Sirte basin has a huge oil-gas reserve. The analysis between tectonic-sedimentary evolution and oil-gas accumulation in this basin has a guiding role in search for similar hydrocarbon-rich basins. According to IHS database, the tectonic evolution of Sirte basin can be divided into four ages: (1) Early riftting age: The Precambrian Pan-African orogenic movement formed the basement. From Caledonian orogenic movement in Carboniferous to Hercynian orogenic movement at the end of late Jurassic, the basin maintained craton-Mediterranean margin sedimentary characteristics. (2) In early Cretaceous, Neo-Tethys opened up, and the basin uplifted and characterized by a large-scale regression. Sirte basin subsided in late Cretaceous, and New-the Tethys sea rapidly invaded. Until Toulon age, ocean transgression further expanded. At the end of Eocene, the basin sank completely with a large-scale regression. (3) A small-scale transgression occurred late Oligocene; Sirte basin uplifted above sea level until late Miocene, and Pliocene and Quaternary deposits were thin or absent. Two large-scale transgressions of Neo-Tethys in early and late Cretaceous laid the foundation of good source rocks in the basin, fluvial sandstones formed by tectonic uplift in early Cretaceous, and the delta-coast or shallow marine sandstones and carbonatites formed by tectonic subsidence in late Cretaceous. Regional shales and local evaporites, formed by Neo-the Tethys sea sustained transgression in late Cretaceous, composed well regional caps. Therefore, upper Cretaceous petroleum system was the dominant, lower Cretaceous petroleum system as the secondary, and the Hercynian unconformity and faults as the main petroleum migration channels in the hydrocarbon accumulation groups. by September 2021, the 2P recoverable reserve of residual oil, natural gas and condensate in Sirte basin were 5420 million BBL, 32.5Tcf and 920 million BBL respectively.

The study area K is located in the center of the Fana Low Uplift in the Termit Basin, Niger, which is known as one of hydrocarbon-prone zones in this basin, where the oil producing Paleogene Sokor reservoir is dominated by the delta front underwater distributary channels and estuary bars, and the facies variation is fast, leaving the prediction of the distribution of favorable sand bodies the key issue for the further oil-fields development. In this article, the regional sedimentary characteristics, drilling and seismic data are integrated to study the sedimentary characteristics. It is believed that the Paleogene Sokor1 Formation mainly developed underwater distributary channel, estuarine bar, distal bar, interdistributary bay, beach bar sand and shore-shallow lake mud sedimentary microfacies. Through intensive well seismic calibration and forward modeling, the logging curves and seismic reflection characteristics of different lithologic associations are identified, and it is believed that seismic reflection characteristics have good correlation with sedimentary microfacies, and the well-seismic characteristics and seis-mic facies identification chart of 6 sedimentary microfacies in the study area are generated. On this basis, the spatial distribution of underwater distributary channel sand bodies are accurately characterized by using Frequency-Decomposed Multi-Seismic-Attributes RGB Fusion, seismic attribute analysis and other research, incorporated with drilling calibration and forward modeling. The result is consistent with the plane calibration of the drilled well, which provides a geological basis for the planning of development wells.

The Sufyan sub-basin is located in the northwestern part of Muglad Basin, Sudan. Because the basin was greatly affected by tectonic activities of the Central African Shear Zone, faults greatly developed and structures are complex, especially in the Sufyan sub-basin. Fluvio-deltaic sandstones within the Abu Gabra Formation represent the primary reservoir. There are great exploration potential of the AG2 interval. The interval is mainly characterized by interbedded mudstones and sandstones. The sand layers are thin and change rapidly in lateral, which brings difficulties in reservoir characterization. The constrained sparse spike inversion (CSSI) is used to predict the reservoir in the Sufyan sub-basin since it does not rely on the model, its accuracy merely depends on the characters of original data. Reservoir distribution characteristics of five layers in AG2 was studied using precise synthetic seismogram calibration, seismic interpretation of complex faulted blocks and seismic inversion. The inversion results, in good agreement with the drilled wells, show that sandstones are well developed in the northern part of the sub-basin. This study provides a guideline for improving well deployment and exploration strategies in the future. This study proves that CSSI can be applied as a rigorous, industry-standard inversion technique in the Sufyan sub-basin, and to recommend further application to much larger data sets in the basin.

Based on the seismic and drilling data, casting thin sections, geochemical analysis of oil and rock samples, and hydrocarbon generation history simulation, the hydrocarbon accumulation characteristics and exploration direction of Termit superimposed marine—continental rift basin are discussed. The Termit basin is superimposed with two-phase rifts (Early Cretaceous and Paleogene). The subsidence curves from two wells on the Trakes slope in the east of the basin show high subsidence rate in the Late Cretaceous, which is believed to be high deposition rate influenced by transgression. However, a weak rift may also be developed. The depositional sequences in the Termit basin were controlled by the Late Cretaceous marine transgression cycle and the Paleogene lacustrine transgression cycle, giving rise to two types of superimposed marine—continental “source-sink” deposits. The marine and continental mixed source rocks developed universally in the whole basinduring the marine transgression period, and are overlaid by the Paleogene Sokor 1 reservoir rocks and Sokor 2 caprocks developed during the lacustrine transgression period, forming the unique superimposed marine—continental basin in WCARS. The early low geothermal gradient in the Termit basin resulted in the late hydrocarbon generated by the source rock of Upper Cretaceous Yogou in Paleogene. Mature source rock of Upper Cretaceous Donga developed in the Trakes slope, so that the double-source-supply hydrocarbon and accumulation models are proposed for the Trakes slope in which formed the oil fields. Due to virtue of the newly proposed hydrocarbon accumulation model and the exploration activities in recent years in the Termit superimposed marine—continental rift basin, an additional effective exploration area of about 2500 km2 has been confirmed in the east of the basin. It is believed that potential domains such as Sokor 1, Donga and Upper Cretaceous lithologic traps in the southeast of the basin are key expected targets for exploration and frontier evaluation in future.

借鉴国内断陷盆地岩性油气藏勘探理论与技术,运用层序地层学分析方法,对中非裂谷系Muglad盆地Fula凹陷开展多级次层序地层划分、烃源岩地化分析、油气成藏规律研究和有利区带划分与潜力评价.研究结果表明:①受基准面旋回发育控制,Fula凹陷AG组可划分为 5 个三级层序,湖泛面附近是岩性油气藏最有利分布位置.②研究区AG组主要发育三大物源体系,福西陡坡带为短轴近物源快速沉积,相带平面展布较窄;东北部发育辫状河三角洲沉积,展布范围较大,沉积持续时间长;AG组沉积晚期在东南部发育一套展布范围较小的辫状河三角洲沉积;三角洲前缘和滨浅湖滩坝是岩性油气藏发育的有利相带.③AG组AG2段(SQ4)暗色泥岩主要沉积于浅湖—半深湖环境,干酪根类型为Ⅰ—Ⅱ1型,TOC平均为 3.41%,生烃潜量(S1+ S2)多大于 8 mg/g,为好—极好烃源岩,可为构造-岩性油气藏的形成提供充足的油气来源.④AG组可划分出 7 个岩性油气区带,其中Fula-Moga斜坡带北部成藏条件优越,勘探潜力大.

尼日尔Termit盆地目前已发现90％的储量位于古近系Sokor1组,但是对其主力产层的砂岩储层质量的影响因素仍然缺乏深入研究.本文基于55口井的71 m岩心和568个井壁取心样品资料,开展普通薄片、铸体薄片、X衍射及扫描电镜分析,研究Sokor1组E5-E1各段的储层特征,并探讨其影响因素.研究表明,E5-E1段储层的岩石类型主要为石英砂岩与岩屑石英砂岩,成分成熟度高;结构成熟度低-中等,以细粒和不等粒结构为主,分选中等-差;磨圆差,一般为次棱角-次圆状.孔隙类型以原生孔隙为主,其次为粒间溶蚀孔;成岩作用弱-中等,主要处于中成岩A期阶段.E5-E1段储层孔渗正相关性好,其中E5和E2段储层质量最好,以中孔-中渗和高孔-高渗为主,E4、E3和E1段储层质量次之且非均质强.通过分析,揭示了沉积微相是影响储层质量的主要因素,成岩作用次之.分流河道和河口坝是优质储层发育的主要环境,砂岩中粘土杂基含量是影响储层非均质性的主要因素.

Research on strike-slip faults and their control on the accumulation and distribution of oil and gas in petroliferous basins plays an important role in guiding oil and gas exploration activities. Based on the interpretation and analysis of seismic and drilling logging data, the geometry, evolution process, genetic mechanism and control on the accumulation of oil and gas of strike-slip faults in the Termit Basin are studied by applying coherent techniques. The results show that the strike-slip faults in the Termit Basin are mainly developed in the Trakes Slope in the eastern margin of the basin. The principal displacement zone of these strike-slip faults extending mainly in NNW-SSE and NW-SE, their en-echelon extension fractures (T fracture) are in south-north trending with dextral movement and right-lateral stepping. Most of these strike-slip faults are transtensional faults with few transpressional faults. Negative flower structures and Y-style fault combinations are widely developed, while straightly steep faults andpositive flower structures are locally developed. These strike-slip faults are the result of Cretaceous normal faults subjected to later shear stress in Paleogene Eocene Oligocene. The strike-slip mechanism is that differentially transverse compressive stress between blocks induces shear deformation of early normal faults. Since the Paleogene, the collision accumulation effect of the Eurasian plate and the African plate has formed a near-EW compressive stress inside the African plate. The nonhomogeneous distribution of stress at the northern boundary of the African plate caused differential movement between the Northwest African block and the Northeast African block, which induced the transformation of the Early Cretaceous normal faults on the Trakes Slope into a transtensional strike-slip faults. This series of strike-slip faults formed a group of antithetic fault block traps in Paleogene Sokor1 Formation,Sokor2 Formation and the Upper Cretaceous Yogou Formation, and these strike -slip faults are also vertical migration channels for oil and gas, which are beneficial for the hydrocarbon generated by Upper Cretaceous source rocks to migrating upward and accumulating in the Paleogene reservoirs.

KN area is located in the East of KN depression in Muglad Basin. It has lower exploratory level, only two-dimensional survey lines are distributed in most areas before, and the quality of seismic data is poor. Three wells have been drilled in this area, only one well has low oil production in Bentiu formation, and the other two wells have failed. However, oil was discovered in multiple targets in H area, which is in the SouthEast of KN area. In order to evaluate the oil and gas potential of KN area, combined with the new seismic data of KN 3D area, it is carried out of comprehensive geological and geophysical research work in KN area. By means of well correlation, precise seismic interpretation, tectonic evolution analysis and drilled wells analysis, and comparing with the reservoir forming conditions of adjacent H area, it is concluded that the oil source fault and forming time of traps are the important factors to form the oil and gas reservoir. On this basis, the residual potential of KN area is reevaluated, and it is concluded that the Eastern fault step zone is a favorable area for further exploration.

Esso等多家国际油公司在尼日尔Termit盆地勘探36年,未获商业开发储量规模而退出.中国石油通过技术评价和商务一体化结合,于2003年进入Termit盆地,制定"分步走"勘探策略,一方面在盆地已有发现的西部进行滚动勘探落实储量,另一方面通过攻关核心地质问题,明确主力含油气层系和勘探方向.研究认为:(1)Termit盆地为发育两期裂谷和两期坳陷的叠合裂谷盆地,且在晚白垩世遭受海侵,与中西非地区其他陆相裂谷盆地有所差异;(2)古近系下部砂泥岩互层与上部区域性泥岩构成主力储盖组合;(3)建立了海陆叠合裂谷油气成藏模式,指导发现了4个亿吨级油田群,勘探获得巨大成功,成为海外自主勘探的又一典型成功案例.形成3个启示:(1)技术评价和商务一体化运作是尼日尔区块获取的重要原因;(2)陆相裂谷石油地质理论和技术的成功应用是Termit盆地勘探成功的前提;(3)建立Termit盆地成藏模式是勘探获得重大突破的主因.

CNPC achieved its scaled hydrocarbon discoveries in the Paleogene Sokor1 Formation in Termit basin, Niger in the recent years. Despite the substantial potential is revealed by the latest exploration activities in the Paleogene Sokor2 Formation, studies and literatures on hydrocarbon accumulation of the Sokor2 Formation are rarely reported. In this study, based on the sequence correlation of wells, sedimentology analysis and seismic data interpretation, the Sokor2 Formation is subdivided into three sand units, i.e. the S21, S22 and S23 sand units. The formation slicing and multi-attribute combined impedance inversion technology are used to carry out reservoir prediction. The characteristics of the sedimentary system of the Sokor2 Formation in the Paleogene are well defined. The sedimentary system of the shoreline shallow lake dominates the development of the underwater distributary channels, estuary dams, and far sand dams in the delta front around the lake. It is pointed out that the S23 sand group can be an effective reservoir. It can be a new exploration play in the Termit basin. During the study, it was further raised that the southern Dinga Terrace, southern Yogou Terrace and southern Moul Trough are favorable zones for the new exploration play of S23 sand unit, which guided the recent exploration activities with new successes. The new understanding raises the “regional cap rocks” as a new hydrocarbon exploration play, which filled the research gap of the region. Through this study, the new hydrocarbon exploration play of Sokor2 Formation is defined to widen the exploration domain, which will support the sustainable hydrocarbon discovery in the Termit basin.

含油气盆地走滑构造及其控藏作用研究可以揭示研究区构造特征、形成演化过程,深化油气成藏条件和油气富集规律认识,对于指导油气勘探部署具有重要意义.基于地震与钻井资料的解释与分析,运用断层相干体切片等三维地震精细解释、复杂构造分析等技术,对在Termit盆地东缘Trakes斜坡首次发现的走滑构造几何学、演化过程、成因机制及其控藏作用进行了研究.研究结果表明,Termit盆地东缘Trakes斜坡发育系列走滑断层,其主走滑带走向为北北西-南南东和北西-南东向,其雁列断层(T破裂)走向近南北,呈右旋右阶排列;走滑构造性质以张扭性为主,少量为压扭性,其剖面样式以负花状构造与Y型断裂为主,少量直立断层,局部发育正花状构造;上述走滑构造是早期先存正断层受后期剪切作用的结果,主走滑变形阶段为古近纪始新世-渐新世;新生代以来欧亚板块与非洲板块碰撞,其累积效应在非洲板块内部形成了近南北向挤压应力,由于挤压应力在非洲板块北部边界的不均衡性,造成西北非陆块与东北非陆块发生差异运动,这种差异运动导致Trakes斜坡早期发育的早白垩世正断层发生张扭性走滑变形.在该系列走滑断层带内,形成一系列古近系Sokor1组和Sokor2组以及上白垩统Yogou组反向断块圈闭,其主走滑位移带构成油气垂向运移通道,有利于上白垩统烃源岩生成油气向上运移、在浅层聚集与成藏.

Almost 90% of reserves was discovered in the Paleogene Sokorl Formation in Termit Basin, Niger. However, impacts on reservoir quality of these sandstones are still poorly studied. Petrographic of these sandstones of 71m conventional cores and 568 sidewall core samples from 55 wells was studied with thin sections, casting thin sections, X-ray diffraction and SEM investigations. Based on the results, the authors analyzed the lithological characteristics of the Sokorl sandstones (ES, E4, E3, E2 and El members) and explore the related factors. The results show that the rock types are quartz sandstones and lithic quartz sandstones which are characterized by high component maturity, low-medium texture maturity and poor-fair rounding. Fine grained and inequigranular textures are dominated types with poor-medium sorting and subangular-subrounded grains. Poor-medium diagenesis and middle diagenetic A stage of E5-E1 sandstones lead to well-developed primitive intergranular and intergranular dissolution pores. Porosity and permeability data based on cores show a good positive relationship in E5-E1 sandstones. E5 and E2 reservoirs are of the highest qualities, and they are characterized by medium porosity and medium permeability, and some with high porosity and high permeability. However, the reservoir quality of E4, E3 and El sandstones are characterized by strong heterogeneity. Microfacies of sandstones is the key controlling factor for the reservoir quality, while diagenesis is the second controlling factor. Distributary channel and mouth bar are the best sedimentary environments for high quality reservoirs in the study area. Clay matrix content in the sandstones plays an important role for reservoir heterogeneity.

F Sub-Basin located in NE of M Basin which is a typical rifted basin in Sudan. With the progress of exploration and development for more than 20 years, remained traps are limited with small area, deep targets, and complex structure and the difficulty increased for exploration and development. More challenges come out for: 1) poor data quality and mis-tie of 2D and 3D seismic data of deep targets resulted from different acquisition and processing parameters in different time; 2) uncertainty and difficulty of identifying faulted traps on deep targets from complex geological conditions. More researches and methods have been tested to solve the problems. Finally, some new integrated trap identification technologies have been formed, such as integrated interpretation with processing technology, integrated seismic interpretation technology with geology and integrated seismic interpretation technology with time and spatial data etc., and new faulted traps which hadn’t been found with normal interpretation methods before have been identified and new break-through have been made for deep targets of AG in old oil fields. It is sure that systematic progressive exploration and development and the application of integrated trap identification technology are efficient ways for less input, more output and early benefit for complex faulted basin.

Sharaf-AG Low Uplift is located in the central area of Nugara Depression in Muglad Basin, Sudan. It has similar faulted system as the other oil and gas rich sub-basin but it doesn’t have much discovery in oil and gas. So the study of tectonic characteristics has been carried. After detailed seismic interpretation and analysis, the traps controlled by the northwest normal fault have a ‘beaded’ distribution characteristic from southwest to northeast under an extensional- torsional stress. And maybe it destroyed the storage of oil and gas in this area.

成岩作用在沉积岩形成演化过程中占有重要位置.由于不同盆地沉积及构造演化的差异性,导致其成岩作用也有不同的特点.以样品实验分析为基础,开展尼日尔Termit盆地白垩系砂岩成岩作用研究,明确了该盆地白垩系砂岩成岩作用的主要类型及其对储层的影响;根据成岩现象、黏土矿物特征与变化规律、包裹体均一温度等多个方面对该盆地白垩系砂岩储层进行成岩阶段划分,认为研究区白垩系砂岩大多处于中成岩A阶段,埋藏较浅的砂岩处于早成岩B阶段.Termit盆地白垩系砂岩的岩石类型是影响成岩作用的一个重要因素,由于该盆地白垩系砂岩以石英砂岩为主,石英颗粒的强支撑作用减弱了压实作用对储层的破坏,原生粒间孔是最为发育的孔隙类型,此外还发育少量粒内孔隙、粒间溶孔等孔隙.Termit盆地不同区带白垩系砂岩储层的发育具有一定的差异,Fana低凸起和Yogou斜坡储层相对较发育,储层物性好;Soudana隆起带和Dinga断阶储层物性差.Fana低凸起具有很好的勘探潜力,从钻探结果中也得到了证实,是后续白垩系勘探的重点区带.

Petrography of the Upper Cretaceous sandstones of 218 side-wall coring samples from 17 wells was described by thin section, cathodoluminescence, X-ray diffraction techniques and heavy mineral analysis. Based on the result, we try to study the lithological characteristics of the Upper Cretaceous sandstones and explore the related factors. The results show that the Upper Cretaceous sandstones, having high component maturity, are quartzarenite with quartz percentage more than 86%. There is little content of potash feldspar, calcite and plagioclase in the rock with the content of about 5%. This kind of rock is more advantageous to the preservation of primary porosity. Pore-filling cements mainly consist of clay minerals with the content of about 7%, which are dominated by kaolinite. It is favourable to the preservation of intergranular pore. The cements are mainly siliceous, calcite and ferruginous. Because the Content of cement is little, the damage to the reservoir is not effective. Main heavy minerals include magnetite, hematite, zircon, apatite, indicating that the Upper Cretaceous sandstones may be source from granite rocks. With low texture maturity, mainly have fine grained texture and minor inequigranular texture. Grains are mainly characterized by point contact and subangular-subcircular rounding, with fair to poor sorting. It is different from domestic quartz sandstone that deposited in coastal environment; the quartz sandstone in the study area has high component maturity and low structural maturity. It Indicate that the source rocks may be rich in quartz, and the same time the sandstone deposited in the near source fluvial deltas. Cementation is the main factor that influences the Upper Cretaceous sandstones. Because main sandstones are quartzarenite, compaction has less negative effect on reservoirs which helps to maintain porosity of sandstones. The face rate is more than 15% if the buried depth of sandstone is less than 2500 meters. Dissolution, common in feldspar dissolution, has certain influence on the Upper Cretaceous reservoir. Dissolution produces intergranular and intragranular dissolved pores, and enlarges primary pores, which improves reservoir performance.

3D structural model building is a frontier technique in tectonic research with superior performance in practicability,accuracy and visualization.This technique is normally used for studying local structures,and its application in basin-level model building has been challenging.Here,we applied 3D structural modeling to the complex structures of the Termit Basin,where two rifts were developed in the Early Cretaceous and Paleogene.Taking the basin (area 30000 km2) as a whole,we built a 3D structural model using 2D and 3D seismic data in addition to more than 100 sets of well logging data,and overcoming technical difficulties such as multi-fault system,structural complexity and large data volume.Layer and fault grading simulations,automatic fault rename and loop generation,and fault relationship definition,were successfully applied to the Termit Basin.Thus we have developed new tools for studying fine structures at the basin scale.We showed that structural sections in any directions or planes and any well-tie sections in the entire basin can be extracted for model building;and 3D model of each zone or local structure can be built to make structural analysis more accurate.Our 3D geological structural model has been widely used in the Termit Basin exploration,in areas such as tectonic units division,exploration-zone evaluation,target optimization and well location demonstration.The model showed that the overlapping sequences of the lower Cretaceous sag and upper Paleogene rift formed the big lower and small upper sag structures in the Termit Basin,respectively.It also showed that in the depression period of the Late Cretaceous,marine source rocks distributed widely;and later in the Paleogene,the superposed rifts formed above the marine source rocks,creating favorable loci for hydrocarbon to accumulate in the Paleogene.Based on the newly established basin structural model,the structural characteristics and hydrocarbon accumulation potential of each structural zone can be further defined.Specifically,the Fana low uplift,located between the Moul and Dinga Sags,has relatively well developed fractures for hydrocarbon migration and accumulation,making it the most favorable exploration zone in the Termit Basin.The Araga graben,where fractures were developed,presents good hydrocarbon accumulation conditions.In contrast,the Moul and Dinga Sags,although having good oil deposit,have poor exploration potential due to poor upward migration caused by weak tectonic activities and undeveloped fractures.Moreover,the basin structural model allowed detailed analysis of the tectonic styles and fractures,resulted from the superposed rifts and their controlling effects on hydrocarbon accumulation in the basin,so as to optimize exploration targeting.Application of the structure model has made breakthroughs in the exploration of the upper Paleogene and lower Cretaceous assemblages.

Niger Termit Basin experienced the first and second rifting cycles during the Early Cretaceous and Eocene-Oligocene,respectively.The two cycles originated through different geodynamic and kinematical mechanisms;as a result,they have different structural styles and basin features.This paper analyzed the geodynamic origin,kinematical features and structural styles of the second rifting cycle,as well as implications of these factors in hydrocarbon accumulation in the Termit Basin,Niger.The findings are the following.During the Eocene-Oligocene,and under the regional compression stress field caused by the Africa-Arab and Eurasia plate collision,the Termit Basin moved as an extrusion from the inner Africa plate in the NEE-SWW direction and acted as typical strike-slip with extensional characteristics.Building on the NW-SE fault system in the first rifting cycle,the second rifting cycle developed the NNW-SSE fault system in the Termit Basin.The basin has primarily graben-horst and half graben structures,with graben style in the north,and Domino half graben style in the south.The Eocene-Oligocene transtension formed a series of en echelon normal faults-connected by soft linkage-and developed a large number of strike slip transfer structures at both basin and sub-basin levels.The Paleogene structure transfer zones could be divided into three basic styles,i.e.,parallel,anti-parallel and back to back styles,of which,overlapping parallel,anti-parallel and back to back overlapping transfer zones are the main structural styles observed in the Termit Basin.The second rifting cycle controlled the Eocene-Oligocene depositional system of the Termit Basin.During the Eocene initial rifting stage,delta system was formed in Sokor-1 Fm.;and during the Oligocene-Early Miocene deep-rifting stage,lacustrine mudstone was deposited in the Sokor-2 Fm.,which generated the most advantage reservoir-seal assemblage in the Termit Basin.Meanwhile,structural transfer in the second cycle helped to form many fault blocks and noses and faulted anticline structures,which account for the main types of traps in the Termit Basin.Furthermore,during the Oligocene-Early Miocene deeprifting stage,the main active fault became connected to the Cretaceous source kitchen,this led to extensive vertical and lateral hydrocarbon migrations in the Termit Basin.The growth indices of the main faults implied that the Paleogene hydrocarbon distribution and accumulation were controlled by the fault activity during the Oligocene-Early Miocene deep-rifting stage.Based on above analysis,the lithological traps of the Sokor-1 and mid-lower Sokor-2 Fms.—located on the strike slope of transfer zones,and new petroleum system in the Upper Sokor-2 Fm.,all have hydrocarbon potentials and could be further explored.

The Termit Basin of Niger,covered with low salinity stratum water (salinity 200 × 10-6-1500 × 10-6),developed a highly complex oil-gas-water system of complex fluid type,with several oil-gas-water systems present including normal and low-resistivity oil zones.Previous studies demonstrated that it is very difficult to identify the complex fluid type by single data analysis,especially in low-resistivity oil zones.It has also been proven by drilling that,in the Termit Basin,low resistivity oil zones were commonly developed in the Sokor 1 and Yogou formations in the Paleogene and Cretaceous,respectively.The low-resistivity oil zones have two main resistivity features:similar resistivity for the reservoir and adjacent water zone within the same sedimentary period,and similar resistivity for the reservoir and adjacent mudstonc.Here,we studied the microscopic mechanism and factors influencing low resistivity oil zones,by using thin section,scanning electron microscopy,X-ray diffraction and clay mineral analysis techniques,combining with capillary pressure data and knowledges of rock size,pore structure,clay mineral content type and thickness of oil layer.The results showed that high saturation of bound water due to rock's fine grain size,high clay content and development of micro pores,was the main microscopic cause for the low resistivity oil zone in the basin;while thin reservoir and invasion of salt-water mud filtrate were largely macro impact factors.According to their dominant characteristics and cause,the low resistivity oil zones can be effectively identified by cross plotting resistivity vs.natural gamma,resistivity vs.relative value of spontaneous potential,GEOFI vs.TG,and using fluid density calculated by RFT pressure data.Furthermore,our research revealed that the low-resistivity oil zones are laterally distributed in the oil field of Dinga fault terrace,Fana low uplift and Yogou slope,and vertically distributed in the fluvial sediments of E1 and E2 sand in the Sokor1 Formation and delta,and lacustrine sediments of the Cretaceous.

采用色谱质谱(GC-MS)技术分析了中西非裂谷系(WCARS) Termit盆地古近系-下白垩统原油中规则甾烷、4-甲基甾烷、三芳甾烷和甲基三芳甾烷的分布特征并据此划分了Termit盆地原油族群.结果表明:研究区绝大多数原油中C29相对于C27和C28规则甾烷含量高;C30 4-甲基甾烷丰度低或未检测出;C26-C27-C28三芳甾烷组成中,C27 20R和C26 20S异构体丰度相对较低;三芳甲藻甾烷相对丰度较高.这些原油应同属一个原油族群(族群Ⅰ),来自同一个烃源灶.而来自DD-1、DD-2、D-1和T-1等部分井的原油中C29规则甾烷相对含量低于族群Ⅰ原油,并检测出较高丰度的C30 4-甲基甾烷;三芳甾烷和三芳甲藻甾烷分布也明显不同,应属于另一原油族群(族群Ⅱ).在Termit盆地寻找族群Ⅱ的原油具有重要的勘探前景.