Superimposed hydrocarbon accumulation through multi-source and multi-stage evolution in the Cambrian Xixiangchi Group of eastern Sichuan Basin:A case study of the Pingqiao gas-bearing anticline

The Xixiangchi Group in eastern Sichuan Basin has great potential for natural gas exploration.However,there is a lack of in-depth studies of the hydrocarbon sources and the formation and evolution of gas reservoirs in this Group.Systematic investigation about the gas reservoir in Pingqiao anticline was consequently carried out in terms of characteristics of reservoir bitumen,the geochemical characteristics of natural gas,diagenetic minerals,and fluid inclusions.Based on this,combined with the reconstruction of the burial history,thermal evolution history and uplifting history of strata,and analysis of the regional tectonic settings,the hydrocarbon sources were identified and the formation and evolutionary processes of the gas reservoirs in Xixiangchi Group was revealed in this study.It was shown that the gas reservoirs have mixed gas sources from the shale source rocks in the Lower Cambrian Qiongzhusi Formation and in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation,and experienced several evolutionary stages,including the paleo-oil reservoir stage from the Late Siliurian to the Middle Permian,the paleo-gas reservoir stage from the Late Permian to the Early Cretaceous,and the superimposed accumulation and mixed-source gas reservoir stage since the Late Cretaceous.The mixed-source gas reservoir is formed by the adjustment of the Xixiangchi Group paleo-gas reservoirs and depressurization of the overpressure Wufeng-Longmaxi shale gas reservoirs and the charging of gas into the Xixiangchi Group reservoir of the Pingqiao anticline since the Late Cretaceous,which show obvious superimposed accumulation characteristics.There are different accumulation patterns in different geological periods.The accumulation pattern of the“old source-young reservoir”(i.e.hydrocarbons generated from older source rocks accumulating in younger reservoirs)dominates before the Late Cretaceous,and that of“juxtaposed young source-old reservoir”(i.e.hydrocarbons generated from younger source rocks accumulating in juxtaposed older reservoirs)dominates after the Early Cretaceous.Moreover,faults acted as critical vertical pathways for hydrocarbon migration during the evolution of the Xixiangchi Group gas reservoirs.This model provides new insights and theoretical basis for evaluation and mapping of the Xixiangchi Group play fairway in eastern Sichuan Basin.

A hydrocarbon enrichment model and prediction of favorable accumulation areas in complicated superimposed basins in China

The geologic conditions of superimposed basins in China are very complicated. This is mainly shown by multi-phase structural evolution, multiple sets of source-reservoir-cap rock combinations, multiple stages of hydrocarbon generation and expulsion from source rocks, multi-cycle hydrocarbon enrichment and accumulation, and multi-phase reservoir adjustment and reconstruction. The enrichment, accumulation and distribution of hydrocarbon is mainly controlled by the source rock kitchen, paleo- anticline, regional cap rock and intensity of tectonic movement. In this paper, the T-BCMS model has been developed to predict favorable areas of hydrocarbon accumulation in complicated superimposed basins according to time and spatial relationships among five key factors. The five factors include unconformity surface representing tectonic balancing （B）, regional cap rock representing hydrocarbon protection （C）, paleo-anticline representing hydrocarbon migration and accumulation （M）, source rock kitchen representing hydrocarbon generation and expulsion （S） and geological time （T）. There are three necessary conditions to form favorable areas of hydrocarbon accumulation. First, four key factors BCMS should be strictly in the order of BCMS from top to bottom. Second, superimposition of four key factors BCMS in the same area is the most favorable for hydrocarbon accumulation. Third, vertically ordered combination and superimposition in the same area of BCMS should occur at the same geological time. The model has been used to predict the most favorable exploration areas in Ordovician in the Tarim Basin in the main hydrocarbon accumulation periods. The result shows that 95% of the discovered Ordovician hydrocarbon reservoirs are located in the predicted areas, which indicates the feasibility and reliability of the key factor matching T-BCMS model for hydrocarbon accumulation and enrichment.

Classification of Complex Reservoirs in Superimposed Basins of Western China

Many of the sedimentary basins in western China were formed through the superposition and compounding of at least two previously developed sedimentary basins and in general they can be termed as complex superimposed basins. The distinct differences between these basins and monotype basins are their discontinuous stratigraphic sedimentation, stratigraphic structure and stratigraphic stress-strain action over geological history. Based on the correlation of chronological age on structural sections, superimposed basins can be divided into five types in this study： （1） continuous sedimentation type superimposed basins, （2） middle and late stratigraphic superimposed basins, （3） early and late stratigraphic superimposed basins, （4） early and middle stratigraphic superimposed basins, and （5） long-term exposed superimposed basins. Multiple source-reservoir-caprock assemblages have developed in such basins. In addition, multi-stage hydrocarbon generation and expulsion, multiple sources, polycyclic hydrocarbon accumulation and multiple-type hydrocarbon reservoirs adjustment, reformation and destruction have occurred in these basins. The complex reservoirs that have been discovered widely in the superimposed basins to date have remarkably different geologic features from primary reservoirs, and the root causes of this are folding, denudation and the fracture effect caused by multiphase tectonic events in the superimposed basins as well as associated seepage, diffusion, spilling, oxidation, degradation and cracking. Based on their genesis characteristics, complex reservoirs are divided into five categories： （1） primary reservoirs, （2） trap adjustment type reservoirs, （3） component variant reservoirs, （4） phase conversion type reservoirs and （5） scale-reformed reservoirs.

Multiple-Element Matching Reservoir Formation and Quantitative Prediction of Favorable Areas in Superimposed Basins

Superimposed basins in West China have experienced multi-stage tectonic events and multicycle hydrocarbon reservoir formation, and complex hydrocarbon reservoirs have been discovered widely in basins of this kind. Most of the complex hydrocarbon reservoirs are characterized by relocation, scale re-construction, component variation and phase state transformation, and their distributions are very difficult to predict. Research shows that regional caprock （C）, high-quality sedimentary facies （Deposits, D）, paleohighs （Mountain, M） and source rock （S） are four geologic elements contributing to complex hydrocarbon reservoir formation and distribution of western superimposed basins. Longitudinal sequential combinations of the four elements control the strata of hydrocarbon reservoir formation, and planar superimpositions and combinations control the range of hydrocarbon reservoir and their simultaneous joint effects in geohistory determine the time of hydrocarbon reservoir formation. Multiple-element matching reservoir formation presents a basic mode of reservoir formation in superimposed basins, and we recommend it is expressed as T-CDMS. Based on the multiple-element matching reservoir formation mode, a comprehensive reservoir formation index （Tcdms） is developed in this paper to characterize reservoir formation conditions, and a method is presented to predict reservoir formation range and probability of occurrence in superimposed basins. Through application of new theory, methods and technology, the favorable reservoir formation range and probability of occurrence in the Ordovician target zone in Tarim Basin in four different reservoir formation periods are predicted. Results show that central Tarim, Yinmaili and Lunnan are the three most favorable regions where Ordovician oil and gas fields may have formed. The coincidence of prediction results with currently discovered hydrocarbon reservoirs reaches 97 %. This reflects the effectiveness and reliability of the new theory, methods and technology.

Alteration and Reformation of Hydrocarbon Reservoirs and Prediction of Remaining Potential Resources in Superimposed Basins

Complex hydrocarbon reservoirs developed widely in the superimposed basins of China formed from multiple structural alterations, reformation and destruction of hydrocarbon reservoirs formed at early stages. They are characterized currently by trap adjustment, component variation, phase conversion, and scale reformation. This is significant for guiding current hydrocarbon exploration by revealing evolution mechanisms after hydrocarbon reservoir formation and for predicting remaining potential resources. Based on the analysis of a number of complex hydrocarbon reservoirs, there are four geologic features controlling the degree of destruction of hydrocarbon reservoirs formed at early stages： tectonic event intensity, frequency, time and caprock sealing for oil and gas during tectonic evolution. Research shows that the larger the tectonic event intensity, the more frequent the tectonic event, the later the last tectonic event, the weaker the caprock sealing for oil and gas, and the greater the volume of destroyed hydrocarbons in the early stages. Based on research on the main controlling factors of hydrocarbon reservoir destruction mechanisms, a geological model of tectonic superimposition and a mathematical model evaluating potential remaining complex hydrocarbon reservoirs have been established. The predication method and technical procedures were applied in the Tazhong area of Tarim Basin, where four stages of hydrocarbon accumulation and three stages of hydrocarbon alteration occurred. Geohistorical hydrocarbon accumulation reached 3.184 billion tons, of which 1.271 billion tons were destroyed. The total volume of remaining resources available for exploration is -1.9 billion tons.

Comparative Analysis of Sequence Characteristics among Different Superimposed Stages of the Chelif Basin,Algeria

Superimposed basins were investigated with respect to tectonic evolution, sediment deposition and petroleum characteristics within a single superposition stage generally. The comparative study was seldom seen. Sequence characteristics were compared for two different superimposed stages - an expanding rifting stage and a depression-foreland transition stage - in the Chelif Basin during the Miocene in this paper. A model and mechanism for sequence evolution of superimposed basins in different dynamic situations are discussed with respect to sequence similarities and differences. The compared characters include sequence thickness, sequence boundaries and system tracts, as well as sediment deposition within sequences and sequence development patterns. Finally, some typical features of sequence development concomitant with changes of superimposed stages in the Chelif Basin are discussed.

Late-Stage Reservoir Formation Effect and Its Dynamic Mechanisms in Complex Superimposed Basins

Complex superimposed basins exhibit multi-stage tectonic events and multi-stage reservoir formation; hydrocarbon reservoirs formed in the early stage have generally late-stage genesis characteristics after undergoing adjustment, reconstruction and destruction of later-stage multiple tectonic events. In this paper, this phenomenon is called the late-stage reservoir formation effect. The late-stage reservoir formation effect is a basic feature of oil and gas-forming reservoirs in complex superimposed basins, revealing not only multi-stage character, relevance and complexity of oil and gas- forming reservoirs in superimposed basins but also the importance of late-stage reservoir formation. Late-stage reservoir formation is not a basic feature of oil and gas forming reservoir in superimposed basins. Multi-stage reservoir formation only characterizes one aspect of oil and gas-forming reservoir in superimposed basins and does not represent fully the complexity of oil and gas-forming reservoir in superimposed basins. We suggest using ＂late-stage reservoir formation effect＂ to replace the ＂late-stage reservoir formation＂ concept to guide the exploration of complex reservoirs in superimposed basins. Under current geologic conditions, the late-stage reservoir formation effect is represented mainly by four basic forms： phase transformation, scale reconstruction, component variation and trap adjustment. The late-stage reservoir formation effect is produced by two kinds of geologic processes： first, the oil and gas retention function of various geologic thresholds （hydrocarbon expulsion threshold, hydrocarbon migration threshold, and hydrocarbon accumulating threshold） causes the actual time of oil and gas reservoir formation to be later than the time of generation of large amounts of hydrocarbon in a conventional sense, producing the late-stage reservoir formation effect; second, multiple types of tectonic events （continuously strong reconstruction, early-stage strong reconstruction, middle-stage strong reconstruction, late-stage strong reconstruction and long-term stable sedimentation） after oil and gas reservoir formation lead to adjustment, reconstruction and destruction of reservoirs formed earlier, and form new secondary hydrocarbon reservoirs due to the late-stage reservoir formation effect.

Superimposed versus residual basin:The North Yellow Sea Basin

北方黄海盆是中生代和新生代盆。把外形基于盆边缘，沉积变瘦，盆和 vitrinite 反射的尺寸和形状，诺思黄海盆不是剩余盆。盆的开发的分析三结构的层，独立石油系统，边界差错活动， MesozoicCenozoic 沉积中心的移植，在不同时期期间形成的不同的盆结构，和二阶段的扩大的盆和一个阶段消沉盆的重叠，北方黄海盆作为附加的盆被认出。

Types, Evolution and Pool-Controlling Significance of Pool Fluid Sources in Superimposed Basins:A Case Study from Paleozoic and Mesozoic in South China

Having multiple tectonic evolution stages, South China belongs to a superimposed basin in nature. Most marine gas pools became secondary pools. The pool fluid sources serve as the principal pool-controlling factors. On the basis of eight typical petroleum pools, the type, evolution in time-space, and the controlling of petroleum distribution of pool fluid sources are comprehensively analyzed. The main types of pool fluid sources include hydrocarbon, generated primarily and secondly from source rocks, gas cracked from crude oil, gas dissolved in water, inorganic gas, and mixed gases. In terms of evolution, the primary hydrocarbon was predominant prior to Indosinian; during Indosinian to Yenshanian the secondary gas includes gas cracked from crude oil, gas generated secondarily, gas dissolved in water, and inorganic gas dominated; during Yenshanian to Himalayan the most fluid sources were mixed gases. Controlled by pool fluid sources, the pools with mixed gas sources distributed mainly in Upper Yangtze block, especially Sichuan （四川） basin; the pools with primary hydrocarbon sources distributed in paleo-uplifts such as Jiangnan （江南）, but most of these pools became fossil pools; the pools with secondary hydrocarbon source distributed in the areas covered by Cretaceous and Eogene in Middle-Lower Yangtze blocks, and Chuxiong （楚雄）, Shiwandashan （十万大山）, and Nanpanjiang （南盘江） basins; the pools with inorganic gas source mainly formed and distributed in tensional structure areas.

New understanding and exploration direction of hydrocarbon accumulation in Termit Basin, Niger

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 km2has 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.

中国中西部含油气盆地超深层油气成藏条件与勘探潜力分析

随着油气工业发展,向深层超深层领域进军已成为常规油气勘探开发的主要趋势。通过对中国中西部含油气盆地超深层油气勘探与研究进展的深入分析,明确深层超深层油气成藏的有利条件,指出中西部叠合盆地的海相碳酸盐岩、碎屑岩、基岩及火山岩3大领域是未来超深层油气勘探重点领域,超深层元古界是值得勘探重视的潜在领域,并指出超深层油气地质理论与关键技术的攻关方向。研究表明:(1)克拉通盆地海相碳酸盐岩发育以多套海相烃源岩、白云岩和断控型缝洞体等规模储集层、3类有利成藏组合,是寻找碳酸盐岩大油气田的重点领域;(2)前陆盆地下组合发育以煤系为主的湖相优质烃源岩、(扇)三角洲砂体为主的规模储集层、大型构造圈闭,是寻找碎屑岩大油气田的重点领域;(3)以花岗岩和变质岩为主的基岩储集层不受埋深限制,源岩-基岩接触型成藏组合最有利,紧邻生烃凹陷及大型走滑断裂带的基岩潜山是深层-超深层基岩油气藏勘探的重点领域;(4)中新元古界受超大陆裂解及全球冰期影响,发育受陆内裂陷控制的优质烃源岩,资源潜力较大,未来勘探地位值得重视。

油气地质勘探将从烃源岩时代进入幔源油气新时代

简要梳理了人类石油勘探发展历程,分析并研究了国内外25个油田(或盆地、油区)的勘探资料,得出结论:石油地质勘探经历过的第一个阶段是背斜(构造)勘探阶段(19世纪60年代~20世纪60年代),第二个阶段是烃源岩勘探阶段(20世纪30年代至今),现在已经进入一个全新的阶段——幔源油气勘探时代。依据幔源油气理论,提出了创新的“盆-壳-幔镜像叠置成藏模式”。

Hydrocarbon migration and accumulation along the fault intersection zone-a case study on the reef-flat systems of the No.1 slope break zone in the Tazhong area, Tarim Basin

Understanding hydrocarbon migration and accumulation mechanisms is one of the key scientif ic problems that should be solved for effective hydrocarbon exploration in the superimposed basins developed in northwest China. The northwest striking No.1 slope break zone, which is a representative of superimposed basins in the Tarim Basin, can be divided into five parts due to the intersection of the northeast strike-slip faults. Controlled by the tectonic framework, the types and properties of reservoirs and the hydrocarbon compositions can also be divided into five parts from east to west. Anomalies of all the parameters were found on the fault intersection zone and weakened up-dip along the structural ridge away from it. Thus, it can be inferred that the intersection zone is the hydrocarbon charging position. This new conclusion differs greatly from the traditional viewpoint, which believes that the hydrocarbon migrates and accumulates along the whole plane of the No.1 slope break zone. The viewpoint is further supported by the evidence from the theory of main pathway systems, obvious improvement of the reservoir quality （2-3 orders of magnitude at the intersection zone） and the formation mechanisms of the fault intersection zone. Differential hydrocarbon migration and entrapment exists in and around the strike- slip faults. This is controlled by the internal structure of faults. It is concluded that the more complicated the fault structure is, the more significant the effects will be. If there is a deformation band, it will hinder the cross fault migration due to the common feature of two to four orders of magnitude reduction in permeability. Otherwise, hydrocarbons tend to accumulate in the up-dip structure under the control of buoyancy. Further research on the internal fault structure should be emphasized.

Structural Characteristics and Formation Dynamics: A Review of the Main Sedimentary Basins in the Continent of China

The formation and evolution of basins in the China continent are closely related to the collages of many blocks and orogenic belts. Based on a large amount of the geological, geophysical, petroleum exploration data and a large number of published research results, the basement constitutions and evolutions of tectonic-sedimentary of sedimentary basins, the main border fault belts and the orogenesis of their peripheries of the basins are analyzed. Especially, the main typical basins in the eight divisions in the continent of China are analyzed in detail, including the Tarim, Ordos, Sichuan, Songliao, Bohai Bay, Junggar, Qiadam and Qiangtang basins. The main five stages of superimposed evolutions processes of basins revealed, which accompanied with the tectonic processes of the Paleo-Asian Ocean, Tethyan and Western Pacific domains. They contained the formations of main Cratons （1850-800 Ma）, developments of marine basins （800-386 Ma）, developments of Marine- continental transition basins and super mantle plumes （386-252 Ma）, amalgamation of China Continent and developments of continental basins （252-205 Ma） and development of the foreland basins in the western and extensional faulted basin in the eastern of China （205~0 Ma）. Therefore, large scale marine sedimentary basins existed in the relatively stable continental blocks of the Proterozoic, developed during the Neoproterozoic to Paleozoic, with the property of the intracontinental cratons and peripheral foreland basins, the multistage superimposing and late reformations of basins. The continental basins developed on the weak or preexisting divisional basements, or the remnant and reformed marine basins in the Meso-Cenozoic, are mainly the continental margins, back-arc basins, retroarc foreland basins, intracontinental rifts and pull-apart basins. The styles and intensity deformation containing the faults, folds and the structural architecture of regional unconformities of the basins, responded to the openings, subductions, closures of oceans, the continent-continent collisions and reactivation of orogenies near the basins in different periods. The evolutions of the Tianshan-Mongol-Hinggan, Kunlun-Qilian-Qinling-Dabie-Sulu, Jiangshao-Shiwandashan, Helanshan-Longmengshan, Taihang-Wuling orogenic belts, the Tibet Plateau and the Altun and Tan- Lu Fault belts have importantly influenced on the tectonic-sedimentary developments, mineralization and hydrocarbon reservoir conditions of their adjacent basins in different times. The evolutions of basins also rely on the deep structures of lithosphere and the rheological properties of the mantle. The mosaic and mirroring geological structures of the deep lithosphere reflect the pre-existed divisions and hot mantle upwelling, constrain to the origins and transforms dynamics of the basins. The leading edges of the basin tectonic dynamics will focus on the basin and mountain coupling, reconstruction of the paleotectonic-paleogeography, establishing relationship between the structural deformations of shallow surface to the deep lithosphere or asthenosphere, as well as the restoring proto-basin and depicting residual basin of the Paleozoic basin, the effects of multiple stages of volcanism and paleo- earthquake events in China.

Processes and causes of Phanerozoic tectonic evolution of the western Tarim Basin,northwest China

This paper addresses the Phanerozoic tectonic evolution of the western Tarim Basin based on an integrated stratigraphic,structural and tectonic analysis.P-wave velocity data show that the basin has a stable and rigid basement.The western Tarim Basin experienced a complex tectonic evolutionary history,and this evolution can be divided into six stages:Neoproterozoic to Early Ordovician,Middle Ordovician to Middle Devonian,Late Devonian to Permian,Triassic,Jurassic to Cretaceous and Paleogene to Quaternary.The western Tarim Basin was a rift basin in the Neoproterozoic to Early Ordovician.From the Middle Ordovician to Middle Devonian,the basin consisted of a flexural depression in the south and a depression that changed from a rift depression to a flexural depression in the north during each period,i.e.,the Middle-Late Ordovician and the Silurian to Middle Devonian.During the Late Devonian to Permian,the basin was a depression basin early and then changed into a flexural basin late in each period,i.e.,the Late Devonian to Carboniferous and the Permian.In the Triassic,the basin was a foreland basin,and from the Jurassic to Cretaceous,it was a downwarped basin.After the Paleogene,the basin became a rejuvenated foreland basin.Based on two cross sections,we conclude that the extension and shortening in the profile reflect the tectonic evolution of the Tarim Basin.The Tarim Basin has become a composite and superimposed sedimentary basin because of its long-term and complicated tectonic evolutionary history,highly rigid and stable basement and large size.

中国超深层油气勘探领域研究进展与关键问题

基于油气勘探发现和地质认识进展,从成盆、成烃、成储及成藏的内在地质过程出发,揭示沉积盆地超深层油气的形成与赋存规律并探讨超深层领域的关键科学问题。中国超深层主要经历中新元古代和早古生代2个伸展-聚敛旋回,构造-沉积分异产生空间上相邻的源-储组合;发育丘滩体型、岩溶缝洞型、断溶型、白云岩型和断裂带型等多种类型规模性碳酸盐岩储集体、超压型碎屑岩和基岩裂缝性储集体;油气多期复合成藏,晚期调整定位;油气分布受高能滩带、区域不整合面、古隆起与大型断裂带等的控制;赋存多种成因的天然气和轻质油。超深层油气资源占剩余总资源量的33%,为中国油气勘探的重要接替领域;超深层的大型成藏地质单元与规模富集区带将是持续取得油气大发现的重点方向,勘探前景广阔。超深层油气地质条件和富集区带预测为油气地质学研究的关键科学问题。

煤系气叠置含气系统与天然气成藏特征——以沁水盆地榆社—武乡示范区为例

中国煤系气资源丰富,其中沁水盆地是中国煤系气分布的主要盆地之一,明确煤系气叠置含气系统分布特征,有助于实现煤系气的共探合采。为此,以沁水盆地榆社—武乡示范区石炭系—二叠系含煤地层为研究对象,在分析煤系气地质特征的基础上,划分了煤系气叠置含气系统,研究了煤系气的源岩—储层共生组合特征、储层分布特征、共生成藏特征,并详细分析了示范井的压裂合采效果,预测了示范井产量。研究结果表明:①研究区目标煤系空间上发育3个独立叠置含气系统,其中含气系统Ⅰ是以15号煤和富有机质泥岩为主要烃源岩的“泥岩—煤—泥岩”组合;含气系统Ⅱ是以11号、12号煤和富有机质泥岩为主要烃源岩的“泥岩—砂岩—煤—泥岩”组合和以8号煤与富有机质泥岩为主要烃源岩的“泥岩—煤—砂岩—泥岩”组合;含气系统Ⅲ是以3号煤和富有机质泥岩为主要烃源岩的“泥岩—煤—砂岩”组合;②煤系气储层具有单层厚度薄、累计厚度大的空间展布特征,各含气系统中气藏组合类型以煤层气为主,页岩气和致密砂岩气发育较差;③示范井煤系气合采甜点含气层段发育于含气系统Ⅱ和Ⅲ,具备压裂合采基础,运用电缆桥塞与射孔联作投球分层压裂工艺配套技术实现了深部煤系气的有效开采。结论认为:①叠置含气系统兼容性是控制煤系气开采的关键因素,未来仍需不断优化排采制度以提高煤系气的合采产能;②研究成果对深化煤系气共生成藏机理、优选合采甜点层段、释放深部煤层气资源和实现煤系气高效合采均具有理论和实践意义。

渤海湾盆地旅大隆起区多期叠加构造及其对潜山的控制作用

旅大隆起区位于渤海湾盆地渤海海域的西北部,经历了中生代—新生代多幕构造运动的叠加改造,内幕断裂发育类型多样、变形复杂,前人对其古生界和中生界的构造研究仍相对薄弱。基于三维地震数据的详细构造解析揭示,研究区印支期主要表现为自南向北的逆冲推覆,形成了北西—近东西向的宽缓褶皱和逆冲推覆断裂;燕山早期和中期主要表现为挤压背景下的局部伸展和沉积,中-下侏罗统和上侏罗统-下白垩统之间未见明显的角度不整合;燕山晚期主要表现为自南东往北西方向的逆冲推覆;早喜马拉雅期在北西-南东向的伸展作用下形成了多米诺式的伸展-拆离断层和箕状断陷沉积。其中,印支期北西—近东西向的逆冲断层控制了研究区的基底构造格局,后期的燕山运动和早喜马拉雅运动继承或改造了早期的断层系统。晚白垩世是旅大隆起区构造格局转变的关键时期,自之前的北西—近东西向转为北东向。位于构造转变区的秦皇岛30-1构造和旅大25-1构造潜山是印支期近南北向挤压、燕山晚期北西-南东向挤压和早喜马拉雅期北西-南东向伸展叠加改造的结果,而南部的428构造潜山则受控于近东西走向的印支期逆冲及燕山期和早喜马拉雅期伸展断裂体系。

尼日尔Termit盆地油气成藏新认识与勘探方向

基于地震、钻井、铸体薄片、油样和岩样地球化学分析、生烃史模拟等资料,研究尼日尔Termit海陆相叠合盆地油气成藏特征,并探讨未来油气勘探方向。研究认为:(1)Termit盆地为早白垩世和古近纪两期裂谷叠合,东部Trakes斜坡2口钻井沉降曲线显示晚白垩世沉降速率高,分析认为是遭受海侵影响造成的高沉积速率,也可能存在一期弱裂谷发育;(2)Termit盆地沉积层序主要受控于晚白垩世海侵期旋回和古近纪湖侵期旋回控制,发育海-陆“两种源汇”沉积叠合,海侵期广覆式发育的海陆相混源型烃源岩全盆地分布,湖侵期形成的古近系Sokor 1组储集层和Sokor 2组盖层叠置其上,形成了中西非裂谷系独特的海陆相裂谷叠合盆地;(3)Termit盆地早期地温梯度低,盆地主力烃源岩上白垩统Yogou组在古近纪晚期生烃。Trakes斜坡发育上白垩统Donga组成熟烃源岩,为“双源”供烃油气成藏模式,形成Trakes斜坡油田群;(4)Termit盆地海陆相裂谷叠合成藏模式新认识和勘探实践,扩大了盆地东部有效勘探面积约2500 km2,认为在盆地东南新区带Sokor 1组、新层系Donga组和上白垩统岩性目标具备勘探潜力,可作为未来勘探和选区重点。

琼东南盆地块体搬运沉积区多类型水合物赋存特征与数值模拟

南海北部琼东南盆地陵水凹陷的钻探、三维地震与地球化学分析表明,该区域发育热成因气控制的呈烟囱状反射特征的裂隙充填型和薄砂层的孔隙充填型水合物.不同站位水合物富集程度、厚度与赋存形态不同,这种复杂水合物富集成藏的控制因素还有待进一步明确.本文利用宽频处理三维地震与随钻测井资料,精细识别了裂隙充填型水合物发育的空间分布,分析了断层与块体搬运沉积物对水合物赋存的影响,通过建立重烃气体影响的Ⅱ型水合物稳定带底界,并结合数值模拟方法,定量模拟了多类型水合物形成与富集的控制因素.结果表明:起源于基底隆起的断层连通了深部气源与浅部水合物稳定带,控制着深部热成因气向上运移,发育的多期块体搬运沉积内局部裂隙及下部的有利砂层,使水合物在垂向上呈多层叠置分布特征.