Hydropyrolysis Research Articles

Semi-closed hydrous pyrolysis of type I source rock using formation water: Implications for biomarker behaviour under supercritical conditions

Hydrous pyrolysis is a useful artificial method to simulate hydrocarbon generation process and investigate the geochemical behaviour of biomarkers with the presence of water, which has great importance for conventional and unconventional oil-gas exploration. Formation water is ubiquitous saline water in oilfields, whereas not commonly utilized in hydrous pyrolysis. To determine the influence of formation water on the expulsion/retention behaviour of commonly utilized oil-source correlation indictors (Pr/Ph, Pr/n-C17, Ph/n-C18, and gammacerane index, C22/C21, C24/C23 and C26/C25 tricyclic terpane ratios, C31R/C30hopane, C31(22S/22S + 22R) hopane, moretane/hopane and Ts/Ts + Tm), two series of semi-closed hydrous pyrolysis experiments were conducted in 300–550 °C for the typical type I Green River Shale source rocks using distilled water and formation water. Such comparative study can also improve the understanding of whether supercritical fluids affect the biomarker behaviour because the temperature for major hydrocarbon generation in hydrous pyrolysis approaches the critical temperature for distilled water. The studied oil-source correlation indictors of immiscible oils generated in both experiments using distilled water and formation water exhibit similar patterns with the increase of thermal maturity levels. Both retained and expelled immiscible oils generated in the experiments using formation water and distilled water are situated in similar area of empirical genetic diagrams (e.g. Pr/n-C17vs Ph/n-C18, C31R/C30 hopanes vs C26/C25 tricyclic terpanes, and ternary plot of C27–C28–C29 regular steranes), suggesting that the presence of formation water/supercritical water does not significantly compromise the utility of these diagrams for oil-source correlation. Outcomes of this study also demonstrate that semi-closed hydrous pyrolysis is a useful artificial method for characterizing biomarker compositions of oils generated by type I source rocks and understanding geochemical behaviour of biomarkers under supercritical conditions.

Catalytic hydropyrolysis of lignin: Insights into the effect of Ni catalyst and hydrogen using ReaxFF molecular dynamics simulation

Catalytic hydropyrolysis (CHP) of lignin as an emerging technology provides an efficient way of utilizing waste resources and promoting the production of alternative fuels and valuable bio-based products. The reinforcement of selective catalysts and hydrogen facilitates the overall conversion process but the mechanism remains difficult to clarify due to the complex nature of the system. This work employs a ReaxFF reactive molecular dynamics simulation method to explore the CHP of lignin dimer DMPD and the reaction mechanism at the molecular level. The results suggest that the hydropyrolysis (HP) system achieves a deoxygenation degree of 12.0 % for liquid products and the incorporation of hydrogen into pyrolysis suppresses the production of CO while promoting H2O and CH4 generation. The introduction of the Ni catalyst in the CHP system results in a liquid product yield of 68.9 wt % at 2000 K with a higher deoxygenation degree of 14.6 % due to the participation of a large amount of •H radicals species dissociated on the catalyst surface. The CHP reactions remarkably promote the production of phenols such as guaiacol and catechol and catechol is more likely to generate from the dynamic evolution of reaction intermediates. The integrated system also improves the production of H2O and light hydrocarbons like CH4 and C2H6. The first-order kinetic model reveals that the average activation energies of C-C, C-H, C-O bonds, and DMPD in the CHP system are significantly reduced to 113.12, 55.79, 59.99, and 132.17 kJ/mol in contrast to HP. The results indicate that the CHP system is more favorable for producing desirable liquid products with lower energy barriers.

Hydrous Pyrolysis of Source Rocks with Different Maturity in Dongying Sag, Bohai Bay Basin, China: Implications for Shale Oil Exploration and Development

Shale oil yield, movability, and reservoir brittleness are three factors that must be focused on for shale oil exploration and development. The yield and composition of hydrocarbons and mineral composition have changed significantly during diagenesis, affecting the yield and movability of shale oil and the brittleness of the rock. In this study, the source rocks at different depths in the Dongying Sag were subjected to hydrous pyrolysis, and the yield and composition of pyrolyzed hydrocarbons and mineral composition were systematically analyzed. The brittleness index (BEI), weighted average specific surface area (SSAWA), and polarity index (PI) have been established to quantitatively characterize the brittleness and adsorption capacity of rock as well as the mobility of shale oil. The results suggest that diagenetic evolution controls rocks’ brittleness and adsorption capacity by changing their mineral composition. In the low-temperature stage, the mineral transformation is not obvious, and the BEI and SSAWA fluctuate in a small range. In the high-temperature stage, the rapid smectite illitization leads to an increase in the brittleness and a decrease in the adsorption capacity. In addition, the nonpolar components such as saturates and aromatics in the pyrolyzed hydrocarbons gradually increased with the increasing temperature, enhancing the mobility of the shale oil. Based on the three evaluation indexes of BEI, PI, and SSAWA, and combined with the changes in hydrocarbon yields during hydrous pyrolysis, we comparatively analyzed the differences in the mobility and yields of original soluble organic matter as well as pyrolyzed hydrocarbons of the source rocks at different depths. Based on the above results, it can be concluded that the shale in the depth range of 3300–3795 m is a favorable area for shale oil exploration and development in the study area. This work suggests that predicting the sweet spot for shale oil exploration and development requires more attention to the impact of diagenetic evolution on the composition of minerals and hydrocarbons.

Pore structure characterization of solvent extracted shale containing kerogen type III during artificial maturation: Experiments and tree-based machine learning modeling

Shale samples with type III kerogen from the Damoguaihe formation were exposed to hydrous and anhydrous pyrolysis (HP and AHP) in the temperature range of 300–450 °C. Next, soluble organic matter (OM) and the liquid yield were removed from the pyrolyzates after each step of thermal maturation. N2 adsorption tests were performed to assess the pore structures of the samples. Furthermore, deconvolution and fractal dimension analyses were executed to unveil pore clusters and discern the complexity of the pore network within each sample. Finally, two tree-based machine learning algorithms, random forest (RF) and extra trees (ET) were applied to model the N2 adsorption/desorption data of pyrolyzates to predict pore structure variations. Based on the results, HP pyrolyzates had higher bitumen reflectance (BRo%) values than AHP ones at all temperature sequences, which confirms water controls thermal maturity. AHP pyrolyzates exhibited larger average pore diameters across all temperatures, while HP pyrolyzates displayed higher BET surface areas in contrast to AHP pyrolyzates. Also, the average pore diameter of HP pyrolyzates with soluble OM and liquid yield extracted did not change significantly during thermal maturation, while the average pore diameter of AHP ones increased, peaking at 400 °C in post-mature stage. The largest total pore volume of HP samples was observed at the end of the wet gas window, while this was observed for AHP samples in the dry gas window. Three mesopore and four macropore clusters were identified in the original sample. Moreover, pore clusters of the pyrolyzates underwent diverse changes during thermal maturation, without following a specific trend, influenced by both temperature and pyrolysis conditions. Abundance of micropores, finer mesopores (2–10 nm), and a smaller average pore diameter in HP pyrolyzates compared to the AHP is the main reason for the higher fractal dimensions showing a more complex pore structure and/or rougher pore surface. Intelligence modeling exhibited that RF outperformed ET in estimating N2 adsorbed/desorbed volumes for the samples. Ultimately, sensitivity analysis revealed that water exerted a more significant influence on pore development in shales during thermal progression, outweighing the impact of temperature.

Hydrocarbon generation differences of shales composed of green algal and cyanobacteria: A case study of Mesozoic and Cenozoic saline lacustrine shales in Junggar Basin, NW China

The Mesozoic and Cenozoic strata in the Junggar basin developed two sets of shallow to semi-deep lacustrine shale, namely, the Cretaceous Qingshuihe Formation (K1q) and the Paleogene Anjihaihe Formation (E2-3a). Through organic petrology and scanning electron microscope (SEM) observation, it is found that the primary hydrocarbon-generating organic matter (OM) in the two sets of strata is different. The biological precursor of the E2-3a OM is mainly green algae (Pediastrum), while the precursor of K1q kerogen is mainly cyanobacteria (Oscillatoria). Then, the E2-3a green algae-rich shale and K1q cyanobacteria-rich shale were subjected to hydrous pyrolysis and kinetic analysis, respectively. The results show that the evolution modes of hydrocarbon generation of the typical shales are very different. Green algae have the characteristics of a low oil generation threshold, heavy oil quality, and no prominent oil peak, while cyanobacteria have the characteristics of late oil generation, concentrated hydrocarbon generation, and relatively light oil quality. The characteristics of oil generation can also be well reflected in the composition evolution of the crude oil components. The carbon isotope of gas, kerogen, and extracts of the E2-3a green algae-rich shale are significantly heavier than the K1q cyanobacteria-rich shale, which may be related to the living habits of their biological precursors, carbon source usage, photosynthesis efficiency, and carbon fixation efficiency.

Experimental investigation and intelligent modeling of pore structure changes in type III kerogen-rich shale artificially matured by hydrous and anhydrous pyrolysis

The occurrence and enrichment of shale plays are highly controlled by pore characteristics of the formation. In this study, an immature sample rich in kerogen type III from the Damoguaihe formation, Hailar Basin in China is subjected to hydrous and anhydrous pyrolysis (HP and AHP) across an extensive temperature range (300–450 °C). Next, low-pressure N2 adsorption analysis was conducted on the pyrolyzate of each maturity stage to study the pore structures’ evolution during thermal maturity simulation. Moreover, deconvolution and fractal dimension analyses were implemented to study pore families and the complexity of pores within the shale samples. Finally, radial basis function (RBF) neural networks optimized by four evolutionary approaches were applied for modeling N2 adsorption data obtained from the HP and AHP samples. According to the results, the original shale sample and all pyrolyzates obtained with HP and AHP scenarios exhibited type IV isotherm with H3 hysteresis loops. As a whole, BET surface area, micro-, meso- and total pore volume of HP pyrolyzates were higher than AHP ones. The unheated shale sample had seven families containing three mesopore and four macropore groups. Although all pyrolyzates obtained from the pyrolysis had families with similar means, their pore volumes were entirely different, which proves that the pore structure of samples undergoes changes during thermal maturation and the presence of water can also enforce these changes. Both fractal dimensions showed a direct relationship with BET surface area and a negative correlation with the average pore diameter of shale samples. The RBF model optimized by differential evolution (DE) delivered a mean absolute percent relative error (MAPRE) value of 4.84% and determination coefficient (R2) of 0.9946 for the total data set, which outperforms other RBF models in predicting N2 adsorption/desorption tests of pyrolyzates. The outcome of sensitivity analysis suggested that the N2 adsorption/desorption behavior of the pyrolyzates was mostly affected by relative pressure and the pyrolysis type (HP or AHP). Ultimately, the results clearly revealed that the effect of water on the pores' alteration of shales with type III kerogen is greater than the effect of temperature or thermal maturity itself.

Petrological Characteristics and Hydrocarbon Generation of Carbonate Source Rocks of the Permian Taiyuan Formation in Central and Eastern Ordos Basin, China

In order to evaluate the hydrocarbon generation potential and effectiveness of the carbonate source rock from the Lower Permian Taiyuan Formation of the Upper Paleozoic gas reservoirs in the central and eastern Ordos Basin, 87 core samples from the formation were analyzed through the comprehensive application of core observation, thin section analysis, lithofacies division, and organic geochemistry experiments. The results show that the carbonate source rocks of the Taiyuan Formation comprise four lithofacies types with type I–II kerogen: laminar argillaceous micritic limestone, massive micrite, massive bioclastic micritic limestone, and massive algae-clotted limestone. Among them, laminar argillaceous micritic limestone and massive micrite are favorable lithofacies for high-quality source rocks, with a TOC distribution range of 0.99% to 6.07% (average 2.56%) and 0.24% to 8.27% (average 1.77%), respectively. Hydrous gold tube pyrolysis showed that the samples of laminar argillaceous micritic limestone and massive micrite attained a peak yield of nearly 115.0 mL/g TOC (heating rate 2 °C/h) and 101.4 mL/g TOC (heating rate 2 °C/h), respectively, for C1–5 compounds. Due to the higher maturity of the samples, the hydrocarbon gases were dominated by residual kerogen pyrolysis gases and lacked liquid hydrocarbon cracking gas. Furthermore, the carbonate source rocks had weak methane absorption ability, with a maximum adsorption capacity of only about 0.15 cm3/g. In addition, the hydrocarbon gas generation of carbonate source rocks of the Taiyuan Formation was far greater than 0.2 mL/g rock, which is the lower limit standard for effective gas source rock. Therefore, the carbonate source rocks of the Taiyuan Formation should be regarded as important gas source rocks in subsequent explorations of the central and eastern Ordos Basin.

Pore structure evolution of Qingshankou shale (kerogen type I) during artificial maturation via hydrous and anhydrous pyrolysis: Experimental study and intelligent modeling

In this study, alterations in the pore structure of the Qingshankou shale during hydrous and anhydrous pyrolysis (HP and AHP) over wide ranges of temperature (300–450 °C) were studied to elucidate the role of water. Mineralogy of the original shale sample along with geochemical properties and pore structure after each step of artificial thermal maturation were analyzed using X-ray diffraction (XRD), Rock-Eval pyrolysis, and N2 adsorption, respectively. Complexity of pore structure was assessed via fractal dimension analysis followed by delineating different pore families in the samples' PSD curves. Next, four common artificial neural networks (ANNs) models were implemented along with Bayesian regularization (BR) and Levenberg-Marquardt (LM) optimization algorithms to model the N2 adsorption/desorption volume as thermal maturity progressed. Results showed that all samples represent Type IV hysteresis loop while the amount of N2 adsorption during HP was much higher than that of the AHP revealing the importance of water. Overall, the complexity of AHP samples’ pore structure was less than that of the HP since the count of pores with smaller pore width was reduced more during thermal progression. Deconvolution analysis showed that the original sample has eight pore families (7 in mesopore and 1 in the macropore range), while pore families with larger mean pore width were formed and expanded and pore families with smaller mean pore width were eliminated as thermal maturation progressed in both HP and AHP. Moreover, the average absolute percent relative error (AAPRE) of 3.74% for the entire data inferred that generalized regression neural network (GRNN) model was superior for the estimation of N2 volume adsorbed and desorbed. Finally, sensitivity analysis revealed that the relative pressure and pyrolysis method (AHP or HP) respectively had the strongest linear and non-linear relationships with the N2 adsorption/desorption volume. Collectively, this case confirmed the role that water plays in the evolution of pore structures throughout thermal maturation, which could be even more significant than temperature.

The role of water in the laboratory thermal advancement of immature type I kerogen from the Cretaceous Qingshankou Formation in China

To understand variations in geochemistry, organic petrology, and chemical composition of crude oil and byproducts, an immature sample from the Cretaceous Qingshankou Formation in the Songliao Basin, China, was analyzed by anhydrous and hydrous pyrolysis (AHP/HP) at a wide range of temperatures ranging from 300 °C to 450 °C. The geochemical parameters: TOC, S2, HI, and Tmax obtained from Rock–Eval pyrolysis showed both a decrease and an increase as thermal maturity progressed under HP and AHP conditions. Gas chromatography (GC) analysis showed the presence of n-alkanes in the C14 to C36 range in both expelled and residual byproducts, a Delta-shaped configuration although many samples had a gradually reducing (tapering) trend toward the high range. Gas chromatography-mass spectrometry (GC–MS) analysis revealed both an increase and a decrease in biomarker and very small changes in aromatic compound variations with increasing temperature during pyrolysis. To be more specific, C29Ts biomarker increased with temperature for the expelled byproduct, while the opposite trend was observed for the residual one. Next, The Ts/Tm ratio initially increased and then decreased with temperature while the C29H/C30H ratio fluctuated for the expelled byproduct but increased for the residual. Moreover, the GI and C30 rearranged hopane to C30 hopane ratio remained unchanged whereas the C23 tricyclic terpane/C24 tetracyclic terpane ratio and the C23/C24 tricyclic terpane ratio showed varying trends with maturity alike the C19/C23 and C20/C23 tricyclic terpane. Ultimately, based on organic petrography observations, increasing the temperature resulted in higher bitumen reflectance (%Bro, r) and optical and structural alterations in the macerals. The findings of this study provide valuable insights for future exploration endeavors in the studied region. Moreover, they contribute to our understanding of the significant role of water in the generation and expulsion of petroleum and associated byproducts, thereby facilitating the development of updated models in this field.

Evolutionary Response Model of Low Maturity Coal Measure Reservoir Space to Temperature-Water Pressure Under Hydrous Pyrolysis

Evolutionary Response Model of Low Maturity Coal Measure Reservoir Space to Temperature-Water Pressure Under Hydrous Pyrolysis

Modified open-system hydrous pyrolysis

As an alternative to classic batch hydrous pyrolysis experiments, this proof-of-concept study presents a version of open-system hydrous pyrolysis (OSHP) in which the design of the apparatus allows for a small, continuous flow of only liquid-phase water to pass through the reactor during artificial maturation. This allows volatile, liquid, and soluble materials to migrate freely through and out of the system, whereas insoluble mineral matter and kerogen remain within the reactor. This apparatus differs from previous OSHP designs in the ability to maintain true open-system conditions, thus minimizing any cracking or back reaction of the products with the residual kerogen.Using the OSHP apparatus, immature Anna Shale (Pennsylvanian age, Illinois Basin) containing Type II marine kerogen was matured artificially at experimental temperatures ranging from 300 to 360 °C for up to 72 h. Petrographically, the immature Anna Shale is dominated by a micrinitic groundmass, and contains lesser amounts of vitrinite (both collotelinite and collodetrinite), inertodetrinite, bituminite, solid bitumen, and alginite. Under run conditions, mean random reflectance increased from 0.46 to 1.81% for vitrinite and from 0.66% to 1.50% for solid bitumen. Alginite fluorescence changed from a bright yellow to dull red-orange and decreased in intensity until all fluorescence was lost in shales pyrolyzed at temperatures ≥350 °C. Rock-Eval Tmax increased from 425° to 520 °C, TOC decreased (e.g., from 12.5% to ∼9% at a run temperature of 360 °C), S1 decreased from 0.71 to ∼ < 0.1 mg HC/g shale, S2 decreased from ∼40 to <1.0 mg HC/g shale, and HI decreased from ∼300 to <10 mg HC/g TOC. These changes are consistent with the maturation of the immature shale through the oil window and into the gas window. With increased maturity, the shale showed a loss in mass: shorter runs (≤ 24 h) typically lost <10%, whereas longer runs (72 h) lost 12–20%. These losses were likely due to the loss of moisture, liberation of hydrocarbons and other gases, and depletion in total sulfur from 2.03 to ∼0.1 wt% (much of which was pyritic sulfur); higher mass losses may have included retention of material in the reactor, tubing, or frits. Petrographic observations revealed that pyrite framboids, which were abundant in the immature shale, decreased in samples pyrolyzed at temperatures >330 °C and showed evidence of alteration to hematite.The OSHP design was intended to mimic normal burial maturation. However, based on the significant depletion in sulfur (i.e., pyrite), the current design and run parameters may more closely replicate conditions associated with hydrothermal alteration, possibly those associated with intrusion of organic-rich rocks. It is also possible that the OSHP approach could lead to a better understanding of organic-mineral interactions and mobility of elements, especially trace elements, during maturation.

Perspectives for Thermochemical Conversions of Lignocellulosic Biomass.

The biorefinery concept of lignocellulosic biomass with focus on thermochemical conversions will be presented and discussed with respect to the advantages, impacts, and methods. Analytics regarding the reaction mechanisms for the decomposition of cellulose, hemicellulose and lignin, respectively, will be presented along with new trends and perspectives within plasma and catalytic pyrolysis of lignin-fractions, artificial neural networks, hydrothermal liquefaction, torrefaction, gasification and combustion, pyrolysis and hydro pyrolysis as well as supercritical fluids for the catalytic thermochemical conversion of biomass and co-processing of upgraded bio-oil in fluidized catalytic cracking (FCC). A few examples are mentioned at this point; however, more details are given in the respective chapters. Concerning the catalytic conversion of lignin fractions the concept of the "catalyst philosophy" has been adapted from crude oil refining by using the hierarchical pore structure of the catalyst to arrive at the desired final products, like fuelcomponents or phenols. As a consequence, the same hierarchical catalysts can be applied in the co-processing of bio-oil with crude oil refined fractions. As a preliminary conclusion, the thermochemical conversion of lignocellulosic biomass has already reached a certain level of insight and understanding, however, there is still room for improvement and even a better understanding, and, last but not least, an upscaling to an industrial scale remains.

Early porosity generation in organic-sulfur-rich mudstones

High total organic sulfur (TOS) content (i.e., Type IIS kerogen) is well known to significantly influence kerogen transformation but the effect of TOS content on the evolution of organic porosity has only rarely and indirectly been investigated. This study demonstrates that organic porosity is generated at lower thermal maturity in mudstones containing Type IIS kerogen relative to those with Type II kerogen. To our knowledge this phenomenon has not been previously demonstrated. The implications are relevant for the characterization of organic-rich mudstones as cap rocks, hydrocarbon reservoirs, and disposal reservoirs for CO2 or nuclear waste because pore systems control storage volumes and matrix fluid flow. Five thermally immature core samples were selected from three organic-rich mudstone units with low to high TOS content: the late Devonian Duvernay Formation (Canada), middle late Miocene Onnagawa Formation (Japan), and early Jurassic Gordondale member of the Fernie Formation (Canada). Hydrous pyrolysis was used to artificially mature splits of the immature samples to four maturity stages, upon which petrophysical and organic geochemical properties were measured and compared to baseline immature samples. Most porosity growth in Type IIS samples occurred below 0.70% VRoeqv, but in Type II samples was broader and robust until 1.1% VRoeqv.

Characterization of free and bound bitumen fractions in a thermal maturation shale sequence. Part 2: Structural evolution of kerogen and bitumen during shale oil generation, expulsion and retention

Knowledge of the formation and enrichment mechanisms of shale oil is essential to understanding its mobility and hence a critical aspect for evaluating shale oil exploration and production. Semi-open hydrous pyrolysis experiments were performed on an organic-rich shale to simulate the petroleum generation and expulsion processes of Type II kerogen. The residual rocks matured to different levels (Easy%Ro = 0.50–1.37) were thereafter treated with stepwise extraction to obtain free and bound bitumen fractions. This study focuses on the structural characteristics of kerogen, bitumen fractions, and expelled oil during shale maturation using Fourier transform infrared (FTIR) spectroscopy and quantitative flash pyrolysis–gas chromatography (Py–GC). The results reveal that the composition of expelled oils changes with increasing maturity, whereas an opposite trend in structural composition was observed for kerogen after significant oil expulsion from the shale occurs, beginning at Easy%Ro = 0.79. A notable change is that aliphatic carbon chains of kerogen became shorter and/or more branched while those of expelled oil appeared to be more aliphatic with longer carbon chains at this stage. However, the overall compositional structures of shale bitumen fractions, both in free and bound phases, show only slight changes within the oil window stage. The bound bitumen is generally enriched in oxygenated functional groups as compared to free bitumen, indicating that the bound bitumen is related mainly to the interaction between the mineral surface and the bitumen–kerogen matrix. During maturation, the cracking (including defunctionalization) and condensation of kerogen and bitumen fractions, as well as a compositional fractionation due to oil expulsion, are likely to be the main factors influencing the opposite trend observed in structural compositions between kerogen and expelled oil. These processes may control the quality and content of expelled oil and bitumen in a petroleum system. Nevertheless, kerogen, expelled oil and bitumen show a gradual trend of decarboxylation during shale maturation in general.

Evolution of reservoir properties of oil shale rocks under hydro-thermal treatment: Investigations from micro- to macro-scale

Treatment with water at sub- and supercritical states which is considered as one of the most promising technologies for oil shale reservoirs development is still understudied. In particular, reliable correlations between most of the reservoir properties and temperature are absent. However, this data may significantly improve the quality of oil recovery predictions applying numerical simulations. This work is devoted to obtaining the dependency between porosity, permeability, organic matter content and temperature through physical modeling of hydrous pyrolysis. A unique experimental program design is proposed to investigate changes in reservoir properties at macro- and micro-scales and connect these changes with composition and pore structure evolution. A set of experiments on hydrous pyrolysis in a closed system was performed at temperatures 110, 250, 300,325, 350, 375, 400, and 450 °C, and the pressure of 23.4 MPa on rock samples of the Bazhenov formation.As a result, the relation between reservoir properties and the temperature was derived, characterized by a few specific temperature zones with particular behaviors of rock porosity and permeability. Effects on reservoir properties were analyzed in a complex way to highlight the mechanisms of void space transformation related both with pore space evolution and reduction. The observed effects include thermal expansion of organic matter with further transformation to synthetic hydrocarbons, formation of new mineral components, mineral matrix swelling and fracturing.

Comment: Suppression of vitrinite reflectance by bitumen generated from liptinite during hydrous pyrolysis of artificial source rock by Peters et al. (2018)

Peters et al. (2018) provide new hydrous pyrolysis data in defining the coal-reflectance and the suppressed-reflectance trends that source rocks may follow during their thermal maturation. The difference in the two trends is between hydrous pyrolysis temperatures of 300 to 360 °C for 72-hour durations. As implied in their title the suppressed-reflectance of vitrinite is a result of bitumen generation from liptinite during hydrous pyrolysis. Their experimental results do show that coal reflectance is lower when mixed with isolated liptinite encased in G-class Portland cement. However, there are published and omitted experimental data that they did not include in their interpretations. These are addressed as concerns and include early experiments of mixtures of Liptinite in source rocks mixed with coal that do not show a reduced reflectance of the coal. Earlier publications show that some source rocks with oil-prone Type-II kerogens also follow the suppressed-reflectance trend. Resinites did not cause reductions in coal reflectance. The validity of using G-class Portland cement as an artificial rock is not established and is unlikely to be an appropriate representative of natural shales. Reflectance suppression by free radicals are also feasible and more research is needed to better define the causes of the suppression.

Geochemical evolution of kerogen type III during hydrous pyrolysis: A case study from the Damoguaihe Formation, Hailar Basin, China

In order to evaluate changes in geochemistry, organic petrology, and chemical composition of petroleum and byproducts, an immature sample from the Damoguaihe Formation in Hailar Basin in China was examined using hydrous pyrolysis (HP) at the following temperature steps: 300 °C, 325 °C, 350 °C, 365 °C, 400 °C, and 450 °C. The final product from each pyrolysis step was assessed with several analytical methods including programmed pyrolysis, Gas Chromatography (GC), Gas Chromatography-Mass Spectrometry (GC-MS) and organic petrology. Rock-Eval pyrolysis revealed that the geochemical parameters including TOC, S2, HI, and Tmax changed as thermal maturity advanced. Both un-extracted and extracted organic matter (OM) showed a steady decrease in TOC, HI, and OI as the temperature increased. On the other hand, a general increase in Tmax values with increasing temperature was observed. Regarding GC analysis, fluctuations were observed in n-alkanes during pyrolysis. In general, lower molecular weight n-alkanes of <C17 increased between 325 °C and 400 °C, and heavier n-alkanes fluctuated with increasing temperature. Similarly, GC-MS results showed variations in biomarkers with increasing pyrolysis temperature. These variations could stem from the GC-MS instrument's inability to detect light hydrocarbons, specifically at higher temperatures beyond the oil generation window into the gas window. Some biomarkers, including Ts/Tm, C29H/C30H, Gammacerane Index (GI), C23 tricyclic terpane/C24 tetracyclic terpane showed that the Damoguaihe Formation has a carbonate lithology and was deposited in a freshwater environment with no water stratification. Based on organic petrography, an increase in temperature caused optical and structural changes in the macerals. Organic petrography also showed that the Damoguaihe Formation contains different maceral groups such as liptinite, vitrinite, and inertinite, and hence a combination of kerogen types II, III, and IV. Based on these observations, a deltaic depositional setting is envisaged for the Damoguaihe Formation in the study area, which is also confirmed by previous studies.

The initiation stage of thermochemical sulfate reduction: An isotopic and computational study

Thermochemical sulfate reduction (TSR) is one of the most important organic-inorganic reactions in petroleum reservoirs which significantly affects production and processing risks. The initiation (non-catalyzed) stage of TSR is critical in constructing a reliable kinetic model to predict this reaction. There is a large gap in our understanding of the mechanisms involved in this stage. In the present study, we used hydrous pyrolysis experiments with Na2SO4 and 1-dodecene as model compounds at pH= 1, and temperatures of 250 °C and 300 °C to simulate this early TSR stage. We measured and calculated the sulfur isotopic fractionations of sulfate, H2S and individual organic sulfur compounds (OSC). A thermodynamic model was used to determine the concentrations of the different sulfate species (H2SO4, HSO4¯, SO42-) at the experimental conditions. We then used ab initio calculations to determine possible radical and non-radical reaction mechanisms to explain the experimental results. During all the experiments, sulfate was consumed gradually while H2S and OSC were produced. The residual sulfate was 34S enriched up to 10.7‰ relative to the initial sulfate as pyrolysis time advanced. The produced H2S and OSC were typically about 21‰ 34S depleted relative to co-existing sulfate. The formation of OSC, such as C24 sulfides and C12 thiophenes, during the experiments and their similar δ34S values, suggest a common precursor and that radical mechanisms are involved in their formation. Calculated activation energies and free energies (Ea and ∆G‡, respectively) for the radical TSR mechanisms (20.6–34.1 and 32.3–44.4 kcal mol−1, respectively) yielded lower values than the non-radical TSR mechanisms (53.5–68.5 and 59.7–78.1 kcal mol−1, respectively). However, the calculated kinetic fractionation factors for the non-radical mechanism correlated better with the 11–12‰ experimental fractionation factor of current and previous studies. This similarity between the experimental and computational results indicates that these non-radical rather than radical mechanisms were likely involved in the reduction of sulfate in our experiments. Despite the lower activation energies, the radical TSR mechanisms are not dominant in our experimental system, probably due to competing reactions of the active radical species (alkyl and allyl radicals). Nevertheless, under natural conditions, the significantly lower amount of alkenes is expected to reduce the competition on the active alkyl and allyl radicals for alkylation, making these radical mechanisms competing pathways for the initiation stage of TSR.

Fractal characteristics of artificially matured lacustrine shales from Ordos Basin, West China

Nanometer scaled pores are critical to studying gas shale reservoirs. In order to obtain the information of the evolution mechanism of nanoscale pore within lacustrine organic-rich shales, artificially matured shale samples from the Ordos Basin were treated using hydrous pyrolysis experiment. Low-temperature nitrogen adsorption, inductively coupled plasma atomic emission spectrometry (ICP-AES), and field emission scanning electron microscopy (FE-SEM) experiments were used to investigate the nanopore evolution with migration and precipitation of materials. The results show that the pore sizes were distributed from 1.1 to 500 nm, and the overall porosity tends to increase first and then decrease. The micropores and fine mesopores (< 10 nm) increased gradually from the 250 to the 350 °C, calcite appeared dissolution following a small peak of feldspar dissolution at this stage, and the CO2 reaches a partial pressure peak at 350 °C. The micropores, mesopores and macropores increased steeply from the 370 °C to the 450 °C. Organic pores were not developed until 350 °C, and well developed at 370 and 400 °C. Organic pores, intergranular pores of clay and intragranular pores of pyrite were well developed at 370 °C. The cumulative specific surface areas increased at 400 °C caused by the dehydration and transformation reaction of clay minerals. This study could provide a reference for the exploration of shale gas in lacustrine shales with different thermal maturities.

Nanopore Evolution of the Upper Permian Organic-Rich Shales from Dalong Formation, Sichuan Basin, during Artificial Hydrous Pyrolysis

Nanopore Evolution of the Upper Permian Organic-Rich Shales from Dalong Formation, Sichuan Basin, during Artificial Hydrous Pyrolysis