Estimation of the oil-and-gas potential of sedimentary depressions in the Far East and West Siberia based on gravimetry and geothermy data

The results of geodensity, geothermal, and paleotectonic modeling of some sedimentary depressions in the Far East region and central West Siberia are interpreted from a petroleum-geological standpoint. The prospects of the possibly oil-and-gas-bearing Paleogene and Upper Cretaceous rock complexes in the Lunsk, Makarovsk, and Aniva troughs, West Sakhalin uplift, and Middle Amur intermontane depression are estimated. Petroleum accumulation zones in the preplate complex are forecasted. Localization of Jurassic oil generation centers is defined at a new large oil field in the central West Siberian plate (West Siberian plate). Experience in petroleum geology modeling for structures of different tectonic patterns, lithologies, and rock ages makes it possible to recommend the adopted methodical approach and technology of gravimetric and geothermal interpretation as universal and efficient methods.     

Structure of the sedimentary cover of the Pugachevo mud volcano area in Sakhalin: Evidence from geophysical modeling

The geological-geophysical data on the Pugachevo mud volcano group located in the zone of the submeridional Central Sakhalin Fault (CSF) are analyzed. The results of the density and geothermal modeling along two orthogonal profiles passing through the central part of the Pugachevo area are examined. It is found that the Late Cretaceous sequence of this fault-related area contains a subvertical narrow anomalous deconsolidation cone-shaped zone widening from 1 km on the surface to 4 km at its base (at the depths more than 6 km). The density of the deconsolidation blocks is 2.20–2.22 g/cm³, whereas that of the adjacent blocks reaches around 2.4–2.5 g/cm³. The largest deconsolidation block is located in the Lower Cretaceous Ai Formation, where a vast reservoir zone with mainly hydrocarbon gas (HC) is inferred at depths of more than 4400 m with temperatures of more than 140°C. The modeling results showed that the main reservoir of gases periodically ejected from the Pugachevo mud volcano is localized in the Ai Formation sequence in the tectonically weakened zone of the CSF at depths of 4.5–5.6 km. The overlying sequences contain smaller intermediate reservoirs. The Pugachevo area is promising for economic hydrocarbon reservoirs.     

Structural features of the northern West Siberian geosyneclise and new exploration targets

The northern part of the West Siberian geosyneclise is characterized by a thick sedimentary cover and widespread Triassic sedimentary and volcanosedimentary rocks and Paleozoic platform structures. New targets have been recognized in the basement and deeply buried horizons of the geosyneclise cover. Reservoirs might be found in the following formations: Paleozoic cover deposits, weathering crusts, zones of Paleozoic rock deconsolidation, Triassic sedimentary and volcanosedimentary deposits, buried structures in the lower part of the cover, Lower and Middle Jurassic basal layers, pinch-outs of Jurassic horizons, Upper Jurassic bituminous shales and cavernous carbonates. Exploration of these potential structures will change the structure of the existing resource base toward the long-term replenishment of hydrocarbon resources and a stable rate of production replacement.     

Reconstruction of the Sakhalin marginal paleobasin by geological and petrochemical data

The structural and compositional volcanosedimentary complexes and igneous rocks of the Sakhalin marginal paleobasin as well as the geodynamic setting were described. The Sakhalin marginal paleobasin was formed in Sakhalin Island and the adjacent water areas at the end of the Early Cretaceous-start of the Late Cretaceous. The paleobasin was a part of the Kula Plate separated from the ocean along with spreading zones and oceanic volcanic islands by the Sea of Okhotsk microcontinent and the Jurassic-Early Cretaceous Sheltinga volcanic island arc. The petrochemical features and geodynamic setting of the igneous rock formation testify to the fact that magma-generating tectonomagmatic structures of the epioceanic Sakhalin marginal paleobasin continued functioning after its isolation under intensive terrigenous sedimentation. The Sakhalin marginal paleobasin had a heterogeneous basement composed of oceanic and continental crust blocks of the Earth. The paleobasin completed its development in the Paleogene.     

张扭性盆地隐性断裂带识别、演化及控藏作用——以苏北盆地金湖凹陷为例

隐性断裂带是由区域或局部应力场或基底断裂活动影响下, 在凹陷沉积盖层中产生的断裂趋势带。重磁、三维地震资料处理解释成果证实苏北盆地金湖凹陷存在北东、北西两组基底断裂。部分北东向的基底断裂活动强烈, 控制了凹陷形成和演化; 北西向和部分北东向的基底断裂活动性较弱, 沉积盖层中形成了隐性断裂带。它们表现为成带分布的雁列式小断层、断断续续沿固定方向分布的小断层、一系列沉积扇体或油气圈闭成带成串分布等线状构造。随机测线的剖面上表现为地震同相轴没有明显错断或呈现杂乱反射。除上述两组隐性断裂带, 区域右行应力场在凹陷内部产生的东西方向的挤压应力分量也形成了断续状、串状的南北向隐性断裂带。研究表明, 隐性断裂带由"隐性"逐渐向"显性"过渡。经历了早期弱雁列式隐性期、早中期强雁列式隐性期、中期断续状隐-显期、中后期串状显-隐期4个隐性阶段, 最终演化为"显性"张扭性走滑断裂。沉积盖层中形成的这些隐性断裂带控制了储集砂体分布、改善了储层物性、使隐性圈闭成带成串分布, 是油气聚集成藏的有利区带。     

俄罗斯的沉积盆地和油气资源(英文)

俄罗斯的内陆和海上大约有 30个盆地赋含油气。这些盆地囊括了所有的以板块构造为分类准则的盆地类型 ,即 :( 1)内陆裂谷和超裂谷台坳 ;( 2 )现代大陆边缘的上叠台坳 ;( 3)与冲断褶皱系统毗邻的被动大陆边缘和 ( 4 )岩石圈板块聚敛带 (即大洋板块俯冲到大陆板块之下的地带 )。第一类盆地包括广袤的西西伯利亚超拗拉槽盆地和西伯里亚的Viluy拗拉槽等。第二类包括一些具油气远景的俄罗斯北冰洋盆地和里海边缘盆地。第三类包括乌拉尔前渊的伏尔加—乌拉尔盆地 (Volga—Urals)、大高加索前渊的亚速—库班盆地 (Azov—Kuban)和捷列克—里海盆地 (Terek—Caspian)以及其它盆地。被动大陆边缘经历了 2个到 3个演化阶段 ,主要油气聚集期通常对应后裂谷期。第四类盆地是指远东和俄罗斯东北部的盆地。在鄂霍次克海 (萨哈林岛—鄂霍次克和西堪察加—鄂霍次克 )已经发现了油气田 ,有一些盆地 (Anadyr和Khatyrka)已被证实含有油气。裂陷作用也控制着弧后盆地的形成。盆地的地球动力学特征控制着油气藏的分布、圈闭类型和资源富集程度。俄罗斯的油气富集区主要集中在伏尔加—乌拉尔、西西伯利亚、铁梓哥—伯朝阿 (Timano—Pechora)和萨哈林 (Sakhalin)地区 ,大约 4 5%的资源量被采出 ,其他盆地有很好的远景。里海的俄?     

金湖凹陷隐性断裂带形成机制及分布

金湖凹陷基底存在北东、北西向两组断裂。北西向基底断裂活动较弱,对盖层变形影响较小,在盖层中多以隐性断裂带显现;北东向基底断裂活动强烈,对凹陷盖层变形影响较大,不仅形成了凹陷东部边界杨村断裂在内的多条显性断裂,而且形成了多条隐性断裂带。凹陷中部的北东向石港显性断裂带将凹陷分割成西部斜坡带和东部凹陷带。东部凹陷带受基底北西向断裂隐性活动的影响呈现南北分段特征。凹陷盖层中还发育了大量近东西走向的三、四级正断层,它们大致平行成带分布,形成了宝应平行雁列式断裂构造带、唐港雁列式断裂构造带、卞闵杨平行雁列式断裂构造带、西斜坡平行入字型断裂构造带、汊涧泥沛平行雁列式断裂构造带等一系列油气富集区带。上述构造带中的油气藏分布明显受到北东和北西向基底断裂活动影响,呈现北东、北西或近南北向成带、成串分布特征。应用区域地质、重磁等资料开展隐性断裂带预测,识别出10条北东向、5条北西向、6条南北向隐性断裂带。沉积盖层中形成的这些隐性断裂带控制了储集砂体分布、改善了储层物性、使隐性圈闭成带成串分布,是油气聚集成藏的有利区带。     

Interpretation of high-accuracy gravity exploration data by mathematic programming

Nonlinear (exponential) regularities of the variation in the density of the rocks from coeval sedimentary complexes are presented. A series of direct and inverse tasks with and without consideration of the vertical density gradient were solved for the detailed and high-accuracy gravity exploration typical of petroleum geology. It was concluded that an increase in accuracy of a gravity survey better than ±0.20 mGal is of doubtful value if there is no possibility to create and account for the petrodensity dependences σ(Z). The lateral variability of the lithophysical properties of petroleum complexes of local objects is characterized. Algorithms of mathematic programming and the method of 3D geodensity modeling of the objects searched for using seismic exploration are suggested. The inverse linear tasks of high-accuracy gravity exploration are solved by a near-real model universal in complexity, which allowed us to reveal and contour noncompact (highly porous) lithofacies. Within the accepted model, the 3D task of the high-accuracy gravity exploration was solved for the Verkhnenysh gas condensate deposit in Sakhalin.     

Radiolarians and stratigraphy of Cenomanian-Coniacian deposits in the Crimean and West Sakhalin Mountains, Pt. 2: Comparative analysis

The work is aimed at summarizing data on Late Cretaceous radiolarians from the Crimean and West Sakhalin mountains. The Cenomanian-lower Coniacian stratigraphic interval of the Crimean Mountains yields 215 radiolarian species, and 80 concurrent species are known from the West Sakhalin Maintains. According to results of comparative analysis, there are 62 species in common from two regions, i.e., most of the species occurring in the West Sakhalin Mountains are also known from southerly regions, which is a good premise for correlation.     

New data on the present-day active fluid regime of fractured zones of crystalline basement and sedimentary cover in the eastern part of Volga-Ural region

The study area is the South Tatarstan Arch located in the Volgo-Ural Region, which is an enigmatic crustal segment occupying one third of the East European Platform. Monitoring studies have shown that fluid discharge processes are still active and time-dependent. This paper presents an integrated review of the geological, geophysical, hydrochemical and geochemical studies of the crystalline basement of Tatarstan. These studies are based on the stratigraphic and compositional schemes within the crystalline basement, the drilling of deep wells, the geodynamic activity of the fractured zones of the crystalline basement and the presence of fluids therein. Furthermore, the changes in the chemical composition of the basement waters are taken into account.     

Gravity and magnetic joint modeling of the Potiguar Rift Basin (NE Brazil): Basement control during Neocomian extension and deformation

A 2.5D gravity and magnetic investigation was conducted along five transects across the Potiguar Basin in the Borborema Province, NE Brazil. The objective of the study is to model the internal architecture of this intracontinental rift basin, which represents the interaction between the heterogeneous Precambrian basement and the Neocomian extensional tectonics, which led to the South Atlantic opening.Joint modeling of the gravity and magnetic data was constrained by Euler deconvolution results, seismic data, well logs and geologic mapping. This integrated approach allowed to determine the rift architecture that is inserted in a complex tectonic and structural framework. Results from joint modeling show that a series of asymmetric half-grabens is oriented in the NE–SW direction and controlled by a system of normal faults with throw greater than 5.5 km. High-density and low-magnetized material constitutes the footwall and intrarift horsts. These supracrustal heterogeneities in association with preexisting shear zones probably guided the Mesozoic rifting process in NE Brazil. Their composition seems to be related to metamorphic rocks of the Proterozoic basement, as suggested by gravity and magnetic anomalies and the geology of the exposed basement. Our interpretation is supported by geophysical studies carried out in the Benue Trough, the counterpart of the Potiguar Basin in West Africa.     

熊耳山北坡含金断裂带显微变形构造及其成因机制探讨

本区金矿化产于太古界结晶基底之上的中元古界熊耳群陆相火山岩中，成矿断裂集中分布在4条带上，断裂构造具多期活动特征，存在两类不同的变形，韧性变形在宏观上表现为强片理化带，显微构造十分发育，脆性变形具张性特征，与矿化关系密切，本对这两类变形的产物－糜棱岩和同生石英脉的显微构造，地球化学特征和形成机制，含金性等方面进行了详细研究。     

Dislocations of the cretaceous and cenozoic complexes of the northern part of the West Sakhalin Terrane

The contemporary structure of the West Sakhalin Terrane started to form in the Pleistocene and the process of its formation continues up to now in a setting of ENE (60°–90°) shortening. Evidence of the preceding NE (30°–45°) compression was revealed during the study. This compression prevailed in the Eocene–Pliocene. Under the settings of NE (30°–45°) compression, dextral displacements occurred along the West Sakhalin and Tym’–Poronai fault systems, bounding the West Sakhalin Terrane.     

Precise Timing of Caledonian Structural Deformation Chronology and Its Implications in Southeast Qilian Mountains, China

The middle Qilian orogenic belt and Lajishan orogenic belt, both of which were formed in the Caledonian, strike NW-SE direction across southeast Qilian Mountains and their basement consists of pre-Caledonian metamorphic rocks with lozenge-shaped ductile shear zones in the crystalline base- ment. The blunt angle between the conjugated ductile shear zones ranges from 104° to 114°, indicating approximate 210° of the maximum principal stress. The plateau ages of muscovite 40Ar/39Ar obtained from the mylonitized rocks in the ductile shear zones of Jinshaxia-Hualong-Keque massif within the middle Qilian massif are (405.1±2.4) Ma and (418.3±2.8) Ma, respectively. The chronology data confirm the formation of ductile shear zones in the Caledonian basement metamorphic rocks during the Cale- donian orogeny. Furthermore, on the basis of basement rock study, precise timing for the closing of the Late Paleozoic volcanic basin (or island-arc basin) and Lajishan ocean basin is determined. This pro- vides us a new insight into the closing of ocean basin in the structural evolution of orogenic belt.     

Radiolarians and stratigraphy of Cenomanian-Coniacian deposits in the Crimean and West Sakhalin Mountains, Pt. 1: Biostratigraphic subdivision and correlation

Radiolarian biostratigraphy suggested in this work for the Cenomanian-Coniacian deposits in the Crimean and West Sakhalin Mountains is enhanced to be of a higher resolution. The Cenomanian-Coniacian succession of the West Sakhalin Mountains is subdivided into nine instead of five biostratigraphic units formerly known in this region. Deposits of the Crimean Mountains are subdivided based on radiolarians within the lower Cenomanian-lower Coniacian stratigraphic interval (the original biostratigraphic chart corresponded here to the upper Cenomanian-middle Turonian interval only). The established biostratigraphic subdivisions are correlated with those of the Tethyan and Pacific scales.     

Nonconventional hydrocarbon targets in the crystalline basement, and the problem of the recent replenishment of hydrocarbon reserves

Analysis of the distribution of oil pools in sedimentary cover has shown that known platform hydrocarbon fields are closely associated with faults in the crystalline basement and the sedimentary cover itself. Oil pools in the lower productive beds of the sedimentary cover are linked to faulted zones in the crystalline basement. A genetic relationship between oil fields and tectonic dislocations indicates a dominant role for vertical migration in the accumulation of commercial hydrocarbons in the Paleozoic. The conducted geochemical, palynological, geophysical and geological studies have shown that oil and gas pools in the upper sedimentary cover have been formed due to the vertical migration of hydrocarbons, which is also confirmed by the vertical alignment of the oil pools.     

Origin of fault domains and fault-domain boundaries (transfer zones and accommodation zones) in extensional provinces: Result of random nucleation and self-organized fault growth

In many extensional provinces, large normal faults dip in the same direction forming fault domains. Features variously named transfer faults, transfer zones, and accommodation zones (hereafter non-genetically referred to as fault-domain boundaries) separate adjacent fault domains. Experimental modeling of distributed extension provides insights on the origin, geometry, and evolution of these fault domains and fault-domain boundaries. In our scaled models, a homogeneous layer of wet clay or dry sand overlies a latex sheet that is stretched orthogonally or obliquely between two rigid sheets. Fault domains and fault-domain boundaries develop in all models in both map view and cross-section. The number, size, and arrangement of fault domains as well as the number and orientation of fault-domain boundaries are variable, even for models with identical boundary conditions. The fault-domain boundaries in our models differ profoundly from those in many published conceptual models of transfer/accommodation zones. In our models, fault-domain boundaries are broad zones of deformation (not discrete strike-slip or oblique-slip faults), their orientations are not systematically related to the extension direction, and they can form spontaneously without any prescribed pre-existing zones of weakness. We propose that fault domains develop because early-formed faults perturb the stress field, causing new nearby faults to dip in the same direction (self-organized growth). As extension continues, faults from adjacent fault domains propagate toward each another. Because opposite-dipping faults interfere with one another in the zone of overlap, the faults stop propagating. In this case, the geometry of the domain boundaries depends on the spatial arrangement of the earliest formed faults, a result of the random distribution of the largest flaws at which the faults nucleate.     

Evolution of mass-transfer during progressive oblique under-thrusting of the Variscan foreland: eastern Bohemian Massif

Abstract

Four ductile shear zones were sampled in the autochthonous Thaya basement and the Upper Bíte? nappe (Moravian unit) at the Eastern margin of the Bohemian massif. In both studied units, the tectono-metamorphic evolution and the chemical mass transfer are different. Two deformational events are recognised: the first deformation stage under amphibolite facies conditions is overprinted by a second event under greenschist facies conditions.

The first deformation affected the western margin of the Thaya basement and the whole Bíte? nappe: microstructures are characterised by dynamic recrystallisation of feldspars and quartz, and occurrence of myrmekites and grain-boundary migration of quartz. None or weak chemical mass transfer is related to this medium to high temperature deformation. This deformation corresponds to the thrusting of Moldanubdian units on the Brunovistulian units (Moravian nappes and autochthonous Thaya basement).

The second deformation generated shear zones in the until then preserved Thaya basement and reactivated both shear zones of the western margin of the Thaya basement and those of the Bíte? nappe. This deformation is retrograde and mainly associated with chemical mass transfer: a decrease of CaO, FeO, FeO/Fe₂O₃ and an increase of MgO, K₂O and H₂O. These chemical changes are related to greenschist metamorphic reactions leading to the destabilisation of feldspars and the crystallisation of white micas and Ca-silicates. The large chemical mass transfer is associated with the circulation of a large volume of fluids. A model of progressive fluid circulation correlated with Variscan prograde and retrograde metamorphism during the collision of Moldanubian and Brunovistulian units is proposed.     

中新生代陆内造山带的地层学研究——以燕辽造山带为例

陆内造山带作为一种特殊类型的造山作用形式，具有明显不同于稳定陆块区和一般造山带的地层学特征。笔者以燕辽造山带为例，将陆内造山带的地层划分为前造山期地层、始造山期地层、主造山期地层和重造山期地层四种类型。并简要介绍了这四种不同构造层的特点及应采取的研究方法。