PETROLEUM POTENTIAL OF THE FALKLAND ISLANDS OFFSHORE AREA

Rocks of Precambrian, Palaeozoic and Early Mesozoic ages are present on the Falkland Islands. The islands are surrounded by extensive Mesozoic-Cenozoic basins that developed as failed rift systems during the initial stages of Gondwana separation. Large tracts of acreage in three of these basins (the Falkland Plateau Basin, South Falkland Basin and North Falkland Basin) were opened for licensing for the first time in October, 1995.
The area has undergone little exploration other than the acquisition of regional seismic data, and interpretations of stratigraphy and basin history are therefore somewhat conjectural. The basins are believed to contain Jurassic to earliest Cretaceous syn-rift sediments. Probable marine and lacustrine source rocks, and reservoir rocks eroded from clean Palaeozoic quartzites, are predicted to occur within this syn-rift succession. Thick argillaceous intervals probably accumulated during a post-Valanginian thermal sag phase. This sag phase was interrupted by regional uplift, particularly during the Early Cenozoic.
A variety of "play" concepts can be established within each basin, and potentially large structural targets can be defined on the reconnaissance seismic data available from the area.
The region is considered to be one of the World's last true "frontier" exploration areas, where large, deep, Mesozoic failed-rift basins remain to be drilled and explored.     

POST-DRILLING ANALYSIS OF THE NORTH FALKLAND BASIN— PART 1: TECTONO-STRATIGRAPHIC FRAMEWORK

Six wells were drilled in the extensional North Falkland Basin in 1998. The wells encountered a Devonian to Cenozoic stratigraphy dominated by thick Mesozoic syn‐ and post‐rift successions. Although most previously published models predicted that the succession would most likely be of marine origin, it is in fact predominantly terrestrial; marine conditions did not become established in the basin until the Late Cretaceous. The oldest rocks recorded are Devonian and these were penetrated in only one well. The overlying succession comprises: a fluvio‐lacustrine, early syn‐rft interval of ?mid‐Jurassic to Tithonian age; a late syn‐rift fluvio‐lacustrine interval of Tithonian to Berriasian age; a rift‐sag transitional unit of Berriasian to Valanginian age; an early post‐rift lacustrine unit of Valanginian to early Aptian age; a middle post‐rift, transgressive unit of Aptian to Albian age; a late post‐rift, terrestrial to marine unit of Albian to early Palaeocene age; and a post‐up lift thermal subsidence unit of Palaeocene to Recent age. Much of the sediment appears to have been derived from volcanic and/or metamorphic terranes, probably located to the north or NW of the basin. As well as the volcanic material which occurs in the ground mass and as lithoclasts in many of the units, some volcaniclastic rocks and minor amounts of ashfall tufls are observed, particularly within the late syn‐rift succession.     

POST-DRILLING ANALYSIS OF THE NORTH FALKLAND BASIN—PART 2: PETROLEUM SYSTEM AND FUTURE PROSPECTS

Six wells were drilled in the North Falkland Basin in 1998. Five of these wells recorded oil shows, and up to 32% gas was also recorded in mud returns to the rig floor. However, none of the wells encountered commercially viable petroleum accumulations.
The syn-rift and early post-rift intervals contain thick, lacustrine claystones with oil source potential as indicated by TOC values up to 7.5% and Rock-Eva1 S₂ values of up to 102 kg HC per tonne of rock. These source rocks were immature or only marginally mature in five of the wells but had attained maturity in one of them. Modelling suggests that the main source interval may well be within the peak oil generation window in deeper, undrilled parts of the basin. Calculations of the amount of oil expelled range up to 60 billion barrels.
Most of the wells tested a closely-related set of plays in large structures asSociated with a sandstone interval near the top of the late syn-rifi to early post-rij? source-rock succession. Post-drilling geological modelling of the basin suggests that oil is unlikely to have migrated into this sandstone play at the localities tested, and that the wells consequently failed largely due to a lack of charge. Howevel_; the play maintains exploration potential elsewhere. Other plays, particularly those stratigraphically asSociated with the base rather than the top of the source rock, may have a higher chance of exploration success.     

The Sedimentary System and Evolution of the Early Tertiary in the Sunda Basin, Indonesia

1.Introduction The Sunda basin covers about7,000km2.Its maximum thickness at the depocenter is around16,000feet(5,000m).It has a north-south direction strike(Fig.1).The basement rock is believed to be Cretaceous granodiorite,metabasalt,mica schist and limestone(Tonkin and Himawan,1999).The basin began to take the shape at the Paleocene-early Oligocene,due to the collision of the Indian plate with the Eurasian plate(Hall,1997;Howells,1997).This collision produced the major NW-SE stress s…     

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笔将四川盆地西部坳陷区的致密砂岩含气区与北美洲深盆气模式进行对比研究，发现川西砂岩太过致密了，孔隙度绝大多数在7％以下，但川西超致密砂岩有很多高产气井和水井，显然与裂缝有关，故笔认为“深盆气”理论不适用于川西坳陷。经过对鄂尔多斯盆地致密砂岩含气区三次评价预测，认为该盆地与北美洲多数深盆气发展模式类似。之所以北部斜坡还未被水占据，在没有完整的局部圈闭条件下，常规级别的储层出现日产百万立方米高产气井，其原因有二：一是深盆气烃源补给能力还很强，认为C—P烃源岩从J到现在都在生气，故属于深盆气第IV阶段前期；二是晚期水回侵受到一定制约，盆内大部分地区，水的问题不严重，而砂岩的发育情况要复杂些。总之，鄂尔多斯深盆气有望成为中国最重要的天然气领域。     

松辽盆地南部下白垩统地震相及沉积体系

依据松辽盆地南部地下区白垩统的各种地震反射标志，总结划分出１０种主要的地震相类型，并将地震相的平面分布特征与钻井及区域构造背景相结合，在各断陷盆地中圈定出冲积扇、扇三角洲、水下扇、三扇、三角洲、三角洲、河道及湖泊等多种沉积体系。     

Sedimentary Characteristics and Evolution of Asri Basin,Indonesia,in Early Tertiary

1.Introduction The Asri basin is oval in shape,covering about2500km2from north to south.The maximum thickness at the depocenter is around18,000feet(5,500m).It is adjacent to the Hera basin in the west and to the Sunda basin in the southwest(Fig.1).Now it is under the Java sea.The basement consists of granites,granodiorites,marbles,schists and quartzites(Tonkin and Himawan,1999).In the early Tertiary,the eastern side of the basin was a steep slope controlled by syn-rifting,and the western s…     

三维多分量地震技术在川西新场地区深层致密砂岩裂缝检测中的应用

针对以往利用三维纵波地震资料无法准确预测川西地区深层致密砂岩裂缝,特别是网状发育的规模裂缝系统的难题,在川西地区实施了三维多分量地震勘探。充分利用三维多分量地震纵横波地震属性、方位各向异性以及横波分裂现象估算裂缝发育的方位和密度,较好地解决了川西新场气田须家河组超致密砂岩裂缝网络系统的预测问题,为勘探和开发井位设计提供了可靠依据;同时,形成了针对不同尺度裂缝的预测方法和技术流程。钻探证实,三维多分量地震技术在川西新场地区深层致密砂岩裂缝预测中效果显著,钻井成功率由过去的50%提高到了89%。     

Seismic stratigraphy of the Upper Pliocene and Quaternary deposits in the South Caspian Basin

More than 10,000 km of seismic data were used for seismic stratigraphic analysis and differentiation of major depositional environments of Upper Pliocene and Quaternary strata in the central deepwater and eastern parts of the South Caspian Basin (SCB). The study shows that the conventional sequence stratigraphy concept works well in the South Caspian Basin. Clinoform complexes within Paleo-Amudarya shelf margin are bounded by regionally, seismically expressed sequence boundaries and flooding surfaces that can be traced to the deep basin. Sequence analysis and seismic facies interpretation showed that deposition of prograding clinoforms and deep-water turbidite systems were controlled by the relative lake-level change. Depositional interpretation of sediment infill indicates that in the South Caspian Basin, as in other closed basins with high terrigineous input, basinal deposition is from turbidity currents and slumps generated from large shelf-edge deltas. There are two distinct stratigraphic complexes interpreted from seismic data: lower, interpreted as homogeneous infill of mud-rich turbidites and deepwater lacustrine deposits (Upper Pliocene, i.e. Akchagyl and Aspheron), and upper, consisting of prograding clinoform packages and coeval deepwater fan systems and slumps (Quaternary). The source of the central basin turbidite infill was primarily the eastern “Paleo-Amudarya” shelf. Growing diapir folds structurally controlled deposition of large-scale fan systems in the central basin. The distribution of these fan systems is tied to location of the coeval thick shelf-margin complexes.     

THE PLESHET BASIN: A NEWLY-DISCOVERED LINK IN THE PERIPHERAL CHAIN OF BASINS OF THE ARABIAN CRATON

Evaluation of existing magnetometric, gravimetric, seismic and well data indicates that a large basin, some 300 km long, 100 km wide and up to 13.5 km deep, occupies the greater part of the Sinai-Israel offshore area. The basin, referred to here as the Pleshet Basin, is flanked by a series of magnetic and gravimetric anomalies, interpreted as being caused by basement highs.
None of the wells drilled in the basin penetrated the Jurassic section. It is suggested, however, that the thick sedimentary sequence filling the basin includes strata of Paleozoic to Quaternary age.
Wells drilled in the SE part of the basin showed an increase in clastic content in a NW direction. The source of these clastics is therefore to be sought in the west. It is perhaps the basement ridge that presumably forms the western flank of the basin, or even a large land-mass further away.
The Pleshet Basin occupies a position similar to that of the prolific basins of the Middle East within the unstable shelf belt that surrounds the Arabo-Nubian Massif. It here postulated that the Pleshet Basin is a potentially hydrocarbon-generative depression.     

BURIAL AND THERMAL HISTORY MODELLING OF THE MANNAR BASIN,OFFSHORE SRI LANKA

The Mannar Basin is a Late Jurassic – Neogene rift basin located in the Gulf of Mannar between India and Sri Lanka which developed during the break‐up of Gondwana. Water depths in the Gulf of Mannar are up to about 3000 m. The stratigraphy is about 4 km thick in the north of the Mannar Basin and more than 6 km thick in the south. The occurrence of an active petroleum system in the basin was confirmed in 2011 by two natural gas discoveries following the drilling of the Dorado and Barracuda wells, located in the Sri Lankan part of the Gulf. However potential hydrocarbon source rocks have not been recorded by any of the wells so far drilled, and the petroleum system is poorly known. In this study, basin modelling techniques and measured vitrinite reflectance data were used to reconstruct the thermal and burial history of the northern part of the Mannar Basin along a 2D profile. Bottom‐hole temperature measurements indicate that the present‐day geothermal gradient in the northern Mannar Basin is around 24.4 ^oC/km. Optimised present‐day heat flows in the northern part of the Mannar Basin are 30–40 mW/m². The heat flow histories at the Pearl‐1 and Dorado‐North well locations were modelled using SIGMA‐2D software, assuming similar patterns of heat flow history. Maximum heat flows at the end of rifting (Maastrichtian) were estimated to be about 68–71 mW/m². Maturity modelling places the Jurassic and/or Lower Cretaceous interval in the oil and gas generation windows, and source rocks of this age therefore probably generated the thermogenic gas found at the Dorado and Barracuda wells. If the source rocks are organic‐rich and oil‐ and gas‐prone, they may have generated economic volumes of hydrocarbons.     

湖相碳酸盐岩—混积岩储层有利相带分析——以柴达木盆地古近系为例

湖相碳酸盐岩广泛发育于中国各陆相含油气盆地,与海相碳酸盐岩相比,湖相碳酸盐岩沉积规模较小,受多物源陆相碎屑体系干扰,易于发育湖相碳酸盐岩—混积岩。近年来,随着油气勘探的深入,湖相碳酸盐岩—混积岩作为一种致密油储层得到重视。干旱气候封闭-咸化湖盆碳酸盐岩致密油储层分布区,以青海古近系、四川侏罗系为典型,称之为内源沉积湖相碳酸盐岩储层沉积有利相带。通过野外露头剖面和钻井岩心、测井资料,对柴达木盆地柴西南地区上干柴沟组进行了横向、纵向的层序地层学和沉积相研究,探索了湖相碳酸盐岩—混积岩的沉积模式及其石油地质意义。研究认为湖侵体系域—高位体系域的演化为湖相碳酸盐岩—混积岩致密油储层提供了有利相带,从滨浅湖到半深湖—深湖区,存在湖相混积滩坝、滨湖白云岩化泥灰坪/泥云坪、浅湖叠层石礁滩和半深湖相裂缝性泥灰岩有利微相带,对柴达木盆地及其相类似盆地湖相碳酸盐岩—混积岩致密油储层油气勘探具有一定的参考价值。     

北部湾盆地福山凹陷流沙港组湖底扇沉积特征及发育背景

福山凹陷流沙港组内发育一套具有一定规模的湖底扇沉积,其中可识别出浊流沉积、水下泥石流沉积和滑塌堆积3种沉积相单元。湖底扇沉积主要发育于低位域及水进早期,地震剖面特征显示为双向下超的丘形反射复合体,测井曲线特征为箱形、钟形或漏斗形。湖底扇在平面上由扇根、扇中和扇端沉积所组成。垂向层序上湖底扇下部常见厚度较大的重力流沉积充填的下切水道,中上部发育多个叠置的浊积扇体组成。湖底扇的发育主要受控于盆地东西两侧的断层活动、湖平面变化及物源供给。流二段时期沉积的较大规模的湖底扇与这一时期的构造快速沉降和充足的物源供给有关。      

南海珠江口盆地深水扇系统的发现

深水扇系统已成为近20年来国际石油产量与储量增长的主体.对南海珠江口盆地层序地层学的研究和分析发现,在盆地内面积最大、最具生烃潜力的白云凹陷发育有大批相互叠置的低水位深水扇.基于勘探与研究成果,通过剖析典型高分辨二维地震资料,证实白云深水凹陷是自30Ma以来古珠江水系的沉积中心,与全球海平面变化周期相协调.在对应的各个三级层序的低水位发展阶段形成深水沉积体系,并具备独特的地震相组合结构.深水扇系统广布于受同沉积断层控制的古陆架坡折带及其下倾方向.由富砂的古珠江孕育并叠置在巨厚的下第三系湖相烃源岩之上的深水扇系统具有良好的油气勘探前景.     

北黄海盆地下白垩统层序构成特点及控制因素

北黄海盆地下白垩统属于湖相沉积。通过钻井及高精度三维地震资料可以清楚地在下白垩统下部地层中识别出层序的低位体系域、水进体系域、高位体系域、初次水进面以及最大洪泛面的特征。低位体系域包括下切谷、低位进积楔以及低位扇;高位体系域被层序顶界面及最大洪泛面所限定,并以发育有进积型准层序组为特征;水进体系域位于低位体系域与高位体系域中间,以退积型准层序组为主要特征。通过地质分析可以概括出层序发育的主要控制因素:1根据火成岩测试年龄及地震解释成果认为,晚侏罗世晚期-早白垩世早期岩浆活动造成地层抬升减薄,导致了构造坡折带的形成。2基于坡折带以上4口井的岩性资料发现,水进体系域和高位体系域沉积夹杂有红色泥岩。地震剖面显示层序顶界面超覆于底界面之上,层序分布范围明显小于其上覆和下伏层序的范围,同时在坡折带以下地区识别出了低位扇体和进积楔。以上证据表明该时期湖平面下降至坡折带以下地区且沉积中心发生迁移。3地震资料所显示的斜坡扇沉积,岩心资料所证实的砾石颗粒支撑和泥质填隙、泥砾的存在以及录井岩性所显示的高含砂量(60 % ~70 % )均显示出早白垩世早期为持续大物源供给。因此,控制北黄海盆地下白垩统层序形成的3个控制因素可以概括为构造坡折带的形成、湖平面的下降以及大物源的供给。     

北部湾盆地海中凹陷涠三段沉积体系与沉积模式

北部湾盆地海中凹陷渐新世涠三段是该凹陷最主要的储集层,因此对其沉积体系发育规律的研究对于该地区的油气勘探具有重要的意义。从研究区钻井岩心精细描述入手,结合测井相、地震相、地震属性特征,确定了涠三段的沉积相并建立了断陷湖盆背景下的沉积模式。研究表明：碟状—席状反射、前积反射、水道充填反射是涠三段最富砂的地震相。涠三段发育滨浅湖相、辫状河三角洲、扇三角洲、冲积扇4种沉积相类型。在滨浅湖背景下,受控于南缓北陡的半地堑湖盆结构,海中凹陷整体呈现出南北分异的沉积特征,表现为在南部缓坡带发育辫状河三角洲,在北部发育辫状河三角洲与扇三角洲;同时坡折带、断裂样式、沟渠古地貌等因素控制着来自三大不同方向物源的三角洲,南部企西隆起物源主要发育辫状河三角洲,并受坡折带控制在平面上划分出平原与前缘,中部涠西南低凸起物源受断裂控制在西侧发育辫状河三角洲与扇三角洲,西北部万山隆起物源的沉积物通过远距离搬运在研究区西北侧湖盆边缘形成辫状河三角洲。     

GEOLOGY AND EXPLORATION IN THE TAKUTU GRABEN OF GUYANA BRAZIL

The Takutu basin is a Mesozoic graben 280 km long and 40 km wide in northern Brazil and adjoining Guyana. It occupies an ancient Pre Cambrian shear zone within the heart of the Archean Guyana shield. Metavolcanic rocks and thick Proterozoic quartzites crop out north of the basin. Granitic rocks border the graben on the south and east. Mesozoic basalt forms a band of outcrop along the southern and eastern margins of the modern-day valley. The basin is filled with up to 5,400m (18,000 ft) of Mesozoic sedimentary rocks, underlain by more than 1,700m (5,600 ft) of mafic volcanics of Jurassic and possibly older (i.e, Proterozoic) ages. Six regional unconformities were recognized within the basin fill. The geologic history of the graben is characterized by one volcanicphase and three depositional phases. Rifting began in Late Triassic to Early Jurassic time with the extrusion of thick Apoteri flow basalts. Lower Jurassic non-marine clastics of the Manari Formation overlie the eroded basalt. They are overlain by the thick Lower and Middle Jurassic non-marine salt and gray shale of the Pirara Formation. These sediments were deposited over most of the basin and contain good oil source-rocks. Middle and Upper Jurassic non-marine clastics of the Takutu Formation overlie the evaporites. They were deposited in lacustrine and deltaic environments, as interpreted from seismic and well data. There are two contrasting structural styles, of Late Triassic to Early Jurassic, and Cretaceous to Tertiary ages. Block-faults are common in the pre-salt section, and non-piercement halokinetic structures in thepost-salt rocks. The graben contains a cross-basin arch, evidence of wrench faults and minor salt solution. Four exploratory wells have been drilled to date. Home Karanambo No. 1 discovered highquality crude oil in the fractured volcanic basement. Seismic stratigraphic interpretations indicate that alluvial fan and deltaic reservoirs may overlie undrilled structures elsewhere in the basin.     

WORLD‐CLASS PALEOGENE OIL‐PRONE SOURCE ROCKS FROM A CORED LACUSTRINE SYN‐RIFT SUCCESSION,BACH LONG VI ISLAND,SONG HONG BASIN,OFFSHORE NORTHERN VIETNAM

Oil‐prone source rocks occurring in lacustrine syn‐rift successions have generated significant amounts of hydrocarbons in many Cenozoic basins in SE Asia. As most exploration wells are located on structural highs, the source rock successions are seldom drilled and their initial composition and generation potential are poorly known. The inverted Bach Long Vi Graben is located at the intersection of the NW–SE trending Song Hong Basin (Yinggehai Basin) and the NE–SW trending Beibuwan Basin in the Gulf of Tonkin, offshore northern Vietnam. The uppermost part of the inverted graben is exhumed and exposed on Bach Long Vi island. In order to investigate the amount and source rock quality of the syn‐rift mudstones, the ENRECA‐3 well was drilled on the island and cored some 500 m of the syn‐rift succession. The well provided excellent cores with a recovery of 99%, dominated by lacustrine mudstones interbedded with various gravity flow deposits. Organic petrography shows that the mudstones are thermally immature and contain sapropelic Type I and mixed Types I and III kerogen. Source rock screening data from more than 300 samples demonstrate that the lacustrine source rocks have an average TOC content of 2.88 wt% and an average Hydrogen Index of 566 mg HC/g TOC. The average Hydrogen Index of the reactive kerogen was determined to be 769 mg HC/g TOC. The Source Potential Index (SPI) is 9 tons HC/m² and the mudstones will, upon full maturation, generate black oil with a gas‐liquid ratio not exceeding ～1700 scf/stb. The mudstones are thus highly oil‐prone. In addition, several tens of metres of source rock within the overlying succession are exposed on Bach Long Vi island and in the surrounding seafloor, and the well did not reach the base of the source rock succession. Although the net‐source rock thickness of the ENRECA‐3 well is estimated to be 233 m, the net thickness of the entire source rock succession will be greater. The present study is the first organic geochemical assessment of a thick lacustrine source rock section in the petroliferous NE Song Hong Basin, and the promising results may be applied not only to other parts of the basin but also to other Cenozoic basins with syn‐rift successions containing significant source rock intervals.     

高邮凹陷邵伯地区近岸水下扇的地震预测

我国东部地区的许多断陷湖盆在中新生代处于扩张期，普遍发育近岸水下扇。水下扇一般沿大断裂下降盘展布，且多分布在湖盆陡坡的一侧。扇中砂岩因断层遮挡形成构造岩性复合型油气藏。苏北盆地高邮凹陷南部陡坡一侧，早期根据构造圈闭模式发现的真武、富民等油田，经进一步开发落实均为扇中砂岩与构造控制的复合型油气藏。如何利用地震技术预测扇体展布范围以及扇中砂岩发育区是南部陡坡带扇体勘探的关键。综合利用了多种地震解释手段，对高邮凹陷南部陡坡带邵伯工区近岸水下扇进行了预测，为勘探提供了依据，经钻探取得了较好的效果。     

松辽盆地苏家屯次洼初始裂陷期扇三角洲沉积特征

扇三角洲沉积砂砾岩体作为良好的油气储层，一直备受重视。为了深化对断陷盆地初始裂陷期扇三角洲沉积特征的认识，以松辽盆地苏家屯次洼火石岭组为研究对象，综合运用岩心、测井、三维地震资料和古地貌恢复技术，对初始裂陷期扇三角洲的发育规律、沉积特征和控制因素展开深入研究，建立了断陷湖盆初始裂陷期扇三角洲沉积模式。结果表明：①苏家屯次洼初始裂陷期发育东西双断的地堑式断陷湖盆，区内地形高差较大、构造运动活跃，沉积物源主要来自次洼西北、西南和东部等3个方向；②火石岭组形成时期广泛发育扇三角洲沉积体系，岩性以厚层杂色、灰色砂砾岩夹薄层灰色泥岩为主，测井曲线多呈高幅箱形或钟形，在地震剖面上多表现为斜交前积反射、楔状或丘状杂乱反射结构；③沉积体系展布受控盆断裂和古地貌控制，形成"中部凹陷带湖相、东西断阶带扇三角洲相"的沉积格局以及"中部生烃、两侧储集"的生储配置关系；④初始裂陷期构造活动是控制扇三角洲体系发育的主导因素，控盆断裂不仅控制着沉积相带和储层砂体的分布，也持续影响着断陷湖盆的沉积充填演化。该研究成果可为陆相盆地断陷深部的油气勘探提供地质依据。