A temperature model of the crust beneath the Barents Sea: Investigations along geotraverses

2D and 3D modeling of the geothermal field was carried out along seven extended geotraverses in the Barents Sea compiled on the basis of CMP profiling and results of deep drilling. Depths of the zone characterized by catagenetic transformation of organic matter were calculated for different areas of the sedimentary basin. The minimal depth is confined to the South Barents Basin with the highest hydrocarbon resource potential established by geological exploration. In 3D models, this area is distinguished by a thermal dome recognized for the first time.     

塔里木盆地海相石油的真实勘探潜力

塔里木盆地古生界蕴藏了丰富的海相油气资源,储集层目前埋深在5500～10000m。深部流体的相态或者说液相石油大量消失的深度下限是学术界比较关心的理论问题,而塔里木盆地海相到底富油还是富气也是关系到塔里木油田未来产能规划的现实问题。通过对塔里木盆地原油的热稳定性分析,特别是低地温梯度和晚期快速深埋过程的补偿效应研究,认为液态石油大量消亡(油裂解成气)的深度下限在9000～10000m以下,对应的储层温度大于210℃,在此深度之上液态石油可以大量存在。通过对油气聚集与保存的关键地质科学问题的研究,认为晚海西期是台盆区油藏的主要成藏期,烃源灶区生成的油气主要分布在稳定的古隆起及其围斜区域;而晚海西期这些古隆起及其围斜区碳酸盐岩储层埋藏深度在800～2500m范围内,岩溶储集体发育,这是台盆区形成大面积层状油气聚集的基础,也决定了现今埋深在7000～9000m深度范围内的斜坡区将成为黑油和凝析油的重要勘探接替区。     

Formation mechanisms of ultradeep sedimentary basins: the North Barents basin. Petroleum potential implications

Consolidated crust in the North Barents basin with sediments 16–18 km thick is attenuated approximately by two times. The normal faults in the basin basement ensure only 10-15% stretching, which caused the deposition of 2–3 km sediments during the early evolution of the basin. The overlying 16 km of sediments have accumulated since the Late Devonian. Judging by the undisturbed reflectors to a depth of 8 s, crustal subsidence was not accompanied by any significant stretching throughout that time. Dramatic subsidence under such conditions required considerable contraction of lithospheric rocks. The contraction was mainly due to high-grade metamorphism in mafic rocks in the lower crust. The metamorphism was favored by increasing pressure and temperature in the lower crust with the accumulation of a thick layer of sediments. According to gravity data, the Moho in the basin is underlain by large masses of high-velocity eclogites, which are denser than mantle peridotites. The same is typical of some other ultradeep basins: North Caspian, South Caspian, North Chukchi, and Gulf of Mexico basins. From Late Devonian to Late Jurassic, several episodes of rapid crustal subsidence took place in the North Barents basin, which is typical of large petroleum basins. The subsidence was due to metamorphism in the lower crust, when it was infiltrated by mantle-source fluids in several episodes. The metamorphic contraction in the lower crust gave rise to deep-water basins with sediments with a high content of unoxidized organic matter. Along with numerous structural and nonstructural traps in the cover of the North Barents basin, this is strong evidence that the North Barents basin is a large hydrocarbon basin.     

Devonian Reef Formation in the Caspian Basin Framing

The Devonian reef formation in the Caspian Basin framing is related to two different formations. The Middle Devonian reefs are confined to an autochthonous terrigenous?carbonate sequence of the Eifelian–lower Frasnian interval marked by the appearance of isolated domal reefs. The middle–upper Frasnian reefs are related to the carbonate formation and represented by two types: (i) asymmetric reefs on walls of the deep-water bays opening toward the Caspian microcean-bay; and (ii) solitary, relatively symmetric (in transverse section) reefs within these bays. The reef formation was characterized by prominent cyclic pattern. The framework reef formation ended before the terminal Frasnian, i.e., before the Kellwasser Event, with which the biotic crisis and faunal mass extinction was related.     

Fundamental challenges of the location of oil and gas in the South Caspian Basin

Subvertical and subhorizontal bodies were identified in the South Caspian Basin. They are a new class of geological structures with a complicated form, which can serve as migration pathways and hydrocarbon accumulation zones. The basin incorporates a few autonomous sources of oil and gas occurrences with their own distribution areas and spatial–temporal evolution. HC generation sources are displaced relative to each other. The lower boundary of the oil and gas occurrence reaches depths of more than 12–15 km, while the upper boundary of the “oil window” is confined to hypsometric depths of 5–7 km.     

全球大型凝析气田的分布特征及其形成主控因素

随着勘探的不断深入,越来越多的凝析气藏被发现,并受到重视。目前全球共发现106个大型凝析气田,分布于全球70多个沉积盆地。凝析气田主要分布于西西伯利亚盆地、滨里海盆地、波斯湾盆地、扎格罗斯盆地、美国墨西哥湾及塔里木盆地等。通过对全球各大凝析气田进行系统的研究,发现凝析气藏主要分布在石炭系—新近系储层中,以构造圈闭为主,储集体物性较差,属于低孔低渗型,凝析气和凝析油的密度均相对较低。凝析气田的形成和展布主要受控于有效烃源岩分布、有利的储盖组合、圈闭类型、晚期成藏、特殊的温压系统和烃类体系组分等条件。根据其成因机理,将凝析气藏分为原生凝析气藏和次生凝析气藏。     

Influence of saline deposits on the conditions of petroleum generation in the rocks underlying the salt complex of the northern part of the Precaspian Basin

Numerous studies on the potential of hydrocarbon generation by the rocks of the sedimentary cover of the northern Precaspian Basin are based either on the interpolation of measurements from a relatively sparse boreholes network or on the numerical estimations of the history of development of the hydrocarbon potential under the assumption of a steady temperature gradient both with depth in the sedimentary cover and with time during basin evolution. By the example of sedimentary sections from the northeastern part of the Precaspian Basin, variations in thermal history and petroleum formation conditions were numerically analyzed for the rocks underlying the salt complex of the basin. Variations in the temperature gradient and thermal properties of the rocks with depth and time were accounted for in the modeling. Numerical reconstructions of the thermal and maturation history of sedimentary sections from the basin were used to estimate the influence of evaporite sequences on the thermal history, the maturation level of organic matter, and the hydrocarbon generation potential of the subsalt complex of the basin. The calculations showed that this influence could be significant, but there remained an uncertainty related to the absence of reliable data on the time and rate of salt diapir formation.     

Mud volcanic natural phenomena in the South Caspian Basin: geology,fluid dynamics and environmental impact

The South Caspian sedimentary basin is a unique area with thick Mesozoic-Cenozoic sediments (up to 30–32 km) characterized by an extremely high fluid generation potential. The large amount of active mud volcanoes and the volumes of their gas emissions prove the vast scale of fluid generation. Onshore and offshore mud volcanoes annually erupt more than 10⁹ cubic meters of gases consisting of CH₄ (79–98%), and a small admixture of C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, CO₂, N, H₂S, Ar, He. Mud volcanism is closely connected to the processes occurring in the South Caspian depression, its seismicity, fluctuations of the Caspian Sea level, solar activity and hydrocarbon generation.The large accumulations of gas hydrates are confined to the bottom sediments of the Caspian Sea, mud volcanoes crater fields (interval 0–0.4 m, sea depth 480 m) and to the volcanoes body at the depth of 480–800 from the sea bottom. Resources of HC gases in hydrates saturated sediments up to a depth of 100 m and are estimated at 0.2×10¹⁵–8×10¹⁵ m³. The amount of HC gases concentrated in them is 10¹¹–10¹² m³.The Caspian Sea, being an inland closed basin is very sensitive to climatic and tectonic events expressed in sea level fluctuations. During regressive stages as a result of sea level fall and the reducing of hydrostatic pressure the decomposition of gas hydrates and the releasing of a great volume of HC gases consisting mainly of methane are observed.From the data of deep drilling, seismoacoustics, and deep seismic mud volcanic activity in the South Caspian Basin started in the Lower Miocene. Activity reached its highest intensity at the boundary between the Miocene and Pliocene and was associated with dramatic Caspian Sea level fall in the Lower Pliocene of up to 600 m, which led to the isolation of the PaleoCaspian from the Eastern ParaTethys. Catastrophic reduction of PaleoCaspian size combined with the increasing scale of mud volcanic activity caused the oversaturation and intoxication of water by methane and led to the mass extinction of mollusks, fishes and other groups of sea inhabitants. In the Upper Pliocene and Quaternary mud volcanism occurred under the conditions of a semi-closed sea periodically connected with the Pontian and Mediterranean Basins. Those stages of Caspian Sea history are characterized by the revival of the Caspian organic world.Monitoring of mud volcanoes onshore of the South Caspian demonstrated that any eruption is predicted by seismic activation in the region (South-Eastern Caucasus) and intensive fluid dynamics on the volcanoes.     

Late Cenozoic deformation in the South Caspian region: effects of a rigid basement block within a collision zone

Active deformation in the South Caspian region demonstrates the enormous variation in kinematics and structural style generated where a rigid basement block lies within a collision zone. Rigid basement to the South Caspian Basin moves with a westward component relative both to stable Eurasia and Iran, and is beginning to subduct at its northern and western margins. This motion is oblique to the approximately north–south Arabia–Eurasia convergence, and causes oblique shortening to the south and northeast of the South Caspian Basin: thrusting in the Alborz and Kopet Dagh is accompanied by range-parallel strike–slip faults, which are respectively left- and right-lateral. There are also arcuate fold and thrust belts in the region, for two principal reasons. Firstly, weaker regions deform and wrap around the rigid block. This occurs at the curved transition zone between the Alborz and Talysh ranges, where thrust traces are concave towards the foreland. Secondly, a curved fold and thrust belt can link a deformation zone created by movement of the basement block to one created by the regional convergence: west-to-east thrusts in the eastern Talysh represent underthrusting of the South Caspian basement, but pass via an arcuate fan of fold trains into SSW-directed thrusts in the eastern Greater Caucasus, which accommodates part of the Arabia–Eurasia convergence. Each part of the South Caspian region contains one or more detachment levels, which vary dependent on the pre-Pliocene geology. Buckle folds in the South Caspian Basin are detached from older rocks on thick mid-Tertiary mudrocks, whereas thrust sheets in the eastern Greater Caucasus detach on Mesozoic horizons. In the future, the South Caspian basement may be largely eliminated by subduction, leading to a situation similar to Archaean greenstone belts of interthrust mafic and sedimentary slices surrounded by the roots of mountain ranges constructed from continental crust.     

Seismostratigraphic complex of Jurassic deposits, Barents Sea shelf

The Jurassic deposits of the Barents Sea are very promising for hydrocarbon prospecting. This complex of deposits occurs at a depth that is accessible for drilling. Using the seismostratigraphic method, the environments and stages of sedimentation in Jurassic are found. The alimentary zones and migration routes are defined. The most promising zones for prospecting for new large hydrocarbon fields are determined.     

A review of the geochemistry of methane in natural gas hydrate

The largest accumulations on Earth of natural gas are in the form of gas hydrate, found mainly offshore in outer continental margin sediment and, to a lesser extent, in polar regions commonly associated with permafrost. Measurements of hydrocarbon gas compositions and of carbon-isotopic compositions of methane from natural gas hydrate samples, collected in subaquatic settings from around the world, suggest that methane guest molecules in the water clathrate structures are mainly derived by the microbial reduction of CO₂ from sedimentary organic matter. Typically, these hydrocarbon gases are composed of > 99% methane, with carbon-isotopic compositions (δ¹³C_PDB) ranging from − 57 to − 73‰. In only two regions, the Gulf of Mexico and the Caspian Sea, has mainly thermogenic methane been found in gas hydrate. There, hydrocarbon gases have methane contents ranging from 21 to 97%, with δ¹³C values ranging from − 29 to − 57‰. At a few locations, where the gas hydrate contains a mixture of microbial and thermal methane, microbial methane is always dominant. Continental gas hydrate, identified in Alaska and Russia, also has hydrocarbon gases composed of > 99% methane, with carbon-isotopic compositions ranging from − 41 to − 49‰. These gas hydrate deposits also contain a mixture of microbial and thermal methane, with thermal methane likely to be dominant. Published by Elsevier Science Ltd     

琼东南盆地现今地层温度分布特征及油气地质意义

温度状态是决定油气形成与保存的关键因素，精准的深部地层温度预测对盆地油气资源战略评价和勘探开发具有重要意义。琼东南盆地是我国当前深水油气资源勘探的重点区块，揭示盆地深部地层温度分布格局及主控因素是深水油气勘探研究的一项基础工作。结合钻孔实测温度和系统的岩石热物性参数，文章揭示了琼东南盆地现今深部地层温度分布特征。研究表明，琼东南盆地的优势储层温度为90~150℃ （数据占比>70%），高于国外学者提出的储层“黄金温度带”（60~120℃），推测与南海北部大陆边缘盆地高地热背景有关。此外，盆地T30—T70 界面处的估算温度均表现为“西高东低”的特征，高温区域位于西部的崖南凹陷；深部温度分布格局与地层的埋深、热导率结构以及因区域拉张程度不同引起的基底热流差异等诸因素有关。成果为琼东南深水油气勘探开发及钻井工艺设计提供了坚实的地热学依据。     

琼东南盆地现今地层温度分布特征及油气地质意义

温度状态是决定油气形成与保存的关键因素,精准的深部地层温度预测对盆地油气资源战略评价和勘探开发具有重要意义。琼东南盆地是我国当前深水油气资源勘探的重点区块,揭示盆地深部地层温度分布格局及主控因素是深水油气勘探研究的一项基础工作。结合钻孔实测温度和系统的岩石热物性参数,文章揭示了琼东南盆地现今深部地层温度分布特征。研究表明,琼东南盆地的优势储层温度为90~150℃ （数据占比>70%）,高于国外学者提出的储层“黄金温度带”（60~120℃）,推测与南海北部大陆边缘盆地高地热背景有关。此外,盆地T30—T70 界面处的估算温度均表现为“西高东低”的特征,高温区域位于西部的崖南凹陷;深部温度分布格局与地层的埋深、热导率结构以及因区域拉张程度不同引起的基底热流差异等诸因素有关。成果为琼东南深水油气勘探开发及钻井工艺设计提供了坚实的地热学依据。     

Geological evolution and petroleum systems in the North Caspian Region

The structure and formation evolution of the principal North Caspian zones (North Caspian Basin, Karakul-Smushkovskii Foredeep, South Emba Foredeep, Karpinsky Range Fold Zone, Mangyshlak-Central Ustyurt Fold Zone, etc.) are discussed. Drilling data and seismic profiles were utilized in the study, and an analysis of hydrocarbon systems has been performed.     

辽河盆地桃园-荣兴屯地区煤和炭质泥岩成烃模拟

在考虑剥蚀作用与火成岩影响的基础上分别进行了地史和成熟史恢复，根据工区热模拟资料建立了炭质泥岩成烃模式，在分析国内有关煤成烃热模拟实验资料的基础上，建立了工区下第三系煤成烃模式，进而对目的层进行了生烃史模拟。结果表明，这种方法是准确而可靠的。     

哈萨克斯坦共和国油气地质资源分析

哈萨克斯坦共和国地处中亚并与我国接壤,石油天然气资源潜力巨大,陆上油、气可采储量分别为21亿吨和16000亿立方米,而海上油气资源更加丰富,目前已发现油气田200余个,包括油田、油气田、凝析气田和气田等多种油气组合,集中分布在哈萨克斯坦国西部各含油气省.该国含油气面积约为170万平方公里,滨里海、中里海-曼格什拉克和乌斯丘尔特沉积盆地具有十分丰富的油气资源,楚河-萨雷苏伊盆地和锡尔河盆地也有油气发现.     

http://www.sciencedirect.com/science/article/pii/S1674987112000849

New methods are presented for processing and interpretation of shallow marine differential magnetic data,including constructing maps of offshore total magnetic anomalies with an extremely high resolution of up to 1-2 nT,mapping weak anomalies of 5-10 nT caused by mineralization effects at the contacts of hydrocarbons with host rocks,estimating depths to upper and lower boundaries of anomalous magnetic sources,and estimating thickness of magnetic layers and boundaries of tectonic blocks. Horizontal dimensions of tectonic blocks in the so-called "seismic gap" region in the central Kuril Arc vary from 10 to 100 km,with typical dimensions of 25-30 km.The area of the "seismic gap" is a zone of intense tectonic activity and recent volcanism.Deep sources causing magnetic anomalies in the area are similar to the "magnetic belt" near Hokkaido. In the southern and central parts of Barents Sea,tectonic blocks with widths of 30-100 km,and upper and lower boundaries of magnetic layers ranging from depths of 10 to 5 km and 18 to 30 km are calculated.Models of the magnetic layer underlying the Mezen Basin in an inland part of the White Sea-Barents Sea paleorift indicate depths to the lower boundary of the layer of 12-30 km.Weak local magnetic anomalies of 2-5 nT in the northern and central Caspian Sea were identified using the new methods,and drilling confirms that the anomalies are related to concentrations of hydrocarbon.Two layers causing magnetic anomalies are identified in the northern Caspian Sea from magnetic anomaly spectra.The upper layer lies immediately beneath the sea bottom and the lower layer occurs at depths between 30-40 m and 150-200 m.     

Tectonics of the Devonian Complex of the Southern Sector of the Caspian Basin (Kazakhstan): A Set of Geological and Geophysical Methods

The paper presents a comprehensive analysis of new data for drilling and seismic survey of the oil and gas potential of deep-seated Paleozoic horizons of the Caspian Basin in Kazakhstan. The features of the development and occurrence of large Paleozoic uplifts and sedimentary strata promising for prospecting are specified. A set of geological and geophysical methods was applied, and magnetic and gravitational anomalies of potential fields were analyzed in the southern, southeastern, and eastern marginal parts of the southeastern sector of the Caspian Basin. This is supplemented with new data obtained by a set of reconnaissance methods, and the section attributed to the Paleozoic at depths up to 5.5–8.0 km and its Devonian–Lower Carboniferous sequence are specified. New data were obtained on the area of distribution and occurrence of Upper Devonian and Lower Carboniferous sediments, geological conditions and prerequisites were revealed that refined the trace of the pre-Devonian complex and of the Lower–Middle Devonian sediments. Analysis of the distribution of large local prospecting objects has confirmed the presence and development of megauplifts, which are zones of hypsometrically elevated Devonian–Lower Carboniferous sediments. In the contour of the megauplift, structural elements have developed that are less significant, but promising in terms of hydrocarbon content. Based on the results of studying and refining the distribution patterns of large Devonian‒Lower Carboniferous objects and identifying megauplifts, it is possible to optimize regional studies in the Caspian Basin for the period of 2020–2030.

     

Modeling of gas generation from the Alam El-Bueib formation in the Shoushan Basin, northern Western Desert of Egypt

The Shoushan Basin is an important hydrocarbon province in the northern Western Desert, Egypt, but the burial/thermal histories for most of the source rocks in the basin have not been assigned yet. In this study, subsurface samples from selected wells were collected to characterize the source rocks of Alam El-Bueib Formation and to study thermal history in the Shoushan Basin. The Lower Cretaceous Alam El-Bueib Formation is widespread in the Shoushan Basin, which is composed mainly of shales and sandstones with minor carbonate rocks deposited in a marine environment. The gas generative potential of the Lower Cretaceous Alam El-Bueib Formation in the Shoushan Basin was evaluated by Rock–Eval pyrolysis. Most samples contain sufficient type III organic matter to be considered gas prone. Vitrinite reflectance was measured at eight stratigraphic levels (Jurassic–Cretaceous). Vitrinite reflectance profiles show a general increase of vitrinite reflectance with depth. Vitrinite reflectance values of Alam El-Bueib Formation range between 0.70 and 0.87 VRr %, indicating a thermal maturity level sufficient for hydrocarbon generation. Thermal maturity and burial histories models predict that the Alam El-Bueib source rock entered the mid-mature stage for hydrocarbon generation in the Tertiary. These models indicate that the onset of gas generation from the Alam El-Bueib source rock began in the Paleocene (60 Ma), and the maximum volume of gas generation occurred during the Pliocene (3–2 Ma).     

Generation of hydrocarbons in the burial history of Silurian formations in the Libyan part of the Ghadames Basin

Burial history, temperature variations, and organic matter maturation in the sedimentary rocks in the Ghadames Basin were numerically reconstructed using the GALO system for basin modeling taking into account repeated tectonic (stretching) and thermal activation events in the basin lithosphere. The modeling improved the reconstruction of the thermal history of the basin and hydrocarbon generation potential compared with previous model estimates based on the assumption of a constant temperature gradient during the whole period of basin development. In particular, the results of modeling suggest that the amplitude of Cenozoic erosion was smaller than that proposed in previous studies. The central part of the Ghadames Basin, which was considered in this study, is the western part of the Libyan sector of the basin, which underwent intense subsidence reaching 4000 m already in the Carboniferous. Given the relatively active thermal history of the basin, the modeling suggests high degrees of organic maturity in the source rocks of the Lower Silurian in the modern section of the basin and confirms the high generation potential of liquid and gaseous hydrocarbons in these formations. Significant hydrocarbon generation has occurred there since the Late Carboniferous. On the other hand, the generation potential of the Late Devonian (Frasnian) sequences is limited and strongly dependent on burial depth. The main stage of hydrocarbon generation in these rocks coincided with the Cenozoic thermal activation of the basin lithosphere. In all the areas considered, the oil window overlaps a significant portion of the modern sedimentary section of the Ghadames Basin.