Development Of Source Rocks Research Articles

Distribution characteristics and its controlling factor of lacustrine high-quality source rocks in the Bozhong sag, Bohai Bay Basin

Distribution of Paleogene lacustrine high-quality source rocks in the Bozhong sag in Bohai Bay Basin is analyzed through data of geochemistry, geology and well logging, and its differences under the control of climate and tectonics is also well discussed. Distribution characteristics of the high-quality source rocks developed in the saline environment controlled by the climate are quite different from that developed in the rapid subsidence environment controlled by tectonics. The high-quality source rocks in Member 1 of Shahejie Formation developed in the saline environment account for 81.9% of total subsag area, and are distributed widely and extensively. The high-quality source rocks in Member 3 of Shahejie Formation and Member 3 of Dongying Formation is developed in the tectonic subsidence environment, and horizontally, the subsag subsidence rates has a positive correlation with the area proportion of the high-quality source rocks in the sag; vertically, the reduction-oxidation interface of the lake controls the enrichment of high-quality source rocks. Controlled by the saline environment and rapid subsidence environment, the high-quality source rocks in the Bozhong sag and adjacent areas have three types of development condition: the saline water, the tectonic subsidence, and joint control of the saline water and the tectonic subsidence. The humid climate and low subsidence rate are not favorable for development of high-quality source rocks.

Astronomical time scale of the Paleogene lacustrine paleoclimate record from the Nanxiang Basin, central China

The chronostratigraphy of the Paleogene succession of the Nanxiang Basin, a petroliferous basin in central China with a predominantly lacustrine fill, remains controversial due to the lack of an accurate geological time scale. In this work, high-resolution gamma-ray (GR) logs from the B270 and BS1 boreholes from depocenters in the Biyang Depression of the Nanxiang Basin were used to analyze the cyclostratigraphy. Paleocene floodplain facies of red clastics and purple mudstone is conformably overlain by Eocene through Oligocene lacustrine facies of gray mudstone, oil shale, and clayey dolomite interbedded with siltstone-sandstone. The multitaper method of spectral analysis and Gaussian bandpass filtering were used to identify Milankovitch cycles. Based on the recognition of 405-kyr long-eccentricity cycles, the series was tuned to establish a 46-Myr floating astronomical time scale (ATS), which was then anchored to the Paleogene/Neogene boundary age of 23.03 Ma. The ATS enables the assignment of the ages to non-marine biozones, depositional facies and rifting episodes within the Nanxiang Basin. The subsidence and rates of sediment accumulation within the rift basin of the Nanxiang Basin has an inverse relationship to the convergence rates between Pacific plates and the eastern margin of Eurasia. The middle Eocene slowing of the convergence rate at ~50 Ma, coupled with the onset of the collision of the Indian and Eurasian plate, corresponds to the beginning of the climax stage of rifting, the development of deep lakes and the deposition of oil shales in the Nanxiang Basin. The organic-rich 3rd member of the Hetaoyuan Formation (Eh3) during this middle Eocene interval preserved a range of climatic cycles from annual varves to a ~1.2-Myr modulation of obliquity cycles, indicating the importance of climatic oscillations on the development of those hydrocarbon source rocks.

Activity of hydrothermal fluid at the bottom of a lake and its influence on the development of high-quality source rocks: Triassic Yanchang Formation, southern Ordos Basin, China

Evidence for hydrothermal activity, such as siliceous rocks, iron dolomite layer deposits, and hydrothermal mineral combinations of ilmenite + pyrite + anhydrite, has been found in the high-quality source rocks from the Chang 7 layer in the Triassic Yanchang Formation from the southern margin of the Ordos Basin, China. In this paper, elemental geochemical analysis is carried out on a large number of samples collected from an outcrop geological section and drill core from the Chang 7 layer. We use elemental ratios to study the hydrothermal activity; the Al/(Al + Fe + Mn) ratio reflects the paleoproductivity, and the P/Al and P/Ti ratios and total S contents reflect the redox environment. The relationships between the hydrothermal activity and paleoproductivity, redox conditions and organic matter content are discussed. The correlation coefficients between the hydrothermal index Al/(Al + Fe + Mn) and the (Fe + Mn)/Ti ratio and total organic carbon are as high as –0.88 and 0.87, respectively, demonstrating a close relationship between hydrothermal activity and source-rock deposition. The correlation coefficients between the Al/(Al + Fe + Mn) ratio and the P/Al and P/Ti ratios, and total S contents are –0.81, –0.80, and –0.89, respectively, supporting this relationship. Hydrothermal activity can promote productivity at the lake surface and the development of a bottom-water anoxic environment. The paleoproductivity level of the Chang 7 sedimentary period is relatively high and represents an oxygen-poor anaerobic environment. The hydrothermal activity in the southern margin of the basin is strong, whereas the activity in the north is gradually weakened. Studies have shown that the hydrothermal activity at the bottom of the lake plays an important role in promoting the large-scale development of the Chang 7 high-quality source rocks. The organic matter abundance in samples with hydrothermal alteration are greater than in samples elsewhere.

Characteristics, differences and main controlling factors of source rocks in the central‐southern South China Sea Basins

The South China Sea is rich in oil and gas resources. With the increasing exploration of oil and gas resources in the northern South China Sea and the increasing demand for energy in the world, The central‐southern South China Sea have become important constituencies for oil and gas resources. The central‐southern basins of South China Sea can be divided into three types of basin groups, namely, the southern basin group (Zengmu Basin, Brunei‐Sabah Basin), the western basin group (Wan'an Basin, Zhong jiannan Basin) and the Central Basin Group (Liyue Basin, Beikang Basin, Nanweixi Basin and Palawan Basin). At present, the degree of exploration is relatively low, and the source rock has not yet formed a understanding of the system. The main source rock development time, source rock characteristics, hydrocarbon generation potential and control factors of each basin group are still unclear, which seriously restricts the exploration of oil and gas. Based on the sedimentary facies distribution and sedimentary filling evolution, combined with the geoche mical characteristics of the source rocks, the source age, organic matter type, hydrocarbon generation potential and main controlling factors of the basins in the central‐southern basins are discussed. By the detailed research on delta scale, provenance system, paleoclimate conditions, ancient vegetation development and hydroca rbon generation parent material, the main controlling factors of hydrocarbon generation potential of source rocks in each basin group are revealed.

Mineralogy and organic geochemistry of the terrestrial lacustrine pre-salt sediments in the Qaidam Basin: Implications for good source rock development

Abstract Terrestrial pre-salt sediments are not only good lithologic reservoirs similar to marine pre-salt carbonates, but also are supposed to have high hydrocarbon generation potential because the overlying terrestrial thick-bedded salts are generally preserved in basin centers. However, their status as source rock has attracted much less attention than as reservoir. In this paper, we choose the Qaidam Basin as an example and study the minerology, organic geochemistry, and organic petrology of the pre-salt sediments in a hydrocarbon-rich unit, where abundant petroleum resources have been discovered under halite beds. LithoScanner logging of six wells and X-ray diffraction results of 378 samples show that terrestrial pre-salt sediments are characterized by mixed siliciclastic-carbonate-sulphate rocks and their relative proportions are laterally varied. Quartz, feldspar and clay minerals are of allochthonous origin and classified as argillaceous endmember while dolomite and ankerite are of autochthonous origin as carbonate endmember. Organic geochemistry analysis of 118 samples show great variability in TOC, S2, and Tmax values, and this variability is not related to mineral composition heterogeneity as hydrogen index is not well correlated with detritus, carbonate, and sulphate minerals contents, indicating the interacting controls of source rocks by both exogenetic and endogenetic processes in brackish-mesosaline lakes. Strong bacterial reworking of organic matter results in the dominant macerals of pre-salt sediments as bituminite and oil generation at low maturity levels. Sealed by impermeable halite beds and in close proximity to reservoirs, the generating hydrocarbon by pre-salt good source rocks is effectively accumulated, which entails hydrocarbon exploration under halite beds in other terrestrial salt-bearing basins.

Dynamic interaction between basin redox and the biogeochemical nitrogen cycle in an unconventional Proterozoic petroleum system

Precambrian hydrocarbons and their corresponding source rocks are distinctly different from their Phanerozoic counterparts, having been deposited in persistently anoxic environments in ecosystems dominated by bacteria. Here, we show that cyclic enrichment of organic matter in the world’s oldest hydrocarbon play (ca. 1.38 Ga), is not associated with flooding surfaces and is unrelated to variations in mineralogy or changes in the relative rate of clastic to biogenic sedimentation—factors typically attributed to organic enrichment in Phanerozoic shales. Instead, the cyclic covariation of total organic carbon, δ15N, δ13C and molybdenum are explained by the feedback between high levels of primary productivity, basin redox and the biogeochemical nitrogen cycle. These factors are important in constraining productivity in the marine biosphere, the development of Precambrian hydrocarbon source rocks, and more generally in understanding oxygenation of the ocean and atmosphere through Earth history; as all are ultimately related to organic carbon burial.

Influence of volcanic activities on redox chemistry changes linked to the enhancement of the ancient Sinian source rocks in the Yangtze craton

Volcanic eruptions and related submarine hydrothermal activities were very extensive during the Precambrian periods in the Yangtze craton in southern China. How these geological events affected redox chemistry changes linked to the enhancement of mudstone/shale hydrocarbon source rocks in ancient strata is an important concern for oil and gas exploration in the Precambrian strata. Samples were collected from two Sinian (Ediacaran) outcrops in the northern Sichuan Basin, the Zhaiziyan and Yanhe outcrops, which revealed Doushantuo Formation (Z1ds) shales approximately 30.5 m in thickness, and shales in the third member of the Deying Formation (Z2dn3) approximately 30.0 m in thickness. TOC contents of the black carbonaceous shales in the Doushantuo Formation of the Zhaiziyan outcrop are mostly greater than 5.0% (up to 12.9%). Positive correlations were observed between TOC contents and trace and rare earth element concentrations in the shales: samples with high concentrations of trace elements such as V, Ni, Cu, Zr, Rb, and Pb and total rare earth element (∑REE) concentrations had relatively high TOC contents. The shales are rich in volcanic ash interlayers and thin siliceous layers and have positive Eu anomalies, indicating that volcanic activities and related hydrothermal activities significantly impacted the development of black shale source rocks. In the rifting background of the Sinian cratonal marginal, extensive volcanic activities brought rich nutrients to the seawater, which may have promoted the breeding of cyanobacteria and multicellular algae. At the same time, the volcanic activities released large amounts of H2S and SO2, which could cause the seawater to become a euxinic environment in which the bottom seawater was sulfurized and anoxic. Massive amounts of organic matters formed in the surface seawater entered the anoxic bottom seawater and were well preserved in the shale sediments. Therefore, under the influence of volcanic activities, ancient Sinian organic-rich high-quality source rocks were widely developed and had a large hydrocarbon supply potential for the Sinian dolomite reservoirs.

Characterizations and accumulation of lacustrine source rocks in the Zhu I Depression, Pearl River Mouth Basin, China

The study of source rocks is a key component in the exploration and discovery of hydrocarbon plays in the offshore petroliferous basins of China. Geochemical analyses, drilling, seismic, and microfossil data were integrated to document the formation mechanism of lacustrine source rocks contained in the Wenchang Formation in the Zhu I Depression of the Pearl River Mouth Basin, China. Several factors that control the development of lacustrine source rocks were evaluated in this study, including tectonics, sedimentary conditions, palaeoclimate, the supply of organic matter, and redox conditions. The deposition and occurrence of source rocks is a combined function of these factors. Lacustrine source rocks are characterized by high organic matter contents (average TOC value = 1.33 wt.%) and are dominated by type I and type II1–2 kerogen, which primarily originate from planktonic algae. The rifting of basement rocks, syn‐sedimentary faults, and palaeoclimate played significant roles in controlling the geochemical properties of the source rocks (e.g., controlling the abundance and types of organic matter). The Eocene lacustrine source rocks were deposited when the palaeoclimate was characterized by humid to semi‐humid, subtropical to tropical weather that did not have a stable temperature or humidity. Controlled by large‐scale faults, “Half‐graben patterns” and “Graben patterns” are the two main palaeotopographic patterns where the thermal stratification of deep lake water resulted in flourishing planktonic algae in its surface zones. Dysoxic to anoxic conditions prevailed during the deposition of the lacustrine source rocks. An underfilled basin situation caused the occurrence of abundant organic matter during the period of maximum surface flooding.

The scientific connotation of oil and gas formations under deep fluids and organic-inorganic interaction

As a relatively stable craton block in the earth system, the petroliferous basin is influenced by the evolution of the earth system from the early development environment of source rocks, hydrocarbon formation, and reservoir dissolution to hydrocarbon accumulation or destruction. As a link between the internal and external factors of the basin, deep fluids run through the whole process of hydrocarbon formation and accumulation through organic-inorganic interaction. The nutrients carried by deep fluids promote the bloom of hydrocarbon-generating organisms and extra addition of carbon and hydrogen source, which are beneficial to the development of high-quality source rock and enhancement of the hydrocarbon generation potential. The energy carried by the deep fluid promotes the early maturation of the source rock and facilitates the hydrocarbon generation by activation and hydrogenation in high-mature hydrocarbon sources. The dissolution alteration of carbonate rocks and clastic reservoirs by CO2-rich deep fluids improves the deep reservoir space, thus extending the oil and gas reservoir space into greater depth. The extraction of deeply retained crude oil by deep supercritical CO2 and the displacement of CH4 in shale have both improved the hydrocarbon fluidity in deep and tight reservoirs. Simultaneously, the energy and material carried by deep fluids (C, H, and catalytic substances) not only induce inorganic CH4 formation by Fischer-Tropsch (F-T) synthesis and “hydrothermal petroleum” generation from organic matter by thermal activity but also cause the hydrothermal alteration of crude oil from organic sources. Therefore, from the perspective of the interaction of the earth’s sphere, deep fluids not only input a significant amount of exogenous C and H into sedimentary basins but also improve the reservoir space for oil and gas, as well as their enrichment and accumulation efficiencies.

Development and exploration practice of the concept of hydrocarbon accumulation in rifted-basin troughs: A case study of Paleogene Kongdian Formation in Cangdong sag, Bohai Bay Basin

Abstract Based on the merged 3D seismic data, well logging, formation testing, analysis and testing data, the structural evolution, sedimentary reservoirs, thermal evolution of source rocks were investigated of Paleogene Kongdian Formation in the trough area of Cangdong sag, Bohai Bay Basin. A conventional-unconventional hydrocarbon accumulation pattern in the trough area of rifted basin was revealed. The reservoir forming elements in the trough area of Cangdong sag have a zonation feature in terms of reservoirs and source rocks. There are two types of reservoir forming models, primary trough and reformed trough. The formation and evolution of trough controlled the orderly distribution of conventional oil to unconventional oil in the trough. Particularly, structural reservoirs occur in the upper part of the trough, stratigraphic-lithologic reservoirs are likely to form in the delta front deposits at the outer ring of trough, the middle ring transitional belt is the favorable site for tight oil reservoirs, while the fine grain deposits zone in the inner ring is shale oil and gas exploration area. The study has pointed out the new domains and directions for searching reserves in the secondary exploration of mature oilfields.

Petrologic and geochemical characteristics of high-quality saline lacustrine source rocks in western Qaidam Basin

The main oil source in western Qaidam Basin is the Paleogene saline lacustrine source rocks. Traditionally, it was considered that these source rocks were characterized by low abundance and poor type of organic matter as well as limited oil generation potential, but this poor source rock condition was very inconsistent with good hydrocarbon exploration results. A previous study has just confirmed that this area develops high-quality source rocks, which is of great significance for recognizing potential of hydrocarbon resource and consolidating confidence to search large and medium-sized oil and gas fields in western Qaidam Basin. Based on fine geochemical analysis of source rocks, petrology, element geochemistry and organic geochemistry are applied to discuss development conditions of high-quality source rocks in this area. The results showed that the saline lacustrine sediments in western Qaidam Basin were deposited in relatively shallow and quiet water with relatively high salinity and low nutrient content; influenced by the drought and cold climate, the terrigenous supply of fresh water was limited, and few aquatic organisms were developed. Good preservation condition is favorable for rapid preservation of oil generating biomass (such as aquatic organisms), to form source rocks rich in hydrogen element with high soluble organic matter content; but relatively lower paleo-productivity makes organic matter abundance lower than that in the eastern saline lacustrine basins. The semi-deep lake, with relatively low salinity and abundant nutrients, is the most favorable are for development of high-quality source rocks; the source rocks have large thickness in the sedimentary depression areas, but due to high water salinity and far away from the provenance area, the water stratification was obvious, so it have moderate to high organic matter abundance.

Evaluation of coal and shale reservoir in Permian coal-bearing strata for development potential: A case study from well LC-1# in the northern Guizhou, China

Indentifying reservoir characteristics of coals and their associated shales is very important in understanding the co-exploration and co-production potential of unconventional gases in Guizhou, China. Accordingly, comprehensive experimental results of 12 core samples from well LC-1# in the northern Guizhou were used and analyzed in this paper to better understand their vertical reservoir study. Coal and coal measured shale, in Longtan Formation, are rich in organic matter, with postmature stage of approximately 3.5% and shales of type III kerogen with dry gas generation. All-scale pore size analysis indicates that the pore size distribution of coal and shale pores is mainly less than 20 nm and 100 nm, respectively. Pore volume and area of coal samples influenced total gas content as well as desorbed gas and lost gas content. Obvious relationships were observed between residual gas and BET specific surface area and BJH total pore volume (determined by nitrogen adsorption). For shale, it is especially clear that the desorbed gas content is negatively correlated with BET specific surface area, BJH total pore volume and clay minerals. However, the relationships between desorbed gas and TOC (total organic carbon) as well as siderite are all well positive. The coals and shales were shown to have similar anoxic conditions with terrestrial organic input, which is beneficial to development of potential source rocks for gas. However, it may be better to use a low gas potential assessment for shales in coal-bearing formation because of their low S1+S2 values and high thermal evolution. Nevertheless, the coalbed methane content is at least 10 times greater than the shale gas content with low desorbed gases, indicating that the main development unconventional natural gas should be coalbed methane, or mainly coalbed methane with supplemented shale gas.

Impact of rift dynamics on palaeoenvironmental conditions and hydrocarbon system development (northern Upper Rhine Graben, SW Germany)

The Upper Rhine Graben (URG), a classical hydrocarbon (HC) province, is part of the European Cenozoic Rift System. The rift graben development has led to a complex basin fill of terrestrial and marine Cenozoic deposits, providing several HC source and reservoir units. The aim of this study is the multidisciplinary analysis of the palaeoenvironmental conditions and source-rock development within the transgressive marine intervals, and the palaeothermal history of the graben system to improve the understanding of the HC system development. Palaeoenvironmental conditions are strongly influenced by rift-related tectonic activity. Transgressive marine intervals in times of major subsidence show high terrestrial input from the graben shoulders, leading to mainly terrigenous gas-prone kerogen, while transgressive marine intervals during weak tectonic activity are dominated by marine–brackish palaeoenvironments and oil-prone kerogen. This differs clearly from the previously suggested HC potential of these intervals. Thermal maturation analysis shows nearly constant maturation with depth, which is atypical for burial-controlled maturation. It indicates significant secondary thermal overprinting related to long-lasting very hot hydrothermal fluid systems, concentrated along fault zones. Therefore the development of the depositional setting, kerogen composition, thermal maturation and the HC potential is directly linked to the dynamics of the rift system development. Supplementary material: detailed results of all three wells are available at https://doi.org/10.6084/m9.figshare.c.4183106

Factors controlling the petroleum generation characteristics of Palaeogene source rocks in the Austrian Molasse Basin as revealed by principal component analysis biplots

Abstract After Rock-Eval & TOC screening and heterogeneity evaluation on 91 Palaeogene source rock samples from a well drilled in the Austrian Molasse Basin, ten shale samples were selected for detailed investigations by means of pyrolysis-gas chromatography, bulk kinetics and biomarker identification and quantification. Afterwards, 2-D biplots based on principal component analysis were applied to unravel the palaeo-environmental control on the development of petroleum source rocks. All samples are immature source rocks with good petroleum generation potentials. The redox environment during deposition was generally reducing, and palaeosalinity is suggested to be the main factor causing the differences in organic carbon contents among the samples. The hydrogen index values, the gas generation preferences and the aromaticity of the products are controlled by both depositional environment and precursors, and the product of a salinity indicator (MTTC) and the oleanane index is introduced as predictive proxy to evaluate these features. The maturity indicator (Tmax) is revealed as dominated by the stability of the kerogen structure which is controlled by the proportion of organic sulphur compounds in the kerogen. The global Eocene-Oligocene climate change from a greenhouse to an icehouse world is suggested to play an important role in changing the palaeoenvironment and further in influencing the development of petroleum source rocks by triggering upwelling, increasing the palaeo-sea water salinity and decreasing the deposition of carbonate-minerals. The chemometric method suggested here acts as a powerful tool in identifying the controlling factors for the petroleum generation potential among many variables, and can be applied more widely in petroleum geology when multi-parameters are involved to get quick and meaningful correlations.

Genetic causes of oil-rich and oil-poor reservoirs: Implications from two Cenozoic basins in the eastern North China Craton

The Bohai Bay and Hehuai (southern North China) rift basins in the eastern part of the North China Craton are south-north-adjacent. They have shown synchronous evolutionary processes, and possess generally identical superficial and shallow structural characteristics as well as similar basin areas. However, there is a large difference in the richness of oil resources between the two basins. The Bohai Bay Basin has extremely abundant oil reserves, while commercial oil reserves have not been found in the Hehuai Basin. The deep tectonic structures, magmatic activities, and modern and paleo-geothermal fields of the two basins are significantly different. Compared with the Hehuai Basin, the Bohai Bay Basin has a thinner crust and more complex structure with multiple low-velocity layers. It is also characterized by intense magmatic activity, high modern and paleo-geothermal fields, frequent seismic activity, and active deep interactions, small effective elastic thickness of the isotropic lithosphere, and shorter balanced transformation wavelength of the lithosphere with a high likelihood of local compensation. The Hehuai Basin has a simple deep structure and homogeneous crustal composition, with a high likelihood of regional compensation. The characteristics of the deep structures mentioned above are generally similar to those of the southern part of the stable Ordos Basin, except for the smaller crust thickness. This indicates the presence of differences in Mesozoic destruction between the southern and northern zones in the eastern part of the North China Craton. The northern zone was subjected to significant destruction, while the southern zone was subjected to modifications, primarily in the form of local changes in the structures and/or properties of the crust or lithospheric mantle, with the overall structure and stability of the craton kept intact. The formation of high-quality source rock is primarily influenced by the abnormal flourishment of organisms in water bodies during the syndepositional period, and is also strongly associated with the high geothermal setting of basins and nutrients from hydrothermal solutions and volcanoes. In other words, it is mainly controlled by deep processes and deep-major fault activity. The differences in the deep structures and modern and paleo geothermal fields of the two basins correspond to the difference in richness of oil resources, suggesting that there is an important internal or causal relationship between the two aspects. This viewpoint coincides with the conditions and environments required for the development of high-quality source rock in hydrocarbon-rich basins (sags) in China and other countries, and is evidenced by the modern lake basin of the East African Rift. A new hydrocarbon generation model is proposed in this work: petroleum is a comprehensive product of the integration of bioenergy, thermal energy, and other related energies (such as chemical and kinetic energy) and their interactions; the degree of richness of petroleum is generally controlled by the regional tectonic structure, thermal environment, and deep processes; nonmarine basins or depressions with abundant resources are closely related to active deep processes, intense exchange of material between the deep and shallow layers, participation of external hydrocarbons, and energy integration and conversion.

Discovery of the lower Cambrian high-quality source rocks and deep oil and gas exploration potential in the Tarim Basin, China

The global Precambrian–Cambrian system includes an important series of hydrocarbon-bearing strata. However, because rocks of this age are typically deeply buried, few petroleum exploration breakthroughs have been made, and the presence of source rocks remains somewhat controversial. Recently, commercial condensate and gas were discovered from the deep (∼6900 m [∼22,600 ft]) Zhongshen 1C (ZS1C) exploratory well drilled in the Tazhong uplift of the Tarim Basin, China, leading to renewed interest in the development of Cambrian source rocks in the basin. On the basis of outcrop reconnaissance and sample testing from around the Tarim Basin, we show that a set of high-quality source rocks were developed within the lower Cambrian Yuertusi Formation (J1y), at the base of the lower Cambrian. These rocks are black shales and typically have a total organic carbon content between 2% and 6% but extending as high as 17% in selected regions. This marine sequence is 10–15 m (33–49 ft) thick in some outcrops along the margins of the basin. Seismic data indicate that these high-quality source rocks may cover an area as large as 260,000 km2 (100,000 mi2). Their main organic parent material was benthic multicellular algae. On the basis of high-temperature thermal simulations conducted on these source rocks, we show that the gas composition and carbon isotopes from the ZS1C well are similar to the products generated at a thermal evolution stage corresponding to a vitrinite reflectance of between 2.2% and 2.5%. Late-stage natural gas accumulated within these rocks over time. The δ34S correlation of organic sulfur compounds in the condensate with Cambrian sulfates provides further evidence for a J1y source rock origin of the ZS1C condensate and gas. The Cambrian dolomites in association with a salt seal exhibit favorable geological conditions for large-scale hydrocarbon accumulation. A new set of deep exploration strata can, therefore, be developed, guiding future deep Cambrian hydrocarbon exploration in the Tarim Basin.

Hydrocarbon expulsion history in Kuonamka formation of North Tunguska Petroleum region

The computer modelling results for Kuonamka source rock evolution in catagenesis are represented for the area of North Tunguska petroleum region for pre-igneous period. Petroleum generation hotbeds are determined. Petroleum resources indirect assessment is made for Kuonamka source rock for pre-igneous period.

Burial and thermal evolution of coal-bearing strata and its mechanisms in the southern North China Basin since the late Paleozoic

During the interaction between the South China plate and the North China plate, the southern North China Basin (SNCB) underwent a strong tectonic thermal evolution in the early Mesozoic. Recently, burial history reconstruction and thermal maturity simulation of coal-bearing strata from the Late Carboniferous to the present were carried out in the SNCB. Rock-Eval pyrolysis (12 samples), vitrinite reflectance (60 samples), apatite fission track (AFT) analysis (17 samples), and PetroMod 1D were performed on wells located in the SNCB. Geothermal gradients were found to range between 30.3 and 36.4 °C/km, averaging 31.0 °C/km, and present heat flow was found to vary between 51 and 58, averaging 55 mW/m2. The paleo heat flow model with higher heat flow peaks of 86 mW/m2 during the first rifting phase resulted in the best fit between the calculated and the observed vitrinite reflectance and bottom hole temperatures in the modeling. Using this model of thermal maturity history combined with AFT analysis, we analyze the main hydrocarbon generation stages and discuss the coupling relationship of thermal maturity history with tectonic evolution. The results indicate that tectonic activities restrict the thermal maturity evolution of source rocks to a large extent by controlling the geotemperature. The thermal history demonstrates that two phases of heating (315–163 Ma, 83–38 Ma, depositing) happened to the source rocks, separated by two cooling (163–83 Ma, 38–23 Ma, uplifting) events. The maturity history indicates that the process of hydrocarbon generation can be divided into three stages in the SNCB (315–163 Ma, thermal genesis gas generation stage; 163–83 Ma, gas reservoir destruction stage; 83–0 Ma, secondary biogas generation stage). Hydrocarbon generation started as early as 198 Ma with a peak at 162 Ma, and expulsion started at around 195 Ma. The Taiyuan and Shanxi formations' source rocks reached a high maturity (1.0% < Ro < 1.3%) with a greater potential for hydrocarbon generation, and the Xiashihezi formation is mid-mature (0.7% < Ro < 1.0%) with limited hydrocarbon generation potential at the present day.

Relationship between source rock development and petroleum accumulation in the Erlian Basin, northern China

AbstractThe Wuli and Saihan sags in the Erlian Basin, the most petroliferous basin in northern China, were analysed with bulk geochemical analysis, carbon isotopic composition, microthermometry of fluid inclusions, and basin modelling to characterize the organic matter abundance and composition, to construct source rock development models, and to reveal the relationship between source rock development and hydrocarbon accumulation. The samples display wide variations in total organic carbon content and Rock‐Eval indices, suggesting heterogeneity of organic matter richness and type. The Wuli Sag has oxic depositional environment, high productivity, and high total organic carbon content; the effective oil source rocks are mainly distributed in the deep sag where the productivity is high; and there is plenty of organic matter left and preserved after degradation. In the Saihan Sag, there is a small amount of organic matter deposited because of low productivity; the effective oil source rocks are mainly distributed in the slope by the deep sag where the reducing degree is the strongest. The source rock development models controlled the geochemical characteristics and distribution of source rocks, which are the keys to hydrocarbon potential and accumulation. The oil of Wuli Sag is mainly distributed in the deep sag, whereas the oil of Saihan Sag is mainly distributed in the slope by deep sag, which is in agreement with the previously effective oil source rocks distribution. In the strong division sags, the region where source rock distributed is beneficial to hydrocarbon accumulation. The conclusions may have important implications for petroleum exploration in other small lacustrine depositional systems.

Characteristics and genetic types of natural gas in the northern Dongpu Depression, Bohai Bay Basin, China

The Dongpu Depression, especially the northern part, is an important natural gas-rich area in the Bohai Bay Basin, China. The gases found in Es3M, Es3L and Es4 are mainly distributed in the western part of Qianliyuan, in Weicheng, and in the middle of the Wenliu area, respectively. However, few studies have been conducted on the relationship between the development of source rock and the enrichment of gas in different hydrocarbon-generating sags. In this paper, gas genetic types, distribution characteristics and gas-source correlations were analyzed using data from molecular and stable carbon isotope components of natural gas, biomarkers and thin sections. The results indicate that Es3M gas is predominantly oil-type gas and that Es3L gas is mainly mixed gases dominated by coal-type gas, with average dryness coefficients (C1/C1–5) of 0.877 and 0.920, respectively. By contrast, Es4 gas is dry with an average dryness coefficient of 0.970 and displays the typical characteristics of coal-type gas from Carboniferous-Permian coal measures. Carbon isotope reversals are common in the gas samples, while their causes are different. The mixing of coal-type gas and oil-type gas is the main reason for the gas carbon isotope reversals in Es3M and Es3L. By contrast, the widely existing carbon isotope reversal in Es4 gas in the central part of Wenliu is related to the long-term migration and enrichment of coal-type gas from Carboniferous-Permian rocks. Gas-source correlations indicate that Es3M gas is predominantly from the in situ cracking of Es3M oil and that coal-type gas mixed within Es3L gas is from the Carboniferous-Permian coal measures.