Formation,evolution,reconstruction of black shales and their influence on shale oil and gas resource

Black shales are important products of material cycling and energy exchange among the lithosphere,atmosphere,hydrosphere,and biosphere.They are widely distributed throughout geological history and provide essential energy and mineral resources for the development of human society.They also record the evolution process of the earth and improve the understanding of the earth.This review focuses on the diagenesis and formation mechanisms of black shales sedimentation,composition,evolution,and reconstruction,which have had a significant impact on the formation and enrichment of shale oil and gas.In terms of sedimentary environment,black shales can be classified into three types:Marine,terrestrial,and marine-terrestrial transitional facies.The formation processes include mechanisms such as eolian input,hypopycnal flow,gravity-driven and offshore bottom currents.From a geological perspective,the formation of black shales is often closely related to global or regional major geological events.The enrichment of organic matter is generally the result of the interaction and coupling of several factors such as primary productivity,water redox condition,and sedimentation rate.In terms of evolution,black shales have undergone diagenetic evolution of inorganic minerals,thermal evolution of organic matter and hydrocarbon generation,interactions between organic matter and inorganic minerals,and pore evolution.In terms of reconstruction,the effects of fold deformation,uplift and erosion,and fracturing have changed the stress state of black shale reservoirs,thereby having a significant impact on the pore structure.Fluid activity promotes the formation of veins,and have changed the material composition,stress structure,and reservoir properties of black shales.Regarding resource effects,the deposition of black shales is fundamental for shale oil and gas resources,the evolution of black shales promotes the shale oil and gas formation and storage,and the reconstruction of black shales would have caused the heterogeneous distribution of oil and gas in shales.Exploring the formation mechanisms and interactions of black shales at different scales is a key to in-depth research on shale formation and evolution,as well as the key to revealing the mechanism controlling shale oil and gas accumulation.The present records can reveal how these processes worked in geological history,and improve our understanding of the coupling mechanisms among regional geological events,black shales evolution,and shale oil and gas formation and enrichment.

GEOTHERMAL EVOLUTION AND TECTONOSEDIMENTATION OF THE NORTH CHINA CRUSTOBLOCK AND THEIR EFFECTS ON THE FORMATION OF OIL/GAS POOLS

The geothermal history of North China can be divided into at least four stages, i. c. Archaean (much hisher geothermal) stage, Paleoprotcrozoic (hish geothermal)stage, which resulted in four geotectonic stages (pregeosynehoe, geosyncline, platform and diwa stage) in the region. The geothermal field consists of three subgeothermal fields, theupper subgeothermal field with its depth of less than 2000 m, the middle subgeothermal field ranging from 2000 m to 5000 m in depth and the lower subgeothcrmal field locating at more than 5000 m in depth in North China. Sis thermostructural layers are recognised in North China, i. e. the mantle, the lower erust with its heat generation ratc of 0. 6 HGU. Oeothermal field is Corresponding to tectonosedimentary divisions in North China, controlling the tectonosedimentation, the evolution of souree rocks and the formation oF the oil/gas pools.

Conditions for the Formation of Oil and Gas Pools in Tertiary Volcanics in the Western Part of the Huimin Sag, Shandong and Their Distribution

Conditions for the Formation of oil and gas pools in Tertiary volcanics in the western part of the Huimin sag, Shandong and then (?)stribution have been studied based on the geological, seismic and well-logging information. In this paper, the types and lithofacies of the volcanic rocks in the western part of the Huimin sag are described; the relationship between rocks and electrical properties, the seismic reflection structures, the development and distribution of the volcanic rocks are expounded; and the fourfold role of the volcanic activities in the formation of the oil and gas pools is also dealt with. It is considered by the authors that the volcanic activities were not destructive to the formation of oil and gas pools but a factor favourable to the accumulation of organic matters and their conversion to hydrocarbon. The volcanic rocks might have served as reservoir rocks and cap rocks, or as a synsedimentary anticline. The prerequisites and important factors for the formation of oil and gas pools and their distribution are pointed out in the paper.

Enrichment Mechanism and Prospects of Deep Oil and Gas

With the deepening of oil and gas exploration,the importance of depth is increasingly highlighted.The risk of preservation of storage space in deep reservoirs is greater than that in shallow and medium layers.Deep layers mean older strata,more complex structural evolution and more complex hydrocarbon accumulation processes,and even adjustment and transformation of oil and gas reservoirs.This paper systematically investigates the current status and research progress of deep oil and gas exploration around the world and looks forward to the future research focus of deep oil and gas.In the deep,especially the ultra-deep layers,carbonate reservoirs play a more important role than clastic rocks.Karst,fault-karst and dolomite reservoirs are the main types of deep and ultra-deep reservoirs.The common feature of most deep large and medium-sized oil and gas reservoirs is that they formed in the early with shallow depth.Fault activity and evolution of trap highs are the main ways to cause physical adjustment of oil and gas reservoirs.Crude oil cracking and thermochemical sulfate reduction(TSR)are the main chemical modification effects in the reservoir.Large-scale high-quality dolomite reservoirs is the main direction of deep oil and gas exploration.Accurate identification of oil and gas charging,adjustment and reformation processes is the key to understanding deep oil and gas distribution.High-precision detection technology and high-precision dating technology are an important guarantee for deep oil and gas research.

Molecular reconstruction of vacuum gas oils using a general molecule library through entropy maximization

Vacuum gas oil(VGO)is the most important feedstock for hydrocracking processes in refineries,but its molecular composition cannot be fully acquired by current analysis techniques owing to its complexity.In order to build an accurate and reliable molecular-level kinetic model for reactor design and process optimization,the molecular composition of VGO has to be reconstructed based on limited measurements.In this study,a modified stochastic reconstruction-entropy maximization(SR-REM)algorithm was applied to reconstruct VGOs,with generation of a general molecule library once and for all via the SR method at the first step and adjustment of the molecular abundance of various VGOs via the REM method at the second step.The universality of the molecule library and the effectiveness of the modified SR-REM method were validated by fifteen VGOs(three from the literature)from different geographic regions of the world and with different properties.The simulated properties(density,elemental composition,paraffin-naphthene-aromatics distribution,boiling point distribution,detailed composition of naphthenes and aromatics in terms of ring number as well as composition of S-heterocycles)are in good agreement with the measured counterparts,showing average absolute relative errors of below 10%for each property.

Discussion of the Mode and Mechanism of Oil and Gas Accumulation in the Nanbaxian Pool in the North of the Qaidam Basin

Because of the difference ofoil and gas accumulation condition between the hanging wall and the footwall of a fault, there is a peculiar accumulation mechanism that oil and gas mainly exists in the hanging wall of the basement fault, but in the footwall of the shallow detachment fault in the Nanbaxian pool. The oil and gas of the Nanbaxian pool came from the mature Jurassic hydrocarbon source rock of the Yibei depression located at the south of the Nanbaxian pool. Firstly, the oil and gas accumulated in the traps of the hanging wall of the basement fault by way of the unconformity and the basement faults, and turned into some primary deep pools; and then, the shallow detachment fault that formed in the later tectonic movement broke into the deep primary pools, which caused the oil and gas migration upwards along the basement faults and the shallow detachment faults and the evolvement into some secondary oil and gas pools later. The history of the Nanbaxian oil and gas accumulation can be summarized successively as the syndepositional upheaval controlled by faults; single hydrocarbon source rock; unconformities and faults as migration channels; buoyancy, overpressure and tectonic stress as dynamic forces; multistage migration and accumulation of oil and gas; and finally an overlapped double-floor pattern of oil and gas accumulation. The most important explorative targets in the north of the Qaidam Basin are traps connected with the primary pools in the footwall by shallow detachment faults.

Formation conditions and exploration direction of large natural gas reservoirs in the oil-prone Bohai Bay Basin, East China

The Bohai Bay Basin is a typical oil-prone basin, in which natural gas geological reserves have a small proportion. In this basin, the gas source rock is largely medium-deep lake mudstone with oil-prone type Ⅱ2-Ⅱ1 kerogens, and natural gas preservation conditions are poor due to active late tectonic movements. The formation conditions of large natural gas fields in the Bohai Bay Basin have been elusive. Based on the exploration results of Bohai Bay Basin and comparison with large gas fields in China and abroad, the formation conditions of conventional large-scale natural gas reservoirs in the Bohai Bay Basin were examined from accumulation dynamics, structure and sedimentation. The results show that the formation conditions of conventional large natural gas reservoirs in Bohai Bay Basin mainly include one core element and two key elements. The core factor is the strong sealing of Paleogene "quilt-like" overpressure mudstone. The two key factors include the rapid maturation and high-intensity gas generation of source rock in the late stage and large scale reservoir. On this basis, large-scale nature gas accumulation models in the Bohai Bay Basin have been worked out, including regional overpressure mudstone enriching model, local overpressure mudstone depleting model, sand-rich sedimentary subsag depleting model and late strongly-developed fault depleting model. It is found that Bozhong sag, northern Liaozhong sag and Banqiao sag have favorable conditions for the formation of large-scale natural gas reservoirs, and are worth exploring. The study results have important guidance for exploration of large scale natural gas reservoirs in the Bohai Bay Basin.

Geological characteristics and co-exploration and co-production methods of Upper Permian Longtan coal measure gas in Yangmeishu Syncline, Western Guizhou Province, China

Coal measure gas(also known as coal-bearing unconventional gas)is the key field and development direction of unconventional natural gas in recent years.The exploration and evaluation of coal measure gas(coalbed methane,coal shale gas and coal measure tight sandstone gas)from single coalbed methane has greatly expanded the field and space of resource evaluation,which is of positive significance for realizing the comprehensive utilization of coal resources,maximizing the benefits and promoting the innovation of oil and gas geological theory and technological advances in exploration and development.For the first time,in Yangmeishu Syncline of Western Guizhou Province,the public welfare coalbed methane geological survey project of China Geological Survey has been carried out a systematic geological survey of coal measure gas for the Upper Permian Longtan Formation,identified the geological conditions of coal measure gas and found high quality resources.The total geological resource quantity of coalbed methane and coal shale gas is 51.423×109 m3 and the geological resource abundance is up to 566×106 m3/km2.In this area,the coal measures are characterized by many layers of minable coal seams,large total thickness,thin to the medium thickness of the single layer,good gas-bearing property of coal seams and coal measure mudstone and sandstone,good reservoir physical property and high-pressure coefficient.According to the principle of combination of high quality and similarity of key parameters of the coal reservoir,the most favorable intervals are No.5-2,No.7 and No.13-2 coal seam in Well YMC1.And the pilot tests are carried out on coal seams and roof silty mudstone,such as staged perforation,increasing hydraulic fracturing scale and"three gas"production.The high and stable industrial gas flow with a daily gas output of more than 4000 m3 has been obtained,which has realized the breakthrough in the geological survey of coal measure gas in Southwest China.Based on the above investigation results,the geological characteristics of coal measure gas in the multi-thin-coal-seam-developed area and the coexploration and co-production methods,such as the optimization method of favorable intervals,the highefficiency fracturing and reservoir reconstruction method of coal measures,and the"three gas"drainage and production system,are systematically summarized in this paper.It will provide a reference for efficient exploration and development of coal measure gas in similar geological conditions in China.

Three-Dimensional Reconstruction of Welding Pool Surface by Binocular Vision

Current research of binocular vision systems mainly need to resolve the camera’s intrinsic parameters before the reconstruction of three-dimensional(3D)objects.The classical Zhang’calibration is hardly to calculate all errors caused by perspective distortion and lens distortion.Also,the image-matching algorithm of the binocular vision system still needs to be improved to accelerate the reconstruction speed of welding pool surfaces.In this paper,a preset coordinate system was utilized for camera calibration instead of Zhang’calibration.The binocular vision system was modified to capture images of welding pool surfaces by suppressing the strong arc interference during gas metal arc welding.Combining and improving the algorithms of speeded up robust features,binary robust invariant scalable keypoints,and KAZE,the feature information of points(i.e.,RGB values,pixel coordinates)was extracted as the feature vector of the welding pool surface.Based on the characteristics of the welding images,a mismatch-elimination algorithm was developed to increase the accuracy of image-matching algorithms.The world coordinates of matching feature points were calculated to reconstruct the 3D shape of the welding pool surface.The effectiveness and accuracy of the reconstruction of welding pool surfaces were verified by experimental results.This research proposes the development of binocular vision algorithms that can reconstruct the surface of welding pools accurately to realize intelligent welding control systems in the future.

A Study of Thin Sandstone Reservoirs by High-resolution Seismic Inversion

In this paper seismic inversion was used as a key technique and the seismic wavelet most suitable to the actual underground situation was extracted with the higher-order statistics algorithm. The wavelets extracted in this way and the wavelets extracted with the seismic statistics techniques were used separately for inverting the seismic data of the southern part of Tahe oilfield, Tarim basin. The results showed that the resolution of the wavelet inversion with the higher-order statistics method was greatly improved, and the wavelet-inverted section could better distinguish the thin sandstone reservoirs of the upper and lower Carboniferous and their lateral distribution, providing a reliable basis of analysis for the study of thin sandstone reservoirs.

Formation Models and Distribution of Oil and Gas Pools in Tarim Basin, China

This article reports the main formation models and distribution of the oil and gas pools in Tarim basin, China, including （1） occurrence of the found oil and gas pools, （2） main formation models of oil and gas pools, and （3） distribution law of oil/gas pools. Petroleum is distributed widely in the strata of Tarim basin from the Sinian at the bottom to the Neogene at the top. However, the found oil and gas fields are mainly distributed in Shaya （沙雅） uplift, Tazhong （塔中） uplift, and Kuche （库车） depression. This article presents 4 main formation models, namely, early formation and long-term preservation, early formation and late reformation, middle-late multiphase-multisource formation, late single-stage formation. Tarim basin is very rich in petroleum resources. Long-term inherited intrabasinal paleohighs and slope zones are the most favorable areas for accumulation of hydrocarbons, but the types of oil and gas pools are different from area to area. The control of unconformities and faults on hydrocarbon accumulating is prominent in Tarim basin. Preservation conditions are of utmost importance. Formation of some oil and gas pools is the result of reforming and re-accumulating of early accumulated hydrocarbons.

Characteristics of China’s oil and gas pool formation in latest geological history

The structural activities took place extensively in the Asia continent during the Cenozoic era owing to the strong continent-to-continent collision and continuous compression between the India Plate and the Eurasia Plate. Huang Jiqing called such structural activities Himalayan movement. China’s sedimentary basins developed and took shape mainly during the Himalayan movement period. It is also the main period for formation and development of the oil and gas reservoirs. Of 366 large and medium-sized oil and gas fields currently found in China, 212 reservoirs were formed in the Neo- gene-Quaternary period. The proportion is as high as 68.2%. The oil and gas migration and accumu- lation in the latest geological period, which were controlled by the times, properties, styles and strength of the Himalayan movement, took place mainly in eight regions, such as the low uplift area of Bohai Sea, the onshore faulted sag area of Bohai Bay, anticlinorium zone in Daqing, the foreland fold-and-thrust belt in West China, the tilted structural zone in West China, the cratonic palaeohigh in the Tarim Basin, the zone of fault and fold belt in the East Sichuan Basin, and the biological gas zone in the East Qaidam Basin. The oil and gas pool formations in those regions have their own charac- teristics. With the great potential and broad prospect, those regions are the main exploration areas in China in the future.

Petroleum Exploration of Craton Basins in China

Craton basins are a significant petroliferous provenance. Having undergone multiple open- dose tectonic cycles and strong reworking of the late Cenozoic tectonic movement, the craton basins in China are highly broken. This has resulted in multi-source and multiphase hydrocarbon generation and later hydrocarbon accumulation so that a complicated spatial assemblage of primary, paraprimary and secondary oil-gas pools has been formed. The primary factors controlling hydrocarbon accumulation include hydrocarbon-generating depressions, paleouplifts, paleoslopes, unconformity surfaces, paleo-karst, faults and fissure systems as well as the later conservation conditions. In consequence, the strategy of exploration for China＇s craton basins is to identify the effective source rocks, pay attention to the different effects of paleohighs and late reworking, enhance studies of the secondary storage space, attach importance to the exploration of lithologic oil-gas reservoirs and natural gas pools, and approach consciously from the secondary oil pools to the targets near the source rocks. At the same time, a complete system of technologies and techniques must be built up.

Process and mechanism for oil and gas accumulation, adjustment and reconstruction in Puguang Gas Field, Northeast Sichuan Basin, China

With the discoveries of a series of large gas fields in the northeast of Sichuan Basin, such as Puguang and Longgang gas fields, the formation mechanism of the gas reservoir containing high H2S in the ancient marine carbonate formation in superposition-basin becomes a hot topic in the field of petroleum geology. Based on the structure inversion, numerical simulation, and geochemical research, we show at least two intervals of fluid transfer in Puguang paleo-oil reservoir, one in the forepart of late Indo-Chinese epoch to early Yanshan epoch and the other in the metaphase of early Yanshan epoch. Oil and gas accumulation occurred at Puguang structure through Puguang-Dongyuezhai faults and dolomite beds in reef and shoal facies in Changxing Formation (P2ch) - Feixianguan Formation (T1f) in the northwest and southwest directions along three main migration pathways, to form Puguang paleo-oil reservoir. Since crude oil is pyrolysised in the early stage of middle Yanshan epoch, Puguang gas reservoir has experienced fluid adjusting process controlled by tectonic movement and geochemical reconstruction process controlled by thermochemical sulfate reduction (TSR). Middle Yan-shan epoch is the main period during which the Puguang gas reservoir experienced the geochemical reaction of TSR. On one hand, TSR can recreate the fluid in gas reservoir, which makes the gas drying index larger and carbon isotope heavier. On the other hand, the reciprocity between fluid regarding TSR (hydrocarbon, H2S, and water) and reservoir rock induces erosion of the reservoir rocks and anhydrite alteration, which improves reservoir petrophysical properties. Superimposed by later tectonic movement, the fluid in Puguang reservoir has twice experienced adjustment, one in the late Yanshan epoch to the early Himalayan epoch and the other time in late Himalayan epoch, after which Puguang gas reservoir is finally developed.

Geological constraints of giant and medium-sized gas fields in Kuqa Depression

There is a gas-rich and well-charged petroleumsystem in the Kuqa Depression where Triassic and Jurassicsource rocks play important roles. Distributed in an area ofmore than 10000 km and with a thickness of up to 1000 m,they are composed of dark mudstones, carbonaceous mud-stones and coal seams containing 6%, 40% and 90% of TOC,respectively, and are mainly the humic organic matter. Ashigh-quality regional cap rocks, the Neogene and Eogenegypsum rocks and gypseous mudstones matched well withthe underlying Neogene and Cretaceous-Eogene sandstones.They have formed the most favorable reservoir-seal assem-blages in the Kuqa Depression. Also the Jurassic sandstonesand mudstones formed another favorable reservoir-seal as-semblage. The traps are shaped late in the fold-thrust belt,mainly fixed in the Tertiary-Quaternary, where ten structurestyles have been distinguished. These traps spread as a zonein N-S, are scattered like a segmental line in W-E and showtier-styled vertically. The best traps are gypsum-salt coveredfault-bend anticlines related to the passive roof duplex. Thispetroleum system is characterized by late accumulation. Inthe early Himalayan Movement, mainly gas condensate andoil accumulated and were distributed in the outer circularregion of the kitchen; whereas in the middle and late Hima-layan the gas accumulations mainly formed and were dis-tributed in the inner circular region near the kitchen. Theoverpressure of gas pools is common and is formed by sealcapacity of thick gypsum layers, extensive tectonic compres-sion and large uplift. The well-preserved anticline traps un-derlying the high-quality regional cap rocks of the Tertiarygypsum rocks and gypseous mudstones are the main targetsfor the discovery of giant and medium-sized gas fields. Aboveconclusions are important for the petroleum geology theoryand the exploration of the fold-thrust belt in foreland basinsin central and western China.

改造盆地研究和油气评价的思路

改造盆地在我国分布广、数量多 ,为未来油气资源的主要接替区。这由中国大陆结构复杂、活动性强等基本特征所决定。油气的聚散、成藏和分布既严格受成盆期和成盆期前构造格局的控制 ,又明显受成盆期后每一次构造运动和任一种改造形式的影响 ,因而油气成藏过程复杂、分布规律多变 ,研究和勘探难度颇大。改造盆地研究与评价的思路和程式为 :( 1 )厘定盆地属性 ,分析动力环境 ;( 2 )恢复原始盆地 ,回归今盆位置 ;( 3)揭示改造过程 ,明确几个时期 ;( 4 )确定改造程度 ,划分保存单元 ;( 5)探讨聚散特点 ,评价资源规模 ;( 6)重视多源油气 ,突破单一模式 ;( 7)多期动态聚散 ,突出晚期成藏 ;( 8)注意差异改造 ,切忌以点代面。

中国克拉通盆地油气成藏特点和勘探思路

克拉通(内)盆地是重要的含油气领域。中国的克拉通破碎性强,经历了多次开合构造旋回并受到晚新生代构造运动的强烈改造,决定了该类盆地油气藏一般有多期多源生烃、晚期定型或成藏的特点,形成原生、准原生和次生油藏的复杂空间组合。其主要成藏控制因素为生烃坳陷、古隆起和古斜坡、不整合和岩溶作用、断裂和裂缝系统、后期保存状况等。适于该类盆地的勘探思路为:确定有效烃源岩,强调古隆起和晚期改造的不同作用,强调对次生储集空间的研究,明确岩性油气藏和天然气勘探的重要地位,自觉地从次生油气藏向近源层逼近,同时还必须形成与之配套的技术工艺体系。

辽河高成熟探区持续勘探发现技术及应用

历经50多年勘探,辽河探区整体进入高成熟勘探阶段,老区如何持续获得勘探新发现,是解决资源接替矛盾的首要问题。“十三五”期间,以老资料重建为基础,以“两宽一高”等新技术为手段,以构建新的油气藏模型为核心,对辽河探区各凹陷开展“整体认识、整体评价、整体部署”全方位勘探,发现了陡坡带砾岩体油藏、深层超压火成岩油藏、洼陷中心页岩油藏、残留型中生界潜山油藏、中浅层复杂断块油气藏五大勘探领域,落实了1个亿吨级、8个千万吨级规模储量区带。“十三五”勘探实践证明,解放思想、坚定信心、突破理论、优化技术,高成熟探区勘探仍大有可为。