Oil-gas Accumulation Research Articles

Condensate origin and hydrocarbon accumulation mechanism of the deepwater giant gas field in western South China Sea: A case study of Lingshui 17-2 gas field in Qiongdongnan Basin

Abstract Based on the geochemical characteristics of condensates and gases, in combination with geological background, the origin and formation of condensate and oil-gas accumulation mechanism of the deepwater Lingshui 17-2 gas field in the Qiongdongnan Basin, western South China Sea are discussed. The condensate from Lingshui 17-2 gas field has the features of low density, low wax content and high Pr/Ph value. The condensate is generated at mature stage while the co-existing gas is dominated by high mature gas. The oil and gas are derived from the Oligocene Yacheng Formation source rocks rich in terrestrial organic matter. The formation of the condensate is related not only to the source rock, but also to the later “gas-washing”. The light oil and gas which was generated at oil-window stage and accumulated in reservoirs have strong reaction of evaporation fractionation during “gas-washing” by high mature natural gas injected largely at later period. The Yacheng source rocks provided sufficient gas and some light oil, diapiric fractures formed migration paths for oil and gas, and two stages of hydrocarbons charged and accumulated. The Miocene Huangliu Formation turbidite sandstones lithologic trap and Paleogene structural trap close to source Kitchen in the central canyon have favorable oil-gas exploration potential.

鄂尔多斯盆地南部富县地区三叠系延长组长8油层组油气成藏期次与时限

多旋回叠合盆地的油气成藏期次与时限研究是成藏地质学研究热点及前缘领域。鄂尔多斯盆地延长组长8油层组作为深层油气勘探的重点层位，其成藏期次与时限鲜有报道。根据含油气砂岩样品的包裹体薄片岩相学与荧光分析分析，研究区存在两期不同产状的烃类流体包裹体(FI)，第一期烃类FI呈带状分布在石英加大边、石英矿物早期裂缝中，显示褐色或浅绿色荧光；第二期烃类FI分布在切穿石英及其加大边裂缝，或晚期方解石胶结物，显示浅黄色或黄绿色荧光。根据与烃类FI同期的盐水FI均一温度的测试分析，早期FI均一温度分布在85℃~135℃，峰值接近105℃；晚期分布在135℃~155℃，峰值接近145℃。结合构造热演化史，该区存在两期幕式充注成藏过程，主要成藏时限为164 Ma和 127 Ma。为盆地延长组油气成藏机理及过程研究提供了新认识。 Timing and stages of oil-gas accumulation (OGA) are hot spots and key frontier for petroleum accumulation geology in multi-cycle superimposed basin. As the important deep oil-gas reservoir of exploration, timing and stages of OGA of Chang 8 member of Yanchang formation in Ordos Basin are rarely reported. According to the lithofacies and fluorescence analysis of hydrocarbon fluid inclusions (FI) from sandstone samples, there are two different occurrence fluid inclusions for Chang 8 member of Yanchang formation in the study area. The first occurrence of hydrocarbon FI is banded in the quartz plus side, quartz mineral early cracks, showing brown or light green fluorescence. The second occurrence of the hydrocarbon FI is distributed in the cut-off quartz and its increased fissures, or late calcite cements, showing light yellow or yellowish green fluorescence. According to the test analysis of the homogeneous temperature of the salt water FI with the hydrocarbon FI, the early FI homogeneous temperature distribution is in a range of (85˚C - 135˚C) with the peak of 105˚C; the late distribution is in a range of (135˚C - 155˚C) with the peak of 145˚C. Combined with the history of tectonic thermal evolution, it reveals that the Chang 8 reservoirs went through 2-stage OGA of 164Ma and 127 Ma, which provides a new understanding for the mechanism and process of hydrocarbon accumulation in the Yanchang Formation.

Play types, geologic characteristics and exploration domains of lithological reservoirs in China

Abstract By dissecting thirty-six representative oil-gas reservoirs and analyzing accumulation conditions of giant oil and gas provinces in four prototype basins, including the Songliao Rift and Depression Basin, the Mesozoic Ordos Depression Basin, the Bohai Bay Rift and Depression Basin, the Mesozoic Junggar Depression Basin, the West Sichuan Foreland Basin and the Tarim Craton Basin, the hydrocarbon plays classification scheme of lithologic reservoirs is established and improved from the perspective of oil-gas accumulation zone and exploration target. The results reveal the accumulation characteristics and controlling factors of lithologic reservoirs including three kinds of slopes, three kinds of sag centers, three kinds of hydrocarbon accumulation assemblages and multiple genetic types. Based on the understandings on reservoir formation mechanisms and enrichment regularities of different hydrocarbon provinces, six major assessment indexes, parameter system and grading standard of lithologic plays are established, including hydrocarbon source rock condition, transportation pathway, reservoir condition, reservoir-cap assemblage, fluid property, and time-space configuration etc. Through comprehensive analysis of burial history, hydrocarbon-generation history, digenesis history, tectonic history, trap-forming history and accumulation history, plays of lithologic reservoirs are evaluated and optimized. The results show that the middle-shallow layers in the slope zones of the Songliao and Bohai Bay Basins oil-rich sags, the Mesozoic in the Ordos Basin, the Permian-Jurassic in the Junggar Basin, etc. are the major oil exploration areas in the future, with oil resources of about 42×10 8 t–67×10 8 t; the deep volcanic rocks of the Songliao Basin, the Carboniferous of the Junggar Basin, the Cambrian of the Tarim and Sichuan Basins, the Permian-Triassic reefs and shoals within the platform and on the platform margin of the Sichuan Basin are the major gas exploration areas in the future, with gas resources of about 1.5×10 12 m 3 −2.0×10 12 m 3 .

Simulation of oil–gas migration and accumulation in the East China Sea Continental Shelf Basin: a case study from the Xihu Depression

AbstractThe oil–gas accumulation process is a tectonic indicator, and the oil–gas trap is generally a result of tectonic movement. In order to explore the law of oil–gas migration and accumulation in the East China Sea Continental Shelf Basin, this paper analyses the dynamic process of hydrocarbon accumulation based on a geological model, taking the Xihu Depression as an example and using the IES PetroMod basin modelling software. Combined with the seismic data and drilling data, the burial history, thermal evolution history and hydrocarbon generation, expulsion and migration history of the Xihu Depression is simulated in this study. The simulation results show that (1) the tectonic framework of the Xihu Depression developed as an inversion structure from an early extensional stage or transtensional faulting stage to a later compressional or transpressional inversion stage; (2) the Pinghu and Huagang formations of the Xihu Depression are still currently at the peak stage of oil–gas generation, and the Xihu Depression is a depression which has abundant hydrocarbon generation and expulsion at a later stage; (3) oil–gas resources vertically migrated to the structural highs from the eastern and western sub‐sags along faults and ultimately accumulated in favourable traps, which developed a migration pattern of interbedded sandstone–fault–sandstone like an upward ‘staircase’. In particular, faults and the potential energy state played an important role in hydrocarbon migration of the Xihu Depression, which has a guiding significance for understanding hydrocarbon migration and accumulation law and reducing the risk in oil–gas exploration in the East China Sea Continental Shelf Basin. Copyright © 2016 John Wiley & Sons, Ltd.

The Top Eroded Thickness Recovery of Volcanic Rocks in Yingcheng Formation of Yingshan Fault Depression

Since the discovery of business flow in volcanic rocks of Yingcheng formation, the deep volcanic rocks of Songliao basin have become another advantaged target for oil-gas exploration. To reproduce the the development process of oil-gas generation, migration and accumulation, accurately calculating the oil-gas accumulation time is a very important work. To minimize the error, we must seriously study the regional tectonic evolution history and recover the eroded thickness. According to the actual situation of the study area, trend method can be used to recover the top eroded thickness of volcanic rocks in Yingcheng formation. Finally we get the maximum eroded thickness in the basin is between 120 m to 240 m, located in the southeastern basin.

Geological Controls and Mechanism of Shale Gas and Shale Oil Accumulations in Liaohe Western Depression, China

Recently, the accumulation of shale gas and shale oil in the rifted lacustrine basin of China has garnered increasing interest. In this paper, the shale located in the Shahejie Formation of the Liaohe western depression of the Bohai Bay Basin was selected as the focus of a comprehensive evaluation of the geological controls of shale gas and shale oil accumulation. (1) In a rifted lacustrine basin, the subsidence rate of the stratigraphy is rapid, which results in a massive sedimentation of organic-rich shale. The shale that developed in the deep and semi-deep lacustrine facies is characterized by a high concentration of organic matter, with an average total organic carbon (TOC) content over 2.0% being measured. The TOC consists primarily of type I-II1 kerogen, which contains abundant sapropelic materials and has relatively low thermal maturity, ranging from 0.4 to 0.9% Ro, due to the shallow burial depth and the young deposition epoch. (2) Various pore-fractures in the core samples and erosion occurring in the calcareous and dolomitic shales were observed, which provide storage space for oil-gas accumulations. Furthermore, the mechanisms of the accumulation of shale gas and shale oil in the study area were established according to analyses of the geochemistry characteristics and the sedimentary environment, as well as a thermal pressure simulation experiment. Overall, the accumulation model of shale oil-gas is characterized by “upper oil and lower gas”. In addition, oil-gas resources in siltstone, dolomite and limestone, which are adjacent to or interbedded with organic-rich shale, are also important targets in shale reservoirs.

Geochronological Records of Oil‐Gas Accumulations in the Permian Reservoirs of the Northeastern Ordos Basin

AbstractGeochronology of oil‐gas accumulation (OGA) is a challenging subject of petroleum geology in multi‐cycle superimposed basins. By K‐Ar dating of authigenic illite (AI) and fluid inclusion (FI) analysis combined with apatite fission track (AFT) thermal modeling, a case study of constraining the OGA times of the Permian reservoirs in northeast Ordos basin (NOB) has been conducted in this paper. AI dating of the Permian oil‐gas‐bearing sandstone core‐samples shows a wide time domain of 178–108 Ma. The distribution of the AI ages presents 2‐stage primary OGA processes in the Permian reservoirs, which developed in the time domains of 175–155 Ma and 145–115 Ma with 2‐peak ages of 165 Ma and 130 Ma, respectively. The FI temperature peaks of the samples and their projected ages on the AFT thermal path not only present two groups with a low and a high peak temperatures in ranges of 90–78°C and 125–118°C, respectively corresponding to 2‐stage primary OGA processes of 162–153 Ma and 140–128 Ma in the Permian reservoirs, but also appear a medium temperature group with the peak of 98°C in agreement with a secondary OGA process of c.∼30 Ma in the Upper Permian reservoirs. The integrated analysis of the AI and FI ages and the tectono‐thermal evolution reveals that the Permian reservoirs in the NOB experienced at least 2‐stage primary OGA processes of 165–153 Ma and 140–128 Ma in agreement with the subsidence thermal process of the Mid‐Early Jurassic and the tectono‐thermal event of the Early Cretaceous. Then, the Upper Permian reservoirs further experienced at least 1‐stage secondary OGA process of c.∼30 Ma in coincidence with a critical tectonic conversion between the slow and the rapid uplift processes from the Late Cretaceous to Neogene.

Seismic Reservoir Prediction in Lengjia-Leijia Area

Through the deep exploration in Lengjia-Leijia area, four reservoirs were found: the lower sub-section of the third member of Shahejie formation, the fourth member of Shahejie formation, Mesozoic, and Archean. The fourth member of Shahejie formation and the layer below it had fewer drilling reach; its reservoir stratums are different. Seismic reservoir prediction has become the major means of oil-gas reservoir evaluation. The logging-constrained inversion method was applied in this study. A geologic model was established based on the detailed interpretation of seismic data; then, inversion and prediction were performed to describe and evaluate the distribution, thickness, and physical characteristics of the reservoirs. The results showed that the reservoir in the fourth member of Shahejie formation, Mesozoic, and Archean are well developed, and that oil-gas accumulation is in good condition. Therefore, the deep layer in this area is an important exploration direction. This study also provided the preliminary prediction that a favorable trap area exists.

Main Factors Controlling Oil-Gas Enrichment Regularities and Accumulation Modes of Putaohua Oil Layer in Chaochang Region

In order to clarify some kinds of geological conditions on the hydrocarbon accumulation process, this paper analyses the main factors controlling oil-gas enrichment regularities of Putaohua oil layer in Chaochang region of Daqing city, which conclude tectonics, sedimentary characteristics, oil source condition and the mutual relationship between of them. The results show that the organic abundance of hydrocarbon source rocks of Qing1 section control oil and gas distribution range. The configuring relationships of oil-source fault and reservoir sand body control oil and gas migration. The configuring relationship of sedimentary micro-facies types and structures controls oil and gas distribution. On the basis of these studies, oil and gas accumulation mode in Putaohua reservoir are summarized in Chaochang region. There are two accumulation models: nearby accumulation mode in northwest and updip accumulation mode in southeast.

Detailed assessement of a single-combination oil-gas accumulation zone in a mature exploration basin, China

Abstract As some basins or blocks in China, especially matured and gas fields, have already entered the mature or highly mature stage in exploration, the old traditional assessment method that treats “complex horizons” as a whole part can not meet the high resolution and precision requirements for detailed exploration in these areas. By comparing oil-gas evaluation systems at home and abroad and considering the evaluation method for “play” abroad, a single-combination assessment method for oil and gas accumulations in high matured exploration basins were put forward. The new method, composed of geological evaluation, resources estimation and target selection, focuses on conducting a division of the assessment horizon based on a combination of a regional/sub-regional seal and its corresponding reservoirs and hydrocarbon-supplying area, confirms the test results of drilled wells and the distribution of known reservoirs, and depicts boundaries of every key geological element. Finally, these preliminary maps of key elements are overlapped to figure out the scope and type of favorable exploration targets, hydrocarbon-supplying system, channel types, charge capacities, and the most favorable prospective traps. Detailed exploration practices in Qikou depression, Bohai Bay Basin, show this evaluation method works well.

Controlling Factors for Reservoirs Distribution of the Putaohua Oil Layer in the Saozhao Sag

Types of found reservoirs and its distribution characteristics of Putaohua oil layer in the Sanzhao Sag were analyzed. The controlling factors of hydrocarbon distribution were investigated. Sanzhao Sag is Sag-wide oil-bearing, but its distribution of oil and water is extremely complicated. The reservoir types are mainly fault block reservoirs, low amplitude structure reservoirs, fault-lithologic reservoirs and lithologic reservoirs. The distribution of reservoirs is mainly controlled by three geological factors: first, long-term inherited nose-like structure is predominant direction of petroleum migration; it induced oil and gas migration at a critical period of hydrocarbon accumulation and formed oil-gas accumulation area. Second, fault across main-line of hydrocarbon migration and high angle skew plug off hydrocarbon, and its side adjacent to Sag is a large number of hydrocarbon accumulation areas. Third, multi-fault region can easily form a fault (-lithological) reservoir accumulation area in the slope of sag.

Detailed compositional analysis of hydrocarbons in soil gases above multi-horizon petroleum deposits – A case study from western Poland

A surface geochemical survey was carried on in an area with a cluster of petroleum deposits in western Poland. The largest of these accumulations is the Paproć-Cicha Góra dry gas deposit reservoired in the Rotliegend sediments. Other, similar gas deposits are: the Paproć gas field discovered in the top part of the Carboniferous formation and the Paproć W, Paproć N, and Nowy Tomyśl gas fields localized in the Zechstein Limestone reef structures. Moreover, the Paproć gas-condensate and the Jastrzębsko oil deposits were found at shallower depths, in the Main Dolomite formation. This paper aims to analyze the variability of composition and distribution of near-surface gaseous hydrocarbons in relation to hydrocarbon accumulations reservoired in various stratigraphic units at depths. The occurrence of CH4, its heavier homologues and unsaturated hydrocarbons was measured in 267 soil gas samples. The sampling sites were located along six survey lines (A–A, B–B, C–C, D–D, E–E and F–F) at a 200 m spacing. Concentrations of CH4, total alkanes (C2–C4) and total alkenes (C2–C3) reached maxima of 0.26 vol.%, 5.32 ppm and 5.88 ppm, respectively. Soil–gas alkanes heavier than CH4 were interpreted as being derived from subsurface hydrocarbon accumulations. These compounds penetrated to the near-surface zone by means of active and passive microseepage. Source strength of alkanes microseepage from subsurface accumulations to the land surface (determined by the C2H6/C2H4 ratio) is not a factor that substantially changes the patterns of surface anomalies. Analysis of the values of CH4/C2H6 and C2H6/C3H8 coefficients confirmed the presence of compositionally diversified, deep hydrocarbon accumulations. The study revealed that even small accumulations of gas condensate produce very strong surface geochemical signatures, contrasting with dry gas deposits. The reason may be a specific effect of hydrocarbon migration within the existing petroleum system. The Main Dolomite, which is both the source and the reservoir rock in the Fore-sudetic monocline, plays the role of a “filter”, which modifies the flux of gases ascending from deep-seated reservoirs. As a result of such “filtering”, the geochemical signature of hydrocarbons recorded at the surface indicates the dominance of gas condensate and oil–gas accumulations at depths, giving rise to obviously incorrect interpretations. These interpretations were evidenced by compositional analysis of soil gases, which did not explicitly confirm the existence of a dry gas deposit in the Rotliegend reservoir (Paproć-Cicha Góra gas field). On the other hand, the identified anomalies generally reflect the outline of this accumulation. It supports the applicability of surface geochemical surveys to hydrocarbon exploration in the Fore-sudetic Monocline. The presence of the Main Dolomite at shallower depth must be taken into account in the interpretation of data used for positioning of seismically identified Rotliegend structures. The results of this project indicate that the Main Dolomite may obscure the geochemical signature of near-surface gases derived from dry gas accumulations in both the deeper Rotliegend and Carboniferous reservoirs.

Geochemistry of Heavy Oil in the T Block, Oriente Basin and its Origin Mechanism

Abstract:Exploration and development experience show that there is obvious oil gravity difference between the southern part and northern part of the “M1” reservoir in the Fanny oil field in the slope of the Oriente Basin, Ecuador. The American Petroleum Institute Gravity (API) values of oils in the northern part are higher than the one in the southern part of the Fanny oil field, with the values of 20° and 10.0°–13.0°, respectively. So the primary purpose of this study was to analyze the heavy oil characteristics of biodegradation and the oil–oil correlation according to the biomarker data and the δ13C signature of oil samples from T block. The results of the hydrocarbon gas chromatography fingermark and the inversion attribute characteristics indicated that there are fluid compartments between the “M1” reservoir of Fanny south. Finally, the models of oil–gas accumulation under the control of multiple‐activities of complicated fault systems, as well as the origin of heavy oil, are contended. The early stage oils from the western part of the basin were biodegraded heavily in varying degrees in the whole basin, and the later stage oils were derived from the southern part in a large scale and were mature and lighter. Generally, oil mixing is the primary control of net oil properties, such as API gravity in Oriente Basin. We therefore predicted that the API gravity variation of oil pools radically depends on the injection amount of the later stage oil. Because of the shale barrier in the “M1” reservoir of Fanny south, the later stage hydrocarbon could not pass through and contribute to increase the oil API value.

Upwind finite difference method for miscible oil and water displacement problem with moving boundary values

The research of the miscible oil and water displacement problem with moving boundary values is of great value to the history of oil-gas transport and accumulation in the basin evolution as well as to the rational evaluation in prospecting and exploiting oil-gas resources. The mathematical model can be described as a coupled system of nonlinear partial differential equations with moving boundary values. For the two-dimensional bounded region, the upwind finite difference schemes are proposed. Some techniques, such as the calculus of variations, the change of variables, and the theory of a priori estimates, are used. The optimal order l2-norm estimates are derived for the errors in the approximate solutions. The research is important both theoretically and practically for the model analysis in the field, the model numerical method, and the software development.

Paleozoic reservoir beds and their favorableness in Tazhong Areas of Tarim Basin, Northwest China

Tarim Basin is the largest petroleum potential in the west of China. Tazhong Areas are located in the centre of the Tarim, and have been thought to be the key region for seeking the large oil–gas fields in the Tarim. Paleozoic is presently the major oil–gas producing strata in the Tazhong Areas, and it is really important to petroleum exploration and development in the basin. Therefore, the basic characteristics of the Paleozoic reservoir beds of the Tazhong Areas were described in detail in this paper by collecting and processing plenty of existing data. Several points about reservoir bed and oil–gas accumulation, which are presently paid close attention to, were discussed based on the reservoir bed characteristics. The results showed that clastic-rock reservoir beds with high porosity and permeability are distributed in the southeastern part of the Tazhong Areas, while carbonate reservoirs with good physical properties are all along the No. 1 Fault belt. Cements (especially carbonate cement) amount is the major factor controlling physical properties of clastic rock reservoir beds, and the sedimentary environment is that controlling those of the carbonate reservoir beds. In the Tazhong Areas, the oil–gas distributions within the Carboniferous and Silurian clastic-rock reservoir beds are closely related to the physical properties; the distributions within the Ordovician carbonates have close relation to the reservoir bed type. Finally, favorable belts for petroleum exploration in the Tazhong Paleozoic strata were predicted on the basis of relationship between oil–gas distributions and reservoir bed characteristics.

Geochemical Characteristics of Oils from Chepaizi Area, Northwestern Junggar Basin, China

In recent years, great progress in petroleum exploration has been made obtained for Chepaizi Swell along the northwestern margin of Junggar Basin. But, the hydrocarbon sources of this area are still unknown, and this results in difficulty of determining the migration path system and migration trend. This also leads to difficulty in studying the oil-gas accumulation pattern of the area. In order to understand the oil sources, samples were systematically collected in the Swell and were analyzed for investigation of physical properties, chemical compositions and characteristics of bio-markers, carbon isotope and nitrogen compounds of the oils from Chepaizi. Through comparisons of physical and chemical characters, oils from different intervals of Chepaizi can be classified into two groups. One is the oils trapped in layers of Jurassic and below Jurassic (named as Lower Series of Strata oils), and another is those in layers of Cretaceous and above Cretaceous (named as Upper Series of Strata oils). Oils from the same group have similar densities, viscosities, group compositions and characteristics of saturated hydrocarbon, bio-marker and carbon isotope, while the oils from different groups are obviously different for the above-mentioned parameters. By fine oil-oil correlation, one can know that the lower-layer oils have the same oil source (from the Permian source rocks), and the upper-layer oils also have the same source (mainly from the Jurassic source rocks). In Chepaizi, the hydrocarbons stored in reservoirs originated mainly from Jurassic and Permian rocks. However, Cretaceous source rocks also have some contribution to oil-gas supply for oil pools. The oil-source division results based on nitrogen compounds (carbazoles) are completely identical with those by common geochemical indices, indicating that carbazoles are of importance in oil type division and oil-source correlation.

Density modeling of the basement of sedimentary sequences and prediction of oil-gas accumulation: Evidence from South SakhAlin and West Siberia

The zones of deconsolidation and consolidation in the lower parts of the sedimentary cover and in the basement are considered as an important exploration indicator of oil-gas accumulation zones. The described zones are mapped using geodensity modeling (in a gravity field) in the MZ-PZ basement and Cretaceous deposits of South Sakhalin, as well as in the pre-Jurassic basement and plate complex of the central part of West Siberia. It was found that the most promising zones are confined to the Central Sakhalin Fault and Krasnoleninsk arch in Sakhalin and to the Visim megaswell in the West Siberian plate. Recent prospecting drilling revealed that deconsolidation zones are correlated with hydrocarbon reservoirs. The presented technique of geodensity modeling can be applied for petroleum-geological explorations of structures formed in different geological and tectonic settings.

Characteristic finite difference method and application for moving boundary value problem of coupled system

The coupled system of multilayer dynamics of fluids in porous media is to describe the history of oil-gas transport and accumulation in basin evolution. It is of great value in rational evaluation of prospecting and exploiting oil-gas resources. The mathematical model can be described as a coupled system of nonlinear partial differential equations with moving boundary values. A kind of characteristic finite difference schemes is put forward, from which optimal order estimates in l 2 norm are derived for the error in the approximate solutions. The research is important both theoretically and practically for the model analysis in the field, the model numerical method and software development.

The deep-lake deposit in the Upper Triassic Yanchang Formation in Ordos Basin, China and its significance for oil-gas accumulation

The deep-lake facies of the Yanchang Formation represents a large outflowing lake basin in the Ordos area. Its deposition can be divided into four stages: lake genetic and expanding stage, peak stage, inversion stage and dying stage. All the stages are obviously consistent with the evolution of depositional environment and the paleoclimate in the region. The study indicates that the lake basin has evolution fluctuations from highstand to lowstand for four times in its evolution history, and the deposition center of the lake has not obviously moved, staying along the Huachi-Yijun belt. The deep lake sedimentary system mainly consists of deep water deltas and turbidite fans during the entire evolution course of the lake basin in the Late Triassic. The former mainly developed on the slope of steep shore of the delta in the early period of the deep-water expansion and gradually experienced a big shift from deep-water deltas to shallow-water platform delta. And the latter appeared almost in all the above stages and had two types of turbidite fans, slope-moving turbidite fans and slump turbidite fans. The slope-moving turbidite fans have relatively complete facies belts overlapping one another vertically and consist of the slope channel of inter fans, the turbidite channel, inter turbidite channel and turbidite channel front of middle fans and outer fans (or lakebottom plain). However, the slide-moving turbidity fans are formed in the deep lake with their microfacies difficult to be distinguished, and only the center microfacies and edge microfacies can be determined. The two types of the turbidity fans are similarly distributing in the near-root-slope and far-root-slope regions. The deep-lake deposition governs the distribution of the hydrocarbon and reservoir, while the slope-moving turbidite fans are excellent reservoirs for oil-gas exploration due to their great thickness, widespread distribution and accumulation properties.

Characteristics and dynamic settings of the Central-east Asia multi-energy minerals metallogenetic domain

That more than 82 percent of proved sandstone-type uranium deposits coexist with proved oil-gas or coalfields in the world reflects the fact of coexistence and accumulation of multi-energy minerals including oil, gas, coal and uranium in the same basin. Especially, this phenomenon is most typical in the Central-east Asia energy basins. Across China, Mongolia and some central Asian countries, the giant Central-east Asia metallogenetic domain (CEAMD) stretches more than 6,000 km from Songliao Basin of China in the east to the Caspian Sea in the west. The multi-energy minerals distribution characteristics of the domain include: their spatial distribution is complicated and ordered; the ore-bearing horizon relates closely to the geographical region; the accumulation/mineralization and localization time is the same or close; the occurrence setting and accumulation/mineralization have close correlation; and they have rich provenance for all the minerals. All of these imply that they have close relations between each other under a unified geodynamic background. The exogenetic uranium mineralization process in CEAMD can be divided into five phases using time limits of 100 Ma, (50±2) Ma, 20±(2–4) Ma, 8–5 Ma. The major mineralization periods and their differences in each primary uranium-bearing basin are identical to the oil-gas accumulation and localization periods and phases in the same basin, and are also in response to regional tectonics and controlled in general by the regional geodynamic environment. For industrial application and commercial exploitation, it is suggested that an important period for coexistence, accumulation and localization of oil, gas, coal and uranium and their interaction mainly occur in the late/last and post basin evolution. Through generalized analysis and comparison of accumulation/mineralization environment of the energy basins in CEAMD, the authors propose that the relatively stable regional tectonic background and moderate (weaker) structural deformation probably are necessary for formation, coexistence and preservation of large and medium-scaled sandstone-type uranium ore deposits, oil-gas fields and coalfields, while basins in favor of coexistence and accumulation are those intracratonal, intermediary massif basins and corresponding reformed basins.