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.

Superimposed versus residual basin:The North Yellow Sea Basin

The North Yellow Sea Basin is a Mesozoic and Cenozoic basin. Based on basin-margin facies, sedimentary thinning, size and shape of the basin and vitrinite reflectance, North Yellow Sea Basin is not a residual basin. Analysis of the development of the basin＇s three structural layers, self-contained petroleum systems, boundary fault activity, migration of the Mesozoic--Cenozoic sedimentation centers, different basin structures formed during different periods, and superposition of a two-stage extended basin and one-stage depression basin, the North Yellow Sea Basin is recognized as a superimposed basin.

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.

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.

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.

Dynamic simulation of differential accumulation history of deep marine oil and gas in superimposed basin:A case study of Lower Paleozoic petroleum system of Tahe Oilfield,Tarim Basin,NW China

According to the complex differential accumulation history of deep marine oil and gas in superimposed basins,the Lower Paleozoic petroleum system in Tahe Oilfield of Tarim Basin is selected as a typical case,and the process of hydrocarbon generation and expulsion,migration and accumulation,adjustment and transformation of deep oil and gas is restored by means of reservoine-forming dynamics simulation.The thermal evolution history of the Lower Cambrian source rocks in Tahe Oilfield reflects the obvious differences in hydrocarbon generation and expulsion process and intensity in different tectonic zones,which is the main reason controlling the differences in deep oil and gas phases.The complex transport system composed of strike-slip fault and unconformity,etc.controlled early migration and accumulation and late adjustment of deep oil and gas,while the Middle Cambrian gypsum-salt rock in inner carbonate platform prevented vertical migration and accumulation of deep oil and gas,resulting in an obvious"fault-controlled"feature of deep oil and gas,in which the low potential area superimposed by the NE-strike-slip fault zone and deep oil and gas migration was conducive to accumulation,and it is mainly beaded along the strike-slip fault zone in the northeast direction.The dynamic simulation of reservoir formation reveals that the spatio-temporal configuration of"source-fault-fracture-gypsum-preservation"controls the differential accumulation of deep oil and gas in Tahe Oilfield.The Ordovician has experienced the accumulation history of multiple periods of charging,vertical migration and accumulation,and lateral adjustment and transformation,and deep oil and gas have always been in the dynamic equilibrium of migration,accumulation and escape.The statistics of residual oil and gas show that the deep stratum of Tahe Oilfield still has exploration and development potential in the Ordovician Yingshan Formation and Penglaiba Formation,and the Middle and Upper Cambrian ultra-deep stratum has a certain oil and gas resource prospect.This study provides a reference for the dynamic quantitative evaluation of deep oil and gas in the Tarim Basin,and also provides a reference for the study of reservoir formation and evolution in carbonate reservoir of paleo-craton basin.

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.

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.

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。

鄂尔多斯盆地及周缘岩相古地理与沉积演化

鄂尔多斯盆地的沉积演化起始于中元古代,发育陆缘裂谷和陆内拗拉槽,沉积滨海相碎屑岩和潮坪相碳酸盐岩,新元古代盆地性质为大陆边缘地堑型坳陷,沉积滞留海盆碎屑岩、冰水沉积物组合及陆棚碎屑岩;早古生代寒武纪和奥陶纪的克拉通盆地主要沉积浅海碳酸盐岩,在西南缘发育沟-弧-盆体系;经过加里东运动抬升剥蚀后,开始了华北克拉通坳陷盆地的沉积演化过程,晚石炭世和早二叠世发育了陆表海沉积,早二叠世晚期—中三叠世形成了近岸碎屑湖盆沉积;中晚三叠世延长期至早白垩世,鄂尔多斯盆地最终形成,进入大型内陆差异沉积盆地的形成和发展时期,上三叠统、侏罗系和下白垩统是在鄂尔多斯盆地缓慢沉降过程中堆积的以河流-三角洲-湖泊相为特征的陆源碎屑岩系;新生代进入周边断陷发育阶段,先后发育河流-湖泊及风成沉积。这一系列沉积演化过程揭示了鄂尔多斯盆地复杂的地质历史和多样的沉积环境。

四川盆地中部地区震旦系大型碳酸盐岩气藏开发技术新进展

四川盆地中部地区(以下简称川中地区)震旦系灯影组气藏为大型古老深层岩溶风化壳型碳酸盐岩气藏,气藏整体表现为低孔隙度低渗透率,储集空间小尺度缝洞发育,储层非均质性强特征,气藏开发面临储层表征难、井位部署和效益开发难度大等系列挑战。为此,以川中地区安岳气田灯影组气藏为对象,通过地质工程一体技术化攻关,深化了对储层发育特征和成因机理的认识,提出了气藏开发新模式,创建形成了气藏高效开发的关键技术。研究结果表明:①灯影组储层主要为岩溶成因储层,具有“叠合岩溶差异控储”的发育特征;②岩溶储层非均质性强,“溶蚀相成因控储”可精细刻画储层的非均质性;③灯影组气藏宜采用“单井指标叠加论证气藏规模”的开发新模式;④创新形成了“双界面”岩溶古地貌恢复及定量刻画方法,并指导平面选区,其中Ⅰ+Ⅱ类井比例由评价期的40%提高到方案建设期的100%;⑤创建了小尺度缝洞识别、刻画及表征技术,并指导钻井轨迹设计,测试百万立方米气井比例由开发评价期的41.6%提高到建产期的60%;⑥配套完善了分段酸压工艺技术,高效动用了优质储层,并解放了低品位储层,储层渗透率由改造前的0.62 mD提高到酸压改造后的6.77 mD。结论认为,“十四五”期间,在上述开发技术的支持下,安岳气田由台缘带灯四段高效开发转向长期稳产和台内地区多层系效益开发,蓬莱含气区由单井高产转向区块高产和气藏规模建产,将强力支撑中国石油西南油气田公司“十四五”末天然气上产500×10^(8)m^(3)。

中国含油气盆地不同构造样式及其油气地质意义

多类型构造样式的控油气作用是油气勘探面临的重要科学问题。基于前人研究认识成果、勘探经验的总结,对中国含油气盆地内不同构造样式的演化及成因模式进行了系统梳理,解析了不同构造样式对油气成藏的控制作用。研究认为:①中国含油气盆地主要发育伸展构造、收缩构造、走滑构造和叠加构造4种构造样式。伸展构造主要控制盆地建造过程,收缩构造、走滑构造主要控制盆地改造过程。②不同构造类型的控油气作用差异明显,伸展构造主要控制盆地烃源岩、有利储集体和盖层等油气聚集成藏要素的发育,收缩构造、走滑构造和叠加构造主要控制油气运移与圈闭条件的演化。③在构造与其他要素复合作用下,断裂自身也可以作为一类储集体,成为油气聚集的空间,这一类断裂油气藏是当前油气勘探的新领域。

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”。

柴达木盆地东部尕海南山地区新生代叠加褶皱与油气运移

柴达木盆地石炭系主要分布于盆地东部地区,石炭系油气勘探已获重大发现,为柴达木盆地古生代油气勘探开启了新局面。柴达木盆地石炭系烃源岩在早二叠世进入生烃门限,以生油为主;古新世—上新世为石炭系主力生烃期,以产气为主。前人针对该盆地石炭系油气的赋存条件和成藏机理研究较少,为揭示柴达木盆地石炭系油气的有利成藏条件,本次选择柴达木盆地东部德令哈坳陷尕海南山地区开展石炭系油气成藏机理研究,在青德参1井中发现了石炭系克鲁克组和古近系上干柴沟组两套含油气层。依据区内构造要素统计分析、叠加构造填图、地震综合解释和油气成藏条件分析,揭示柴达木盆地东部尕海南山地区晚新生代发育早期北西—北西西向和晚期北北东—南南西向的叠加褶皱,北西—北西西向褶皱及断裂活动形成了石炭系晚期生烃的有利圈闭,北北东—南南西向构造挤压激活了先存的北西—北西西向断裂,并导致石炭系油气沿该断层向上运移至上干柴沟组形成次级含油气层,最终造就了尕海南山地区上下两套油气组合并存的特征。本研究对柴达木盆地石炭系油气勘探具有借鉴意义。