Natural Gas Diffusion Research Articles

Hydrophobic-treated yolk-shell SnS2@CSs Z-scheme confinement reactor for solar-electro-driven hydrogen peroxide production in neutral media

The diffusion and adsorption properties of the O2/H2O corpuscles at active sites play a crucial role in the fast photo-electrocatalytic reaction of hydrogen peroxide (H2O2) production. Herein, SnS2 nanosheets with abundant interfacial boundaries and large specific areas are encapsulated into hollow mesoporous carbon spheres (CSs) with flexibility, producing a yolk-shell SnS2@CSs Z-scheme photocatalyst. The nanoconfined microenvironment of SnS2@CSs could enrich O2/H2O in catalyst cavities, which allows sufficient internal O2 transfer, improving the surface chemistry of catalytic O2 to O2− conversion and increasing reaction kinetics. By shaping the mixture of SnS2@CSs and polytetrafluoroethylene (PTFE) on carbon felt (CF) using the vacuum filtration method, the natural air-breathing gas diffusion photoelectrode (AGPE) was prepared, and it can achieve an accumulated concentration of H2O2 about 12 mM after a 10 h stability test from pure water at natural pH without using electrolyte and sacrificial agents. The H2O2 product is upgraded through one downstream route of conversion of H2O2 to sodium perborate. The improved H2O2 production performance could be ascribed to the combination of the confinement effect of SnS2@CSs and the rich triple phase interfaces with the continuous hydrophobic layer and hydrophilic layer to synergistically modulate the photoelectron catalytic microenvironment, which enhanced the transfer of O2 mass and offered a stronger affinity to oxygen bubbles. The strategy of combining the confined material with the air-breathing gas diffusion electrode equips a wide practical range of applications for the synthesis of high-yield hydrogen peroxide.

Effect of burner structural parameters on combustion characteristics and NOx emission of natural gas

The low-nitrogen combustion of natural gas has always been a crucial topic in environmental protection. Currently, small and medium-sized industries use straight-through pipelines as their burner nozzles. This design results in poor heat diffusion capacity after mixed combustion and a long time of temperature diffusion, leading to low combustion efficiency and high NOx emissions. To address this issue, a new type of natural gas low-nitrogen burner with a multi-port diffusion nozzle was developed. The burner’s structure was optimized through a combined approach of experiment and numerical simulation. The optimal structural parameters for the burner are a 40° swirl angle and 8 swirl blades, as indicated by the numerical simulation research results. The designed multi-port diffusion nozzle is matched with the appropriate swirl angle and number of blades to promote natural gas diffusion, forming an annular space region flames and a stable flame shape with a height of 0.64 m. After optimization, the average concentration of NOx at the outlet of the combustion chamber decreased from 61.5 ppm to 20.81 ppm. A natural gas low-nitrogen combustion experimental system was designed and constructed based on simulation results. The experimental results were analyzed in terms of flame structure characteristics, temperature distribution, and NOx emissions. The results indicate that the trend in temperature change is consistent with the simulation process. The NOx concentration at the outlet of the combustion chamber was measured by the flue gas analyzer to be 34.1 ppm, which was 5.3 ppm lower than the NOx concentration calculated by numerical simulation. The new burner exhibited better flame stability and a 12.6 % reduction in NOx emissions compared with a traditional straight-through pipeline burner of the same size. The designed natural gas low-nitrogen burner appears to be a suitable device for reducing NOx emissions in small and medium-sized industries.

Upgrading waste tire to a carbon-based natural gas diffusion electrode for efficient H2O2 production

Carbonaceous material, especially carbon black, is crucial in H2O2 production due to its exceptional catalytic properties. However, the traditional carbon black production process faces the challenges of significant CO2 emissions and high costs. To overcome these challenges, porous carbon nanoparticles (TPCNs) are derived from cheap, sustainable waste tires by a facile pyrolysis process, which is then used to fabricate a natural gas diffusion electrode (GDE) for efficient H2O2 electrogeneration. The obtained TPCNs are amorphous carbon with high graphitization, hierarchically porous architecture, and have high oxygen functional group content of CO, C-O-C, and COOH that are favorable for the high H2O2 selectivity. Hence, the fabricated TGDE exhibits efficient H2O2 electrogeneration of 694 mmol L–1 H2O2 concentration with 62% current efficiency after 60 min electrolysis without aeration. Moreover, this H2O2 production process utilizing waste tire can decrease by 19.6% CO2 emissions compared with that using commercial carbon black. This work proposes a protocol for the high-value reuse of waste tires and provides a sustainable carbon-based catalyst production for efficient H2O2 electrogeneration.

Investigation on natural gas leakage and diffusion characteristics based on CFD

The transportation of hazardous gases such as natural gas and hydrogen through buried pipelines is widely considered the most economically safe method. In recent years, due to the extension of service time and material aging, gas leakage incidents have become more common during transportation, leading to significant hazards such as fires and explosions. This paper aims to study the leakage and diffusion behavior of buried pipelines, help emergency personnel more accurately determine the areas that may be affected, and provide theoretical support for risk assessment and emergency planning of natural gas pipeline leaks. In this paper, the influence of different factors on the diffusion law of gas leakage is analyzed, and the factors that have the greatest influence on the diffusion are obtained through exploratory data analysis. Findings reveal pressure, leak size and soil temperature are positively correlated with methane concentration and dangerous area. Conversely, soil moisture negatively correlates with methane concentration and lateral diffusion distance. Soil type significantly impacts methane concentration, with sand facilitating the most diffusion, followed by loam, and least in clay. Therefore, soil compaction is recommended to mitigate gas diffusion rates during leaks, reducing hazardous zone extents. Additionally, the study delves into the emerging trend of transporting natural gas blended with hydrogen. Higher hydrogen ratios result in quicker reaching of Lower Explosive Limit and larger hazardous zones. In order to study the complex dynamics of multi-source leakage scenarios, two pipeline leakage diffusion simulations are carried out in this paper. The results showed increased horizontal spacing reduces maximum methane concentrations on the surface. However, this also enlarges gas alert and hazardous zone areas, heightening the risk of explosion-related incidents. These conclusions provide a theoretical framework for risk assessment and emergency treatment of pipeline leakage.

Study on the Leakage and Diffusion Characteristics of Buried Hydrogen-Blended Natural Gas Pipelines

Abstract Utilizing existing natural gas pipelines to transport hydrogen-blended natural gas is a primary strategy for achieving cost-effective, long-distance, and large-scale hydrogen transportation. However, blending hydrogen with natural gas alters its physical properties, resulting in changes in leakage and diffusion characteristics and the affected range. To illustrate this, we focus on the Jingxi Third Line natural gas long-distance pipeline and develop a buried hydrogen blended natural gas pipeline model to analyze the concentration distribution of hydrogen-blended natural gas and the temporal variation of gas velocity at the leakage point. We explore the influence of various factors, including pressure, leak orifice size, wind speed, and hydrogen-blending ratio, on the diffusion range of hydrogen-blended natural gas. The research findings demonstrate that in the vicinity of the leakage point, the methane concentration significantly exceeds the upper explosive limit while the hydrogen concentration remains within the explosive limit range. The hazardous range of hydrogen-blended natural gas leakage and diffusion is slightly larger than that of natural gas alone. Furthermore, both the vertical and horizontal hazardous ranges of hydrogen-blended natural gas leakage and diffusion exhibit positive correlations with pressure and leak orifice size. Additionally, as wind speed increases, the maximum impact distance in the vertical direction gradually decreases, while it gradually increases in the horizontal direction.

Analysis and prediction of hydrogen-blended natural gas diffusion from various pipeline leakage sources based on CFD and ANN approach

The influences of pipeline leakage source types on the hazard area distribution caused by accidental hydrogen-blended natural gas leakage are still the focus of gas leakage accidents. Three types of pipeline leakage sources are discussed in this study. Namely, the gas in the vertical pipeline flows from top to bottom, and the leakage orifice is in the pipeline wall; the gas in the vertical pipeline flows from bottom to top, and the leakage orifice is in the pipeline wall; the leakage orifice is in the horizontal pipeline end. The common feature of the above three pipeline leakage sources is that the normal of leakage orifice is parallel to the horizontal plane. The differences in the flow field distribution of hydrogen-blended natural gas released from three pipeline leakage sources are compared through numerical simulation. The effect of various factors on the jet centerline, concentration decay, and maximum horizontal diffusion distance of hydrogen-blended natural gas released from three pipeline leakage sources are analyzed. The predictive models of hydrogen-blended natural gas's maximum horizontal diffusion distance in three pipeline leakage sources under multi-factor coupling are established through a backward propagation neural network (BPNN). Results show that the angle between the gas flow direction in the pipeline and the normal of the leakage orifice, and the background step flow cause differences in the concentration field near the leakage orifice from the three pipeline leakage sources at the same working conditions. In the near-field region, the leakage orifice diameter has the most significant influence on the jet centerline of three hydrogen-blended natural gas jets among three factors. The concentration decay rate of gas released from the horizontal pipeline end is greater than that of gas released from the other two pipeline leakage sources. With the increase of volumetric flow rate, the maximum horizontal diffusion distances of methane released from three pipeline leakage sources all increase, while the maximum horizontal diffusion distances of hydrogen released from three pipeline leakage sources have little change. The predictive models of the maximum horizontal diffusion distance of hydrogen-blended natural gas released from three pipeline leakage sources are established through BPNN. The maximum horizontal hazard distances of the new working conditions are predicted, and the predicted results are in good agreement with the numerical simulation results. This investigation has guiding value for fast and accurate prediction of flammable gas hazard areas.

Study on the leakage and diffusion behavior of hydrogen-blended natural gas in utility tunnels

Incorporating the hydrogen-blended natural gas pipeline into utility tunnels increases the potential safety risk caused by gas leakage and diffusion. In this paper, a numerical model for the leakage and diffusion of hydrogen-blended natural gas in the tunnel was established to study the influences of ventilation mode, initial pipeline pressure, hydrogen blend ratio (HBR), and leak size on gas leakage and diffusion. The results indicate that gas accumulates at the tunnel's top under natural ventilation. When the HBR exceeds 20%, the safety risk in the tunnel increases significantly. Unlike natural ventilation, mechanical ventilation significantly reduces the high-concentration area's impact range. Under the dynamic adjustment of ventilation frequency, the leak size significantly impacts gas diffusion concentration, while the HBR has the slightest impact. When the HBR is no higher than 40%, the pipeline pressure is no higher than 0.4 MPa, and the leak size is no high than 5 mm, the accident ventilation frequency of 12 times/h could ensure the leaked gas concentration is lower than the alarm concentration. A leaked gas concentration prediction model was established to provide a basis for predicting the distribution of the leaked gas concentration in actual engineering.

Study on numerical simulation of leakage and diffusion law of parallel buried gas pipelines in tunnels

Parallel buried gas pipelines in tunnels are located in a confined space environment, where natural gas is vulnerable to accumulating to the minimum explosion limit concentration after a leakage accident. Therefore, to reduce the time for locating the leakage source after an accident and compensate for the loss of emergency response, an experimental model for scaling parallel gas transmission pipelines in tunnels was established and the dispersion characteristics and influencing factors of continuous leakage of natural gas within buried soil and in tunnel space were investigated numerically, and the correlation between the volume of the explosion range of natural gas within the tunnel space and each influencing factor was explored using gray correlation analysis. The research shows that the leakage dispersion process of parallel buried gas pipelines in tunnels includes seepage leakage in the soil region and diffusion transport in the tunnel air region. In the soil region, natural gas from the pipeline leak forms a circular shape and tends to percolate upward due to the combined effect of pressure and concentration gradients.In the tunnel air region, the spatial dispersion of natural gas concentration obeys a multivariate Gaussian distribution, and the temporal dimension is divided into three phases: the initial phase of leakage, the spreading phase and the stable phase of leakage. The diffusion speed of natural gas is positively correlated with the operating pressure of pipeline. The concentration peak value (ymax) at the leakage orifice position and the leakage aperture (dx) approximately meet the linear relationship: ymax= 7.62dx. The diffusion path of natural gas is greatly influenced by the orientation of the pipeline perforations, and the tunnel walls have a directional effect on the diffusion of natural gas. The main factors affecting the volume of the explosion range of natural gas within the tunnel space are parallel pipeline leakage pressure, pipeline leakage aperture, parallel pipeline leakage position, pipeline operating pressure, and pipeline leakage direction, with grey correlation coefficients of 0.76, 0.675, 0.662, 0.553, and 0.55. The proposed model was demonstrated be able to simulate and predict the diffusion of natural gas under the accidental leakage of buried gas pipelines in tunnels. And the results of this study can guide the installation of buried gas pipelines crossing mountain tunnels to prevent accidents.

Quantitative Analysis of Natural Gas Diffusion Characteristics in Tight Oil Reservoirs Based on Experimental and Numerical Simulation Methods.

As an important mechanism in gas injection development, the diffusion characteristics of natural gas in tight reservoirs are important in the dynamic prediction of the development effect and optimization of injection-production parameters. In this paper, a high-pressure and high-temperature oil-gas diffusion experimental device was built, which was used to study the effects of the porous medium, pressure, permeability, and fracture on oil-gas diffusion under tight reservoir conditions. Two mathematical models were used to calculate the diffusion coefficients of natural gas in bulk oil and cores. Besides, the numerical simulation model was established to study the diffusion characteristics of natural gas in gas flooding and huff-n-puff, and five diffusion coefficients were selected based on experimental results for simulation study. The remaining oil saturation of grids, the recovery of single layers, and the distribution of CH4 mole fraction in oil were analyzed based on the simulation results. The experimental results show that the diffusion process can be divided into three stages: the initial stage of instability, the diffusion stage, and the stable stage. The absence of medium, high pressure, high permeability, and the existence of fracture are beneficial to natural gas diffusion, which can also reduce the equilibrium time and increase the gas pressure drop. Furthermore, the existence of fracture is beneficial to the early diffusion of gas. The simulation results show that the diffusion coefficient has a greater influence on the oil recovery of huff-n-puff. For gas flooding and huff-n-puff, the diffusion features both perform such that a high diffusion coefficient results in a close diffusion distance, small sweep range, and low oil recovery. However, a high diffusion coefficient can achieve high oil washing efficiency near the injecting well. The study is helpful to provide theoretical guidance for natural gas injection in tight oil reservoirs.

Inhibitory effects of water mist containing alkali metal salts on hydrogen–natural gas diffusion flames

Fire extinguishing technologies of fine water mist containing additives have good application prospects. Additives that are efficient, nontoxic, nonpolluting, widely used, economical and reliable provide a reference for the application and promotion of fine water mist fire extinguishing systems containing alkali metal salts. In this paper, six potential alkali metal salt additives were selected: potassium carbonate (K2CO3), sodium carbonate (Na2CO3), potassium oxalate (K2C2O4·H2O), potassium acetate (CH3COOK), potassium chloride (KCl), and potassium bicarbonate (KHCO3); these additives were delivered into the fires as mists of their solutions at certain concentrations, the extinguishing time was recorded, and the minimum fire extinguishing concentration (MEC) of fine water mist containing alkali metal salt was tested by using a cup burner experimental apparatus. In addition, different types of alkali metal salts were compared to determine the anions and cations with better fire suppression performance levels. The suppression efficiencies of different ratios of additive packages for hydrogen-doped natural gas diffusion flames were studied to determine a specific ratio of additive packages. Based on the results of the experiment, in contrast to the pure water mist, the suppression efficiency of alkali metal salt greatly improved. The cation extinguishing ability was K+>Na+, and CO32- and CH3COO− were better than other anions in alkali metal salts. An efficient compound additive was identified as 1.5% K2CO3 + 0.5% CH3COOK. With increasing hydrogen addition, the MEC of fine water mist with additives increased.

Leakage and diffusion behavior of a buried pipeline of hydrogen-blended natural gas

Buried pipelines are one method of conservation transfer for widely used gases such as natural gas and hydrogen. The safety of these pipelines is of great importance because of the potential leakage risks posed by the flammable gas and the special properties of the hydrogen mixture. Estimating the leakage behavior and quantifying the diffusion range outside the pipeline are important but challenging goals due to the hydrogen mixture and presence of soil. This study provides essential information about the diffusion behavior and concentration distribution of underground hydrogen and natural gas mixture leakages. Therefore, a large-scale experimental system was developed to simulate high-pressure leaks of hydrogen mixture natural gas from small holes in three different directions from a pipeline buried in soil. The diffusion of hydrogen-doped natural gas in soil was experimentally measured under different conditions, such as different hydrogen mixture ratios, release pressures, and leakage directions. The experimental results verified the applicability of the gas leakage mass flow model, with an error of 6.85%. When a larger proportion of a single component was present in the hydrogen-doped natural gas, the leakage pressure showed a greater diffusion range. In addition, the diffusion range of hydrogen-doped natural gas in the leakage direction was larger at 3 o'clock than that at 12 o'clock. The hydrogen blend carried methane and diffused, which shortened the methane saturation time. Moreover, a quantitative relationship between the concentration of hydrogen-doped natural gas and the diffusion distance over which the hydrogen-doped natural gas reached the lower limit of the explosion was obtained by quantitative analysis of the experimental data.

Natural fiber-derived gas diffusion layers for high performance, lower cost PEM fuel cells

Natural fiber-derived gas diffusion layers for high performance, lower cost PEM fuel cells

Effects of Pipeline Pressure on Diffusion Characteristics of Leaked Natural Gas in Tunnel Space.

Pipeline transportation has become the main mode of natural gas transportation. Due to inevitable aging, corrosion, and third-party damage, natural gas pipeline leakage accidents occur frequently. Leakage in the tunnel will lead to the leakage and accumulation of natural gas, and the potential explosion risk will threaten the tunnel's safety. It is significant to elaborate on the diffusion behavior of leaked natural gas in tunnel space for the traceability of leakage points and the formulation of safety technical measures. In this paper, a scale-down experimental platform for natural gas pipeline leakage in the tunnel is built, and the influence of pipeline pressure on natural gas diffusion characteristics is described. The results show that the diffusion process of leaked natural gas in the tunnel space shows obvious segmentation characteristics, and the concentration of natural gas reaches the maximum at the end of the continuous leakage stage. The increased pipeline pressure promotes natural gas diffusion, and the concentration of natural gas under 1.0 and 1.2 MPa rises sharply. First dangerous time (FDT) and maximum accumulated concentration (MAC) have a negative correlation with the leakage distance, while FDT and MAC have a good exponential and linear relationship with the pipeline pressure (0.2-1.2 MPa), respectively.

CT-based 3D pore-fracture network analysis of volcanic reservoirs of Lower Cretaceous Yingcheng formation in southern Songliao Basin, China: Impact on natural gas migration

Volcanic rocks as an important part of basins are found in almost all basins in the world. Although volcanic rock reservoirs are denser and more heterogeneous than conventional reservoirs, they still have good storage capacity in the deeper hydrocarbon-bearing basins. Due to the presence of a large number of irregular and random pores, throats and fractures in volcanic reservoirs at micron-nano scale, its permeability and reservoir capacity are complex. A series of experiments show an abnormal negative correlation between porosity, permeability and natural gas diffusion coefficient in volcanic reservoir rocks of the Yingcheng Formation in the southern Songliao Basin. The dacite sample from CS105 well in Changling Fault Depression and the andesite sample from DS9 well in Dehui Fault Depression with this negative correlation phenomenon were selected, the micron-nano CT scanning technology and Avizo software are applied to quantitively evaluate the 3D pore-fracture network system of the volcanic reservoir samples at multiscale. By comparing the statistical results from CT scanning of the two samples, the dacite sample of CS105 well with higher diffusion coefficient has higher porosity, more connected pores, larger average pore volume and higher average coordination numbers, in addition, the micro-fractures in the CS105 sample promotes the development of secondary pore-throats through later dissolution and further improve the physical properties of volcanic rock reservoirs. In the meantime, the gas seepage simulation results also prove the positive correlation between porosity, permeability and diffusion coefficient of volcanic rock reservoir. The micron-nano CT scanning can more accurately evaluate the physical properties of volcanic rock reservoirs with a large number of pore-throats and fractures at the micron-nano scale, providing theoretical basis for the study of natural gas migration mechanism in highly heterogeneous tight volcanic rock reservoirs.

Numerical simulation and experimental study of gas diffusion in a ship engine room

Research on the engine room's natural gas leakage and diffusion has great significance for the LNG Powered ships' design, the fire risk assessment and explosion. In this paper, a model experiment system with a scale ratio of 1:10 was established. Helium gas was used instead of natural gas to study the evolution law of light gas concentration distribution in the model engine room over time. The CFD model of light gas diffusion in the indoor thermal environment is verified by experimental data and used to simulate the natural gas diffusion behavior in a full-size ship's engine room. The influence of leakage amount, cabin temperature, ventilation conditions, leakage location and other factors on the distribution of natural gas concentration was analyzed. The results show that the established CFD model has good predictive power for the diffusion behavior of light gas in the ship's engine room, and the numerical simulation results of the trend of leakage gas concentration with time are consistent with the experiment, and the maximum error is not more than 20%. The amount of leakage has a great influence on the concentration near the leakage location. The larger the initial volume flow and the higher the temperature of the leakage, the larger the dangerous area in the ship's engine room. Increasing ventilation flow is an effective way to reduce the diffusion area and control the concentration of natural gas in the engine room. When the ventilation flow is doubled, the diffusion area of natural gas reduces to 1/3. The leaked natural gas will gather at the location nearing the obstacles which block the jet flow and the upper layer of the engine room. The research results provide a basis for accurately predicting the spatial and temporal distribution model and method of gas diffusion concentration in the engine room environment.

Experimental investigation of hydrogen enriched natural gas diffusion reactions using preheated air in a hot coflow burner

The present paper analyzes experimentally the morphology of a set of non-premixed diffusion reactions of hydrogen enriched natural gas (NG). For the analysis the H2 content was varied from 0 to 100 vol.-% and the mixture issues in a co-flow at variable preheating temperatures, from ambient conditions of 25 °C and up to 400 °C. For the various NG-H2 blends the thermal power input was held constant at 0.8 kW. For processing the images, a bitmap filter was used to isolate visible flame height, visible width variations, and soot free length fraction (SFLF). The results show that visible flame height always decreases when increasing H2 content in NG at any preheating temperature. The effects of air preheating summarize as follows: for NG enriched up to 75 vol.-% H2, the visible flame height reduces when increasing the air preheating temperature from 25 °C to 200 °C, then at 300 °C the visible flame height increases when rising the air temperature up to 400 °C. For the 100% H2 non-premixed flame the visible height presents a linear trend to increase as air temperature rises. Roper's theory for non-premixed flames in circular ports correlates reaction length to air preheating temperature and fuel composition variations, however those trends neglect buoyancy and diffusion phenomena, which results in significant error on predicting the effects of hydrogen addition to NG on the reaction length. A modified correlation is proposed to predict accurately the effects of air preheating and H2 fraction on visible flame height. Finally, a multidimensional scaling analysis shows that hydrogen addition up to 50 vol.-% does not modifies the visible flame morphology significantly when compared to pure NG.

Experimental and Numerical Prediction Model for the Dangerous Radius of Natural Gas Leakage in Soil.

Prediction of the dangerous radius of natural gas plays an important role in reducing the hazards of a buried natural gas pipeline after leakage. The factors affecting the diffusion law of natural gas in soil after leakage are mainly divided into the pipe, soil, and environmental sides. Previous studies focused on the effects of leakage pressure, leakage aperture, and leakage direction on the pipe side and porosity and water content on the soil side. In this paper, experiments and numerical simulations are conducted for further investigating the effects on the diffusion of natural gas in soil of the soil type (porosity and granule diameter) and layered structure among the soil side factors and soil temperature as environmental side factors. The contour radius corresponding to 5% volume concentration (the lower limit of natural gas explosion in soil) is defined as the natural gas dangerous radius for analysis. Based on comprehensive analysis of the effects of the factors, a prediction model is proposed for the dangerous radius of natural gas in soil with leakage pressure, leakage aperture, porosity, and granule diameter as the dominant influencing factors, which is of great significance for locating the source of the leakage.

Evaluation Methods and Indexes for Ultra‐deep Petroleum Reservoir Preservation with Case Studies

AbstractFollowing consideration of the characteristics of high temperature, high pressure and high in‐situ stress in ultra‐deep sedimentary basins, together with the existence of hydrocarbon phase state transformation, hydrocarbon‐water‐rock interaction and rock mechanical property transition at those depths, the evaluation index system for hydrocarbon preservation was established. The physical leakage evaluation indexes can be divided into three categories: the dynamic efficiency indexes of micro‐sealing, caprock integrity and natural gas diffusion. The chemical loss evaluation indexes can be divided into two categories: the thermochemical sulfate reduction (TSR) index in marine gypsum‐bearing carbonate strata and the thermochemical oxidation of hydrocarbons (TOH) index in clastic strata. The slippage angle and overconsolidation ratio (OCR) are the key evaluation indexes in the evaluation of the integrity of shale caprocks. TSR intensity can be quantitatively calculated by use of the ZnPVT state parameter method. The TOH strength can be used to estimate the degree of hydrocarbon chemical loss, based on the TOH‐related authigenic calcite cement content or the degree of negative δ13C of authigenic calcite. For the evaluation of ultra‐deep preservation in specific areas, key indexes can be selected according to the local geological conditions, instead of all indexes needing to be evaluated for every scenario.

Geochemical Characteristics of the Jurassic Alkane Gas in the Muli Depression, South Qilian Basin: Implications for Potential of Light Oil and Condensate

The discovery of gas hydrates in the Muli Depression has made the South Qilian Basin (SQB) a hotspot for oil and gas exploration. Although many studies have been carried out on the gas hydrates, the geochemical characteristics have rarely been reported, which can effectively indicate the genetic type, diffusion, biodegradation, and thermal maturity of natural gas. In this contribution, the molecular composition and carbon isotopes of alkane gases were collected from gas hydrates and free gases in drilled boreholes of the Muli Depression. The results show that the majority of natural gases are oil-type gases, with a little coal-type gases. The natural gases have undergone biodegradation, leading to a decrease in the propane content and an increase in the methane content, with a heavier carbon isotope of propane and a lighter carbon isotope of methane. Some of the natural gases have experienced diffusion, resulting in a decrease in the methane content and an increasing value of Δ(δ13C1-δ13C2). Furthermore, the wet gases from natural gases were derived from the cracking of kerogen and crude oil at the thermal maturity stage. The dry gases in small quantities were produced by biodegradation of the wet gases. We propose that the potential for light oil and condensate exists in the Jurassic Yaojie Formation. Our new findings on the geochemical characteristics of natural gases provide new constraints for the study of petroleum systems and deeply buried sediments in the SQB.

Research on natural gas leakage and diffusion characteristics in enclosed building layout

There are many people in urban construction areas, and natural gas leakage can potentially cause serious accident consequences. Predicting the consequences of gas dispersion is important to react rapidly and adequately in the event of an incident. Currently, computational fluid dynamics (CFD) models are an important tool to predict gas dispersion. However, in most cases, considering computational cost, the building layouts is ignored, so the flow field influence near the building area cannot be considered. In this research process, a realizable k-ε turbulence model is used to simulate the natural gas leakage process in a typical building layout (enclosed building layout), while focusing on wind speed and the leakage position. The validity of realizable k-ε turbulence model is verified by experimental data. The results show that under conditions of high wind speed (wind speed≥ 6 m/s), the reverse vortex formed by the shear flow of wind can cause the natural gas cloud to sink. When the leak hole is located in the influence area of the turbulent vortex, it easily induces R-H instability. When combined with the stronger K-H instability at high wind speeds, natural gas clouds may accumulate. This then leads to serious leakage accidents, knowledge of which may be the key component of emergency management during an accidental natural gas leakage. The research results can guide the building layout plan and gas pipeline construction to prevent accidents.