Cracking Of Oil Research Articles

Multifractal Methods in Characterizing Pore Structure Heterogeneity During Hydrous Pyrolysis of Lacustrine Shale

By using gas physisorption and multifractal theory, this study analyzes pore structure heterogeneity and influencing factors during thermal maturation of naturally immature but artificially matured shale from the Kongdian Formation after being subjected to hydrous pyrolysis from 250 °C to 425 °C. As thermal maturity increases, the transformation of organic matter, generation, retention, and expulsion of hydrocarbons, and formation of various pore types, lead to changes in pore structure heterogeneity. The entire process is divided into three stages: bitumen generation stage (250–300 °C), oil generation stage (325–375 °C), and oil cracking stage (400–425 °C). During the bitumen generation stage, retained hydrocarbons decrease total-pore and mesopore volumes. Fractal parameters ΔD indicative of pore connectivity shows little change, while Hurst exponent H values for pore structure heterogeneity drop significantly, indicating reduced pore connectivity due to bitumen clogging. During the peak oil generation stage, both ΔD and H values increase, indicating enhanced pore heterogeneity and connectivity due to the expulsion of retained hydrocarbons. In the oil cracking stage, ΔD increases significantly, and H value rises slowly, attributed to the generation of gaseous hydrocarbons further consuming retained hydrocarbons and organic matter, forming more small-diameter pores and increased pore heterogeneity. A strongly negative correlation between ΔD and retained hydrocarbon content, and a strongly positive correlation with gaseous hydrocarbon yield, highlight the dynamic interaction between hydrocarbon phases and pore structure evolution. This study overall provides valuable insights for petroleum generation, storage, and production.

Thermo-hydro-mechanical modelling of the heterogeneous subsidence and swelling in the desiccation cracked clayey strata

Soil desiccation cracking as a consequence of severe environmental changes alters soil deformation mechanisms significantly. Therefore, this study aims to explore the effect of crack characteristics and environmental conditions on the heterogeneous deformation of desiccation-cracked soils using thermo-hydro-mechanical analyses. The model framework consists of balance equations, thermal, hydraulic, and mechanical constitutive equations, while the model scenarios were determined based on statistical analyses. The meteorological record of Qom city was used for three years, from 2015 to 2017, to capture long-term behaviour under wetting-drying cycles. Findings revealed that cracks extend the deformation range, potentially up to six times, with variation based on crack dimensions and spacing. Notably, narrower cracks experienced more pronounced deformation than wider ones. The cracked soil with a crack depth of 2.5 m showed 1.5 times higher swelling and subsidence than crack depth of 1 m. Furthermore, the wider cracks indicated a lower rate of increase in their dimensions compared to the initial state during drying. The investigation also highlights the mechanisms of soil surface shape due to swelling and shrinkage, resulting in concave and convex surfaces, respectively. The results provide new perspectives on the behaviour of fine-grained deposits in arid to semi-arid climates with deep groundwater levels.

Effective cracking of heavy crude oil by using shock-induced nanobubble collapse: A molecular dynamics study

We investigate molecular mechanisms of hydrocarbon cracking in heavy crude oil promoted by nanobubble collapse due to ultrasound-originated shock wave. Our millions-atom molecular dynamics simulations reveal rapid flow of molecules, causing nanobubble collapse and formation of energetic nanojet with a mushroom-like shape. The nanojet apex exhibits extremely high temperature before and just after the bubble collapse, which makes a favorable condition for effective cracking of paraffin molecules. The cracking rate and portion of nanobubble-containing systems are larger than those of perfect system before the bubble collapse, and larger size of nanobubble is preferable for the cracking. The cracking efficiency is improved for the paraffin molecules with longer carbon chain.

Steam cracking in a semi-industrial dual fluidized bed reactor: Tackling the challenges in thermochemical recycling of plastic waste

Steam cracking is an integral process in the plastic manufacturing industry. Conventional steam crackers are tubular reactors and use fossil-based feedstocks like naphtha and LPG. This work presents steam cracking in a dual fluidized bed (DFB) reactor as an alternative for the direct steam cracking of plastic waste. Experiments were performed on a semi-industrial DFB system using naphtha, clean polyolefins, real-life plastic wastes, and a polyolefin-derived pyrolysis oil. The results show that steam cracking in a DFB is fundamentally equivalent to steam cracking in tubular reactors. Selective production of light olefins and monoaromatics was achieved within a temperature range of 700–825 °C. Naphtha yielded up to 56 % light olefins and 7 % BTXS, with ethylene and BTXS production positively correlating with cracking severity, while C3 and C4 olefins show a negative correlation. These results confirm that the established steam cracking mechanisms also apply to large-scale DFB steam crackers. The yield of light olefins is consistently obtained at approximately 52 % relative to the polyolefin content of the feedstock, regardless of the non-polyolefin content. This highlights the DFB steam cracker’s ability to produce light olefins directly from plastic waste without presorting. However, steam cracking in DFB results in significantly higher CO and CO2 yields than conventional steam cracking, especially with feedstocks containing non-polyolefins like PET and cellulose. Additionally, steam cracking of an olefin-rich pyrolysis oil yields up to 50 % light olefins with minimal coke formation, highlighting the potential in processing plastic waste pyrolysis oils without pretreatment steps such as distillation and hydrotreatment.

Pore-fluid salinity effect on desiccation cracking of fine-grained soils

Pore-fluid salinity effect on desiccation cracking of fine-grained soils

Progressive failure mechanism of existing-supplementary double-layer piles retaining excavation beneath existing underground space

The increasing degree of urbanization has resulted in traffic and space congestion. When there is no longer any aboveground space for development, the existing space underground is excavated, and the construction of underground buildings is expected to solve the above problems. In the excavation of an underground layer, it is necessary to drive supplementary and existing piles into the soil to form a double-layer pile-supported structure. Aiming at an existing–supplementary double-layer pile-supported structure and considering the pile spacing of the supplementary piles, use of crown beams, and other factors, this study performed a series of indoor model tests and an simulation analysis in combination with finite element analysis software to reveal the bearing characteristics of this structure. The results showed that the installation of supplementary piles could effectively inhibit soil slippage after pile driving, redistribute the soil pressure load of the existing piles, and reduce the number of soil cracks between the piles. With the increase in the supplementary pile spacing, the deformation of the existing–supplementary double-stacked piles gradually intensified, and the bending moment of the pile body and the horizontal displacement at the top of the piles increased. The installation of crown beams in the existing piles could strengthen the connection between the existing and supplementary piles, reduce the number of soil cracks between these piles, and change the force mode of the pile body. Considering the geological conditions and the influence of existing buildings, the deformation laws of the supporting structure and the soil around the foundation piles during the excavation of an underground layer of an L-shaped foundation pit were revealed. The research results are expected to provide a scientific and theoretical basis for the design and construction of downward additional support structures for existing buildings, along with socio-economic significance.

Differences in the Genesis and Sources of Hydrocarbon Gas Fluid from the Eastern and Western Kuqa Depression

The Kuqa Depression is rich in oil and gas resources and serves as a key production area in the Tarim Basin. However, controversy persists over the genesis of oil and gas in the various structural zones of the Kuqa Depression. This study employs natural gas composition analysis, gas carbon isotope analysis and gold pipe thermal simulation experiments, to comprehensively analyze the differences in the genesis and sources of hydrocarbon gas fluid from the eastern and western Kuqa Depression. The results show that the Kuqa Depression is dominated by alkane gas, with an average gas drying coefficient of 95.6, with nitrogen and carbon dioxide as the primary non-hydrocarbon gases. The average of δ13C1, δ13C2 and δ13C3 values in natural gas are −27.70‰, −20.43‰ and −21.75‰, respectively. Based on comprehensive natural gas geochemical maps, the CO2 in the natural gas from the Tudong and Dabei areas, as well as the KT-1 well of the Kuqa Depression, is thought to be of organic origin. Additionally, natural gas formation in the Tudong area is relatively simple, consisting entirely of thermally generated coal gas derived from the initial cracking of kerogen. The natural gas in the KT-1 well and the Dabei area are mixed gasses, formed by the initial cracking of kerogen from highly evolved lacustrine and coal-bearing source rocks, exhibiting characteristics resembling those of crude oil cracking gas. The methane (CH4) content of natural gas in the Dabei area is high and the carbon isotopes are unusually heavy. Considering the regional geological background, potential source rock characteristics and geochemical features may be related to the large-scale invasion of dry gas contributed by CH4 from highly evolved, underlying coal-bearing source rocks. Consequently, the CH4 content in the mixed gas is generally high (Ln (C1/C2) can reach up to 5.38), while the relative content of heavy components is low, though remains relatively unchanged. Thus, the map of the relative content of heavy components still reflects the characteristics of the original gas genesis (initial cracking of kerogen). Mixed-source gas was analyzed using thermal simulation experiments and natural gas composition ratio diagrams. The contributions of natural gas from deep, highly evolved coal-bearing source rocks in the KT-1 well and the Dabei area accounted for more than 90% and approximately 60%, respectively. This analysis provides theoretical guidance for natural gas exploration in the research area.

Organic geochemistry and 1D-basin modeling in the Taranaki Basin, New Zealand: Implications for deltaic-source rocks of the cenozoic oil and condensate reservoirs

The Taranaki Basin in New Zealand is an area of active exploration for oil and condensate. This research focuses on integrating geochemical characteristics and 1-D basin modeling to Late Cretaceous to Miocene source rock systems, along with oil and condensate data from fifty-seven wells in the Taranaki Basin. The geochemical study reveals that the oil and condensate samples were generated from clay-rich source rocks, containing mixed organic matter, with large amounts of terrestrial organic matter input. These source rocks were deposited in fluvial to fluvio-deltaic environments under oxic conditions. The presence of oleanane in both oil and condensate samples suggests that the source rocks had a significant terrestrial component and deposited during the Late Cretaceous to Cenozoic. Using various biomarker proxies, oil-source rock correlation along with 1-D basin modeling revealed that the oil and condensate were mainly derived from the Late Cretaceous Rakopi and Paleocene Farewell formations at different maturity stages. The oils were generated within the peak-mature oil window, while the condensates primarily resulted from the secondary cracking of oil taking place in the source rock within the gas generation window. This finding is consistent with the 1-D basin modeling results. The model shows that the Paleocene Farewell source rock has achieved the primary stage of oil generation (0.55–0.95 Easy %Ro), contributing to most of the discovered oils in the Cenozoic reservoir rocks. Meanwhile, the Late Cretaceous Rakopi source rock reached the gas window with a higher vitrinite reflectance of more than 1.30 Easy %Ro, indicating greater gas generation potential.

Hydrocarbon accumulation and reconstruction in the Ediacaran Dengying carbonate reservoirs of the southeastern and central Sichuan Basin, SW China

The carbonate reservoirs of the Ediacaran Dengying Formation (Z2dn) in the southeastern Sichuan Basin (SESB) and central Sichuan Basin (CSB) experienced different tectonic movements during the Caledonian, Yanshanian, and Himalayan orogenies, resulting in distinct hydrocarbon accumulation processes in these two regions. Based on a detailed analysis of diagenetic sequences, pore-fluid pressure evolution, hydrocarbon charge history, and regional tectonic structural analysis, the hydrocarbon accumulation processes in the Dingshan and Ziyang areas can be divided into three stages, namely Triassic to Jurassic, Jurassic to Cretaceous, and from Late Cretaceous to the present. The first stage was characterized by the formation of paleo-oil pools, marked by an episode of oil charge in the Z2dn reservoirs, as evidenced by solid bitumen and bitumen-bearing inclusions. During the second stage, pore fluid pressure increased from normal to overpressure due to oil cracking in the favorable preservation conditions, leading to the formation of paleo-gas pools in the SESB and CSB. The timing of gas charge in the Dingshan and Ziyang area was at 173 Ma and 165 Ma, respectively, according to the trapping temperature of gas inclusions. The third stage was marked by a pressure drop from overpressure to normal pressure, possibly due to gas dissipation during the Yanshanian-Himalayan uplift. The destruction of paleo-gas pools in the Dingshan area, accompanied by gas leakage through faults and fractures, was caused by intense tectonic movement in the SESB. In contrast, the low gas productivity in the Ziyang area of the CSB was attributed to the migration of natural gas into the Weiyuan area. The fluid evolution of carbonate reservoirs and various tectonic characteristics reveal similar hydrocarbon accumulation but different reconstruction processes in the SESB and CSB, providing greater insight into the mechanism of hydrocarbon enrichment in the Sichuan Basin and other multi-cyclonic composite basins.

Genetic mechanism and exploration progress of global deep alkane gases and small molecule gases (H2, He)

From the perspective of global oil and gas exploration trends, deep to ultra-deep gas exploration has emerged as a focal point in the past decade, shaping the future landscape of fossil energy exploration. Specifically, China has undertaken oil and gas exploration ventures reaching depths of 10,000 m, drawing significant attention to the genesis of gas accumulation at such extreme depths. An analysis of crucial geological factors including basin formation, hydrocarbon generation, storage and accumulation reveals that kerogen cracking gas, crude oil cracking gas, and coal cracking gas served as vital gas sources for ultra-deep paraffin gas in highly over-mature oil-bearing basins, establishing a model for the formation, evolution, and accumulation of natural gas. With the continuous expansion of hydrocarbon genesis theory and the increasing global demand for clean energy, hydrogen, as an important link between inorganic and organic hydrocarbon generation theory, and as a promising clean energy, has gradually aroused extensive attention in the academic community. The genetic types of natural hydrogen are mainly generated from inorganic genetic mechanisms, including earth degassing, water-rock interaction, and water radiolysis. The lithology of the reservoir and the sealing property of the cap layer control the accumulation of natural hydrogen, with the salt-rock cap layer beneficial to the large-scale preservation of natural hydrogen reservoir. Helium, as a constituent resource of natural gas, represents the primary target for exploration among deep small molecule gases. Helium within natural gas reservoirs can be categorized into atmospheric, crust-source and mantle-source varieties based on their origins. Helium source rocks exhibit significant disparities in helium generation capacity attributed to variations in rock types, mineral compositions, and ages, resulting in a relatively complex mechanism governing helium reservoir release, migration and accumulation. Typically, helium-rich gas reservoirs lack optimal cap sealing performance, as excessive sealing inhibits the formation of pressure relief conduits, thereby impeding the supply of helium-rich fluid to the reservoir. Through an analysis of genetic types, formation and evolution models, and reservoir preservation mechanisms pertinent to deep alkane gases and small molecule gases, it is revealed that the large-scale pool-forming geologic units and giant hydrocarbon enrichment zones in ultra-deep strata are key and promising prospects for delivering successive discoveries, and the energy significance and development trend of natural hydrogen and helium in the future were pointed out, in order to provide references for promoting the transition from high carbon to low carbon and carbon-free energy in the energy field.

Biochar–water–soil interactions: Implications for soil desiccation cracking behavior in subtropical regions

In subtropical regions, soil desiccation cracking often exerts a significant impact on the interactions between soil water and the atmosphere, making it a subject of great interest in the fields of geotechnical and geoenvironmental engineering. Despite the growing utilization of biochar as a sustainable soil amendment, there remains a lack of in-depth understanding of biochar–water–soil interactions, as well as its impact on soil desiccation cracking behavior. To address this gap, this study investigated the influence and mechanism of woody biochar dosages and particle sizes on the cracking behavior of three typical clayey soils in subtropical regions in China, namely Pukou expansive soil (PKE), Xiashu soil (XS), and Zhongshan lateritic soil (ZSL). The quantitative analysis of crack images revealed that the use of biochar was not consistently effective in preventing soil cracking. The application of biochar reduced the crack ratio in PKE and XS by up to 24.03% and 53.89%, respectively. In contrast, ZSL exhibited a 74.57% increase in crack ratio with the addition of 10% biochar. This influence can be further enhanced by increasing the dosage and reducing the particle size of biochar. The microstructural analysis demonstrated that biochar exerts an inhibitory effect on PKE and XS primarily through direct replacement, direct barrier, and indirect physical mechanisms. Moreover, an indirect chemical effect between biochar and clay particles was proposed to explain the exacerbated cracking observed in biochar-amended ZSL. To effectively utilize biochar for soil cracking mitigation in subtropical regions, it is essential to evaluate the initial mineral composition and cation type of the soil.

Effect of pre-oxidation on the rate of formation of sulfur-containing aromatic compounds during vacuum gas oil thermal cracking

It was shown that oxidation followed by heat treatment is an effective method for desulfurization of vacuum gas oil. Patterns of changes in the quantitative content of the thiophene series compounds in liquid cracking products of vacuum gas oil and liquid cracking products of pre-oxidized vacuum gas oil are described. A mixture of hydrogen peroxide and formic acid (molar ratio 3:4) was used as the oxidation system. The hypothetical mechanism for the formation of thiophene, benzo- and dibenzothiophene and their homologues from high-molecular weight components of the initial vacuum gas oil and its oxidation products is proposed. Presumably, main path of formation considerate compounds is thermal decomposition of high-molecular weight sulfur-containing components. On the basis of IR spectroscopy and structure-group analysis data, the averaged structures of such components were constructed. The influence of pre-oxidation and its conditions on the value of the rate constants for the formation of thiophene, benzo- and dibenzothiophene and their homologues during thermal cracking of initial and oxidized vacuum gas oils is studied.

Calcite U[sbnd]Pb dating and geochemical constraints on fracture opening in organic-rich shales

Gas-bearing, organic-rich shales commonly host numerous opening-mode fractures; however, their formation mechanism remains controversial, with competing arguments of tectonic-origin and/or hydrocarbon generation pressurization-origin. Here, we studied fracture fillings in shale reservoirs of the lower Silurian Longmaxi Formation in the Luzhou area, southern Sichuan Basin, SW China. Using in-situ UPb geochronology, rare earth elements (REEs) and C-O-Sr isotope geochemistry, and fluid inclusion analyses, we investigated the timing and geochemical attributions of fracture fills and identify the mechanism of fracture formation. The results show that, the cements that occupy fractures in the Longmaxi Formation shales contain mainly calcite and quartz. The calcite cements show crack-seal and fibrous textures, indicating that they are syn-kinematic mineral deposits. The 87Sr/86Sr values of the calcite cements essentially overlap with those of their proximal host shales. This result, combined with slight depletions in δ13CPDB and relatively uniform fluid δ18OSMOW isotopic features, indicate that the fluids from which the calcite precipitated were largely derived from their surrounding host shales. Abundant methane inclusions are present in fracture cements, with trapping pressures of 104.5–157.5 MPa and pressure coefficients of 1.92–2.43, suggesting they were trapped in an overpressurized fluid system. In-situ UPb dating of calcite cements yielded ages of ca. 160 Ma and ca. 110 Ma, which coincide with the timing of thermal cracking of oil to gas during burial. In combination with the overpressurized, geochemically closed fluid system, the fractures were most likely triggered by gas generation. Our study emphasizes that natural fracturing induced by hydrocarbon generation overpressurization is an essential mode of brittle failure in tectonically quiescent basins worldwide.

INFLUENCE OF MODIFICATION OF KAOLINITES BY ALUMINUM OXIDE ON THE CRACKING ACTIVITY OF PETROLEUM RESIDUE

The preparation of matrices of zeolite-containing catalysts using acid-treated (20% H2SO4) kaolinites from the Pavlodar region of Kazakhstan (NPK-1, NPK-2 and NPK-3) with subsequent modification with aluminum hydroxo complexes of different concentrations (2.5, 5.0 and 7.5 mmol Al3+/g) was studied. and aluminum hydroxide gel prepared by the ammonia method for activity in cracking residual petroleum feedstock. In the experimental part of the article for kaolinites of the Pavlodar region of Kazakhstan - PK-1, PK-2 and PK-3, the values of the SiO2/Al2O3 molar ratios in the original samples, the change in these ratios during acid activation and subsequent modification with aluminum hydroxo complexes are considered. It has been shown that the criterion for choosing kaolinites as matrices for zeolite catalysts can be the increased content of aluminum oxide in the original kaolinite. From the analysis of data on the matrix activity of kaolinites in the cracking of vacuum gas oil, it follows that in order to achieve optimal yields of gasoline and light gas oil for samples with lower Al2O3 content, the introduction of a higher concentration of hydroxo complex is required. Using the example of the Al(2.5)NPK-1 sample, it is shown that the additional introduction of aluminum hydroxide gel (5% Al2O3 by weight of the catalyst) obtained by the ammonia method into the modified kaolinite matrix, followed by drying and heat treatment leads to the production of a catalyst with high activity. The catalyst was tested in the cracking of fuel oil, a mixture of vacuum gas oil (VG) with fuel oil (30%). For comparison, data on cracking of heavy vacuum gas oil are presented. Gasoline yields for these types of raw materials at 5000C are 26.8; 31.9 and 39.1%; respectively, with raw material conversion of 88.4% and 92.1%. Cracking gasolines are characterized by a high content of iso-paraffin and aromatic hydrocarbons. Al(2.5)NPK-1+Al2O3 can be an economically beneficial and environmentally friendly catalyst and adsorbent.

Maturity characterization and formation mechanisms of nano-scale anisotropic pyrobitumen based on atomic force microscopy (AFM)

Highly evolved pyrobitumen is an important and realistic object for maturity characterization of ancient and deeply buried organic matter, but measurement of its reflectance is challenging due to its strong optical anisotropy and nano-scale relief. Here we conducted a case study in the Sinian (Ediacaran) Dengying Formation of the Sichuan Basin, China. High-resolution, three-dimensional, morphological imaging by atomic force microscopy (AFM), laser Raman (LRM) spectroscopy, and reflectance studies were conducted on the reservoir pyrobitumen. Our results show that Young’s modulus and adhesion, which are mechanical maturity parameter, provides effective characterization of maturity. The increase in Young’s modulus of pyrobitumen lags that of the vitrinite, given that pyrobitumen is formed by oil cracking and is more hydrogen-rich than vitrinite. A quantitative relationship between Young’s modulus, adhesion and reflectance in bright and dark areas of pyrobitumen was established, which can be used for maturity characterization. The changes in Young’s modulus of the pyrobitumen is related to the condensation of organic matter and directional arrangement of microcrystals. Young’s modulus of organic matter is a robust mechanical maturity index at high organic matter maturity (Ro > 2.0 %), but it is important to pay attention to the influence of anisotropy. Compared to Young’s modulus, adhesion is less affected by anisotropy. The nano-mechanics such as Young’s modulus and adhesion will be new maturity indicator in addition to conventional optical and spectroscopic method. The nano-mechanical properties of organic matter are expected to be applied to maturity indicators and macerals classification in the field of organic petrology in the further research.

Impact of Overpressure on the Preservation of Liquid Petroleum: Evidence from Fluid Inclusions in the Deep Reservoirs of the Tazhong Area, Tarim Basin, Western China

The complexity of petroleum phases in deep formations plays an important role in the evaluation of hydrocarbon resources. Pressure is considered to have a positive impact on the preservation of liquid oils, yet direct evidence for this phenomenon is lacking in the case of deep reservoirs due to late destruction. Here, we present fluid-inclusion assemblages from a deep reservoir in the Tazhong area of the Tarim Basin, northwestern China, which formed as a direct consequence of fluid pressure evolution. Based on thermodynamic measurements and simulations of the coexisting aqueous and petroleum inclusions in these assemblages, the history of petroleum activities was reconstructed. Our results show that all analyzed fluid-inclusion assemblages demonstrated variable pressure conditions in different charging stages, ranging from hydrostatic to overpressure (a pressure coefficient of up to 1.49). Sequential petroleum charging and partial oil cracking may have been the main contributors to overpressure. By comparing the phases of petroleum and fluid pressures in the two wells, ZS1 and ZS5, it can be inferred that overpressure inhibits oil cracking. Thus, overpressure exerts an important influence on the preservation of liquid hydrocarbon under high temperatures. Furthermore, our results reveal that the exploration potential for liquid petroleum is considerable in the deep reservoirs of the Tarim Basin.

In-situ hydrothermal upgrading and mechanism of heavy oil with nano-Fe2O3 in the porous media

Hydrothermal upgrading is a promising technology for heavy oil, yet the impact of reservoir conditions on the catalytic effect of catalysts and the pathway are not clear. In this study, the effect of the formation environment on the catalytic upgrading process was investigated through simulating the reservoir conditions (2000 mD permeability, 25 % porosity) for catalytic hydrothermal cracking of heavy oil. Under the hydrothermal upgrading conditions（240 ℃, 24 h, 50 wt%, 0.1 wt% nano-Fe2O3）, 9.15 % of the heavy component(5.1 % resin and 4.05 % asphaltene) was converted to light component. The content of hydrocarbons below C17 in the saturated fraction increased from 36.29 % to 59.85 %. The structure of the asphaltene was disrupted resulting in a lower level of asphaltene stacking, and NC/NH ratio increased 13.61 % compared to heavy oil. In addition, the reservoir condition with quartz as the supporting medium improved the catalytic ability of iron oxide nanoparticles. When injected into the reservoir medium, nano-size facilitated dispersion on the surface of the proppant and inhibited the aggregation of nanoparticles, which ensured the continuous operation of the active sites on the surface of the catalyst. Electron transfer of Fe2+/Fe3+ catalyzed the heterolytic cleavage of covalent bonds of H2O/heavy oil molecules was the mechanism for heavy oil upgrading. These findings demonstrated the feasibility of in-situ upgrading of heavy oil through the use of nano-catalysts under reservoir conditions.

Catalytic Cracking of Waste Cooking Oil to Alkane-Based Hydrocarbon Over Activated Carbon Supported La and Ce Oxides

Catalytic Cracking of Waste Cooking Oil to Alkane-Based Hydrocarbon Over Activated Carbon Supported La and Ce Oxides

Patchy degradation‐induced changes in soil aggregates and organic carbon in an alpine swamp meadow on the Qinghai‐Tibetan Plateau

AbstractSoil cracking induced by grassland degradation has become increasingly common in the Qinghai‐Tibetan Plateau in recent decades, and the intensification of soil cracking has implications for soil carbon (C) cycling. However, how patchy degradation affects soil aggregates and organic C and the underlying mechanisms remain unclear. In the present study, we investigated the changes in soil aggregates and organic C across various degradation stages in patchy alpine swamp meadows. The results showed a hump‐shaped trend in the proportion of macroaggregates, mean weight diameter (MWD), macroaggregate‐associated organic C (MAOC), and their contribution to soil organic carbon (SOC) throughout the degradation sequence. Conversely, the proportion of microaggregates initially decreased and then increased, with the contribution of microaggregate‐associated organic C (MIOC) to SOC increasing as degradation progressed. Regression and piecewise structural equation modeling (SEM) showed that soil texture played a decisive role in the change in MAOC and MIOC, and enzyme activity was the key factor leading to the difference between MAOC and MIOC. Enhanced enzyme activity accelerated the decomposition of MAOC while favoring the accumulation of MIOC. These findings are crucial for understanding the mechanisms influencing the physical protection of SOC by aggregates under patchy degradation. This emphasized soil cracking as a turning point in aggregate and organic C changes and a trigger for severe degradation in alpine swamp meadows, warranting proactive measures to mitigate its onset and progression.

Study on the pathways of thermochemical sulfate reduction between sulfates and alkanes at low temperatures

To reduce the energy consumption of heavy oil thermal recovery, low-temperature hot water flooding is becoming popular. The occurrence of thermochemical sulfate reduction (TSR) reactions during the hot water flooding process generates H2S, which can corrode equipment and jeopardize personnel safety. Preventing and managing H2S requires studying TSR reactions. The study investigated the reactivity of SO42-, HSO4-, and [MgSO4]CIP in the TSR reaction during heavy oil low-temperature hot water flooding. The results indicated that during low-temperature hot water flooding, no significant thermal cracking of heavy oil occurs, only a minor aquathermolysis takes place, while the TSR reaction proceeds vigorously. The TSR reaction leads to increased yields of H2S, CH4, and CO2, as well as a higher S content in the heavy oil. Based on experimental results, numerical simulations of the reaction process between SO42- and CH4 were conducted using density functional theory and transition state theory. The results indicated that the reduction of SO42- to produce SO32- is the rate-limiting step in the entire reaction pathway between SO42- and CH4. Further analysis of the reaction barriers and chemical reaction rates of the three sulfates (SO42-, HSO4-, and [MgSO4]CIP) and C1-C5 alkanes was conducted based on the limiting step. Through macro and micro analysis, this study not only confirmed previous findings regarding the order of alkanes participating in TSR reactions from the perspective of microscopic molecular but also clarified the oxidation order of sulfate species under heavy oil low-temperature thermal water flooding conditions, with the sequence being HSO4- > [MgSO4]CIP>SO42-. This study provides a foundational understanding of TSR reactions during heavy oil low-temperature hot water flooding and is of significance for the prediction and management of H2S.