Quantitative effect of kerogen type on the hydrocarbon generation potential of Paleogene lacustrine source rocks,Liaohe Western Depression,China

Kerogen types exert a decisive effect on the onset and capacity of hydrocarbon generation of source rocks.Lacustrine source rocks in the Liaohe Western Depression are characterized by thick deposition,high total organic carbon(TOC)content,various kerogen types,and a wide range of thermal maturity.Consequently,their hydrocarbon generation potential and resource estimation can be misinterpreted.In this study,geochemical tests,numerical analysis,hydrocarbon generation kinetics,and basin modeling were integrated to investigate the differential effects of kerogen types on the hydrocarbon generation potential of lacustrine source rocks.Optimized hydrocarbon generation and expulsion(HGE)models of different kerogen types were established quantitatively upon abundant Rock-Eval/TOC/vitrinite reflectance(R_(o))datasets.Three sets of good-excellent source rocks deposited in the fourth(Es4),third(Es3),and first(Es1)members of Paleogene Shahejie Formation,are predominantly types I-II_(1),II_(1)-II_(2),and II-III,respectively.The activation energy of types I-II_(2)kerogen is concentrated(180-230 kcal/mol),whereas that of type III kerogen is widely distributed(150-280 kcal/mol).The original hydrocarbon generation potentials of types I,II_(1),II_(2),and III kerogens are 790,510,270,and 85 mg/g TOC,respectively.The Ro values of the hydrocarbon generation threshold for type I-III source rocks gradually increase from 0.42%to 0.74%,and Ro values of the hydrocarbon expulsion threshold increase from 0.49%to 0.87%.Types I and II_(1)source rocks are characterized by earlier hydrocarbon generation,more rapid hydrocarbon expulsion,and narrower hydrocarbon generation windows than types II_(2)and III source rocks.The kerogen types also affect the HGE history and resource potential.Three types(conventional,tight,and shale oil/gas)and three levels(realistic,expected,and prospective)of hydrocarbon resources of different members in the Liaohe Western Depression are evaluated.Findings suggest that the Es3 member has considerable conventional and unconventional hydrocarbon resources.This study can quantitatively characterize the hydrocarbon generation potential of source rocks with different kerogen types,and facilitate a quick and accurate assessment of hydrocarbon resources,providing strategies for future oil and gas exploration.

Influence of Magmatic Intrusion on Abnormal Hydrocarbon Generation and Expulsion of Source Rock:A Case Study of the Dongying Sag,Bohai Bay Basin

How gabbro affects the generation and expulsion of hydrocarbons in muddy surrounding rocks is clarified by analyzing thin section,major and trace elements,total organic carbon(TOC),pyrolysis,extracts and vitrinite reflectance data from source rocks in the Chunxi area the Dongying Sag,Bohai Bay Basin,eastern China.The results show that a magma intrusion brings copious heat to the source rocks,which promotes abnormal maturation of organic matter(OM)and rapid hydrocarbon generation.The CH_(4)and H_(2)produced by gabbro alteration play a role in hydrocarbon generation of source rocks.The hydrothermal process during magma intrusion provides many different minerals to the source rock,resulting in carbonate-rich surrounding mudstone.The carbonate and clay minerals produced by volcanic mineral alteration jointly catalyze the hydrocarbon generation of the source rock.The high-temperature baking of the intrusion results in hydrothermal pressurization and hydrocarbon generation pressurization,causing many fractures in the surrounding rock.The generated oil and gas are discharged through the fractures under diffusion and pressure.Mantle-derived CO_(2)is also conducive to the expulsion of hydrocarbons because of its strong enrichment capacity for hydrocarbons.

Impact of volcanism on the formation and hydrocarbon generation of organic-rich shale in the Jiyang Depression, Bohai Bay Basin, China

Globally,most organic-rich shales are deposited with volcanic ash layers.Volcanic ash,a source for many sedimentary basins,can affect the sedimentary water environment,alter the primary productivity,and preserve the organic matter(OM)through physical,chemical,and biological reactions.With an increasing number of breakthroughs in shale oil exploration in the Bohai Bay Basin in recent years,less attention has been paid to the crucial role of volcanic impact especially its influence on the OM enrichment and hydrocarbon formation.Here,we studied the petrology,mineralogy,and geochemical characteristics of the organic-rich shale in the upper submember of the fourth member(Es_(4)^(1))and the lower submember of the third member(Es_(3)^(3))of the Shahejie Formation,aiming to better understand the volcanic impact on organic-rich shale formation.Our results show that total organic carbon is higher in the upper shale intervals rich in volcanic ash with enriched light rare earth elements and moderate Eu anomalies.This indicates that volcanism promoted OM formation before or after the eruption.The positive correlation between Eu/Eu*and Post-Archean Australian Shale indicates hydrothermal activity before the volcanic eruption.The plane graph of the hydrocarbon-generating intensity(S1+S2)suggests that the heat released by volcanism promoted hydrocarbon generation.Meanwhile,the nutrients carried by volcanic ash promoted biological blooms during Es_(4)^(1 )and Es_(3)^(3) deposition,yielding a high primary productivity.Biological blooms consume large amounts of oxygen and form anoxic environments conducive to the burial and preservation of OM.Therefore,this study helps to further understand the organic-inorganic interactions caused by typical geological events and provides a guide for the next step of shale oil exploration and development in other lacustrine basins in China.

Hydrocarbon Generation Potential and Organic Matter Enrichment Mechanism of the Cambrian Marine Shale in the Tadong Low Uplift,Tarim Basin

Cambrian shales in China and elsewhere contain abundant oil and gas resources.However,due to its deep burial and limited outcrop,there has been relatively little research conducted on it.The Cambrian shale of the Tadong low uplift in the Tarim Basin of western China,specifically the Xidashan-Xishanbulake Formation(Fm.)and overlying Moheershan Fm.provide a case study through the use of organic petrology,mineralogy,organic and elemental geochemistry,with the aim of analyzing and exploring the hydrocarbon generation potential(PG)and organic matter(OM)enrichment mechanisms within these shale formations.The results indicate that:(1)the Cambrian shale of the Tadong low uplift exhibits relatively dispersed OM that consists of vitrinite-like macerals and solid bitumen.These formations have a higher content of quartz and are primarily composed of silica-based lithology;(2)shale samples from the Xidashan-Xishanbulake and Moheershan formations demonstrate high total organic carbon(TOC)and low pyrolytic hydrocarbon content(S_(2))content.The OM is predominantly typeⅠand typeⅡkerogens,indicating a high level of maturation in the wet gas period.These shales have undergone extensive hydrocarbon generation,showing characteristics of relatively poor PG;(3)the sedimentary environments of the Xidashan-Xishanbulake and Moheershan formations in the Tadong low uplift are similar.They were deposited in warm and humid climatic conditions,in oxygen-deficient environments,with stable terrigenous inputs,high paleoproductivity,high paleosalinity,weak water-holding capacity,and no significant hydrothermal activity;and(4)the relationship between TOC and the paleoproductivity parameter(P/Ti)is most significant in the Lower Cambrian Xidashan-Xishanbulake Fm.,whereas correlation with other indicators is not evident.This suggests a productivity-driven OM enrichment model,where input of landderived material was relatively small during the Middle Cambrian,and the ancient water exhibited lower salinity.A comprehensive pattern was formed under the combined control of paleoproductivity and preservation conditions.This study provides valuable guidance for oil and gas exploration in the Tarim Basin.

Contrasting on Hydrocarbon Generation Modeland Characteristics of Pyrolysis of Modern Aquatic Plant(Gloeocapsa) vs MarineAnimal(Mantis Shrimp)

A hydrocarbon model of the modern aquatic plant Gloeocapsa and the aquatic animal mantis shrimp was found in thermal simulating experiment. The results show that the modern aquatic plant Gloeocapsa is characterized by late generation, late termination and a long duration of oil generation, while the aquatic animal mantis shrimp is characterized by early generation, early termination and a short duration of oil generation. The nalkanes from Gloeocapsa and mantis shrimp are characterized by peak carbon C 15 -C 17 . With increasing thermal simulating temperature, the peak carbon changes from C 17 to C 15 , and the odd-even predominance of nalkanes becomes less clear. The products from Gloeocapsa contain abundant phenanthrene and naphthalene compounds, and even a little retene, while those from mantis shrimp are dominated by naphthalene compounds, and are poor in phenanthrene compounds. Gloeocapsa and mantis shrimp are rich in C 27 sterane, relatively rich in tricyclic terpanes (C 19 -C 29 ) and hopanes (C 27 -C 35 ), poor in 5α,14β,17β sterane, and coprostane does not disappear until 450 ℃. The tricyclic terpanes in Gloeocapsa are characterized by peak carbon C 23 and C 23 >C 21 , and in mantis shrimp by C 21 and C 21 >C 23 . The content of pregnanes is very low at low temperature of thermal simulation, while above 360 ℃, high levels of pregnane series compounds and even degraded C 25 and C 26 steranes occur in thermal simulation products.

Effects of hydrocarbon generation on fluid flow in the Ordos Basin and its relationship to uranium mineralization

The Ordos Basin of North China is not only an important uranium mineralization province, but also a major producer of oil, gas and coal in China. The genetic relationship between uranium mineralization and hydrocarbons has been recognized by a number of previous studies, but it has not been well understood in terms of the hydrodynamics of basin fluid flow. We have demonstrated in a previous study that the preferential localization of Cretaceous uranium mineralization in the upper part of the Ordos Jurassic section may have been related to the interface between an upward flowing, reducing fluid and a downward flowing, oxidizing fluid. This interface may have been controlled by the interplay between fluid overpressure related to disequilibrium sediment compaction and which drove the upward flow, and topographic relief, which drove the downward flow. In this study, we carried out numerical modeling for the contribution of oil and gas generation to the development of fluid overpressure, in addition to sedi- ment compaction and heating. Our results indicate that when hydrocarbon generation is taken into account, fluid overpressure during the Cretaceous was more than doubled in comparison with the simu- lation when hydrocarbon generation was not considered. Furthermore, fluid overpressure dissipation at the end of sedimentation slowed down relative to the no-hydrocarbon generation case. These results suggest that hydrocarbon generation may have played an important role in uranium mineralization, not only in providing reducing agents required for the mineralization, but also in contributing to the driving force to maintain the upward flow.

A hydrocarbon enrichment model and prediction of favorable accumulation areas in complicated superimposed basins in China

The geologic conditions of superimposed basins in China are very complicated. This is mainly shown by multi-phase structural evolution, multiple sets of source-reservoir-cap rock combinations, multiple stages of hydrocarbon generation and expulsion from source rocks, multi-cycle hydrocarbon enrichment and accumulation, and multi-phase reservoir adjustment and reconstruction. The enrichment, accumulation and distribution of hydrocarbon is mainly controlled by the source rock kitchen, paleo- anticline, regional cap rock and intensity of tectonic movement. In this paper, the T-BCMS model has been developed to predict favorable areas of hydrocarbon accumulation in complicated superimposed basins according to time and spatial relationships among five key factors. The five factors include unconformity surface representing tectonic balancing （B）, regional cap rock representing hydrocarbon protection （C）, paleo-anticline representing hydrocarbon migration and accumulation （M）, source rock kitchen representing hydrocarbon generation and expulsion （S） and geological time （T）. There are three necessary conditions to form favorable areas of hydrocarbon accumulation. First, four key factors BCMS should be strictly in the order of BCMS from top to bottom. Second, superimposition of four key factors BCMS in the same area is the most favorable for hydrocarbon accumulation. Third, vertically ordered combination and superimposition in the same area of BCMS should occur at the same geological time. The model has been used to predict the most favorable exploration areas in Ordovician in the Tarim Basin in the main hydrocarbon accumulation periods. The result shows that 95% of the discovered Ordovician hydrocarbon reservoirs are located in the predicted areas, which indicates the feasibility and reliability of the key factor matching T-BCMS model for hydrocarbon accumulation and enrichment.

A unified model for the formation and distribution of both conventional and unconventional hydrocarbon reservoirs

The discovery and large-scale exploration of unconventional oil/gas resources since 1980s have been considered as the most important advancement in the history of petroleum geology;that has not only changed the balance of supply and demand in the global energy market,but also improved our understanding of the formation mechanisms and distribution characteristics of oil/gas reservoirs.However,what is the difference of conventional and unconventional resources and why they always related to each other in petroliferous basins is not clear.As the differences and correlations between unconventional and conventional resources are complex challenging issues and very critical for resources assessment and hydrocarbon exploration,this paper focused on studying the relationship of formations and distributions among different oil/gas reservoirs.Drilling results of 12,237 exploratory wells in 6 representative petroliferous basins of China and distribution characteristics for 52,926 oil/gas accumulations over the world were applied to clarify the formation conditions and genetic relations of different oil/gas reservoirs in a petroliferous basin,and then to establish a unified model to address the differences and correlations of conventional and unconventional reservoirs.In this model,conventional reservoirs formed in free hydrocarbon dynamic field with high porosity and permeability located above the boundary of hydrocarbon buoyancy-driven accumulation depth limit.Unconventional tight reservoirs formed in confined hydrocarbon dynamic field with low porosity and permeability located between hydrocarbon buoyancy-driven accumulation depth limit and hydrocarbon accumulation depth limit.Shale oil/gas reservoirs formed in the bound hydrocarbon dynamic field with low porosity and ultra-low permeability within the source rock layers.More than 75%of proved reserves around the world are discovered in the free hydrocarbon dynamic field,which is estimated to contain only 10%of originally generated hydrocarbons.Most of undiscovered resources distributed in the confined hydrocarbon dynamic field and the bound hydrocarbon dynamic field,which contains 90%of original generated hydrocarbons,implying a reasonable and promising area for future hydrocarbon explorations.The buried depths of hydrocarbon dynamic fields become shallow with the increase of heat flow,and the remaining oil/gas resources mainly exist in the deep area of“cold basin”with low geothermal gradient.Lithology changing in the hydrocarbon dynamic field causes local anomalies in the oil/gas dynamic mechanism,leading to the local formation of unconventional hydrocarbon reservoirs in the free hydrocarbon dynamic field or the occurrence of oil/gas enrichment sweet points with high porosity and permeability in the confined hydrocarbon dynamic field.The tectonic movements destroy the medium conditions and oil/gas components,which leads to the transformation of conventional oil/gas reservoirs formed in free hydrocarbon dynamic field to unconventional ones or unconventional ones formed in confined and bound hydrocarbon dynamic fields to conventional ones.

A review of carbonates as hydrocarbon source rocks: basic geochemistry and oil–gas generation

Carbonates have been known to act as hydrocarbon source rocks, but their basic geochemical and associated hydrocarbon generation characteristics remain not well understood as they occur with argillaceous source rocks in most cases, and the hydrocarbon generation from each rock type is di cult to distinguish, forming one of puzzling issues within the field of petroleum geology and geochemistry. To improve the understanding of this critical issue, this paper reviews recent advances in this field and provides a summary of key areas that can be studied in future. Results show that carbonate source rocks are generally associated with high-salinity environments with low amounts of terrestrial inputs and low dissolved oxygen contents. Petrographically, these source rocks are dark gray or black, fine-grained, stratified, and contain bacterial and algal bioprecursors along with some other impurities. They generally have low organic matter contents, although these can vary significantly in di erent cases(e.g., the total organic carbon contents of marine and lacustrine carbonate source rocks in China are generally 0.1%–1.0% and 0.4%–4.0%, respectively). These rocks contain type I and type II kerogen, meaning there is a lack of vitrinites. This means that assessment of the maturity of the organic matter in these sediments needs to use non-traditional techniques rather than vitrinite reflectance. In terms of molecular geochemistry, carbonate source rocks have typical characteristics indicative of generally reducing and saline environments and lower organism-dominated bioprecursors of organic matter, e.g., high contents of sulfur compounds, low Pr/Ph ratios, and dominance of n-alkanes. Most of the carbonate source rocks are typically dominated by D-type organic facies in an oxidized shallow water mass, although high-quality source rocks generally contain A-and B-type organic facies in saline lacustrine and marine-reducing environments, respectively. The hydrocarbon generation model for the carbonate source rocks can involve early, middle, and late stages, with a diversity of hydrocarbons within these rocks, which can be aggregated, adsorbed, enclosed within minerals, or present as inclusions. This in turn implies that the large-scale hydrocarbon expulsion from these rocks is reliant on brittle deformation caused by external forces. Finally, a number of aspects of these source rocks remain unclear and need further study, including the e ectiveness of carbonates as hydrocarbon source rocks, bioprecursors, and hydrocarbon generation models of carbonate source rock, and the di erences between marine and lacustrine carbonate source rocks.

Hydrocarbon generation history constrained by thermal history and hydrocarbon generation kinetics:A case study of the Dongpu Depression,Bohai Bay Basin,China

With the increasing exploration and development of typical hydrocarbon-rich depressions,such as the Dongpu Depression,the exploitation difficulty of shallow formations is increasing.There is an urgent need to clarify the hydrocarbon generation mode and hydrocarbon generation histories in deep formations.In this study,a gold tube-autoclave closed system was used to simulate the hydrocarbon generation processes and establish the hydrocarbon generation mode of different types of kerogen.Then,constrained by the thermal history and hydrocarbon generation kinetics,hydrocarbon generation histories were modeled.The results show that hydrocarbon generation evolution can be divided into five stages,and the maturity of each stage is different.The hydrocarbon generation history of the source rocks of the Shahejie 3 Formation mainly dates from the early depositional period of the Shahejie 1 Formation to the middle depositional period of the Dongying Formation.Hydrocarbon generation history constrained by thermal history and hydrocarbon generation kinetics is more in line with actual geological conditions.Moreover,this research can provide important hydrocarbon generation parameters for deep oil and gas exploration and exploitation of the Shahejie 3 Formation in the Dongpu Depression.

Hydrocarbon generation from Carboniferous-Permian coaly source rocks in the Huanghua depression under different geological processes

Natural gas and condensate derived from Carboniferous-Permian(C-P)coaly source rocks discovered in the Dagang Oilfield in the Bohai Bay Basin(east China)have important implications for the potential exploration of C-P coaly source rocks.This study analyzed the secondary,tertiary,and dynamic characteristics of hydrocarbon generation in order to predict the hydrocarbon potentials of different exploration areas in the Dagang Oilfield.The results indicated that C-P oil and gas were generated from coaly source rocks by secondary or tertiary hydrocarbon generation and characterized by notably different hydrocarbon products and generation dynamics.Secondary hydrocarbon generation was completed when the maturity reached vitrinite reflectance(Ro)of 0.7%-0.9%before uplift prior to the Eocene.Tertiary hydrocarbon generation from the source rocks was limited in deep buried sags in the Oligocene,where the products consisted of light oil and gas.The activation energies for secondary and tertiary hydrocarbon generation were 260-280 kJ/mol and 300-330 kJ/mol,respectively,indicating that each instance of hydrocarbon generation required higher temperature or deeper burial than the previous instance.Locations with secondary or tertiary hydrocarbon generation from C-P coaly source rocks were interpreted as potential oil and gas exploration regions.

Hydrocarbon expulsion model and resource potential evaluation of high-maturity marine source rocks in deep basins:Example from the Ediacaran microbial dolomite in the Sichuan Basin,China

Hydrocarbon expulsion features and resource potential evaluation of source rocks are crucial for the petroleum exploration.High-maturity marine source rocks have not exhibited a hydrocarbon expulsion mode owing to the lack of low-maturity source rocks in deep petroliferous basins.We considered the Ediacaran microbial dolomite in the Sichuan Basin,the largest high-maturity marine gas layer in China,to exhibit a method that quantitatively characterizes the hydrocarbon expulsion of high-maturity marine source rocks.The experiment of fluid inclusion,rock pyrolysis,and vitrinite reflectance(Ro)of 119 microbial dolomite core samples obtained from the Dengying Formation were performed.A hydrocarbon expulsion model of high-maturity source rock was established,and its resource potential was evaluated.The results showed that the Ediacaran microbial dolomite in the Sichuan Basin is a good source rock showing vast resource potential.The hydrocarbon expulsion threshold is determined to be vitrinite reflectance at 0.92%.The hydrocarbon expulsion intensities in the geologic history is high with maximum of 1.6×10^(7)t/km^(2).The Ediacaran microbial dolomite expelled approximately 1.008×10^(12)t of hydrocarbons,and the recoverable resource was 1.5×10^(12)m^(3).The region can be categorized into areasⅠ,Ⅱ,Ⅲ,andⅣ,in decreasing order of hydrocarbon expulsion intensity.Areas with a higher hydrocarbon expulsion intensity have a lower drilling risk and should be prioritized for exploration in the orderⅠ>Ⅱ>Ⅲ>Ⅳ.Two areas,northern and central parts of Ediacaran in the Sichuan Basin,were selected as prospects which had the drilling priority in the future gas exploration.The production data of 55 drilled wells verified the high reliability of this method.This model in this study does not require low-maturity samples and can be used for evaluating high-maturity marine source rocks,which has broad applicability in deep basins worldwide.

Hydrocarbon Generation Evolution of Permo-Carboniferous Rocks of the Bohai Bay Basin in China

The Bohai Bay Basin is a Mesozoic subsidence and Cenozoic rift basin in the North China Craton. Since the deposition of the Permo-Carboniferous hydrocarbon source rock, the basin has undergone many tectonic events. The source rocks have undergone non-uniform uplift, twisting, deep burying, and magmatism and that led to an interrupted or stepwise during the evolution of hydrocarbon source rocks. We have investigated the Permo-Carboniferous hydrocarbon source rocks history of burying, heating, and hydrocarbon generation, not only on the basis of tectonic disturbance and deeply buried but also with new studies on apatite fission track analysis, fluid inclusion measurements, and the application of the numerical simulation of EASY % Ro. The heating temperature of the source rocks continued to rise from the Indosinian to Himalayan stage and reached a maximum at the Late Himalayan. This led to the stepwise increases during organic maturation and multiple stages of hydrocarbon generation. The study delineated the tectonic stages, the intensity of hydrocarbon generation and spatial and temporal distribution of hydrocarbon generations. The hydrocarbon generation occurred during the Indosinian, Yanshanian, and particularly Late Himalayan. The hydrocarbon generation during the late Himalayan stage is the most important one for the Permo-Carboniferous source rocks of the Bohai Bay Basin in China.

Thermal Evolution of Organic Matter and Secondary Hydrocarbon Generation from Upper Paleozoic Coal Deposits in Northern China

The metamorphism and hydrocarbon generation from the Upper Paleozoic coal-bearing strata in Northern China have been widely studied by Chinese geologists since the 1990s. Based on a large amount of data of Ro values,combined with geological background,we have systematically analyzed the thermal evolutionary characteristics of or-ganic matter and the stages of hydrocarbon generation from the Permo-Carboniferous coal deposits and discussed the condition of secondary hydrocarbon generation. The distribution range of secondary hydrocarbon generation in North-ern China is thus determined. It is shown that the coal ranks of the Upper Paleozoic coal deposits are higher in the southern and western belts than those in the northern and eastern belts. Really significant secondary hydrocarbon gen-eration is mainly related to the thermal evolution of organic matter during the Himalayan Period. Profitable areas for secondary hydrocarbon generation should be buried at 3000-4000 m up to the present. Maturity of the Permo-Carbon-iferous source rocks is not very high. It is suggested that the Bohai Bay depression is favourable for secondary hydro-carbon generation and has good oil and gas prospects.

Study on the relationship between hydrocarbon generation and pore evolution in continental shale from the Ordos Basin,China

The relationship between hydrocarbon generation and the evolution of shale pore structure and its heterogeneity of continental shale from the Ordos Basin,China was quantitatively studied based on thermal simulation experiment,mercury injection capillary pressure(MICP),gas adsorption,vitrinite reflectance(R_(o))analysis,and hydrocarbon generation test combined with Frenkel-Halsey-Hill(FHH)fractal model.The result shows that the pore volume(PV)and specific surface area(SSA)of pores with different pore sizes show a trend of decreasing first and then increasing as the maturity increases in general,R_(o)>1.59%is initially defined as a favorable stage for pore development in continental shale.Hydrocarbon generation has different effects on pore heterogeneity of different scales.For the N_(2)adsorption,the roughness of small pore surface(D_(1))decreases in the oil window;the complexity of large pore structure(D_(2))increases in the oil window but decreases in the gas window.For the MICP,the heterogeneity of small pore(D_(1))increases in the oil window and increases first and then decreases in the gas window;D_(2)remains basically constant during the whole stage and is close to 3,indicating that the heterogeneity of large pores is extremely strong and is not affected by hydrocarbon generation.

Kinetics and model of gas generation of source rocks in the deepwater area, Qiongdongnan Basin

In order to investigate the hydrocarbon generation process and gas potentials of source rocks in deepwater area of the Qiongdongnan Basin, kinetic parameters of gas generation （activation energy distribution and frequency factor） of the Yacheng Formation source rocks （coal and neritic mudstones） was determined by thermal simulation experiments in the closed system and the specific KINETICS Software. The results show that the activation energy （Ea） distribution of C1–C5 generation ranges from 50 to 74 kcal/mol with a frequency factor of 2.4×1015 s–1 for the neritic mudstone and the Ea distribution of C1–C5 generation ranges from 49 to 73 kcal/mol with a frequency factor of 8.92×1013 s–1 for the coal. On the basis of these kinetic parameters and combined with the data of sedimentary burial and paleothermal histories, the gas generation model of the Yacheng Formation source rocks closer to geological condition was worked out, indicating its main gas generation stage at Ro （vitrinite reflectance） of 1.25%–2.8%. Meanwhile, the gas generation process of the source rocks of different structural locations （central part, southern slope and south low uplift） in the Lingshui Sag was simulated. Among them, the gas generation of the Yacheng Formation source rocks in the central part and the southern slope of the sag entered the main gas window at 10 and 5 Ma respectively and the peak gas generation in the southern slope occurred at 3 Ma. The very late peak gas generation and the relatively large gas potential indices （GPI：20×10^8–60×10^8 m^3/km^2） would provide favorable conditions for the accumulation of large natural gas reserves in the deepwater area.

Hydrocarbon Generation Kinetic Characteristics from Different Types of Organic Matter

In order to contrast the hydrocarbon generation kinetic characteristics from different types of organic matter（OM）,18 samples from different basins were pyrolyzed using Rock-Eval-Ⅱapparatus under the open system.From the experimental results,the curve of hydrocarbon generation rate vs.temperature can be easily obtained,which usually can be used to optimize kinetic parameters （A,E,F）of the hydrocarbon generation model.In this paper,the parallel first-order reaction with a single frequency factor model is selected to describe the hydrocarbon generation kinetic characteristics. The hydrocarbon generation kinetic parameters reveal that the types of compound structures and chemical bonds of the lacustrine fades typeⅠOM are relatively homogeneous,with one dominating activation energy.The types of chemical bonds of the lacustrine facies typeⅡ2 OM and the terrestrial facies typeⅢOM are relative complex,with a broad activation energy distribution,and the reaction fraction of the preponderant activation energy drops with the decrease of hydrogen index.The impact of the activation energy distribution spaces on the geological extrapolation of kinetic parameters is also investigated.The results show that it has little effect on the hydrocarbon transformation ratio（TR）and therefore,the parallel first-order reaction model with proper number of activation energies can be better used to describe the hydrocarbon generation process.The geological extrapolation results of 18 samples of kinetic parameters show that the distribution range of the hydrocarbon generation rate of the typeⅠOM is relatively narrow and the hydrocarbon generation curve is smooth.In comparison,the distribution range of the hydrocarbon generation for typeⅢand typeⅡ2-ⅢOM are quite wide,and the hydrocarbon generation curves have fluctuation phenomena.The distribution range of the hydrocarbon generation rate and the fluctuation phenomena are related to the kinetic parameters of OM;the narrower the activation energy distribution,the narrower the hydrocarbon generation rate distribution,and the smoother the hydrocarbon generation curve,and vice versa.

Diversified roles of mineral transformation in controlling hydrocarbon generation process,mechanism,and pattern

Organic matter(OM)is intimately associated with minerals in clay-rich mudstones,leading to widespread organic-mineral interaction during hydrocarbon generation in argillaceous source rocks.What we are concerned is the effects of the different mineral properties on hydrocarbon generation process and mechanism during mineral transformation.In this way,pyrolysis experiments with smectite-octadecanoic acid complexes(Sm-OA and Ex-Sm-OA)were conducted to analyze correlation of mineralogy and pyrolysis behaviors.Based on organicmineral interaction,hydrocarbon generation process was divided into three phases.At 200–300℃,collapse of smectite led to desorption of OM,resulting in high yield of resin and slight increase in saturates.Subsequently,enhanced smectite illitization at 350–450℃was accompanied with large amounts of saturates and a mere gaseous hydrocarbon.Featured by neoformed plagioclase,ankerite,and illite,500C saw plenty of asphaltene and methane-rich gaseous hydrocarbons,revealing cracking reactions of OM.Noteworthy is that saturated and gaseous hydrocarbons in Ex-Sm-OA were considerably more than that in Sm-OA during second and third phases.Quantitative calculation of hydrogen revealed organic hydrogen provided by cross-linking of OM could not balance hydrogen consumed by cracking reactions,but supply of inorganic hydrogen ensured cracking could readily occur and consequently greatly promoted hydrocarbon generation.Further investigating characteristics of mineralogy and pyrolytic products,as well as effects of solid acidity on hydrocarbon generation,we concluded desorption of OM and decarboxylation promoted by Lewis acid were dominated at 200–300C,resulting in lowdegree hydrocarbon generation.While high yield of saturated and gaseous hydrocarbons in second and third phases,together with occurrence of ankerite,indicated predominance of decarboxylation and hydrogenation promoted by Lewis and Brønsted acid,respectively.Variations in organic-mineral interactions indicated(1)the controls of mineral transformation on hydrocarbon generation process and mechanism include desorption,decarboxylation,and hydrogenation reactions;(2)clay minerals acted as reactants evolving together with OM rather than catalysts.These findings are profoundly significant for understanding the hydrocarbon generation mechanisms,organic-inorganic interactions,and carbon cycle.

Environmental Capacity of Petroleum Hydrocarbon Pollutants in Jiaozhou Bay, China: Modeling and Calculation

An environmental capacity model for the petroleum hydrocarbon pollutions （PHs） in Jiaozhou Bay is constructed based on field surveys, mesocosm, and parallel laboratory experiments. Simulated results of PHs seasonal successions in 2003 match the field surveys of Jiaozhou Bay resaonably well with a highest value in July. The Monte Carlo analysis confirms that the variation of PHs concentration significantly correlates with the river input. The water body in the bay is reasonably subjected to self-purification processes, such as volatilization to the atmosphere, biodegradation by microorganism, and transport to the Yellow Sea by water exchange. The environmental capacity of PHs in Jiaozhou Bay is 1500 tons per year IF the seawater quality criterion （Grade Ⅰ/Ⅱ, 0.05 mgLl） in the region is to be satisfied. The contribution to self-purification by volatilization, biodegradation, and transport to the Yellow Sea accounts for 48%, 28%, and 23%, respectively, which make these three processes the main ways of PHs purification in Jiaozhou Bay.

Geothermal Regime,Thermal History and Hydrocarbon Generation Types of Sedimentary Basins in the Continental Area of China

The thermal regimes in sedimentary basins in the continental area of China are varied and reflect differences in geological settings. As a result of these variable thermal regimes, the history of hydrocarbon generation in each basin is also different. An east-west profile of the thermal threshold across the continental basins of China, like the Liaohe Basin, the North China Basin, the Ordos Basin, the Qaidam Basin and the Tarim Basin, was constructed using large numbers of heat flow measurements, temperature data and rock thermophysical parameters. Isotherms, surface heat flow, mantle heat flow and Moho temperature beneath the basins are shown in the profile, which illustrates changes in some thermal characteristics between basins in east China and those in west China. Thermal evolution histories in basins were reconstructed using Easy%Ro method, apatite fission track annealing and other paleothermometers. Typical hydrocarbon generation histories of the primary source rocks were modeled by referring to the thermal evolution data. Thermal stages controlled source rocks maturation and oil and gas generation, and influenced the type of hydrocarbon (oil and gas) production in the basins.