Highlighting relationships between sand thicknesses,reservoir-seal pairs and paleobathymetry from a sequence stratigraphic perspective:An example from Tortonian Serravallian deposits,onshore Niger Delta Basin

The utilization of sequence stratigraphic concepts in identifying sands and their spatial continuity in distinct gross depositional settings is key,especially in frontier settings where data paucity is a common challenge.In the Baka field,onshore Niger Delta,detailed reservoir correlation guided by sequence stratigraphic framework analysis showed the distribution of sand and shale units constituting reservoirseal pairs(RSP)correlatable across the field.Within the 3rd-order packages,it is observed that the lowstand systems tract(LST)and highstand systems tract(HST)contain more RSPs and thicker 4th-and 5th-order sands than the transgressive systems tract(TST).In terms of bathymetry,it is noted that irrespective of systems tracts,the RSP Index(RI)decreases from the proximal shallow/inner shelf settings to the more distal outer shelf areas.Amongst all three systems tracts,intervals interpreted as lowstand prograding complexes contain the best developed sands and highest RSP.Sand development within the LSTs has been controlled by a pronounced growth fault regime accompanied by high subsidence and sedimentation rates.This is linked to the basinward migration of the sands during prolonged sea-level fall,creating significant accommodation space for sand deposition.On the other hand,the TSTs known to mark periods of progressive sea-level rise and landward migration of sandy facies,show thinner sands enclosed in much thicker,laterally extensive,and better-preserved deeper marine shales.Interpreted seismic sections indicate intense growth faulting and channelization that influenced the syn-and postdepositional development of the sand packages across the field.The initial timing of deformation of subregional faults in this area coincides with periods of abrupt falls in sea level.This approach could be useful for predicting sand-prone areas in frontier fields as well as possible reservoir-seal parameters required for some aspects of petroleum system analysis and quick-look volume estimation.

Hydrocarbon Prospectivity and Risk Assessment of “Bob” Field Central Swamp Depobelt, Onshore Niger Delta Basin, Nigeria

This paper evaluates the hydrocarbon prospectivity and play risks of “Bob” field in Niger Delta Basin, Nigeria. The aim is to enhance exploration success through improved approach/technique by incorporating risk analysis that previous studies have not fully considered. This approach combines a set of analyses including stratigraphic/structural, amplitude, petrophysical parameter, volumetric and play risk using a suite of well logs and 3D seismic data. Maximum amplitude anomaly map extracted on the surfaces of delineated 3 reservoirs revealed 6 prospects, namely: Dippers, Cranes, Turacos, Nicators, Jacanas and Pelicans with hydrocarbon accumulation. Petrophysical analysis showed ranges of values for porosity, permeability and water saturation of 0.21 to 0.23, 158.96 to 882.39 mD, and 0.07 to 0.11, respectively. The various prospects yielded the following stock tank volumes 12.73, 6.84, 3.84, 11.32, 7.42 and 4.76 Million barrels (Mbls) each respectively in a column of 66 ft reservoir sand in the study area. Play risk analysis results gave: Pelicans and Nicators (low), Turacos and Dippers (moderate), while Jacanas and Cranes show high risk with minimal promise for good oil accumulation. The prospects possess good reservoir petrophysical properties with low to moderate risk, thus, viable for commercial hydrocarbon production, which increases confidence in management decisions for production.

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

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.

Origin and depositional environments of source rocks and crude oils from Niger Delta Basin: Carbon isotopic evidence

Thirty-nine crude oils and twenty-one rock samples from Niger Delta Basin,Nigeria have been characterized based on their isotope compositions by elemental analysis-isotope ratio mass spectrometry and gas chromatography-isotope ratio mass spectrometry.The bulk carbon isotopic values of the whole rock extracts,saturate and aromatic fractions range from–28.7‰to–26.8‰,–29.2‰to–27.2‰and–28.5‰to–26.7‰,respectively while the bulk carbon isotopic values of the whole oils,saturate and aromatic fractions range from–25.4‰to–27.8‰,–25.9‰to–28.4‰and–23.5‰to–26.9‰,respectively.The average carbon isotopic compositions of individual alkanes(nC12-nC33)in the rock samples range from–34.9‰to–28.2‰whereas the average isotopic values of individual n-alkanes in the oils range from–31.1‰to–23.8‰.Theδ13C isotope ratios of pristane and phytane in the rock samples range from–29.2‰to–28.2‰and–30.2‰to–27.4‰respectively while the pristane and phytane isotopic values range from–32.1‰to–21.9‰and–30.5‰to–26.9‰,respectively.The isotopic values recorded for the samples indicated that the crude oils were formed from the mixed input of terrigenous and marine organic matter and deposited under oxic to sub-oxic condition in lacustrine-fluvial/deltaic environments.The stable carbon isotopic compositions were found to be effective in assessing the origin and depositional environments of crude oils in the Niger Delta Basin.

The Characteristics and Distribution Pattern of Seafloor Sinuous Pockmark Train in the Niger Delta Basin,West Africa

Objective The term ＂pockmark＂ was introduced by King and MacLean （1970） to describe small ＂circular＂ on echosounder records in Nova Scotia. described as circular, near Pockmarks are usually circular or elongated depressions, generally 10--400 m in diameter and 30-50 m in deep. Pockmarks are normally regarded to be manifestations of fluids escape through the seabed. Pockmarks are valuable features on the seafloor and are useful in constraining the hydrodynamics of sedimentary basins. Since then pockmarks have been recognized in many areas around the world. They occur predominantly in fine-grained siliciclastic depositional settings, although a few case studies have been reported in carbonate settings. In this paper we illustrate a suite of fluid escape features, discovered during the course of petroleum exploration on the West Africa continental margin （Fig. 1）. They are particularly of interest to the oil and gas industry because they could be potential indicators of deeply buried hydrocarbon reservoirs, and fluid flow phenomena in the deep water oilfield are important for the safe and efficient exploration, development and production of hydrocarbons in the area.

3D Seismic Analysis of the Gas Hydrate System and the Fluid Migration Paths in Part of the Niger Delta Basin, Nigeria

Comprehensive qualitative and semi-quantitative seismic analysis was carried out on 3-dimensional seismic data acquired in the deepwater compressional and shale diapiric zone of the Niger Delta Basin using an advanced seismic imaging tool. The main aim of this work is to obtain an understanding of the forming mechanism of the gas hydrate system, and the fluid migration paths associated with this part of the basin. The results showed the presence of pockmarks on the seafloor and bottom simulating reflectors(BSRs) in the field, indicating the active fluid flux and existence of gas hydrate system in the area. In the area of approximately 195 km^2 occupying nearly 24% of the entire study field, three major zones with continuous or discontinuous BSRs of 3 to 7 km in length which are in the northeastern, southern and eastern part of the field respectively were delineated. The BSR is interpreted to be the transition between the free gas zone and the gas hydrate zone. The geologic structures including faults(strike-slip and normal faults), chimneys and diapirs were deduced to be the main conduits for gas migration. It is concluded that the biogenic gases generated in the basin were possibly transported via faults and chimneys by advection processes and subsequently accumulated under low temperature and high pressure conditions in the free gas zone below the BSR forming gas hydrate. A plausible explanation for the presence of the ubiquitous pockmarks of different diameters and sizes in the area is the transportation of the excessive gas to the seafloor through these mapped geologic structures.

Heavy Minerals and Geochemical Characteristics of Sandstones as Indices of Provenance and Source Area Tectonics of the Ogwashi-Asaba Formation, Niger Delta Basin

Heavy mineral petrographic and geochemical compositions (major and trace/rare earth elements)?of sandstones obtained from the Oligocene-Miocene Ogwashi-Asaba Formation, Niger Delta were studied to determine their provenance, source area weathering conditions and tectonic setting. The heavy mineral suite (opaque minerals, zircon, tourmaline, and rutile) revealed that the sandstones are mineralogically mature and implied rapid disintegration and chemical decomposition of sediments mostly of recycled orogen. The sandstones were geochemically classified as Fe-sand and partly quartz arenitic. Chemical Index of Alteration and Chemical Index of Weathering values of 89.92% and 91.87% respectively suggest that the source region was predominantly felsic and was subjected to intense chemical weathering probably under tropical palaeoclimatic conditions with abundant rainfall that enhanced sediment recycling. Major element concentration discriminant plots also indicated that the sediments were derived from mixed sources (granitic, gneissic or recycled orogen) under passive margin setting. Chondrite normalized plot of the rare earth element pattern is marked by light rare earth element enrichment and negative Eu anomalies, interpreted to mean that provenance was mainly continental crustal rocks. Trace elemental ratios that are provenance diagnostic (La/Sc, Th/Sc, Cr/Th, La/Co, Th/Co, Th/Cr, Eu/Eu*, and Eu*) all point to sediments derived from felsic source and upper continental crust. The mixed provenance of the sandstones can be traced to the southwestern and southeastern Basement Complex (consisting of granites, gneisses, etc.) and sediments derived from the adjacent sedimentary basins (Anambra and Benue Trough).

Sedimentary-tectonic interaction on the growth sequence architecture within the intraslope basins of deep-water Niger Delta Basin

This paper presents a 3D seismic-based case study from the deep-water Niger Delta Basin to investigate sedimentary-tectonic interaction on growth sequence architecture within the thrust-related intraslope or piggyback basins. Gravitational contraction in the lower continental slope had yielded a series of thrust faults and associated folds in the study area, which formed several piggyback basins. These basins were filled by a suite of growth sequences with varying stratigraphic architecture. Analysis of the 3D seismic data recognized three primary seismic facies types respectively as: convergent, draping and chaotic, which contain seven subtypes. These facies types are combined to form different filling successions for convergent or chaotic growth sequences. The convergent growth sequences mainly occur in the deep section of basin fills during strong gravitational deformation, and always began with convergent-baselapping strata succeeded by convergent-thinning strata, representing pond-to-bypass transition in the ponded-basin accommodation space. The chaotic growth sequences mainly occur in the shallow section of basin fills in response to weak gravitational deformation, and usually began with debris-flow deposits succeeded by channel-levee complexes, reflecting dominant erosion-bypass processes in the slope accommodation space. A dynamic fill-andspill model considering relationship between episodic sedimentation rate and structural growth rate is proposed to explain the formative mechanisms of growth strata units and associated successions. Interaction between glaciation or deglaciation and sea-level change and gravitational deformation history are suggested to be the factor which resulted in the complex stratal stacking patterns, including progradational or retrogradational stacking patterns within convergent growth sequences, and progradational stacking patterns within chaotic growth sequences.

Research on the architecture of submarine-fan lobes in the Niger Delta Basin,offshore West Africa

As one of the most important reservoirs in submarine fan, submarine lobes are hot fields for the deep-water oil-gas exploration in the world. Although a large amount of researches have been carried out on the architecture model of submarine lobes throughout the world, some controversies still exist on aspects such as the differential distribution of composite patterns and the quantitative relationships among different sedimentary settings. This paper, which took an oilfietd in the Niger Delta Basin offshore West Afnca as an example and utilized abundant core, welt-logging and seismic data comprehensively, established the semi- quantitative to quantitative architecture model for individual lobe and lobe complex. Results show that （1） A lobe complex was composed of multiple individual lobes as the compensational stacking pattern. According to the stacked relationship among individual lobes, four types of compensational stacking pattern were classified as the inordered type, the lateral migration type, the retrograding type and the prograding type. Influenced by the laterally confined degree of palaeotopography, the basin floor fan lobe complex was easily superimposed as inordered type, showing relatively large lateral width but relatively small thickness; the slope fan lobe complex was easily superimposed as lateral migration, retrograding and pro- grading types, showing relatively small lateral width but relatively large thickness. （2） Influenced by the laterally confined degree of palaeotopography, the basin floor fan individual lobes showed relatively large planar distribution area but relatively small thickness, while the slope fan individual lobes showed relatively small planar distribution area but relatively large thickness. An individual lobe was composed of multiple lobe stories by the way of aggradation-progradation pattern. From proximal to middle and distal part of individual lobes, the bottom mass-transport-deposits and the top branch channels disappeared gradually, and the amalgamated degree of the middle tabular sandbodies weakened as well with gradually developing of muddy interlayers. The formation of an individual lobe generally includes three stages as ＂rapid accumulation-progradation-aggradation＂.

Palynomorph assemblage biozonation of Paleogene strata in Bende–Umuahia Area,Niger Delta Basin, southeastern Nigeria

Cenozoic sediments form extensive outcrops in the Niger Delta Basin. Detailed palynostratigraphic study was undertaken across Paleogene sequences exposed in Bende–Umuahia Area in up-dip sectors of the Niger Delta Basin, southeastern Nigeria, to establish different palynomorphs assemblage zones, with their corresponding ages.Palynological analysis was carried out on 27 selected outcrop samples, using the conventional maceration technique for recovering acid-insoluble organic-walled microfossils from sediments. Three Cenozoic lithostratigraphic units, including Imo Formation, Ameki Formation, and Ogwashi Formation, are exposed in the study area. Lithologies are sandstone, carbonaceous shale, mudstone, limestone, and the lignite. A total of 65 species of sporomorphs and 51 dinoflagellate cysts were identified. The recovered spores and pollen grains were used to establish six informal palynomorph assemblage zones, labeled as zone A – zone F, based on the first and the last occurrences of two or more species. These palynomorph assemblage zones include:(1) zone A — middle Paleocene Scabratriporites simpliformis–Bombacidites annae zone;(2) zone B — late Paleocene Foveotricolporites crassiexinus–Mauritidiites crassiexinus zone;(3) zone C — early Eocene Striatopollis catatumbus–Momipites africanus zone;(4) zone D — middle Eocene Margocolporites umuahiaensis–Gemmastephanocolporites brevicolpites zone;(5)zone E — late Eocene Cicatricosisporites dorogensis–Perfotricolpites nigerianus zone;and,(6) zone F — Oligocene–early Miocene Verrucatosporites usmensis–Magnastriatites howardii zone. The erected palynozones were correlated and compared with existing biozones in subsurface, down-dip sectors of the Niger Delta Basin, with pantropical palynological zones in tropical areas of Africa, and with palynofloral provinces of northern South America. A comparison of palynozones studied in southeastern Nigeria with other international palynozones, in this study, will assist in establishing the correlation of sediments for these areas.

A Probable Connection between a Bitumen Sample from the Western Niger Delta and Isan Well Sample from the Lower Cretaceous (Neocomian) Shale

An earlier study of GC-MS analysis on bitumen samples from the Agbabu area in Western Niger Delta showed the significant presence of gammacerane and no Oleanane and is suggested to be generated from the Lower Cretaceous (Neocomian) source rock, however, twelve core samples were obtained from the geological survey of Nigeria for both optical geochemical and biomarker analysis, two of the samples from Isan-9 well indicated the presence of Botryococcus braunii a freshwater alga which is characteristic of a lacustrine lake type environment. The extracts from the same core showed m/z = 191 chromatogram with the significant presence of gammacerane which is diagnostic for stratified water columns and characterizes a typical lake environment. However, the m/z = 191 chromatogram also shows the presence of Oleanane which is diagnostic for vascular plant materials, this doesn’t corroborate with that of the Ise-2 well. The Isan-9 well source rock is suggested to have occurred due to the evolving structural geology of the continental shelf after the onset of the rifting, whereby the dominant lake-type environment in the Early Cretaceous was accompanied by a sediment fill of continental runoffs containing vascular plant materials. This implies that an ancient lacustrine lake system was gradually modified as a result of sedimentary infill. And that the bitumen is sourced from the lower Cretaceous Neocomian source rocks.

三角洲型被动陆缘盆地陆坡地貌演化研究——以尼日尔三角洲盆地某深水研究区为例

【目的】陆坡因其巨大的沉积物总量和丰富的油气资源而成为勘探的热点领域。明确陆坡地貌演化特征能够助力于深水沉积学研究和油气勘探。研究旨在针对三角洲型被动陆缘盆地陆坡具有强物源供给条件的特征,探索一种基于沉积构型原理的古陆坡地貌演化研究新方法。【方法】以尼日尔三角洲盆地某陆坡研究区为例,综合应用地震、测井和岩心资料,根据13个层序的沉积构型时—空演化规律反演古陆坡地貌演化特征。【结果】研究区中新世至今的地貌演化过程经历了两个阶段。阶段1中,地貌演化受大型三角洲进积驱动,研究区由深海平原演化为陆坡,地貌始终为非限制型。阶段2中,在重力滑动作用下先后经历了由逆冲断层、泥底辟、填平补齐主导的演化过程,地貌由限制型、半限制型演变为现今的非限制型。逆冲断层期,泥底辟强度有限,地貌形态受控于断层活动,研究区处于重力滑动体系的远缘逆冲构造区。泥底辟期,底辟强度大幅增强,具备了独立改造地貌格局的能力,研究区由逆冲构造区向泥底辟构造区转化。【结论】重力滑动体系由沉积作用驱动,表现出与沉积相类似的空间组合与演化特征。平面上相邻的伸展、泥底辟、逆冲构造区存在成因关联,与具有排序特征的沉积相类似。因此,研究区两期构造活动的叠合关系指示了陆坡向海推进的过程。综上,典型深水研究区沉积构型的时—空演化特征能够为陆坡古地貌演化过程的恢复提供重要依据。

非洲西海岸里奥-德雷盆地泥底辟平面地质结构特征研究

位于西非尼日尔三角洲盆地东缘的里奥-德雷盆地发育了大规模泥底辟,其活动时间和形成机理存在一定争议。基于对里奥-德雷盆地三维地震剖面的精细解释和平面成图,对其中中新世Nguti构造层顶面的泥底辟平面分布特征进行了重新厘定。结果表明:(1)Nguti构造层顶面的泥底辟可分为北部隐伏区、中部刺穿区和南部刺穿区;(2)北部隐伏区的泥底辟形成于Nguti构造层沉积前,是受早期沉积作用控制的被动泥底辟;中部刺穿区的泥底辟形成于上新世S0构造层沉积前,是受重力构造作用控制的主动泥底辟;南部刺穿区的泥底辟形成于Nguti构造层沉积后,是受重力构造前缘逆冲断层控制的逆冲泥底辟;(3)泥底辟整体上为向南凸出的舌状体,分东、西两段,西段为北北西-北西走向,东段为北北东-北东走向。

尼日尔三角洲盆地深水沉积储层预测及烃类检测

尼日尔三角洲盆地深水A目标已钻2口井,揭示储层较薄、横向变化快,且主力油层高部位钻遇油水界面,前期评价无经济效益。针对目标储层展布特征及含油分布规律不明、含水砂岩与含油砂岩均表现为强振幅的"亮点"特征的难题,运用基于叠前同时反演的岩相概率体分析技术,提高了砂岩预测的准确度,明确了主力目的层甜点储层发育规律。通过AVO属性分析类比,明确流体因子属性在烃类检测中具有明显的优势:可以明显地识别油层与水层;通过流体因子的变化规律可以推测油层厚度的变化趋势;横向连续性较好,对油层平面展布规律有较好地体现。综合地震平点分析及油气成藏研究,在近逆冲断层处构造低部位的砂岩概率体高异常区、AVO流体因子高异常区、地震平点界面之上部署一口探井,实钻取得了很好的勘探成效。

深水浊积水道体系构型模式研究——以西非尼日尔三角洲盆地某深水研究区为例

深水浊积水道体系作为重要的油气储集体受到世界油气行业的重点关注。目前,针对浊积水道体系构型模式的研究,国外学者已取得了一系列成果,但仍有大量科学问题有待解决,表现为:①已有的构型级次划分方案还不完善,并且缺乏对不同级次水道单元的明确定义;②已有的构型模式研究极少涉及单一微相及其内部规模;③已有的构型模式研究远未达到定量或半定量程度。相比国外,国内的相关研究则尚处在探索阶段,科学成果甚少。为此,笔者以西非尼日尔三角洲某深水研究区为例,利用丰富的高品质资料,开展了浊积水道体系的定量—半定量构型模式研究。研究表明,浊积水道体系的构型单元可划分为7级,其中3～5构型单元分别为:单一水道、水道复合体、水道复合体组合。单一水道的宽深之间呈正相关对数关系,内部砂体以垂向加积形式分布于轴部。依据岩石相垂向充填特征,单一水道可分为4类,不同类型的单一水道具有一定的时空演化规律。依据外部形态与边界特征,水道复合体组合可分为限制性与非限制性2类,其内部的水道复合体具有5种分布样式。水道复合体的宽深之间整体呈正相关幂函数关系,但在弯曲段和顺直段的规律不尽相同。本文的研究不仅可以深化浊积水道体系的地质理论,而且可以有效降低此类油气田的勘探开发风险,具有重要的理论和实际意义。

尼日尔三角洲盆地深水油田A海底扇储层质量差异

深水海底扇沉积位置特殊、形成过程复杂,关于其储层质量的研究明显滞后于陆上和浅水沉积,研究成果尚不能有效指导储层的油气开发。为此,以西非尼日尔三角洲盆地某深水油田A为例,采用岩心观察描述、测井交会分析、地震属性切片等多种技术手段,深入分析了海底扇储层的质量差异及主控因素。研究结果表明,研究区海底扇储层的原生孔隙发育,所经历的成岩作用较弱,储层质量主要受控于沉积因素。依据岩性和沉积构造,可将研究区储层的岩石相分为交错层理细砂岩、平行层理中-细砂岩、块状中-细砂岩等6类。从微观上看,岩石颗粒的分选和杂基含量分别控制着研究区海底扇储层的储集能力与渗流能力,而粒度中值对于储层孔渗的影响则较小,这一特点导致不同岩石相、不同沉积相之间的储层质量变化表现出特有的规律性;从宏观上看,层序主要通过控制不同沉积相的时空分布以及同类沉积相内部的岩石相组合来影响储层质量的空间差异。

基于深水浊积水道构型的流动单元分布规律

深水浊积水道发育位置与形成过程复杂,目前国内外学者致力于其沉积机理和模式的研究。相对于陆上沉积,这些研究成果尚不能高效地运用到油气田开发中。因此,将构型模式与流动单元研究相结合的意义重大,表现为:1已有的构型级次的划分能够有效地指导流动单元渗流屏障和连通体的层次分析;2已有的沉积模式研究能够约束流动单元的分布规律;3二者的结合能将构型模式研究成果运用到油气田开发中。为此,以西非尼日尔三角洲深水浊积水道储层为例,在储层构型级次划分的基础上,分级次识别了渗流屏障和连通体;并运用多参数流动单元的划分方法,将储层划分为A,B,C,D 4类流动单元;最后,在构型模式的指导下进行了流动单元的单井解释及单一水道剖面与复合水道平面的流动单元分布特征研究,并以此指导油气田开发。研究表明:在单一水道级次,不同类型的单一水道内部流动单元发育类型和分布特征存在差异,流动单元的分布规律受控于不同单一水道类型的分布规律;在复合水道级次,水道体系不同时期水道迁移与叠置样式的差异,造就了流动单元平面分布特征的差异性。

深水浊积水道储层多参数流动单元划分方法及其分布规律研究

多参数储层流动单元识别是深水浊积水道研究的发展方向,其中判别参数的选择是多参数流动单元识别的关键。以西非尼日尔三角洲深水浊积水道储层为例,结合开发中的动态资料,优选了泥质含量、孔隙度和渗透率三个判别参数。运用快速聚类分析的方法,将储层划分为A,B,C,D四类流动单元,并通过判别分析建立了流动单元的判别函数。最后根据流动单元的判别函数进行了流动单元的单井解释,在沉积相研究的基础上分析了深水浊积水道储层流动单元的剖面与平面分布规律。研究表明:A类和B类流动单元储层质量最好,一般在水道体系的中部和浊积水道的主体较为发育。在水道体系演化过程中,不同期次的浊积水道迁移与叠置样式以及发育规模的不同,导致内部流动单元分布样式和类型存在差异,平面非均质性很强。

澳大利亚西北大陆架与尼日尔三角洲、坎波斯盆地油气地质条件的对比研究

坎波斯盆地、尼日尔三角洲和澳大利亚西北大陆架这3个典型的被动大陆边缘盆地既有相似性,也有不同点,其不同之处表现在:①坎波斯盆地和尼日尔三角洲均只有一期裂谷,西北大陆架各盆地均有多期裂谷,这种多期裂谷使得西北大陆架的油气主要富集在裂谷层系中,而前两者主要分布在漂移层序;②由于烃源岩生烃性质不同,导致不同盆地油气分布特征有差异,前两者油多气少,而西北大陆架富气贫油;③三者油气分布主控因素不同,坎波斯盆地油气藏分布主要与浊积岩和盐岩运动有关,尼日尔三角洲油气藏分布与同生断层有关,西北大陆架油气分布则主要受构造所控制。

尼日尔三角洲盆地陆坡逆冲构造区海底扇分布规律

近年来的深水油气勘探揭示了陆坡逆冲构造区复杂的海底扇分布特征。目前,国内外学者重点研究了逆冲相关地貌对海底扇宏观分布的影响,但对于不同逆冲活动阶段的海底扇分布及空间演化规律仍缺乏系统的认识。文章以尼日尔三角洲盆地某深水研究区为例,综合地震和测井资料,开展陆坡逆冲构造区的海底扇分布规律研究。研究表明,研究区目的层段(上中新统—第四系)可依据地层超覆及海平面变化划分为9个三级层序,在其内部共识别出了块体搬运沉积、水道沉积及朵叶沉积3类海底扇沉积单元。垂向上,海底扇主要分布在三级层序的海退域;而在平面上,受控于不同逆冲活动阶段的差异古地貌特征,海底扇可表现出复杂的分布演化规律。综合分析表明,研究区海底扇的沉积演化可分为4个阶段:(1)均衡陆坡阶段,该阶段逆冲断层未开始活动,陆坡地貌相对平缓,其对海底扇的限制性较弱,此时海底扇体系主要由高弯度条带状水道组成,发育于研究区中部;(2)逆冲断层阶段,该阶段逆冲断层向深水区强烈挤压,在其上盘处形成微盆地,阻止了重力流的搬运,形成大型连片状的复合朵叶;(3)泥底辟阶段,该阶段逆冲断层活动减弱,并在核部伴随有向上的泥底辟作用,此时在研究区中部发育泥底辟背斜,而在其东西两侧发育顺陆坡倾向的微盆地,大量的重力流沉积物沿这些纵向微盆地沉积过路,形成东西分异的海底扇水道-朵叶复合体;(4)沉积填平补齐阶段,该阶段逆冲活动基本停止,陆坡地貌逐渐趋于均衡,此时研究区内均匀发育低弯度条带状的水道沉积。