the Baiyun deep-water slope below the big paleo Pearl River and its large delta. Based on a mass of exploration wells and 2-D seismic data of the shallow shelf region, a interpretation of sequence stratigraphy confirmed the existence of deep-water fans. The cyclic falling of sea level, abundant detrital matter from the paleo Pearl River and the persistent geothermal subsidence in the Baiyun sag are the three prerequisites for the formation and development of deep-water fans. There are many in common between the deep-water shelf depositional system of the northern South China Sea and the exploration hotspots region on the two banks of the Atlantic. For example, both are located on passive continent margins, and persistent secular thermal subsidence and large paleo rivers have supplied abundant material sources and organic matter. More recently, the discovery of the big gas pool on the northern slope of the Baiyun sag confirms that the Lower Tertiary lacustrine facies in the Baiyun sag has a great potentiality of source rocks. The fans overlying the Lower Tertiary source rocks should become the main exploration areas for oil and gas resources.

Characteristics of the turbidite fan in the Wenchang Formation of the Enping Sag, Pearl River Mouth Basin, China and its hydrocarbon significance

A turbidite fan in the Eocene upper Wenchang Formation in the Enping Sag, Pearl River Mouth Basin （PRMB） has been studied using seismic, logging and borehole data. The fan is characterized by parallel progradation on the dip seismic profile and is mound-shaped or lenticular-shaped on the strike seismic profile. The study of the core and logging data from well EP17-3-1, which is located in the front side of the turbidite fan, shows that this fan is a set of normal grading sand beds, interbedded within thick dark grey mudstones of semi-deep to deep lake deposits in the Wenchang Formation. The fan is interpreted as a sand/mud-rich turbidite fan that has an area of over 140 km2 and a maximum thickness of over 340 m. Combined with a study of the regional geological background and previous provenance analysis of the Eocene Wenchang Formation, the main potential provenances for the turbidite fan are considered to be the Panyu low-uplift and northern fault terrace zone. The Enping Sag is considered to be a half graben-like basin whose north side is faulted and whose south side is overlapped. Basement subsidence in the Eocene was mainly controlled by boundary faults which dip relatively steeply on the north side, causing the subsidence center of the Enping Sag in this stage to be close to the north boundary faults. Sustained faults developed in the Enping Sag during the Eocene caused an increase of the relative height difference between the north and the south uplift zone in the Enping Sag. Affected by the second episode of the Zhuqiong movement （39-36 Ma） in late Eocene, sediments which had accumulated on the Panyu low-uplift zone were triggered and moved toward the subsidence center of the Enping Sag and formed the turbidite fan. The second episode of the Zhuqiong movement is the most important triggering factor for the formation of the turbidite fan in the Wenchang Formation. Seismic attribute characterization shows that the low frequency energy is enhanced and high frequency energy is weakened when seismic waves propagate through the oil-bearing zone in this fan. Amplitude versus offset （AVO） anomalies are observed in the seismic data and abnormally high pressure is encountered. The turbidite fan in the Wenchang Formation has provided important information for sedimentary evolution in deep layers of the Enping Sag and pointed to a new direction for the hydrocarbon exploration in the study area.

Control effects of the synsedimentary faults on the basin-marginal fans in the central part of the deep-water area of early Oligocene Qiongdongnan Basin, South China Sea

The synsedimentary faults and basin-marginal fans located in the central part of the deep-water area of the early Oligocene Qiongdongnan Basin have been investigated using seismic profiles,boreholes,and well-log data.Through the formations of the characterized paleogeomorphology,such as transverse anticlines,fault ditches,and step-fault belts,the synsedimentary faults are known to have controlled the development position,distribution direction,and extension scales of the basin-marginal fans.For example,at the pitching ends of two adjacent faults,transverse anticlines developed,which controlled the development positions and distributions of the fans.During the early Oligocene,the faults controlled the subsidence center,and fault ditches were formed at the roots of the faults.In the surrounding salient or low salient areas,which were exposed as provenance areas during early Oligocene,the fault ditches acted as the source channels and determined the flow paths of the clastics,where incised valley fills were obviously developed.The fault ditches which developed in the sedimentary basins were able to capture the drainage systems and influenced the distributions of the fans.The large boundary faults and the secondary faults generated two fault terraces and formed step-fault belts.The first fault terrace caused the clastics to be unloaded.As a result,fans were formed at the entrance to the basin.Then,the second fault terrace caused the fans to move forward,with the fans developing in a larger extension scale.The results obtained in this study will potentially be beneficial in the future prospecting activities for reservoirs and coalmeasure source rocks in the basins located in the deep-water areas of the South China Sea.

Structural characteristics and deep-water hydrocarbon accumulation model of the Scotian Basin, Eastern Canada

Commercial hydrocarbon reservoirs have been discovered in shallow-water areas of the Scotian Basin, Eastern Canada. However, knowledge about the structure and hydrocarbon accumulation characteristics of the basin is still insufficient, which constrains the oil and gas exploration in deep-water areas. Based on comprehensive data of magnetic anomalies, seismic survey, and drilling, this study determines the structure characteristics of the Scotian Basin and its hydrocarbon accumulation conditions in deep waters and evaluates the deep-water hydrocarbon exploration potential. The transform faults and basement structures in the northern basin control the sedimentary framework showing thick strata in east and thin strata in west of the basin. The bowl-shaped depression formed by thermal subsidence during the transitional phase and the confined environment (micro basins) caused by salt tectonics provide favorable conditions for the development of source rocks during the depression stage (also referred to as the depression period sequence) of the basin. The progradation of large shelf-margin deltas during the drift phase and steep continental slope provide favorable conditions for the deposition of slope-floor fans on continental margins of the basin. Moreover, the source-reservoir assemblage comprising the source rocks within the depression stage and the turbidite sandstones on the continental margin in the deep waters may form large deep-water turbidite sandstone reservoirs. This study will provide a valuable reference for the deep-water hydrocarbon exploration in the Scotian Basin.

A global satellite survey of density plumes at river mouths and at other environments: Plume configurations, external controls, and implications for deep-water sedimentation

The U. S. National Aeronautics and Space Administration(NASA) has archived thousands of satellite images of density plumes in its online publishing outlet called 'Earth Observatory' since 1999. Although these images are in the public domain, there has not been any systematic compilation of configurations of density plumes associated with various sedimentary environments and processes. This article, based on 45 case studies covering 21 major rivers(e.g., Amazon, Betsiboka, Congo [Zaire], Copper, Hugli [Ganges], Mackenzie, Mississippi, Niger, Nile, Rhone, Rio de la Plata, Yellow, Yangtze, Zambezi, etc.) and six different depositional environments(i.e., marine, lacustrine, estuarine, lagoon, bay, and reef), is the first attempt in illustrating natural variability of configurations of density plumes in modern environments. There are, at least, 24 configurations of density plumes. An important finding of this study is that density plumes are controlled by a plethora of 18 oceanographic, meteorological, and other external factors. Examples are: 1) Yellow River in China by tidal shear front and by a change in river course; 2) Yangtze River in China by shelf currents and vertical mixing by tides in winter months; 3) Rio de la Plata Estuary in Argentina and Uruguay by Ocean currents; 4) San Francisco Bay in California by tidal currents; 5) Gulf of Manner in the Indian Ocean by monsoonal currents; 6) Egypt in Red Sea by Eolian dust; 7) U.S. Atlantic margin by cyclones; 8) Sri Lanka by tsunamis; 9) Copper River in Alaska by high-gradient braid delta; 10) Lake Erie by seiche; 11) continental margin off Namibia by upwelling; 12) Bering Sea by phytoplankton; 13) the Great Bahama Bank in the Atlantic Ocean by fish activity; 14) Indonesia by volcanic activity; 15) Greenland by glacial melt; 16) South Pacific Ocean by coral reef; 17) Carolina continental Rise by pockmarks; and 18) Otsuchi Bay in Japan by internal bore. The prevailing trend in promoting a single type of river-flood triggered hyperpycnal flow is flawed because there are 16 types of hyperpycnal flows. River-flood derived hyperpycnal flows are muddy in texture and they occur close to the shoreline in inner shelf environments. Hyperpycnal flows are not viable transport mechanisms of sand and gravel across the shelf into the deep sea. The available field observations suggest that they do not form meter-thick sand layers in deep water settings. For the above reasons, river-flood triggered hyperpycnites are considered unsuitable for serving as petroleum reservoirs in deep-water environments until proven otherwise.

Bed type and flow mechanism of deep water sub-lacustrine fan fringe facies:an example from the Middle Permian Lucaogou Formation in Southern Junggar Basin of NW China

Submarine or sub-lacustrine lobe deposits are important reservoirs,but the fan fringe deposits form heterogeneities within deep water fan deposits.Fan fringe facies records the complex sediment gravity flow types.By understanding of the bed types and flow mechanisms,we can identify the fan fringe deposit,which aids in the reconstruction of deep water fan and reservoir evaluations.The Jiucaiyuanzi and Dalongkou sections in the West Bogda Mountains preserve well-exposed 536-m and 171-m thick successions,respectively,of a deep water lacustrine depositional system from the Middle Permian Lucaogou Formation.Bed types of the Lucaogou Formation include high-density turbidite,low-density turbidite,incomplete Bouma-type turbidite,hybrid event beds,and slump deposits.The Lucaogou Formation is interpreted here as a fan fringe facies due to the thin bed thickness that characterize turbidites and hybrid event beds,as well as the predominance of the isolated sheet architecture.Previous studies suggest that these deposits were considered as deposited in a deep water setting due to the absence of wave-related structures.The presence of abundant mud clasts in massive medium-coarse grained sandstone beds reflects the significant erosional capability and interactions between high-density turbidity currents and lake floor.The fan fringe facies here contains amalgamated and thick-bedded homolithic facies(~30%)and thin-bedded heterolithic facies(~70%).The examination of the bed type is of wider significance for facies prediction and reservoir heterogeneity in the sub-lacustrine fan fringe facies.

沾化凹陷孤北洼陷东三段沉积体系类型及差异分布

沾化凹陷孤北洼陷东营组油气资源十分丰富,但沉积类型及其分布制约了油气勘探方向和精细勘探。文中综合孤北洼陷钻测井、岩心和三维地震资料,详细研究了东营组东三段沉积类型及其时空分布特征。结果表明:1)孤北洼陷东三段(Ed3)发育近岸水下扇、辫状河三角洲、滑塌浊积扇、滨浅湖和半深湖—深湖沉积。2)东三段沉积类型时空分布差异性特征明显。西缘陡坡带发育近源砂砾岩与暗色泥岩组合的近岸水下扇;南侧和东侧缓坡带发育辫状河三角洲;洼陷内发育湖相泥岩,断裂带附近多为滑塌浊积扇。3)沉积相带影响了储层质量。距源区越远,结构成熟度越高,则有利储层越发育;滑塌浊积扇相带储层质量优于辫状河三角洲相带,近岸水下扇相带相对较差。

RECOGNITION OF THE SLUMPING TURBIDITE FANS IN DOWN-FAULTED LACUSTRINE BASINS

In the past 30 years, people have been paying attention to the relation between the deltas located on the slope of a basin border and the turbidite fans located in deep marine plain or deep lake plain, and have found that the turbidites related to the deltas develop in lacustrine basins better than in marine basins. And, it is difficult to use the standard sub-

浊积扇沉积构成及主要单元储层差异:以琼东南盆地梅山组为例

浊积扇沉积构成单元主要包含内扇沟道,中扇沟道、朵叶主体,外扇朵叶、席状砂以及扇缘薄层席状砂等,各单元储层物性差异大,直接影响勘探开发部署,值得开展深入系统研究。本文基于琼东南盆地梅山组20个已钻浊积扇的沉积构成单元储层特征分析,建立了浊积扇主要沉积构成单元的岩—电—震特征及识别标志,详细分析了其主要沉积构成单元的砂体规模、几何形态、厚度变化、粒度分布、储层非均质性等要素。结果表明,中扇沟道—朵叶结合部巨厚层块状砂岩、外扇朵叶厚层砂岩和席状砂岩储层内部均匀,物性较好;内扇沟道砂岩内部非均质严重,储层物性受到影响;扇缘薄层席状砂岩由于层薄、粒度细、高含泥及高含钙而致密。钻探证明多口探井因部署在内扇沟道上未获商业产能;新部署在中扇沟道—朵叶结合部巨厚层砂岩与外扇席状砂的探井均获得了商业成功。

南海东部深水浊积砂岩气藏储层精细描述与连通性研究

南海东部深水区油气资源丰富,深水重力流浊积砂岩展布复杂,砂体构型期次划分、构型单元叠置样式和连通关系直接制约气田的布井开发。以南海东部深水L气田为例开展研究,基于地震沉积学方法,运用沉积模式研究、复合水道体系构型及建模表征方法,开展了基于南海深水重力流复合砂体解剖,建立了本海域深水气田浊积水道复合砂体构型划分方案,开展了单期构型砂体空间演化和展布规律研究。研究成果表明:南海深水L气田浊积水道可划分为复合浊积体、复合水道和单一水道等3个级次,在气田内部平面上发育4条复合水道,纵向上发育2期河道,建立复合水道内部的沉积演化规律,明确了水道间的连通关系,并结合动态生产验证了连通关系的合理性,成功指导相邻B气田部署1口水平井,最高日产达130万方,生产效果较好。研究成果对推动周边气田开发及潜力勘探具有一定借鉴和启示意义。

刚果扇盆地X区块中新统浊积水道类型及沉积演化特征

刚果扇盆地中新统深水沉积领域已发现储量占盆地63%,是该盆地重要的勘探领域。基于井震资料搭建了中新统层序格架,并对浊积砂岩储层发育的主要沉积类型特征进行剖析,指出刚果扇盆地X区块发育侵蚀型、侵蚀-加积型和加积型三种水道类型,并依次剖析了各类水道内部充填结构特征;最后,结合区域构造活动和西非海平面变化,在层序地层格架下总结了浊积水道的沉积演化特征,明确了各三级层序内浊积水道类型、数量及规模,指出研究区主要的勘探层系和水道类型,为刚果扇盆地X区块岩性目标勘探提供了地质依据。

陆相浊流沉积体系与油气

研究描述了陆相浊流沉积体系的概念及形成的大地构造背景、沉积特征、储集性能、识别标志 ,其目的是提供一个概念格架 ,指导应用物探资料对陆相浊流沉积进行识别、解释和工业制图。

鄂尔多斯盆地西南地区上三叠统延长组沉积相及石油地质意义

鄂尔多斯盆地三叠系延长组主要发育东北和西南两大沉积体系 ,东北的河流三角洲体系已为大量的勘探研究资料所证实 ,而西南体系因受勘探程度限制 ,目前研究不够。本文通过最新钻探成果 ,结合盆地西南部露头资料 ,确立盆地西南地区三叠系延长组为冲积扇 -扇三角洲沉积体系 ,发育冲积扇、扇三角洲、湖泊(浊积 )相。冲积扇以西南缘平凉崆峒山和水河剖面为代表 ,扇三角洲及湖泊 (浊积 )相为区内钻井剖面所证实。长 6—长 8为区内主力油层组 ,地层保存完整 ,钻探程度相对较高。扇三角洲前缘砂体类型以水下分流河道为主 ,局部发育河口坝。浊积体以厚层块状为主。长 8亚期为扇三角洲前缘亚相最发育期 ,横向形成自西南向东北延伸的三支前缘砂体带 ,是石油聚集的重要区带 ;长 7亚期随着湖盆沉降 ,周边抬升强烈 ,湖岸较陡 ,大量发育浊积体系 ;长 6亚期湖退导致扇三角洲再次发育 ,但规模较长 8亚期小。扇三角洲前缘砂体单层厚度大 ,砂岩粒度较粗 ,颗粒分选及物性好 ,是石油富集的最有利相带。

精细层序地层格架与地震沉积学研究——以泌阳凹陷核桃园组为例

地震沉积学是当今国际沉积学研究热点,是利用地震资料研究沉积岩及其形成过程的一门新兴边缘学科,是进行高频层序和沉积体系研究的有效工具,在薄层砂体勘探和开发方面具有明显效果。根据泌阳凹陷深凹区地震资料质量高、断层少、发育滑塌浊积扇的地质特点,依据地震沉积学和层序地层学基本原理,建立了层序地层格架,将核桃园组划分为5个三级层序和8个四级层序。进而,在高频层序地层格架中,通过90°相位转换、分频处理、地层切片、岩心刻度等工作,开展了地震岩性学和地震地貌学研究,确定了核桃园组多物源供给形成辫状河三角洲-滑塌浊积扇沉积体系,滑塌浊积扇的发育明显受控于三角洲的发育演化,明确了滑塌浊积扇砂体的形态、分布及其与油气关系,指出核桃园组SQ2—SQ4是深凹区岩性油气圈闭的有利勘探层段,三角洲前缘和浊积扇砂体为有利勘探目标。

水下扇岩相特征及形成机制

２０世纪５０年代初期以来，沉积物重力流研究得到沉积学家们的广泛重视，特别是自６０年代末期，与沉积物重力流密切相关的水下扇研究成为沉积学领域的热点。通过对国内外大量沉积物重力流及水下扇研究成果的总结，结合我国中新生代陆相断陷盆地水下扇发育的特点，将水下扇的组成岩相划分为基质支撑砾岩相、颗粒支撑砾岩相、砾质砂岩相、块状砂岩相、经典浊积岩相。水下扇的形成机制系重力流成因。内扇以杂基支撑、颗粒支撑砾岩组合为特征；中扇以砾质砂岩、块状砂岩组合为特征；外扇以ＣＤＥ序及ＤＥ序经典浊积岩发育为特征。

湖相浊积砂体沉积特征及油气勘探意义

在中国众多陆相含油气盆地中广泛发育浊积砂体,且其早已成为油气勘探的重要领域。根据浊积砂体在层序地层中所处的位置、沉积相带、沉积物组合及平面展布特征等的差异,可将其归纳为近岸浊积扇、远岸浊积扇、三角洲前缘滑塌浊积岩和深水型透镜状浊积岩4种类型,并分析了各自的沉积特征。综合研究表明,良好的储集砂体位于近岸浊积扇的中扇辫状水道、中扇叠置扇叶和远岸浊积扇的中扇水道以及三角洲前缘滑塌浊积岩中,而透镜状浊积砂体储集性能较差。

东营凹陷牛庄洼陷沙三中段浊积扇特征研究

通过对牛庄洼陷牛 30、牛 4 3等钻井沙三中段的岩芯观察以及对大量的测井、分析测试、构造背景等资料的综合研究 ,认为此时该区存在两种类型的浊积扇深水浊积扇和三角洲前缘滑塌浊积扇 ,并对它们的微相类型、沉积特征作了总结 ,探讨了此两类浊积扇之间的关系 ,提出了它们的演化模式。

鄂尔多斯盆地白豹—华池地区长6砂岩储层特征

根据铸体薄片、扫描电镜、碳氧同位素、物性、孔隙结构和声发射、岩心和测井分析和化验资料,对鄂尔多斯盆地白豹—华池地区长6砂岩储层特征进行的研究结果表明,该套储层储集空间以剩余原生粒间孔和次生粒间孔组合为主;储层物性较差,微裂缝对改善储层孔隙渗透性贡献不大;排驱压力和饱和度中值压力较高,孔喉半径小且分选性较差,歪度细,溶蚀作用对改善喉道连通性的效果不佳,孔隙结构参数总体较差。储层质量受沉积微相和成岩作用的综合影响,其中,由三角洲前缘滑塌形成的内-中扇较粗粒水道砂体为最有利储层发育的微相,成岩早期碳酸盐矿物和环边绿泥石胶结作用有利于部分原生孔隙和喉道的保存。利用储层物性和孔隙结构参数,将长6砂岩评价为4类储层,其中Ⅰ、Ⅱ类储层在目前的工艺技术条件下为可动用储层,是增储上产的首选储层。

传递带及其在砂体发育中的作用

有关传递带构造的讨论中 ,以下三个问题应引起重视 :(1)褶皱冲断带中传递带 (或称调节带 )的概念和一般特征 ,传递带可定义为挤压构造变形中区域上保持缩短量守恒而产生的调节构造 ,它可以分为纵向和横向传递带两类 ,褶皱冲断带中分段构造的产生是通过走滑断层型式的横向传递带实现的 ;(2 )伸展构造中传递带的概念和一般特征 ,裂谷系中传递带可定义为区域上为保持伸展量守恒而产生的传递或调节构造 ,它也可以分为纵向和横向传递带两类 ,裂谷系中分段构造的形成是通过横向凸起型式的横向传递带完成的 ;(3)传递带在沉积盆地内砂体发育的作用 ,砂体分布与传递带关系密切 ,一般是在对应横向传递带控制的地势低和河流入盆的地方 ,在陡坡和湖盆中心才能依次发育冲积扇 -扇三角洲