Anhydrous Pyrolysis Research Articles

Composition and Evolution of Hydrogen Isotopes ofn‐Akanes Generated from Anhydrous Pyrolysis of Sediments from Lake Gahai, Gannan, China

AbstractTo understand the thermal evolution of lacustrine sedimentaryn‐alkane hydrogen isotopic composition (δD), especially bacterially derivedn‐alkanes, anhydrous thermal simulation experiments were performed with sediments from Lake Gahai (Gannan, China). We analyzed the original and pyrolysis‐generatedn‐alkanes and theirδDvalues. The results showed that thermal maturity andn‐alkane origins significantly affected the distribution of pyrolysis‐generatedn‐alkanes. In immature to post‐mature sediments, the bacterial‐derived medium‐chainn‐alkanes generally had depletedδDvalues. The maximum difference in averageδDvalues between the bacterial‐and herbaceous plant‐derived medium‐chainn‐alkanes was 32‰, and the maximum difference inδDvalues among individualn‐alkanes was 59‰. We found that the averageδDvalue of pyrolysis‐generatedn‐alkanes from different latitude was significantly different in immature to highly mature sediments, but similar in post‐mature ssediments. The hydrogen isotopes of sedimentaryn‐alkanes can be used as indicators for paleoclimate/paleo‐environment conditions only when sediments are immature to highly mature. During thermal evolution, theδDvalue of generated individualn‐alkanes and the averageδDvalue increased with thermal maturity, indicating that hydrogen isotopes of sedimentaryn‐alkanes can be used as an index of organic matter maturity. We established mathematical models of averageδDvalues of generatedn‐alkanes from immature to post‐mature sediments usingnC21−‐/nC21+and average chain lengths. These results improve our understanding of the distribution andδDvalue of sedimentaryn‐alkanes derived from herbaceous plants in mid‐latitude plateau cold regions.

Thermal evolution of steroids during anhydrous pyrolysis of cholesterol with and without elemental sulfur

Steroids are widely used in geochemical studies. They are common in living organisms, sediments and petroleum, and the diagenetic pathways of steroidal compounds in the subsurface are reasonably well understood. However, there are still some questions concerning their thermal evolution (i.e., isomerization, aromatization, and cracking), such as the rates of formation and alteration of various steroidal compounds and the effects of catalysis on these processes, specifically the possible influence of sulfur-containing species. To address these questions, cholesterol and a mixture of cholesterol and elemental sulfur were reacted to simulate the thermal evolution pathways of steroids in the laboratory. Anhydrous pyrolysis experiments were conducted in sealed gold tubes at temperatures ranging from 150 °C to 600 °C using heating rates of 2 °C/h and 20 °C/h, and the products were analyzed by gas chromatography and gas chromatography-mass spectrometry. For the pure cholesterol experiments, the formation of sterenes, steranes and monoaroamtic steroids, and finally triaromatic steroids occurred at EasyRo ~ 0.42%, 0.73%, and 1.36%, respectively. All species were converted into smaller moieties such as phenanthrenes, pyrenes, etc., at EasyRo > 1.69%. The presence of elemental sulfur in the pyrolysis experiments significantly increased the rate of the thermal evolution of steroids, with an earlier onset of the generation of smaller moieties such as methylphenanthrenes and dimethylphenanthrenes at EasyRo 0.86%. Diasterenes and diasteranes were not observed in either the pure cholesterol or the cholesterol with elemental sulfur experiments. The aromatization path starting from the C-ring of steroids was not observed in the experiments using pure cholesterol but occurred in the sulfur-containing series. The presence of sulfur significantly increased the rate of isomerization and aromatization of steranes, especially sterane ring isomerization, and increased the equilibrium values of isomerization parameters by 0.1–0.2 compared to that of the pure cholesterol series. These findings indicate that the presence of sulfur-containing species has important implications for the thermal evolution of steroids.

Organic-induced nanoscale pore structure and adsorption capacity variability during artificial thermal maturation: Pyrolysis study of the Mesoproterozoic Xiamaling marine shale from Zhangjiakou, Hebei, China

This research analyzed two low-maturity Mesoproterozoic Xiamaling marine shale samples with different TOC contents in Zhangjiakou of Hebei, China. Artificial anhydrous pyrolysis experiment simulated the thermal evolution process of the shale sample from low maturity to over maturity. The evolution characteristics of geochemical parameters and mineralogy of shales with the increase in maturity were investigated. A general evolution model of nanoscale pore structure and methane adsorption content (MSC) was established. Results show that hydrocarbon generation and mineral conversion promote the generation, development, combination, and rearrangement of nanoscale pores in shale samples with the increase in thermal maturation. The maturity increase helps facilitate the generation and evolution of pores in shales. Heating can promote the generation, development, and evolution of nanoscale pores, and this condition can contribute to forming large pore volume and surface area. The formation and evolution of the nanoscale pores in shale can be roughly subdivided into adjustment, development, combination, and rearrangement stages. Nanoscale pore structure parameter and MSC decrease and reach the minimum value as the temperature reaches 350 °C in the adjustment stage. Then, they rise and reach the maximum value at approximately 650 °C during the development stage. Finally, they decline again as the pyrolysis temperature rises at the combination and rearrangement stages. The general evolution model of nanoscale pore structure and MSC was proposed and subdivided into three stages by combining the hydrocarbon generation, mineral conversion, nanoscale pore structure, and MSC evolution of the thermal simulation shale samples. The differences in organic geochemical index, mineral characteristics, nanoscale pore structure, and MSC evolution characteristics of the simulated samples are mainly due to the difference in their TOC content.

Gas generation from coal: taking Jurassic coal in the Minhe Basin as an example

The gas generation features of coals at different maturities were studied by the anhydrous pyrolysis of Jurassic coal from the Minhe Basin in sealed gold tubes at 50 MPa. The gas component yields (C1, C2, C3, i-C4, n-C4, i-C5, n-C5, and CO2); the δ13C of C1, C2, C3, and CO2; and the mass of the liquid hydrocarbons (C6+) were measured. On the basis of these data, the stage changes of δ13C1, δ13C2, δ13C3, and δ13CO2 were calculated. The diagrams of δ13C1–δ13C2 vs ln (C1/C2) and δ13C2–δ13C1 vs δ13C3–δ13C2 were used to evaluate the gas generation features of the coal maturity stages. At the high maturity evolution stage (T > 527.6 °C at 2 °C/h), the stage change of δ13C1 and the CH4 yield are much higher than that of CO2, suggesting that high maturity coal could still generate methane. When T < 455 °C, CO2 is generated by breaking bonds between carbons and heteroatoms. The reaction between different sources of coke and water may be the reason for the complicated stage change in delta^{{{13}}} {text{C}}_{{{text{CO}}_{{2}} }} when the temperature was higher than 455 °C. With increasing pyrolysis temperature, δ13C1–δ13C2 vs ln (C1/C2) has four evolution stages corresponding to the early stage of breaking bonds between carbon and hetero atoms, the later stage of breaking bonds between carbon and hetero atoms, the cracking of C6+ and coal demethylation, and the cracking of C2–5. The δ13C2–δ13C1 vs δ13C3–δ13C2 has three evolution stages corresponding to the breaking bonds between carbon and hetero atoms, demethylation and cracking of C6+, and cracking of C2–5.

Hydrogen Isotope Composition of n-Alkanes Generated during Anhydrous Pyrolysis of Peats from Different Environments

The variation and its level of hydrogen isotopic composition of individual n-alkanes in sediments from different latitudes and climatic environments from immature to post-mature are still unclear. ...

Shale gas reserve evaluation by laboratory pyrolysis and gas holding capacity consistent with field data

Exploration for shale gas occurs in onshore basins, with two approaches used to predict the maximum gas in place (GIP) in the absence of production data. The first estimates adsorbed plus free gas held within pore space, and the second measures gas yields from laboratory pyrolysis experiments on core samples. Here we show the use of sequential high-pressure water pyrolysis (HPWP) to replicate petroleum generation and expulsion in uplifted onshore basins. Compared to anhydrous pyrolysis where oil expulsion is limited, gas yields are much lower, and the gas at high maturity is dry, consistent with actual shales. Gas yields from HPWP of UK Bowland Shales are comparable with those from degassed cores, with the ca. 1% porosity sufficient to accommodate the gas generated. Extrapolating our findings to the whole Bowland Shale, the maximum GIP equate to potentially economically recoverable reserves of less than 10 years of current UK gas consumption.

Carbon and hydrogen isotope fractionation for methane from non-isothermal pyrolysis of oil in anhydrous and hydrothermal conditions

In this study, to ascertain the carbon and hydrogen isotope fractionation of oil cracking gas (secondary gas) in hydrothermal conditions, non-isothermal pyrolysis of oil with and without water was carried out by a gold-tube system. By determination of the yields of individual gas products, it is found that the presence of water enhanced the yields of hydrocarbon gases. However, kinetic calculations indicate that Ea for the generation of methane and C2–5 in pyrolysis in hydrothermal conditions are essentially identical with those in anhydrous pyrolysis. The yields of carbon dioxide (CO2) and alkene gases in pyrolysis in hydrothermal conditions are evidently higher than those in anhydrous pyrolysis. It is reasonable that water–hydrocarbon reactions occurred and contributed to the generation of secondary gas in hydrothermal conditions. Meanwhile, the presence of water resulted in a slight depletion of 13C for methane and an evident depletion of 13C for CO2. Thermodynamic calculations suggest that water–hydrocarbon reactions in non-isothermal pyrolysis are dominated by free radical mechanism rather than ionic mechanism. Moreover, δ2H values of methane are apparently different in pyrolysis involving water with different δ2H. This result demonstrates that water provided hydrogen for hydrocarbon gas generation. Finally, we established mathematical models based on isotope fractionation to quantitatively determine the contribution of water–hydrocarbon reactions for gas generation in both experimental and geological conditions.

The catalytic effect of manganese carbonate on kerogen pyrolysis in the absence and presence of water

To investigate the effect of Mn ore on the chemical components and isotopic compositions of gas products during kerogen pyrolysis in the absence or presence of water, a series of pyrolysis experiments on Type-I kerogen with manganese carbonate and/or water were conducted in closed gold capsules at 325–600 °C for 72 h with 300 bar. The heavy hydrocarbon gas yields increased significantly over 450 °C due to the participation of manganese. As for isotopic compositions, the manganese catalysis caused a decrease in the 13CCH4 and an increase in the 13CC2H6 over 475 °C; the δD values of methane generated during anhydrous pyrolysis with manganese carbonate are much lower than those produced by the pyrolysis of kerogen alone. Furthermore, the δD values are the most negative during hydrous pyrolysis with manganese ore. In addition to the thermal decomposition of manganese carbonate to form carbon dioxide, water provides sources of hydrogen and oxygen to form H2 and CO2. Manganese carbonate inhibits the association of sulfur-free radicals to hydrogen to form H2S. The i-C4/n-C4 ratio for gas products was evidently higher due to the existence of manganese and water, they can enhance the carbocation mechanism.

Evolution characteristics and model of nanopore structure and adsorption capacity in organic-rich shale during artificial thermal maturation: A pyrolysis study of the Mesoproterozoic Xiamaling marine shale with type II kerogen from Zhangjiakou, Hebei, China

Thermal maturity has a considerable impact on hydrocarbon generation, mineral conversion, nanopore structure, and adsorption capacity evolution of shale, but that impact on organic-rich marine shales containing type II kerogen has been rarely subjected to explicit and quantitative characterization. This study aims to obtain information regarding the effects of thermal maturation on organic matter, mineral content, pore structure, and adsorption capacity evolution of marine shale. Mesoproterozoic Xiamaling immaturity marine oil shale with type II kerogen in Zhangjiakou of Hebei, China, was chosen for anhydrous pyrolysis to simulate the maturation process. With increasing simulation temperature, hydrocarbon generation and mineral transformation promote the formation, development, and evolution of pores in the shale. The original and simulated samples consist of closed microspores and one-end closed pores of the slit throat, all-opened wedge-shaped capillaries, and fractured or lamellar pores, which are related to the plate particles of clay. The increase in maturity can promote the formation and development of pores in the shale. Heating can also promote the accumulation, formation, and development of pores, leading to a large pore volume and surface area. The temperature increase can promote the development of pore volume and surface area of 1–10 and 40-nm diameter pores. The formation and development of pore volume and surface area of 1–10 nm diameter pores are more substantial than that of 40-nm diameter pores. The pore structure evolution of the sample can be divided into pore adjustment (T &lt; 350°C, EqRo &lt; 0.86%), development (350°C &lt; T &lt; 650°C, 0.86% &lt; EqRo &lt; 3.28%), and conversion or destruction stages (T &gt; 650°C, EqRo &gt; 3.28%). Along with the increase in maturity, the methane adsorption content decreases in the initial simulation stage, increases in the middle simulation stage, and reaches the maximum value at 650°C, after which it gradually decreases. A general evolution model is proposed by combining the nanopore structure and the adsorption capacity evolution characteristics of the oil shale.

Comparative Study of Hydrogen and Carbon Isotopic Composition of Gases Generated from the Pyrolysis of a Peat under Saltwater and Freshwater Conditions

AbstractTo understand the influence of the diagenetic water medium on the isotopic compositions of thermogenic coalbed gas, both hydrous and anhydrous closed‐system pyrolyses were performed at temperatures of 250°C to 650°C on an herbaceous marsh peat. Compared to the results of anhydrous pyrolysis, the hydrocarbon gases generated from hydrous pyrolyses have very different hydrogen isotopic compositions. However, the carbon isotopic compositions of the hydrocarbon gases became only slightly heavier in hydrous pyrolysis, compared to that from anhydrous pyrolysis. With the progress of thermal evolution from peat to a more advanced thermal maturity of vitrinite reflectance values (Ro) of 5.5% during the pyrolysis, the difference in the average δD value increased from 52‰ to 64‰ between the hydrous pyrolysis with saltwater and anhydrous pyrolysis and increased from 18‰ to 29‰ between the hydrous pyrolysis with freshwater and anhydrous pyrolysis, respectively. The difference in the average δ13C value was only 1‰–2‰ between the hydrous and anhydrous pyrolysis. The relationships between the δD values of the generated hydrocarbon gases and Ro values as well as among δD values of the hydrocarbon gas species are established. The close relationships among these parameters suggest that the water medium had a significant effect on the hydrogen isotopic composition and a minimal effect on the carbon isotopic composition of the hydrocarbon gases. The results of these pyrolyses may provide information for the understanding of the genesis of coalbed gas from herbaceous marsh material with the participation of different diagenetic water media.

Comparative Study of PtCo/MNC and PtCo/Rgo As Anodic Electrocatalysts for Methanol Electro-Oxidation in Acid Medium

PtCo/MNC and PtCo/rGO as anodic electrocatalysts (20 wt% Pt loading) have been synthesized by non-sequential co-impregnation method and chemical reduction route using citric acid and Ar-H2 static atmosphere. Micro-/nano-structured carbon (MNC) sample was synthesized via nanocasting process with anhydrous pyrolysis at 800 °C using SBA-15 as hard template and refined sugar as carbon source. SBA-15 was prepared via sol gel using pluronic P-123 as surfactant. GO was prepared via Hummers modified method. The prepared materials were characterized by means of N2 physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and high resolution transmission electron microscopy (HRTEM). The performance of PtCo/MNC for methanol oxidation reaction (MOR) was measured by cyclic voltammetry (CV), chronoamperometry (CA). The electrochemical characterization techniques revealed that the mass activity of PtCo/MNC, PtCo/rGO and the commercial electrocatalyst PtRu/C at 20 cycles were 473, 322 and 300 mA/mgPt respectively as well as the carbon monoxide tolerance index ICO for these catalysts were 1.38, 1.56 and 0.93 respectively. PtCo/rGO exhibit better electrocatalytic performance, electrochemical stability and best resistance to carbonaceous intermediates species for the electro-oxidation of methanol.

Thermal alteration of biomarkers in the presence of elemental sulfur and sulfur-bearing minerals during hydrous and anhydrous pyrolysis

Although elemental sulfur and sulfur-bearing minerals are not the main constituents of sedimentary rock, they are still important for the formation and destruction of biomarkers. In this study, a bitumen of Sichuan Basin mudstone with abundant biomarkers was separately pyrolyzed (under both hydrous and anhydrous conditions) with elemental sulfur (S0) and sulfur-bearing minerals (including pyrite, ferrous sulfate, and ferric sulfate) at various temperatures (300, 330 and 350 °C). The results show that the effects of different forms of sulfur on the evolution of biomarkers vary. Pyrite (FeS2) had only a slight influence on the characteristics of the biomarkers during anhydrous and hydrous pyrolysis. On the other hand, the presence of S0, ferrous sulfate (FeSO4) and ferric sulfate (Fe2(SO4)3) promoted the thermal cracking of the biomarkers and changed the biomarker distributions under anhydrous conditions. The extent of biomarker thermal alterations decreased in the following order: S0 > Fe2(SO4)3 > FeSO4 > FeS2. Additionally, the presence of water seemed to promote the effects of the sulfur additive on the changes in biomarker compositions, but this did not change their raking in terms of influence. The elemental sulfur alteration of the biomarkers increased with pyrolysis temperature (simulated maturity) and the abundance of elemental sulfur in the sample. The results obtained offer new insights into how biomarkers evolve when elemental sulfur and sulfur-bearing minerals are present.

Experimental Investigation of Evolution of Pore Structure in Longmaxi Marine Shale Using an Anhydrous Pyrolysis Technique

To better understanding the evolutionary characteristics of pore structure in marine shale with high thermal maturity, a natural Longmaxi marine shale sample from south China with a high equivalent vitrinite reflectance value (Ro = 2.03%) was selected to conduct an anhydrous pyrolysis experiment (500–750 °C), and six artificial shale samples (pyrolysis products) spanning a maturity range from Ro = 2.47% to 4.87% were obtained. Experimental procedures included mercury intrusion, nitrogen adsorption, and carbon dioxide adsorption, and were used to characterize the pore structure. In addition, fractal theory was applied to analyze the heterogeneous pore structure. The results showed that this sample suite had large differences in macropore, mesopore, and micropore volume (PV), as well as specific surface area (SSA) and pore size distributions (PSD), at different temperatures. Micropore, mesopore, and macropore content increased, from being unheated to 600 °C, which caused the pore structure to become more complex. The content of small diameter pores (micropores and fine mesopores, &lt;10 nm) decreased and pores with large diameters (large mesopores and macropores, &gt;10 nm) slightly increased from 600 to 750 °C. Fractal analysis showed that larger pore sizes had more complicated pore structure in this stage. The variance in pore structure for samples during pyrolysis was related to the further transformation of organic matter and PSD rearrangement. According to the data in this study, two stages were proposed for the pore evolution for marine shale with high thermal maturity.

Highly dispersed PtCo nanoparticles on micro/nano-structured pyrolytic carbon from refined sugar for methanol electro-oxidation in acid media

Abstract In this work, anodic electrocatalyst (20%wt of metal loading) as PtCo nanoparticles (atomic ratio of 48:52) on micro/nano-structured pyrolytic carbon (MNC) was synthesized by sequential impregnation method and chemical reduction route using citric acid and Ar-H2 static atmosphere. MNC sample was synthesized via nanocasting process with anhydrous pyrolysis at 800 °C using SBA-15 as hard template and refined sugar as carbon source. SBA-15 was prepared via sol gel using pluronic P-123 as surfactant and tetraethoxysilane as silica precursor. The prepared materials were characterized by means of N2 physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and high resolution transmission electron microscopy. The performance of PtCo/MNC for methanol oxidation reaction (MOR) was measured by cyclic voltammetry, chronoamperometry. The electrochemical characterization techniques revealed that the mass activity of PtCo/MNC and the commercial electrocatalyst Pt/C (20%wt of Pt loading) at 20 cycles were 481 and 372 mA/mgPt respectively as well as the resistance to the accumulation intermediate carbonaceous species (methoxy, aldehyde, formaldehyde and carbon monoxide) denoted by the ratio If/Ib for these catalysts were 1.30 and 0.76 respectively. PtCo/MNC exhibit better electrocatalytic performance, electrochemical stability and best resistance to carbonaceous intermediates species in the electro-oxidation of methanol.

The effect of organic matter type on formation and evolution of diamondoids

A series of anhydrous pyrolysis experiments, using sealed gold tubes, were performed on three types of kerogen to investigate the effect organic matter type has on the generation and evolution of thermogenic diamondoids. Based on the compositional variation of pyrolysis products, the cracking of kerogens can be divided into three stages: oil generation (0.6%–1.5% EasyRo), wet-gas generation (1.5%–2.1% EasyRo) and dry-gas generation (>2.1% EasyRo). The experimental results indicate that diamondoids were mainly generated in the oil and wet-gas generation stages and decomposed in the dry-gas generation stage. In addition to thermal maturity, the formation of diamondoids is also influenced by the type of organic matter. Type I and IIA kerogens produced more diamondoids than Type III kerogen, and diamondoids generated from Type III kerogen were dominantly adamantanes. Therefore, the concentration and concentration ratios of diamondoids can be used to assess the maturity of source rocks (1.0%–1.5% EasyRo) and determine the type of organic matter (1.0%–2.0% EasyRo). Isomerization ratios of diamondoids depend mainly on thermal maturity and the type of organic matter has little effect. The use of isomerization ratios to determine thermal maturity is best for source rocks at higher maturity levels (1.5%–3.0% EasyRo). Therefore, bivariate diagrams of concentration versus isomerization indices of diamondoids (e.g., DMAs/MDs vs. DMAI-1 and DMAs/MDs vs. TMAI-1) can be used to evaluate the source rock maturity over a wider EasyRo range (1.0%–3.0% EasyRo) than single diamondoid parameters. As there are differences in the concentration and distribution of diamondoids in the extracts of three source rocks, the possibility exists to use diamondoid indices of immature rocks to determine the type of source rock.

Property changes of oil shale during artificial maturation: The Irati Formation from the Paraná Basin, Brazil

Acquiring elastic property information from oil shale during pyrolysis remains a difficult endeavor. We subject oil shale samples from the Irati Formation in the Paraná Basin, Brazil, to high-temperature, high-pressure hydrous and anhydrous pyrolysis while simultaneously acquiring P- and S-waveform data. We present elastic properties as a function of temperature at constant differential pressure using samples cored in three different directions relative to the bedding plane. Hydrous pyrolysis decreased total organic carbon (TOC) in samples from 25 wt% to 20 wt%, whereas anhydrous pyrolysis had no significant change in TOC. The cores experienced higher strain hysteresis (up to –0.094 residual axial strain) after hydrous pyrolysis compared to after anhydrous pyrolysis ([Formula: see text] residual axial strain). The larger residual strain was accompanied by a larger increase in shear velocity up to 35% after hydrous pyrolysis as compared to the 3% shear velocity increase after anhydrous pyrolysis. The change could be a result of compression and loss of organic content determined at an ambient temperature of 25°C. We quantified sample changes using X-ray computed tomography, scanning electron microscopy, source rock analysis, and X-ray diffraction before and after pyrolysis. Our data on elastic properties and Thomsen’s parameters during pyrolysis can be used to extract material property information useful for improving subsurface well logging and 4D seismic to produce efficiently from oil shale formations.

Effects of oil expulsion and pressure on nanopore development in highly mature shale: Evidence from a pyrolysis study of the Eocene Maoming oil shale, south China

The influence of oil-expulsion efficiency on nanopore development in highly mature shale was investigated by using anhydrous pyrolysis (425–600 °C) on solvent-extracted and non-extracted shales at a pressure of 50 MPa. Additional pyrolysis studies were conducted using non-extracted shales at pressures of 25 and 80 MPa to further characterize the impact of pressure on pore evolution at high maturity. The pore structures of the original shale and relevant artificially matured samples after pyrolysis were characterized by using low-pressure nitrogen and carbon-dioxide adsorption techniques, and gas yields during pyrolysis were measured. The results show that oil-expulsion efficiency can strongly influence gas generation and nanopore development in highly mature shales, as bitumen remained in shales with low oil expulsion efficiency significantly promotes gaseous hydrocarbon generation and nanopore (diameter < 10 nm) development. The evolution of micropores and fine mesopores at high maturity can be divided into two main stages: Stage I, corresponding to wet gas generation (EasyRo 1.2%–2.4%), and Stage II, corresponding to dry gas generation (EasyRo 2.4%–4.5%). For shales with low oil expulsion efficiency, nanopore (diameter < 10 nm) evolution increases rapidly in Stage I, whereas slowly in Stage II, and such difference between two stages may be attributed to the changes of the organic matter (OM)’s mechanical properties. Comparatively, for shales with high oil expulsion efficiency, the evolution grows slightly in Stage I, not as rapidly as shales with low efficiency, and decays in Stage II. The different pore evolution behaviors of these two types of shales are attributed to the contribution of bitumen. However, the evolution of medium–coarse mesopores and macropores (diameter >10 nm) remains flat at high maturation. In addition, high pressure can promote the development of micropores and fine mesopores in highly mature shales.

Effects of U-ore on the chemical and isotopic composition of products of hydrous pyrolysis of organic matter

In order to investigate the impact of U-ore on organic matter maturation and isotopic fractionation, we designed hydrous pyrolysis experiments on Type-II kerogen samples, supposing that the water and water–mineral interaction play a role. U-ore was set as the variable for comparison. Meanwhile, anhydrous pyrolysis under the same conditions was carried out as the control experiments. The determination of liquid products indicates that the presence of water and minerals obviously enhanced the yields of C15+ and the amounts of hydrocarbon and non-hydrocarbon gases. Such results may be attributed to water-organic matter reaction in the high-temperature system, which can provide additional hydrogen and oxygen for the generation of gas and liquid products from organic matter. It is found that δD values of hydrocarbon gases generated in both hydrous pyrolysis experiments are much lower than those in anhydrous pyrolysis. What is more, δD values are lower in the hydrous pyrolysis with uranium ore. Therefore, we can infer that water-derived hydrogen played a significant role during the kerogen thermal evolution and the hydrocarbon generation in our experiments. Isotopic exchange was facilitated by the reversible equilibration between reaction intermediaries with hydrogen under hydrothermal conditions with uranium ore. Carbon isotopic fractionations of hydrocarbon gases were somehow affected by the presence of water and the uranium ore. The increased level of i-C4/n-C4 ratios for gas products in hydrous pyrolysis implied the carbocation mechanism for water-kerogen reactions.

Pyrite‐hydrocarbon Interaction under Hydrothermal Conditions: an Alternative Origin of H2S and Organic Sulfur Compounds in Sedimentary Environments

AbstractSulfate rocks and organic sulfur from sedimentary organic matter are conventionally assumed as the original sulfur sources for hydrogen sulfide (H2S) in oil and gas reservoirs. However, a few recent experiments preliminarily indicate that the association of pyrite and hydrocarbons may also have implications for H2S generation, in which water effects and natural controls on the evolution of pyrite sulfur into OSCs and H2S have not been evaluated. In this study, laboratory experiments were conducted from 200 to 450°C to investigate chemical interactions between pyrite and hydrocarbons under hydrothermal conditions. Based on the experimental results, preliminary mechanism and geochemical implications were tentatively discussed. Results of the experiments showed that decomposition of pyrite produced H2S and thiophenes at as low as 330°C in the presence of water andn‐pentane. High concentrations of H2S were generated above 450°C under closed pyrolysis conditions no matter whether there is water in the designed experiments. However, much more organic sulfur compounds (OSCs) were formed in the hydrous pyrolysis than in anhydrous pyrolysis. Generally, most of sulfur liberated from pyrite at elevated temperatures was converted to H2S. Water was beneficial to breakdown of pyrite and to decomposition of alkanes into olefins but not essential to formation of large amounts of H2S, given the main hydrogen source derived from hydrocarbons. In addition, cracking of pyrite in the presence of 1‐octene under hydrous conditions was found to proceed at 200°C, producing thiols and alkyl sulfides. Unsaturated hydrocarbons would be more reactive intermediates involved in the breakdown of pyrite than alkanes. The geochemistry of OSCs is actually controlled by various geochemical factors such as thermal maturity and the carbon chain length of the alkanes. This study indicates that the scale of H2S gas generated in deep buried carbonate reservoirs via interactions between pyrite and natural gas should be much smaller than that of thermochemical sulfate reduction (TSR) due to the scarcity of pyrite in carbonate reservoirs and the limited amount of long‐chained hydrocarbons in natural gas. Nevertheless, in some cases, OSCs and/or low contents of H2S found in deep buried reservoirs may be associated with the deposited pyrite‐bearing rock and organic matters (hydrocarbons), which still needs further investigation.

Formation and evolution of solid bitumen during oil cracking

Solid bitumen is widespread throughout lower Paleozoic paleo-reservoirs in southern China. However, the processes that control its formation and evolution remain unclear. Here, we document temporal changes in the yield and characteristics of solid bitumen generated during oil cracking using an experimental approach involving the anhydrous pyrolysis of crude oil. The results indicate that solid bitumen is predominantly produced in environments of high thermal maturity associated with the dry gas stage of oil cracking (i.e., during rapid methane generation and C2–C5 gaseous hydrocarbon destruction), with maximum solid bitumen yields up to about 42% of the original amount of crude oil. A near linear relationship exists between solid bitumen yields and methane abundance during the main stage of solid bitumen formation, although there is no clear variation in the δ13C values of solid bitumen produced at any stage of this process. This suggests that the isotopic composition and distribution of solid bitumen within a reservoir can be used to identify hydrocarbon sources, delineate the range of paleo-reservoirs, and assess the size of paleo-oil reservoirs and oil-cracked gas reservoirs within a basin.