Geological conditions of natural gas accumulation and new exploration areas in the Mesoproterozoic to Lower Paleozoic of Ordos Basin, NW China

Based on field outcrop investigation,interpretation and analysis of drilling and seismic data,and consulting on a large number of previous research results,the characteristics of ancient marine hydrocarbon source rocks,favorable reservoir facies belts,hydrocarbon migration direction and reservoir-forming law in the Ordos Basin have been studied from the viewpoints of North China Craton breakup and Qilian-Qinling oceanic basin opening and closing.Four main results are obtained:(1)Controlled by deep-water shelf-rift,there are three suites of source rocks in the Ordos Basin and its periphery:Mesoproterozoic,Lower Cambrian and Middle-Upper Ordovician.(2)Controlled by littoral environment,paleo-uplift and platform margin,four types of reservoirs are developed in the area:Mesoproterozoic-Lower Cambrian littoral shallow sea quartz sandstone,Middle-Upper Cambrian–Ordovician weathering crust and dolomitized reservoir,and Ordovician L-shape platform margin reef and beach bodies.(3)Reservoir-forming assemblages vary greatly in the study area,with"upper generation and lower storage"as the main pattern in the platform,followed by"self-generation and self-storage".There are both"upper generation and lower storage"and"self-generation and self-storage"in the platform margin zone.In addition,in the case of communication between deep-large faults and the Changchengian system paleo-rift trough,there may also exist a"lower generation and upper reservoir"combination between the platform and the margin.(4)There are four new exploration fields including Qingyang paleo-uplift pre-Carboniferous weathering crust,L-shape platform margin zone in southwestern margin of the basin,Ordovician subsalt assemblage in central and eastern parts of the basin,and Mesoproterozoic–Cambrian.Among them,pre-Carboniferous weathering crust and L-shape platform margin facies zone are more realistic replacement areas,and Ordovician subsalt assemblage and the Proterozoic-Cambrian have certain potential and are worth exploring.

A Fine Investigation on Geological Conditions for Oil Accumulation in the Paleogene Intersalt Shale Series in the Qianjiang Depression

This study dealt with the rhythmic Qian 3410 of the intersalt shale series in the Qianjiang Depression,in which the geological condition for oil accumulation in the rhythmic shale was investigated by using the basic drilling,core and well logging data,as well as data obtained from the thin section identification,SEM,mercury injection,X-ray diffraction and rock freezing heat analyses.The study result indicated that:1)the intersalt shale series are characterized by TOC in a range of 0.35%-6.38%(averaging 3.19%),Types I and II1 organic matter,and from immature to mature oil,indicative of a potential for generating a great volume of immature oil;2)in the target layer,mineral compositions are complicated,which can divide into argillaceous dolomite facies,argillaceous limestone facies,dolomitic mudstone facies,and calcium-mirabilite-filling dolomitic mudstone facies;and 3)of them,the argillaceous dolomite facies is the most contributory,with reservoir spaces consisting of intergranular pores as dominant,as well as rare dissolution pores and seams.It is characterized by high organic abundance(4.23%-6.38%),high content of brittle mineral(50%-71%),low content of clay mineral(18%-33%),high porosity(10.8%-26.3%)and good oil-bearing properties(S1 distributed in 3.48-5.64 mg/g,and S1/TOC value in a range of 348-564 oil mg/g).Therefore,the argillaceous dolomite facies was considered the key target series to be explored for the intersalt shale oil in the study area in the coming days.

Geological conditions of coal and gas(oil)-bearingbasins in China

There are various types of coal basins in China. Indosinian movement can be re- garded as their evolutionary limit, and the basins can be divided into two developmental stages, three structural patterns and two sedimentary environments. However, only those coal measure strata that have been deeply buried in the earth are possible to be converted into coal and gas (oil)-bearing basins. Among which, only part of the coal measures possess the essential geo- logical conditions to the formation of commercial humic oil. However, humic gas will be the major exploration target for natural gas in China. Among various coal basins, foreland basins have the best prospect for humic gas. Rift (faulted) basins accumulate the most abundance of humic gas, and are most favorable to generate humic oil. Craton basins have relatively low abundance of humic gas, but the evolution is rather great. The three kinds of coal basins mentioned above constitute China’s three primary accumulation areas of humic gas: western, central and offshore areas. The major basins for humic gas field exploration include Tarim, Ordos, Sichuan, East China Sea and Yingqiong basins.

Basic principles of the whole petroleum system

This paper expounds the basic principles and structures of the whole petroleum system to reveal the pattern of conventional oil/gas-tight oil/gas-shale oil/gas sequential accumulation and the hydrocarbon accumulation models and mechanisms of the whole petroleum system.It delineates the geological model,flow model,and production mechanism of shale and tight reservoirs,and proposes future research orientations.The main structure of the whole petroleum system includes three fluid dynamic fields,three types of oil and gas reservoirs/resources,and two types of reservoir-forming processes.Conventional oil/gas,tight oil/gas,and shale oil/gas are orderly in generation time and spatial distribution,and sequentially rational in genetic mechanism,showing the pattern of sequential accumulation.The whole petroleum system involves two categories of hydrocarbon accumulation models:hydrocarbon accumulation in the detrital basin and hydrocarbon accumulation in the carbonate basin/formation.The accumulation of unconventional oil/gas is self-containment,which is microscopically driven by the intermolecular force(van der Waals force).The unconventional oil/gas production has proved that the geological model,flow model,and production mechanism of shale and tight reservoirs represent a new and complex field that needs further study.Shale oil/gas must be the most important resource replacement for oil and gas resources of China.Future research efforts include:(1)the characteristics of the whole petroleum system in carbonate basins and the source-reservoir coupling patterns in the evolution of composite basins;(2)flow mechanisms in migration,accumulation,and production of shale oil/gas and tight oil/gas;(3)geological characteristics and enrichment of deep and ultra-deep shale oil/gas,tight oil/gas and coalbed methane;(4)resource evaluation and new generation of basin simulation technology of the whole petroleum system;(5)research on earth system-earth organic rock and fossil fuel system-whole petroleum system.

Hydrocarbon accumulation conditions and key exploration and development technologies for PL 19-3 oilfield

The PL 19e3 Oilfield is the only super-large monolithic oilfield with oil and gas reserves up to 1×10^(9) t in the Bohai Bay Basin,and it has been successfully developed.Exploration and development practices have provided abundant data for analyzing formation conditions of this super-large oilfield.On the basis of the exploration and development history,fundamental reservoir features,and with available geological,geophysical and test data,the hydrocarbon accumulation conditions and key exploration&development technologies of the PL 19e3 Oilfield were discussed.The key conditions for forming the super-large Neogene oilfield include four aspects.Firstly,the oilfield is located at the high position of the uplift that contacts the brachy-axis of the multi-ridge slope in the biggest hydrocarbon-rich sag in the Bohai Bay Basin,thus it has sufficient hydrocarbon source and extremely superior hydrocarbon migration condition.Secondly,the large-scale torsional anticlines which formed in the Neogene under the control of the Tanlu strike-slipping movement provide sufficient storage spaces for oil and gas preservation.Thirdly,the“multiple sets of composite reservoir-caprock assemblages”developing in the special shallow-water delta further contributes greatly to the effective storage space for oil and gas preservation.Fourthly,due to the coupling of the uplift and strike slip in the neotectonic period,extensive faulting activities constantly released the pressure while the late period massive hydrocarbon expulsion of the Bozhong took place at the same time,which assures the constant and intense charging of oil and gas.The super-large PL 19e3 Oilfield was controlled by the coupling effects of all those special geologic factors.In view of this oilfield's features(e.g.violently reformation caused by strike slip,and the special sedimentary environment of shallow-water delta),some key practical technologies for exploration and development have been developed.Such technologies include:the special prestack depth migration processing for gas cloud zones,the prediction of thin interbed reservoirs based on high-precision inversion of geologic model,the reservoir description for the shallow-water braided river delta,the quantitative description for remaining oil in the commingled oil reservoirs with wide well spacing and long well interval,and the well pattern adjustment for formations during high water cut period in the complex fluvial-facies oilfields.

Mesh model building and migration and accumulation simulation of 3D hydrocarbon carrier system

Migration and accumulation simulation of oil and gas in carrier systems has always been a difficult subject in the quantitative study of petroleum geology. In view of the fact that the traditional geological modeling technology can not establish the interrelation of carriers in three dimensional space, we have proposed a hybrid-dimensional mesh modeling technology consisting of body(stratum), surfaces(faults and unconformities), lines and points, which provides an important research method for the description of geometry of sand bodies, faults and unconformities, the 3 D geological modeling of complex tectonic areas, and the simulation of hydrocarbon migration and accumulation. Furthermore, we have advanced a 3 D hydrocarbon migration pathway tracking method based on the hybrid-dimensional mesh of the carrier system. The application of this technology in western Luliang Uplift of Junggar Basin shows that the technology can effectively characterize the transport effect of fault planes, unconformities and sand bodies, indicate the hydrocarbon migration pathways, simulate the process of oil accumulation, reservoir adjustment and secondary reservoir formation, predict the hydrocarbon distribution. It is found through the simulation that the areas around the paleo-oil reservoir and covered by migration pathways are favorable sites for oil and gas distribution.

Reservoir formation conditions and key technologies for exploration and development in Qingcheng large oilfield

The Qingcheng oilfield,the largest shale oil field in China,was discovered in 2019 in source rock of Chang 7 Member of Mesozoic Yanchang Formation,Changqing Oilfield in Ordos Basin,with newly increased proven geological reserves of 358 million tons,predicted geological reserves of 693 million tons,and a total of 1.051 billion tons of shale oil resources.This achieves a historic breakthrough in exploration of shale oil in Chang 7 Member.In recent years,focusing on key issues,such as whether there develop sweet spots in source rock,whether commercial oil production capacity can be formed,and whether scale-effective development can be achieved,studies about geological conditions for shale oil accumulation have been continuously carried out,key supporting technologies have been developed,and a series of theoretical innovations and technological breakthroughs have been achieved in oil exploration in source rocks.The results indicate that shale oil accumulation in Chang 7 Member is controlled by following factors.Firstly,lacustrine black shale,dark mudstone and other high-quality source rocks lay a material foundation for shale oil formation.Secondly,sandy deposits intercalated within black shale and dark mudstones are exploration sweet spots,and sandbody combination types are controlled by morphology of bottom of the lacustrine basin.Thirdly,reservoir properties are good due to development of micro-nano pore throats.Finally,reservoirs with high oil saturation and high gas-oil ratio are formed due to high-intensity oil charging in source rock.Effective matching of multiple factors is a key for shale oil accumulation in Chang 7 Member in Ordos Basin.Through innovation of key supporting technologies,exploration and development technologies for shale oil are developed,and substantial breakthrough on exploration and development of shale oil is realized.The first application of logging-seismic combination technology in loess plateau improves significantly quality of 3D seismic data,which effectively guides prediction of sandy sweet spots.Three-quality well logging technology is used for further evaluation of geological and engineering sweet spots of shale oil.With volumetric fracturing technology based on precise segmentation of long horizontal wells,initial daily oil production of individual well is increased from previously 10 tons to more than 18 tons.The exploration breakthrough in source rocks in Chang 7 Member in Qingcheng oilfield provides an important resource base for the second accelerated development of Changqing Oilfield.It is predicated that oil production from shale in Chang 7 Member in Qingcheng oilfield will reach three million tons in 2022 and five million tons in 2025.

Geological characteristics of large gas provinces and large gas fields in China

Based on the examination of the global researches on oil and gas provinces and large gas fields and the analysis of the features,attributes and distribution of large gas provinces and gas fields,this paper puts forward three indicators of determining large oil and gas provinces:spatial indicator,reservoir-forming indicator and resource indicator.It classifies the gas accumulated areas and large gas provinces in China and analyzes the controlling factors on the distribution of large gas provinces and large gas fields:the lateral distribution is mainly controlled by high-energy sedimentary facies and constructive diagenetic facies,palaeo-highs and their periclinal zones,deep faults,etc,and the vertical distribution is mainly controlled by unconformities,series of evaporates and deep low-velocity highly-conductive beds,etc.It also reveals the main geological characteristics of large gas provinces and large gas fields in China.Large gas fields in four-type basins have their own characteristics and onland large gas fields are dominantly developed in foreland basins and craton basins;there are three types of gas sources,of which,coal is the main source with high gas generating intensity and varying origins;reservoir rocks of the large gas fields(provinces)are of various types and dominated generally by low-middle permeability and porosity pore-type reservoirs;structural traps and litho-stratigraphic traps coexist in Chinese large gas fields and form dense high abundance and large-area low and middle-abundance large gas fields;most of the large gas fields have late hydrocarbon-generation peaks and reservoir formation,and experienced the process of multiple-stage charging and late finalization; large gas provinces(fields)have good sealing and preservation conditions,and evaporates seals are largely developed in large and extra-large gas fields.This paper intends to shed light on the exploration and development of large gas fields(provinces)through analyzing their geological characteristics.

南羌塘盆地扎仁地区中侏罗统布曲组沉积环境特征及其对油气地质条件的控制作用

南羌塘盆地扎仁地区地处南羌塘盆地南缘,属油气研究的"空白区",结合羌塘盆地扎仁区块1∶5万石油地质构造详查,笔者重点剖析了扎仁地区布曲组地层中的两个古油藏剖面。依据剖面中碳酸盐岩的岩石类型、结构特征、自生矿物组合、古生物标志以及扎仁地区碳酸盐岩的组合特征,将该区布曲组划分为半局限海台地、局限海台地、开阔海台地和浅滩4种沉积环境。浅滩沉积环境形成的颗粒灰岩在区内广泛分布,沉积厚度大,具有孔隙度好、渗透率高的特征,这些颗粒灰岩的展布决定了区域储集层的规模。局限海台地沉积环境形成的白云岩是区内的另外一套储集层,这套储集层是区内有效的储集层,但这套储集层的有效性与上覆岩层在空间上的展布有关。开阔海台地沉积环境形成的泥晶灰岩夹泥晶砂屑灰岩、泥晶砾屑灰岩的组合为区内较好的生油层,该套烃源岩组合的规模在空间上严格受沉积相的控制。半局限海台地沉积环境形成的泥晶灰岩夹泥晶生屑灰岩、泥晶砂屑灰岩组合是区内有利的盖层,但半局限海台地的性质决定了盖层在区域上的展布。

世界深水油气勘探进展与南海深水油气勘探前景

世界深水油气资源丰富,近年来深水油气勘探已成为当今世界油气勘探开发的热点和油气增储上产新亮点,也是当今海洋油气勘探必然发展趋势和油气资源接替的重要战略选区。南海陆坡深水区属我国油气勘探与研究的新区,处于准被动大陆边缘盆地位置,从烃源岩、含油气储盖组合、圈闭及油气运聚条件等综合考量,具备形成大中型油气田的基本地质条件,颇具油气资源潜力,其应是我国油气资源接替的重要战略选区和增储上产的现实区域。在以往研究和所获地质资料的基础上,重点探讨了围绕南海深水油气勘探的关键问题,以期促进和加快南海深水油气的勘探进程。

四川盆地侏罗系自流井组大安寨段陆相页岩油气地质特征及成藏控制因素

四川盆地侏罗系陆相油气勘探过去主要聚焦在构造-裂缝型常规油气和介壳灰岩及砂岩致密油气上,为实现侏罗系油气重大新突破,思路需要向页岩油气转变。在分析自流井组大安寨段陆相页岩油气的分布、生烃、物性和保存等地质特征基础上,认为大安寨段具备形成大规模页岩油气成藏地质特征,提出3项成藏控制因素。大安寨段二亚段暗色页岩作为页岩油气的供烃源岩,油气显示丰富,页岩厚度在20~80 m,整体分布面积广、厚度大、连续稳定,孔缝发育、物性好,处于中-高成熟热演化阶段,有区域性致密顶底板灰岩封闭的超压页岩油气藏。半深湖-深湖亚相、致密灰岩顶底板与高孔隙储层、中-高成熟热演化阶段这3项因素共同控制自流井组大安寨段页岩油气的生成、储集和富集。

南海北部边缘盆地油气勘探现状与深水油气资源前景

自20世纪60年代初开展浅海油气苗调查及浅井钻探以来,南海北部边缘盆地迄今在陆架浅水区已勘探发现多个油气田,建成了一定储量规模的油气产能,基本构成了南海北部油气富集区的格局。然而,如何保持油气可持续发展,尽快寻找油气储量接替的新领域,这是该区油气勘探所面临的关键问题。南海北部陆坡深水区与世界深水盆地一样,颇具油气资源潜力和勘探前景,近期LW3-1-1深水探井钻探的新发现表明,其应是该区油气资源接替非常现实的战略选区和勘探靶区。

南堡凹陷油气成藏的有利地质条件

为了明确南堡凹陷油气成藏的地质条件,在油气藏类型及分布规律研究的基础上,通过油藏解剖、地化资料分析、断裂活动期次、烃源岩排烃期、盖层识别和砂地比分析等,利用成藏条件综合分析方法,对烃源岩、断裂、盖层、储层和构造部位5个方面的地质条件进行了详细分析,厘定了南堡凹陷油气成藏的有利地质条件及相互关系。结果表明,南堡凹陷的油气成藏具有5个有利地质条件:①2套烃源岩为油气运聚提供充足来源;②油源断裂为油气运移提供输导通道;③3套区域性盖层为油气聚集提供保存条件;④高砂地比地层为油气聚集提供储集空间;⑤油源断裂附近的正向构造为油气聚集提供有利部位。

松辽盆地北部中浅层石油地质条件、资源潜力及勘探方向

为了落实松辽盆地北部中浅层常规油与致密油的资源潜力,明确勘探方向,在系统总结烃源岩、储层等基本石油地质条件的基础上,分析了常规油与致密油成藏模式及主控因素,采用类比法和成因法计算了常规油与致密油资源量,研究了剩余资源分布特征,指出了下步勘探方向。松辽盆地晚白垩世发育青山口组和嫩江组2套分布广、厚度大、有机质丰度高、有机质类型好的优质烃源岩。中央坳陷区青山口组一段、二段烃源岩处于成熟阶段,生排烃能力强,是常规油和致密油的主力烃源岩。大型湖泊三角洲-河流沉积的各种砂体与烃源岩形成了良好的生储盖配置,构成了盆地的上、中、下3套含油气组合,其中致密油主要分布于中部含油组合的高台子油层和下部含油组合的扶余油层。常规油成藏主要具有下生上储、上生下储及异地生储3种模式,致密油成藏主要有自生自储和上生下储2种模式,有效烃源岩控制了常规油油藏和致密油油藏分布,沉积相带控制了常规油油藏类型,储层物性控制了致密油富集。在烃源岩精细评价的基础上,采用盆地模拟法计算的石油总资源量为102×10^8t;通过系统解剖6个常规油和3个致密油区带刻度区,采用类比法精细评价的常规油资源量为88.7×10^8t,致密油资源量为12.7×10^8t。常规油中的葡萄花油层剩余资源潜力大,是近期勘探的主力层系,古龙、长垣和三肇等地区是主要的勘探有利区;长垣、三肇和齐家-古龙的扶余油层是致密油勘探的有利区。

东濮凹陷北部沙三段页岩油成藏地质条件分析

东濮凹陷北部沙三段泥页岩有机质丰度较高,热演化程度适中,含油泥页岩厚度较大,埋深条件较好。通过CT扫描、单偏光显微镜、扫描电镜、比表面分析及全岩分析,认为泥页岩储层孔隙总体以微裂缝为主,结构以中孔为主,脆性矿物含量较高,泥页岩含油率较高,同时盐岩广泛发育,为页岩油的保存提供了良好的条件。结合成藏地质条件、构造因素和常规油气富集条件,认为濮卫次洼、柳屯、胡庆地区为页岩油发育的最优有利区。

南海北部大陆边缘盆地深水油气成藏条件早期预测与评价

与浅水陆架区一样,南海北部深水盆地新生代均处于南海北部准被动大陆边缘的构造环境,具有北部大陆边缘拉张裂陷的区域地质特征,盆地结构与中国东部裂谷断陷盆地类似,属双层或三层结构类型。该深水盆地油气运聚成藏的基本地质条件亦与浅水区类似,但陆坡深水区凹陷裂陷更深、沉积充填规模更大,且发育4套烃源岩和3套储盖组合类型,使深水油气运聚成藏有了良好的基础。基于深水区少井无井、地质资料缺乏的现状,借鉴浅水区油气成藏地质条件,并依据跨越深水区地震剖面层序地层,重点对深水油气运聚成藏条件进行了早期预测与综合评价,旨在加快和推进深水油气勘探进程。

吐哈盆地台北凹陷侏罗系油气富集地质条件及油气分布规律

分析了吐哈盆地台北凹陷侏罗系油气富集地质条件，探讨了其油气分布规律，指出了今后油气勘探的方向。４套２类良好的油源、多套储集性能良好的砂体、有效的圈闭、２套封盖性能极好的区域性盖层及优越的生储盖组合配置是油气富集的基本地质条件；构造、构造—岩性复合是主要的油气藏类型；环主力生油凹陷、沿短轴分布的砂体与燕山期的古构造及喜山期改造加强的构造叠置、多期活动的油源断裂控制油气是油气分布聚集的规律；中部凹陷区的深挖细找，山前褶断带、火焰山背斜带及逆冲断裂上下盘构造，是今后油气勘探的方向。

南沙海域曾母盆地构造样式特征及其与油气聚集和圈闭的关系

南沙海域曾母盆地发育各种类型的构造样式,本文研究与油气聚集和圈闭关系密切的典型构造样式。以盆地构造运动的力学性质为依据,将该盆地的构造样式分为三大类,即伸展构造、挤压构造和走滑构造。伸展构造样式有断块构造和箕状构造;挤压构造样式有褶皱构造、冲断构造和底辟构造;走滑构造样式有花状构造。各种构造样式特征分析结果表明,大部分构造样式可形成能够俘获、圈闭油气的局部构造,部分构造样式除了能形成圈闭以外,其中充填的沉积物还有利于油气的生成。由于这些构造样式的发育时间早于烃源岩的生烃期和大规模的排烃期,因此极易俘获油气而成为有利的油气聚集带和有效的油气圈闭。

中低勘探程度区块油气条件地质风险评价

根据成藏特征与勘探实际，建立了针对中低勘探区块的5项评价条件21项参数的评价体系与评分标准。为了充分反映各项评价条件研究程度以及在评价时所起的不同作用，在确定各项评价参数权重的基础上，采用“评价因素加权求和”的方法计算5项条件评价值，利用“5项条件评价值加权求和”的方法求取区块地质风险评价值。该方法在松南地区的应用表明，16个区块中勘探潜力大的Ⅰ类区块有4个，具有一定勘探潜力的Ⅱ类区块有7个，勘探潜力有限的Ⅲ类区块有5个。为该区下一步的油气勘探部署提供了依据。

从石臼坨凸起浅层油气的重大发现看渤东地区的勘探潜力

渤海海域两个石油地质储量超亿吨的大型油气田均发现于凸起或低凸起之上，说明正向二级构造单元具有明显的成藏优势，文中回顾总结了位于石臼坨凸起上的QHD32－6大型油田的勘探历程与经验，对其成藏条件进行了分析，渤东地区在区域地质环境、主要成藏条件等方面与石臼坨凸起相似，具备形成大、中型油气田的基础，存在油气勘探获重大突破的可能性。