Tectonic and Geodynamic Setting of Oil and Gas Basins in China

About 26 sedimentary basins bearing oil and gas are developed in China. They can be classified into two main types , extensional basins and foreland basins . The former are chiefly distributed in the eastern part and the latter in the central and northwestern parts of the country . The present paper discusses the structural characteristics of these basins , including subsidence history , thermal history and structural style and kinematics . Combined with tectonic setting analysis of geophysical data and eruptive rocks , the geodynamic setting of the basins is established , and the formation mechanism of the basins is deduced to have been related to the subduction of the Izanagi and west Pacific plates and the closing of the Tethys ocean.     

Exploration of Complicated Oil and Gas Fields

Complicated oil and gas fields occupy an important position in oil and gas exploration. In this paper, complicated oil and gas fields are grouped into four types: fault-block, lithologic, stratigraphic and fissure types. On the basis of the new theory of petroleum geological exploration in composite oil and gas accumulation areas within continental basins, a new exploration sequence suitable for complicated oil and gas fields has been established, which comprises four stages:(1) initial exploration;(2) preliminary exploration;(3) early step-by-step exploration and development: and(4) late step-by-step exploration and development. The idea of cybernetics has been taken to control various links of a systematic exploration project so as to fully, effectively and comprehensively utilize the new exploration techniques, eventually realizing the optimization of exploration with the aim of raising the efficiency of exploration of complicated oil and gas fields.     

Application of Organic Inclusions in Offshore Oil—Gas Exploration

Studies of organic inclusions from the offshore oil and gas fields provide much information about the number of times,temperature,depth,time and phase state of oil-gas migration,as well as about the composition of organic inclusions.On the basis of the type,character,composition and distribution of organic inclusions in the Zhu-Ⅲ Depression at the Pearl River Mouth,information can be developed about the source rocks of oil and gas,and their evolution and migration.     

Geological and Geochemical Studies of Heavy Oil Reservoirs in China

Thickened heavy oils in China are genetically characteristic of continenta .As to their physico-chemical properties,these oils are very high in viscosity and low in sulphur and trace element con-tents.In the group constituents,the concentrations of non-hydrocarbons and asphaltene are very high but those of saturated hydrocarbons and aromatics are very low.The gas chromatograms of alkanes show that these heavy oils have high abundances of iso-alkanes and cyclic hydrocarbons.In all the steroids and terpenoids ,bicyclic sesquiterpenoids,tricyclic diterpenoids,re-arranged steranes and gammacerane are strongly bildegradation-resistent.The formation of heavy oil reservoirs is controlled mainly by late basin ascendance,biodegradation,flushing by meteoric water and oxidation in the oil-bearing formations.Ac-cording to their formation mechanisms,heavy oil reservoirs can be classified as four categories:weathering and denudation,marginal oxidation,secondary migration and thickening of bottom water .Spacially,heavy thick oil reservoirs are distributed regularly:they usually show some paragenetic relationships with normal oil reservoirs.Heavy oil reservoirs often occur in structural highs or in overlying younger strata.Their burial depth is about 200m.Horizontally,most of them are distributed on the margins of basins or depressions.     

Fluid Inclusions in the Xichang Basin and Their Applications in Oil—Gas Exploration

Fluid inclusions are commonly observed in various stages during the diage-netic evolution and the generation,migration and accumulation of hydrocarbons in Lower Permian carbonate rocks in the Xichang Basin, providing direct physico-chemical evidence for the process.Altogether seven stages can be recognized,ie.,the penecontemporane-ous, early and mid-late diagenetic stages, the epidiagenetic stage and the early, middle and late reburying stages.Karst and dissolution pores and structural fissures developed during the epidiagenetic and reburying stages constitute the major reservoirs for hydro-carbon accumulation.Oil generation and migration began in the early reburying stage in Late Permian time and developed to its climax in the middle reburying stage in the Triassic period, followed by extensive generation and migration of natural gases during the late stage of reburying in the Jurassic and later periods.The generation,migration and accumulation of hydrocarbons are closely related to Hercynian basalt eruption and Indosinian and Yenshanian tecto-magmatism.     

Tectonic Evolution of China and Its Control over Oil Basins

This paper is a brief review of the tectonic frame and crustal evolution of China and their control over the oil basins. China is subdivided into three regions by the Hercynian Ertix-Almantai(EACZ) and Hegenshan (HGCZ) convergent zones in the north, and the Indusinian Muztagh-Maqen(MMCZ) and the Fengxiang-Shucheng (FSCZ) convergent zones in the south. The northern region represents the southern marginal tract of the Siberian platform. The middle region comprises the SinoKorea (SKP), Tarim (TAP) platforms and surrounding Paleozoic orogenic belts. The southern region includes the Yangtze platform (YZP), the Cathaysia (CTA) paleocontinent and the Caledonides between them in the eastern part, and the Qinghai-Tibet plateau composed of themassifs and Meso-and Cenozoic orogenic belts in the western part. The tectonic evolutions of China are described in three stages: Jinningian and pre-Jinningian, Caledonian to Indusinian, and post-Indosinian. Profound changes occurred at the end of Jinningian (ca. 830 Ma) and the Indusinian (ca. 210 Ma) tectonic epochs, which had exerted important influence on the formation of different types of basins. The oil basins distribute in four belts in China, the large superimposed basins ranging from Paleozoic to Cenozoic(Tarim and Junggar) in the western belt, the large superimposed basins ranging from Paleozoic to Mesozoic (Ordos and Sichuan) in the central belt, the extensional rift basins including the Cretaceous rift basins (Songliao) and the Cenozoic basin (Bohaiwan) in the eastern belt, and the Cenozoic marginal basins in the easternmost belt in offshore region. The tectonic control over the oil basins consists mainly in three aspects: the nature of the basin basement, the coupling processes of basin and orogen due to the plates interaction, and the mantle dynamics, notably the mantle upwelling resulting in crustal and lithuspheric thinning beneath the oil basins.     

A Study on Organic Inclusions in Clastic Reservoir Rocks and Their Application to the Assessment of Oil and Gas Accumulations

Terrigenous clastic reservoir rocks are widespread in China,and nearly all the industrial oil and gas accumulations in eastern China occur in the clastic rocks.The study shows that organic inclusions are mostly distributed in the secondary fissures and pores which were ormed in the process of oil-rock interaction,rather than in the cements or secondary enlargements. The organic inclusions are dominantly organic gas-rich or are composed of pure hydrocarbons.Homogenization temperatures range mainly from 120℃ to 130℃，which shows a relatively high maturity of organic matter.Vertical and horizontal temperature changes provide the grounds for the investigation of basin evolution and thermal fluid-kinetics-model.Fluorescence spectral characteristics o the organic inclusions indicate that oils and gases in the area studied probably have experienced two-stage or two-time migration.Micro-fluorescence rescearch is one of the effective approaches to oil/source correlation and oil migration-stage determination.The abundance and occurrence of organic inclusions is one of the indicators of oil and gas abundance and accumulation in rock layers.With the help of other informatio,organic inclusions can provide the basis for the prospective assessment of oil and gas in clastic reservoir rocks.     

Characteristics of Overpressure Systems and Their Significance in Hydrocarbon Accumulation in the Yinggehai and Qiongdongnan Basins, China

Overpressure systems are widely developed in the central depression and paleo-uplift in the Yinggehai and Qiongdongnan basins. They can be divided into three types according to the origin of abnormally high formation pressure in the reservoirs, i.e. the autochthonous, vertically-transmitted and laterally-transmitted types. The autochthonous overpressure system results from rapid disequilibrium sediment loading and compaction. In the allochthonous overpressure system, the increase of fluid pressure in sandstone originates from the invasion of overpressured fluid flowing vertically or laterally through the conduit units. The autochthonous overpressure system occurs in the deep-lying strata of Neogene age in the central depression of the Yinggehai and Qiongdongnan basins. The vertically transmitted overpressure system is developed in the shallow strata of Late Miocene and Pliocene ages in the diapiric zone of the central Yinggehai basin, and the laterally transmitted overpressure system occurs in the Oligo     

Types, Evolution and Pool-Controlling Significance of Pool Fluid Sources in Superimposed Basins： A Case Study from Paleozoic and Mesozoic in South China

Having multiple tectonic evolution stages, South China belongs to a superimposed basin in nature. Most marine gas pools became secondary pools. The pool fluid sources serve as the principal pool-controlling factors. On the basis of eight typical petroleum pools, the type, evolution in time-space, and the controlling of petroleum distribution of pool fluid sources are comprehensively analyzed. The main types of pool fluid sources include hydrocarbon, generated primarily and secondly from source rocks, gas cracked from crude oil, gas dissolved in water, inorganic gas, and mixed gases. In terms of evolution, the primary hydrocarbon was predominant prior to Indosinian; during Indosinian to Yen- shanian the secondary gas includes gas cracked from crude oil, gas generated secondarily, gas dissolved in water, and inorganic gas dominated; during Yenshanian to Himalayan the most fluid sources were mixed gases. Controlled by pool fluid sources, the pools with mixed gas sources distributed mainly in Upper Yangtze block, especially Sichuan (四川) basin; the pools with primary hydrocarbon sources distributed in paleo-uplifts such as Jiangnan (江南), but most of these pools became fossil pools; the pools with secondary hydrocarbon source distributed in the areas covered by Cretaceous and Eogene in Middle-Lower Yangtze blocks, and Chuxiong (楚雄), Shiwandashan (十万大山), and Nanpanjiang (南盘江) basins; the pools with inorganic gas source mainly formed and distributed in tensional structure areas.     

A Sedimentological Study of Carboniferous Bauxitic Formations in North China

The authors have found in their studies many new genetic types of microtextures of bauxite. A sedimentological genetic classification of bauxites based on these features and a division of the microfacies types of bauxites formed in major microenvironments are proposed. Four kinds of sedimentary sequence of bauxitic sediments have also been recognized. On these bases, a generalized sedimentary model of Carboniferous bauxites in North China is presented, in which storm-turbidite currents play an important role in the formation and enrichment of bauxite deposits.     

Re-Examination of the Oil and Gas Origins in the Kekeya Gas Condensate Field, Northwest China–A Case Study of Hydrocarbon-Source Correlation Using Sophisticated Geochemical Methods

This work discussed the origins, alteration and accumulation processes of the oil and gas in the Kekeya gas condensate field based on molecular compositions, stable carbon isotopes, light hydrocarbons, diamondoid hydrocarbons and biomarker fingerprints. A comparison study is also made between the geochemical characteristics of the Kekeya hydrocarbons and typical marine and terrigenous hydrocarbons of the Tarim Basin. Natural gas from the Kekeya gas condensate field is derived from Middle–Lower Jurassic coal measures while the condensates are derived from Carboniferous–Permian marine source rocks with a higher maturity. In the study area, both natural gas and condensates have experienced severe water washing. A large amount of methane was dissolved into the water, resulting in a decrease in the dryness coefficient. Water washing also makes the carbon isotopic compositions of the natural gas more negative and partially reverse. Considering that the gas maturities are higher than once expected, gas generation intensity in the study area should be much stronger and the gas related to the Jurassic coal measures could promise a greater prospecting potential. As a result of evaporative fractionation, the Kekeya condensates are enriched in saturates and lack aromatics. Evaporative fractionation disguises the original terrigenous characteristics of the light hydrocarbons associated with the natural gas, making it appear marinesourced. Thus, alteration processes should be fully taken into consideration when gas–source correlations are carried out based on light hydrocarbons. With the condensates discovered in the study area all being "migration phase", the pre-salt Cretaceous and Jurassic reservoirs may promise great exploration potential for the "residual phase" hydrocarbons. This research not only is of significance for oil and gas exploration in the southwest Tarim Basin, but also sheds light on the oil/gas-source correlations in general.     

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.     

Geological Features of Devonian Sedimentary Basins in South China and Their Deposition and Mineralization

The Devonian succession in South China is well-known for its complete development, vari-fied sedimentary types, remarkable lithofacies variation and abundant mineral resources. The South China plate was formed by the collision and collage of the Yangtze plate and the Cathaysian plate. The collision began approximately at the Jinningian stage and the collage was not finalized until the Guangxian movement. It was on the South China plate with a somewhat different nature of the basement that the Devonian deposition formed.     

Tectonic Evolution of Tertiary Basins in circum-Pacific Belt of China and Their Geodynamic Setting

ＴｅｃｔｏｎｉｃＥｖｏｌｕｔｉｏｎｏｆＴｅｒｔｉａｒｙＢａｓｉｎｓｉｎＣｉｒｃｕｍ┐ＰａｃｉｆｉｃＢｅｌｔｏｆＣｈｉｎａａｎｄＴｈｅｉｒＧｅｏｄｙｎａｍｉｃＳｅｔｉｎｇ＊ＬｉＳｉｔｉａｎＹａｎｇＳｈｉｇｏｎｇＸｉｅＸｉｎｏｎｇＦａｃｕｌｔｙｏｆＥａｒ...     

Geothermal Regime of Meso-Cenozoic Basins and Their Tectonic Background in East China

ＧｅｏｔｈｅｒｍａｌＲｅｇｉｍｅｏｆＭｅｓｏ－ＣｅｎｏｚｏｉｃＢａｓｉｎｓａｎｄＴｈｅｉｒＴｅｃｔｏｎｉｃＢａｃｋｇｒｏｕｎｄｉｎＥａｓｔＣｈｉｎａ＊ＺｈｕａｎｇＸｉｎｇｕｏＦａｃｕｌｔｙｏｆＥａｒｔｈＲｅｓｏｕｒｃｅｓ，ＣｈｉｎａＵｎｉｖｅｒｓｉｔ...     

Genetic Classification of Natural Gases in the Oil—Gas Zone and Its Application in the Sichuan Basin

On the basis of the carbon isotopic compositions of methane(CH4) and its homologues and the differences in isotopic values for CH4 and ethane (C2H6) and the correlation and compositional char-acteristics of hydrocarbon gases, the author has proposed a genetic classification of natural gases in the oil-gas zone.They are classified as biogenetic and abiogenetic gases in terms of the types of hydrocarbon-generating precursors (or parent materials) and their thermal evolution stages.Biogenetic gases can also be further divided into two series: biochemical and thermochemical gases,with the lat-ter formed at different evolution stages.Gases generated from type-I and -II1 organic matter are called oil-series gases, those from type-III, coal -series ,and those type -II2,mixture-type gases.Gases generated from two or more than two types of precursors are called mixture-source gases.According to those mentioned above, natural gases from the major oil-gas pools in the Sichuan Basin have been discriminantly analyzed,and the results are concordant with the distribution and de-velopment of hydrocarbon-source rocks as well as with their characteristics, indicating a prospective application.     

Supply-Demand Situation and Exploration of Mineral Resources in China during 2016–2017

正During 2016-2017,both the supply and demand of China's main mineral resources continued to grow.The import of major energy resources and metal ore resources,such as iron ores,crude oil,natural gas,coal and bauxite,except for copper,has shown a substantial increase(Table1).In order to guarantee economic development needs,the