Petroliferous Basins In China Research Articles

Assessment of Geothermal Resources in Petroliferous Basins in China

In order to speed up the development and utilization of hydrothermal energy, it is essential to assess the potential of geothermal resources in petroliferous basins. In this paper, the distribution of reservoirs (aquifers) and the characteristics of geothermal fields have been studied systematically based on geological, geophysical, well drilling, temperature, and sample test data obtained from the major petroliferous basins of China. It has been found that some of the porous sandstone formations in these petroliferous basins are major geothermal reservoirs and are extensively thick and widely distributed. In general, the geothermal gradient in China is higher in the eastern basins and lower in the western basins. On average, the geothermal gradient is above 30 °C/km in the Bohai Bay, Songliao, and Subei basins. The geothermal resource abundance is also higher in eastern China and in the Beibuwan basin in southern China, and the geothermal source forming condition is better, followed by the Ordos, Qaidam, and Sichuan basins in Central China. Other potential basins include the Tarim and Junggar basins in western China, where the geothermal gradient ranges between 21 and 22 °C/km, on average. In this paper, three methods, stochastic simulation, unit volumetric, and analogy, were used for the assessment of geothermal resources. Using the stochastic simulation and unit volumetric methods, the geothermal resources, annual recovered geothermal resources, geothermal water resources, and thermal energy of water in 11 basins or blocks of up to 4000 m deep were calculated. Grading evaluation criteria were established by considering the heterogeneity of geothermal reservoirs. The results showed that the petroliferous basins are very rich in geothermal resources. The annual recoverable resources reach 1626.8 × 106 tons of standard coal, in which grade I, grade II, and grade III resources are 641.9 × 106, 298.6 × 106, and 686.3 × 106 tons of standard coal, respectively. The results demonstrate that the development and utilization of geothermal energy in oilfields has a huge potential for industrial production and family use, and a great significance for the development of green oilfields. With the high demand of heat, the eastern oilfields with high geothermal resource abundance should be the first to be considered for the production and utilization of geothermal energy, followed by the central and western oilfields.

Multi-Stage Basin Development and Hydrocarbon Accumulations: A Review of the Sichuan Basin at Eastern Margin of the Tibetan Plateau

Sichuan Basin is one of the uppermost petroliferous basins in China. It experienced three evolutionary phases which were marine carbonate platform (Ediacaran to Late Triassic), Indosinian-Yanshanian orogeny foreland basin (Late Triassic to Late Cretaceous) and uplift and tectonic modification (Late Cretaceous to Quaternary). The present-day tectonics of the Sichuan Basin and its periphery are characterized by three basic elements which are topography, basement type and surface structure, and two settings (plate margin and interior). Therefore, be subdivided into five units which have different structure and tectonic history. The basin contains five different sets of source rocks with thickness up to 2 500 m. These source rocks were well preserved due to the presence of Middel–Lower Triassic evaporites (>∼200 m) and thick terrestrial sediments filling in the Indosinian-Yanshanian foreland basin (>3 000 m). The uplift and erosion since Late Cretaceous has significant influence on cross-strata migration and accumulation of oil and gas. The multi-phase evolution of the basin and its superimposed tectonic elements, good petroleum geologic conditions and diverse petroleum systems reveal its bright exploration prospects.

Hydrocarbon seeps in petroliferous basins in China: A first inventory

Natural hydrocarbon seepage is a widespread phenomenon in sedimentary basins, with important implications in petroleum exploration and emission of greenhouse gases to the atmosphere. China has vast petroleum (oil and gas) bearing sedimentary basins, but hydrocarbon seepage has rarely been the object of systematic studies and measurements. Based on the available Chinese literature, we report a first inventory of 932 hydrocarbon seeps or seepage zones (710 onshore seeps and 222 offshore seeps), including 81 mud volcanoes, 449 oil seeps, 215 gas seeps, and 187 solid seeps (bitumen outcrops). The seeps are located within the main 20 Mesozoic-Cenozoic petroliferous sedimentary basins, especially along the marginal, regional and local faults. The type of manifestations (oil, gas or mud volcano) reflects the type and maturity of the subsurface petroleum system and the sedimentary conditions of the basin. Oil seeps are particularly abundant in the Junggar Basin. Gas seeps mostly developed in the Lunpola Basin, in smaller basins of the eastern Guizhou and Yunnan provinces, onshore Taiwan and in the offshore Yinggehai Basin. Mud volcanoes developed in basins (Junggar, Qaidam, Qiangtang, onshore and offshore Taiwan) that experienced rapid sedimentation, which induced gravitative instability of shales and diapirism. In comparison to available global onshore seep data-bases, China results to be the country with the highest number of seeps in the world. The massive gas seepage in China could represent a considerable natural source of methane to the atmosphere, and a key process that may drive future hydrocarbon exploration.

Enrichment and distribution of shale oil in the Cretaceous Qingshankou Formation, Songliao Basin, Northeast China

The Songliao Basin is a large-scale petroliferous basin in China. With a gradual decline in conventional oil production, the exploration and development of replacement resources in the basin is becoming increasingly important. Previous studies have shown that the Cretaceous Qingshankou Formation (K2qn) has favorable geological conditions for the formation of shale oil. Thus, shale oil in the Qingshankou Formation represents a promising and practical replacement resource for conventional oil. In this study, geological field surveys, core observation, sample tests, and the analysis of well logs were applied to study the geochemical and reservoir characteristics of shales, identify shale oil beds, build shale oil enrichment models, and classify favorable exploration areas of shale oil from the Cretaceous Qingshankou Formation. The organic matter content is high in shales from the first member of the Cretaceous Qingshankou Formation (K2qn1), with average total organic carbon (TOC) content exceeding 2%. The organic matter is mainly derived from lower aquatic organisms in a reducing brackish to fresh water environment, resulting in mostly type I kerogen. The vitrinite reflectance (Ro) and the temperature at which the maximum is release of hydrocarbons from cracking of kerogen occurred during pyrolysis (Tmax) respectively range from 0.5% to 1.1% and from 430 °C to 450 °C, indicating that the K2qn1 shales are in the low-mature to mature stage (Ro ranges from 0.5% to 1.2%) and currently generating a large amount of oil. The favorable depth for oil generation and expulsion is 1800–2200 m and 1900–2500 m, respectively as determined by basin modeling. The reserving space of the K2qn1 shale oil includes micropores and mircofractures. The micropore reservoirs are developed in shales interbedded with siltstones exhibiting high gamma ray (GR), high resistivity (Rt), low density (DEN), and slightly abnormal spontaneous potential (SP) in the well-logging curves. The microfracture reservoirs are mainly thick shales with high Rt, high AC (acoustic transit time), high GR, low DEN, and abnormal SP. Based on the shale distribution, geochemical characteristics, reservoir types, fracture development, and the process of shale oil generation and enrichment, the southern Taikang and northern Da'an are classified as two favorable shale oil exploration areas in the Songliao Basin.

Introduction to special section: Lacustrine shale characterization and shale resource potential in Ordos Basin, China

The Ordos Basin is the second largest petroliferous basin in China, located in the central part of the country. The basin’s petroleum resources are mainly accumulated in fluvio-lacustrine sandstone reservoirs of the Upper Triassic Yanchang Formation. The 800–1500 m thick Yanchang Formation was

Development of sedimentary geology of petroliferous basins in China

Abstract This paper gives a contrastive analysis of the main progress made in petroliferous basins sedimentary geology domestically and internationally, and discusses the main problems and their solutions in the development of petroliferous basins sedimentology in China, New developments include coarse-grained depositional sysytem, shallow-water deltic depositional system, beach bar depositional system, deep-water gravity flows, fine-grained depositional system, carbonate reefs, mixosedimentite, microbialite, seismic sedimentology and sedimentary physical simulation. It also reveals the developing gap of Chinese sedimentology in the areas of microbialite and sedimentary simulation, etc. and analyzes the sedimentary features and paleogeography pattern of prototype basins, multi-scale paleogeographic recovery during major tectonic movements, the different explanation of new sedimentology theories in the deep-buried sandbodies development. The paper details the difficulties when it comes to the typical depositional systems combination and the setup of sedimentary models in China. Therefore, the developing tendency is described of sedimentology theories like source to sink, sedimentary dynamics as well as regional sedimentology in China, seismic sedimentology, and studying methods and technologies in sedimentary simulation.

Typical disequilibrium compaction caused overpressure of Paleocene Dongying Formation in northwest Liaodongwan Depression, Bohai Bay Basin, China

Bohai Bay Basin is an important petroliferous basin in China. Petroleum potential in Liaodongwan Depression of offshore Bohai Bay Basin has been proved by previous exploration and production, and overpressures were encountered. Summarized by the DST measurements and mud weight data of over 60 wells in Liaodongwan Depression, the abnormally high pressures preserved in Paleocene Dongying (Ed) Formation distribute over the entire depression and could reach as high as 64.2MPa around the depth of 3420m. Through the well logs analysis, typical corresponding characteristics to disequilibrium compaction can be found: higher in acoustic transit time and lower in density than normal compaction trend. Based on these corresponding features the pore pressure prediction was carried out for all the wells in the area. Sonic velocity-effective stress relationship and sonic velocity-density cross plots were employed to investigate the origin of overpressure in Ed Formation. Sedimentation rates and geothermal features were studied as well. Combining all the analysis, the overpressure of Ed Formation in northwest Liaodongwan Depression was dominantly generated by disequilibrium compaction. With this widely distributed overpressure, thick layers of mudstone of Ed Formation serve as a regional overpressured caprock.

Distribution, origin and evolution of the Upper Triassic overpressures in the central portion of the Sichuan Basin, SW China

The Sichuan Basin is a prime petroliferous basin in China, and multiple overpressure systems exist vertically in the central portion of the basin. Understanding the mechanisms and evolution of an overpressure system is significant for petroleum migration and accumulation. DSTs and well logs data reveal that the Upper Triassic overpressures start at a depth of about 1300m, and the pressure coefficient (r) is greater in the northwestern part of the study area (r>1.8) and relatively lower in the south (r≈1.3). Sonic transit times of shales in the Upper Triassic Formation are abnormally high, and velocity-density plots deviate from the normal compaction trend, which demonstrate that disequilibrium compaction should be the primary mechanism of overpressures. Evolution history of overpressure was reconstructed based on numerical modeling method. The results from 1D and 2D modeling indicate that the Upper Triassic overpressures began developing at 195Ma because of rapid sedimentation in this period. The maximum overpressure appeared at 90Ma, which is 38MPa in the Bajiaochang field and 50MPa in the Anyue field, respectively. After that, pore pressure reduced to current value due to uplift and erosion that began in the Late Cretaceous. Overpressures are higher in the greater depth area and relatively lower at the structural crest. Gas generation from the Upper Triassic source rocks occurred during 160–90Ma which is coincident with disequilibrium compaction. The contribution of gas generation to the Upper Triassic overpressures is not important, because gases just created small volume increase and likely to be expelled out by the high disequilibrium compaction overpressure in the corresponding period. Permeabilities of 10−22–10−23m2 are required for barriers to maintain the overpressure in geological timescale. Overpressure systems in the central portion of the Sichuan Basin appear to be explained by static paradigms. For that, temperature has significant impact on the sealed systems. Greater pressures are preserved in the area with less temperature reduction.

Reserves growth trend and potential analysis of Junggar Basin

Abstract The Junggar Basin is one of early explored petroliferous basins in China. Since the discovery of the Karamay Oil Field in 1955, over 30 oil fields have been found. The geologic features, hydrocarbon accumulation mechanisms and distribution characteristics of the Junggar Basin were studied in this paper. The basin has under-gone rapid and effective exploration in past years, which helped potential prediction. The present estimate of recoverable oil and gas resources in the basin is 45.3% and 30.3%, respectively. Exploration is in the middle and late stages. There are (9.42~16.92)×108 t oil remaining unproved. Lithologic, igneous rocks and tight sand-stones are the main targets for future exploration in the basin.

Potential evaluation of CO<SUB align="right">2 flooding for EOR and sequestration in YL oilfield of China

Ordos Basin is the largest low permeability onshore petroliferous basin in China, with the total reserve amount of over one billion ton. CO2 EOR and sequestration in this region enjoy huge potential and broad prospect. In this paper, eighteen oilfields in YL City and its surrounding area within 300 kilometres was taken as the study object, potential of CO2 flooding for EOR and sequestration was researched and evaluated. Results show that eight oilfields are suitable for CO2 miscible flooding and ten oilfields are suitable for CO2 immiscible flooding. The predicted enhanced recovery efficiencies are about 12% and 6.5%, respectively. The expected cumulative oil production is 80 million tons with CO2 storage of over 130 million tons.

Stable Carbon Isotopic Characteristics of Alkane Gases in Tight Sandstone Gas Fields and the Gas Source in China

Significant achievements have been obtained in tight sandstone gas exploration in China. At present, tens of tight sandstone gas pools have been discovered in the Ordos basin, the Sichuan basin, the Bohai Bay basin, the Tarim basin, and the Turpan-Harmi basin in China. This study examines the gas components and the stable carbon isotope data of 150 tight sandstone gas samples collected from the main petroliferous basins in China. Tight sandstone gas in China is dominated in alkane gases, and the contents of methane and its homologues decrease with increasing of the carbon number. Major part of the tight sandstone gas have the characteristic of normal stable carbon isotope series (i.e., δ13C1<δ13C2<δ13C3<δ13C4), whereas the rest show a partial reversal, and the reversals between ethane and propane are in dominant (δ13C2>δ13C3). Most of the sandstone gases are coal-derived gas, and mixing of gases from the same humic source but different maturity or from different humic sources caused the partially reversal of the carbon isotopic values. The major part of the tight sandstone gas pools are self-generation and self-accumulation reservoirs formed in coal measures, and the coal measures are the favorable field in tight sandstone gas exploration in China.

Natural gas constituent and carbon isotopic composition in petroliferous basins, China

There are abundant gas resources in petroliferous basins of China. Large to midsize gas fields are found in Eastern, central and Western of China. However, origin, constituents and isotopic composition of natural gas in different gas fields are varied distinctly, and some present strong chemical secondary alteration and show variation both in age and space. Based on the systematic analysis of constituents and carbon isotope of a large number of gas samples, combined with the geological characteristics, this paper classifies the origins of the gases, explores the gas isotope characteristics and evolutionary regulation with the variation time and space, and further discusses the distinctive geochemistry of the gases in China. These gases are dominated by dry gas, its methane carbon isotope values range from −10‰ to −70‰, ethane from −16‰ to −52‰, propane from −13‰ to −43‰, and butane from −18‰ to −34‰. The carbon isotopes of most gases show the characteristics of humic-derived gas and crude oil cracked gas. In addition, large primary biogenic gas fields have been discovered in the Qaidam basin; inorganic-derived alkane gases have been discovered in deep of the Songliao Basin. Half of these gas fields are characterized by the alkane carbon isotope reversal in different degrees. Research indicates there are several reasons can result in carbon isotope reversal. Firstly, gas charge of different genetic types or different source in one gas reservoir may cause carbon isotope reversal. Besides, high-over mature evolution of gas can also lead to the carbon isotopic reversal of alkanes. Thirdly, secondary alteration of hydrocarbons may also result in abnormal distribution of carbon isotope, isotope transforms to unusual light and heavy.

Development characteristics of the fault system and its control on basin structure, Bodong Sag, East China

The Bodong Sag, located in the Bohai Sea, offshore China, is one of the most petroliferous basins in China. Based on three dimensional seismic reflection data and time slice data, we analyze the fault system of the Bodong area in detail, establish the fault structure pattern of different types and summarize the distribution of the fault system. It is concluded that the development characteristics of the Cenozoic fault system are in accordance with the dextral stress field of the Tanlu Fault, which displayed a brush structure with NNE strike-slip faults as its principal faults, NE-trending extensional faults as secondary faults and EW-trending faults as minor faults. Faults can be divided into (1) strike-slip type, (2) extensional type, (3) strike-slip extensional type and (4) extensional strike-slip type. The spatial structures of different faults have obvious differences because of the fault properties and activity intensity. The fault system at different stages shows tremendous differences because of the transition of the Tanlu Fault from sinistral strike-slip to dextral strike-slip, the transition between extension and strike-slip, and the transition from mantle upwelling to thermal subsidence. According to the controlling effect of faults on basin structure, the Cenozoic basin experienced four evolutionary stages, (a) transition stage from sinistral strike-slip to dextral strike-slip, (b) strike-slip extensional faulted stage, (c) extensional strike-slip faulted stage and (d) strike-slip depression stage. The identification of temporal and spatial differences of faults could be used as a significant guideline for oil and gas exploration in the Bodong area.

New insights into petroleum migration-accumulation dynamic systems and their division within petroleum systems

Since the concept of petroleum migration-accumulation dynamic system (PMADS) was introduced in the 1990s, its definition, division and even denomination have long been in disagreement. This article aims to further discuss and try to clarify this concept and to explore more reasonable approaches to the division of PMADSs on the basis of our studies on petroleum migration and accumulation in some petroliferous basins of China, especially those from western China. According to the studies, we define PMADS as a relatively independent natural hydrocarbon migrating and accumulating system within a petroleum system. Its extent is supposed to cover the whole migration pathway starting from a hydrocarbon provenance throughout to an accumulation or a group of accumulations of same source. Just like petroleum systems, a petroleum migration-accumulation system is also an important natural unit for petroleum exploration and assessment in petroleum basins. Its position in a basin is right between a petroleum system and a play. A petroleum system has either a number of migration-accumulation systems or one system only. However, the key element of a petroleum system is the source of hydrocarbon; a petroleum system has a distinct hydrocarbon kitchen and is different from its neighboring ones in terms of hydrocarbon kitchens. In contrast, different migration-accumulation systems within the same petroleum system have a shared source kitchen but different characteristics of migration and accumulation to form hydrocarbon accumulations. As far as the division of petroleum migration-accumulation systems (PMASs) is concerned, 8 major approaches are proposed, including those based on pool-forming dynamic mechanisms, location of hydrocarbon accumulation relative to the source kitchen, phase states of migration and accumulation, migration patterns and directions, geneses of accumulations, reservoir pressure systems, depositional systems and facies, and integrated method, of which the integrated approach is underlined with regard to the division of PMASs in a complex petroleum system like those in West-China superimposed basins.

Carbon Isotopic Characteristics of Different Genetic Type Condensates in China

Condensate pools with reservoir ages of Ordovician, Permian, Triassic, Jurassic, Cretaceous, Eogene, and Neogene were found in every giant petroliferous Basin in China. Condensates generated by sapropelic organic matters (sapropelic condensates) are of high- to over-mature stages, while the maturities of those generated by humic organic matters (humic condensates) cover a wide range, from early mature to over-mature. Carbon isotopes of 143 condensate samples were analyzed in this work, and we found that both the organic matter type and the maturity significantly influenced the isotopic composition of the condensates. The total hydrocarbon isotopic values of the humic condensates range from −29.9% to −21.7%, with an average of −26.0% (94 samples), while those sapropelic condensates are lighter generally, covering a range of −33.9% to −26.0% with an average of −29.5% (40 samples). δ13Caromatics value is strongly inheritable to the organic matter type and it combined with the δ13Csaturates value can be used to distinguish condensates of different types. δ13Caromatics value of sapropelic condensate is less than −27.5%, while the δ13Caromatics and the δ13Csaturates values of humic condensate are larger than −27.5% and −29.5%, respectively.

Geothermal regime and hydrocarbon kitchen evolution of the offshore Bohai Bay Basin, North China

The offshore Bohai Bay Basin, located in the central Bohai Bay Basin, north China, one of the most petroliferous basins in China. In this article, based on formation-testing temperature, drill-stem tests, and bottom-hole temperature data, 80 thermal gradient values at the depth interval of 0 to approximately 3000 m (~9843 ft) in the offshore Bohai Bay Basin were obtained. The basinwide average thermal gradient is 31.8 4.6C/km. Based on the above thermal gradient data and the corresponding average weighted thermal conductivity data, 80 measured terrestrial heat flow values were obtained. These values range from 33.5 to 84.0 mW/m2, with an average value of 60.8 8.7 mW/m2. The heat flow and thermal gradient distribution in this region generally show higher values in the uplifts and lower ones in the sags. A thermal history, derived from vitrinite reflectance and apatite fission-track) data, indicates that Paleogene cooling occurred after a period of much higher paleogeothermal gradient (3854C/km). Tectonic subsidence analysis reveals that the area experienced initial synrift subsidence during the Paleogene followed by subsequent thermal subsidence since the Neogene. Thermal and tectonic subsidence histories of this area are of great significance to petroleum exploration and hydrocarbon resource assessment because they bear directly on issues of petroleum source rock maturation. The maturation and hydrocarbon expulsion histories of the Paleogene Shahejie 3 Formation (E2s3), which is the most important source rock in the offshore Bohai Bay Basin, are modeled. Results show that the Shahejie 3 Formation is in a high mature stage at the present day, and the Bozhong and Qikou sags are the most important kitchens. The Huanghekou sag became the third most important hydrocarbon kitchen in the early Neogene. Based on this hydrocarbon kitchen evolution, oil and gas mainly accumulated after 12 Ma. The evolution of kitchen areas may provide new insights for the understanding of the oil and gas exploration potential of the offshore Bohai Bay Basin.

Lacustrine source rock deposition in response to co-evolution of environments and organisms controlled by tectonic subsidence and climate, Bohai Bay Basin, China

Three Paleogene syn-rift intervals from the Bohai Bay Basin, the most petroliferous basin in China, were analyzed with sedimentological and geochemical techniques to characterize the lateral source rock heterogeneities, to reveal the environmental and ecological changes through geologic time and to construct depositional models for lacustrine source rocks under different tectonic and climatic conditions. The third (Es 3) and first (Es 1) members of the Eocene Shahejie Formation and the Oligocene Dongying Formation (Ed) display widely variable total organic carbon contents, hydrogen indices and visual kerogen compositions, suggesting changes in organic facies from deep to marginal sediments. Carefully selected deep-lake facies samples from any interval, however, display fairly uniform biomarker composition. These three intervals have distinctly different biomarker assemblages, which indicate weakly alkaline, freshwater lakes with a moderately deep thermocline during Es 3 deposition, alkaline-saline lakes with shallow chemocline during Es 1 deposition and acidic, freshwater lakes with deep, unstable thermocline during the deposition of the Dongying Formation. Such environmental changes corresponded to changes in subsidence rate and paleoclimate, from rapid subsidence and wet climate during Es 3 deposition, through slow subsidence and arid climate during Es 1 deposition to rapid subsidence and wet climate during Ed deposition and resulted in synchronous changes in terrigenous organic matter input, phytoplankton community and primary productivity. The co-evolution of environments and organisms controlled by tectonic subsidence and climate accounted for the deposition and distribution of high quality lacustrine source rocks with distinctly different geochemical characteristics. Most rift basins experienced changes in subsidence rates and possibly changes in climates during their syn-rift evolutions. The models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins.

Late-stage rapid accumulation of the PL19-3 giant oilfield in an active fault zone during Neotectonism in the Bozhong depression, Bohai Bay

Late-stage is defined here as the period when Neotectonism occurred since 5.1 Ma. Most petroliferous basins in China lie in the areas where Neotectonism occurred intensively. In recent years, Chinese petroleum geologists have paid much attention to late-stage petroleum accumulation. The PL19-3 giant oilfield is situated where faulting activities occurred violently during Neotectonism. To understand the mechanism of lat-stage rapid accumulation, we discussed the most important aspects responsible for the formation of the giant oilfield, including oil generation, active oil-source rock occurrence, fault activity and fault conduits, late-stage rapid oil injection as well as the distinguishing indicators. This study shows that: (1) sufficient oil was supplied to the PL19-3 field since 5.1 Ma because the PL19-3 structure was surrounded by four sags in which three intervals of high-quality source rocks remained active during Neotectonism; (2) densely distributed faults and high porosity/permeability sandstone carrier beds comprised the effective conduit system for oil migration and injection; (3) oil migrated along the faults and charged the PL19-3 structure rapidly by means of seismic pumping which was triggered by frequent earthquakes during Neotetonism. It is documented that elevated reservoir temperature, abnormal geothermal gradients and abnormally high homogenization temperatures of the fluid inclusions are the indicators for late-stage rapid oil accumulation.

Hydrocarbon Kitchen Evolution of E2s3 Source Rocks in the Bohai Offshore Area, North China

AbstractThe hydrocarbon kitchen is appropriate for characterizing the center of providing hydrocarbon, and the research on its evolution has a great significance for petroleum exploration. The Bohai offshore area is located in the offshore Bohai Bay basin, North China. It is one of the most petroliferous basins in China. There developed four sets of potential source rocks in the Paleocene. The third member of the Shahejie Formation (E2s3) is the most important source rock. In this paper, the evolution histories of the maturation and hydrocarbon generation & expulsion of E2s3 source rocks are modeled based on the depositional and tectonic development history in combination with geochemical and thermal parameters. The hydrocarbon kitchen evolution of the E2s3 source rocks is analyzed using the amount of expelled hydrocarbon of the E2s3 source rocks in the main geological periods. The result shows that there developed two hydrocarbon kitchens at early stage, which then transformed to one main hydrocarbon kitchen and co‐existing multi‐hydrocarbon kitchens with the geological evolution, e.g. two hydrocarbon kitchens in the Bozhong and Qikou sags in the Paleocene and one main hydrocarbon kitchen in the Bozhong sag and multi‐kitchens in the Qikou, Nanpu, Huanghekou, Liaozhong, Liaoxi and Qinnan sags from the Neogene to the present day. Most oil and gas fields are located in the uplifts and slopes around the main hydrocarbon kitchens, thus the study may provide new insights for understanding the petroleum exploration potential of the Bohai offshore area.

Catagenesis of organic matter of oil source rocks in Upper Paleozoic coal formation of the Bohai Gulf basin ( eastern China)

The Bohai Gulf basin is the largest petroliferous basin in China. Its Carboniferous-Permian deposits are thick (on the average, ca. 600 m) and occur as deeply as 5000 m. Coal and carbonaceous shale of the Carboniferous Taiyuan Formation formed in inshore plain swamps. Their main hydrocarbon-generating macerals are fluorescent vitrinite, exinite, alginite, etc. Coal and carbonaceous shale of the Permian Shanxi Formation were deposited in delta-alluvial plain. Their main hydrocarbon-generating macerals are vitrinite, exinite, etc. The carbonaceous rocks of these formations are characterized by a high thermal maturity, with the vitrinite reflectance R 0 > 2.0%. The Bohai Gulf basin has been poorly explored so far, but it is highly promising for natural gas.