Productivity analysis of fractured wells in reservoir of hydrogen and carbon based on dual-porosity medium model

Hydrogen is usually locked in energy-rich organic compounds and there is almost no pure hydrogen in nature. Organic compounds produced in reservoirs of hydrogen and carbon are an important source of hydrogen production. Understanding the productivity characteristics reservoirs of hydrogen and carbon is the important step to ensure adequate hydrogen energy. This study analyzes the production of hydraulically fractured organic reservoir of hydrogen and carbon. First, based on the diffusion mechanism in reservoir matrix, a multi-scale dual-porosity medium model of reservoir of hydrogen and carbon is established. Then, the mathematical model is solved and verified through a historical matching of field gas production data. Finally, parameter analysis was performed to determine the key parameters to improve the recovery efficiency in organic reservoir of hydrogen and carbon. Results show that improving fracture permeability can improve gas recovery efficiency of hydrocarbon reservoirs. The matrix desorption can develop natural gas production for a long period. Long sizes of hydraulic fractures have large contact surfaces for gas diffusion and increase gas generation and cumulative gas production. The proposed model can predict and analyze the production performance of reservoirs of hydrogen and carbon.     

A gaseous compound of hydrogen and carbon production performance model in coalbed reservoir with horizontal fractures

Hydrogen energy can be generated by steam methane reforming method, and methane production from coal seams is important to ensure the abundance of hydrogen energy generation. The gaseous compound of hydrogen and carbon production performance analysis is important and pressure transient analysis can be used to analyze the flow characteristics in the development of gaseous compound of hydrogen and carbon in coalbed reservoir. The computational models on vertical wells, vertically fractured wells and horizontal wells have been studied intensively in coalbed reservoir to predict gaseous compound of hydrogen and carbon production behavior. For a thin coalbed methane reservoir, it will be more effective to develop through forming horizontal fractures near the wellbore. However, such model has not been established. To analyze gaseous compound of hydrogen and carbon production performance for horizontal fractures in coalbed methane reservoirs, this paper presents a 3D point-sink model and the corresponding solution is obtained through using Laplace transform and Fourier transform methods. The point-source integral method is used to obtain the general solutions of gaseous compound of hydrogen and carbon flow through horizontal fractures. The pressure transient solution have been compared with numerical simulation to validate its accuracy. Type curves are established to analyze the flow characteristics of gaseous compound of hydrogen and carbon, which can be divided into four regions, i.e., linear flow region, transition flow region, inter-porosity flow region, and radial flow region. The sensitive analysis of the key model parameters on type curves has been conducted.     

Pressure transient analysis for fluid flow through horizontal fractures in shallow organic compound reservoir of hydrogen and carbon

Pure hydrogen does not occur in large quantities in nature, and it is usually locked up in energy-rich organic compound. One of the challenges to sustain the usage of hydrogen energy is to produce sufficient energy-rich organic compound from the organic compound reservoir of hydrogen and carbon, which requires understanding the fluid flow behavior through such reservoir. The horizontal fractures can be created during the hydraulic fracturing process in shallow energy-rich organic compound reservoirs due to the geo-mechanical effect. However, it lacks of a comprehensive analytical model to describe the transient flow behavior through the horizontal fractures. In this paper, an analytical model for horizontal fractures in shallow organic compound reservoirs considering the effects of wellbore storage and skin factor with constant pressure, closed and infinite boundary conditions, are presented to investigate pressure transient behavior and flow characteristics. The analytical solution is derived in Laplace domain, which may require numerical inverse transform to obtain the solution real space. To obtain the explicit form in real space, the approximate solutions for early time, middle time and late time are also presented to investigate the characteristics of type curves. Type curves are established for the transient pressure analysis to recognize the flow characteristics through horizontal fractures. Flow for horizontal fractures can be divided into five stages according to characteristics of dimensionless pseudo pressure derivative curve. The effects of parameters on pressure behavior are discussed in detail, which include wellbore storage coefficient, dimensionless formation thickness, dimensionless vertical location, and skin factor. The results indicate that horizontal fractures are more applicable in thin instead of thick reservoirs.     

Optimization experimental design of stable production life and estimated ultimate recovery in gaseous compound of hydrogen and carbon from shale reservoir

In this study, a mixed numerical model is established to simulate the production performance of gaseous compound of hydrogen and carbon in shale reservoir. Estimated ultimate recovery (EUR) and stable production life (SPL) of gaseous compound of hydrogen and carbon are affected by reservoir parameters and production control parameters, such as Langmuir pressure, Langmuir volume, critical desorption pressure, fracture half length, permeability in stimulated reservoir volume (SRV) area, bottom hole flow pressure and production of gaseous compound of hydrogen and carbon. Therefore, in the later research, in order to reduce the number of numerical experiments, the orthogonal experimental method is used to optimize the influence of hydrocarbon ERU and SPL, and analyze the main control factors affecting these two indices at the same time. The purpose of this paper is to optimize the production of hydrocarbons by orthogonal experimental method and find the main controlling factors affecting the production of compound of hydrogen and carbon. Two groups of orthogonal experiments were designed to find the best scheme in the process of compound of hydrogen and carbon development. The calculative results show that the output of hydrogen and carbon compounds has a highly significant impact on SPL, Langmuir volume and capability in SRV have a significant impact, and Langmuir pressure Critical destruction pressure and hydraulic fracture half-length had no significant effects.     

Underground hydrogen storage in a naturally fractured gas reservoir: The role of fracture

As hydrogen provides a high heating value with the least environmental impact, it can be considered as an energy carrier pioneer in following the global zero-carbon policies. Then, since storing hydrogen in large quantities can also be a valuable technique for alleviating energy shortages due to energy consumption fluctuations, underground hydrogen storage (UHS) is being explored further in today's world. To the best of our knowledge, the role of fracture on underground hydrogen storage performance has not comprehensively been evaluated. For the first time, in this study, the effects of fracture on hydrogen storage and production were investigated in a naturally fractured gas reservoir in the Middle East using a numerical simulation. Then, to determine whether the fracture was able to accelerate hydrogen production, UHS was evaluated under various conditions, including the fracture system, condensate presence, Initial hydrogen injection stage, cushion gas type, hydrogen storage commence time and different injection/production cycle duration. The results of this study proves that although a huge amount of hydrogen is invaded into the matrix during hydrogen injection, the fracture accelerates hydrogen production, resulting in higher hydrogen recovery and purity, which indicates fractures are suitable media for hydrogen storage. However, it should be noted that the purity of hydrogen produced from naturally fractured reservoirs (NFR) decreases more rapidly than a conventional one during a single cycle due to the higher mixing of gases in the fracture. In the case of the initial stage of hydrogen injection, fractures are not found to be attractive as storage media. Therefore, it is necessary to analyze the fracture effects as a storage media under various situations and stages. In addition, alternative gas injection revealed that nitrogen injection into cushion gas resulted in the highest hydrogen production in the entire porous media, whereas methane injection led to the highest hydrogen recovery in the fracture media. Also, the rapid injection/production cycle duration improved hydrogen recovery, indicating that the required time for high hydrogen invasion into the matrix is not provided during hydrogen injection.     

Simultaneous production of hydrogen and carbon nanotubes from cracking of a waste cooking oil model compound over Ni-Co/SBA-15 catalysts

Hydrogen is considered an ideal energy carrier. However, the use of fossil fuels to produce hydrogen depletes natural resources and causes environmental problems. Therefore, there is an urgent need to find alternative raw materials and technologies for the production of hydrogen. Waste cooking oil (WCO) is a renewable energy source that has emerged as a potential raw material for hydrogen production. This study describes the production of hydrogen and carbon nanotubes (CNTs) by catalytic cracking of a WCO model compound (WCOMC) performed in a lab-scale fixed bed using Ni-Co/SBA-15 catalysts. The phase, structure and reduction properties of the catalyst were analysed by using different characterisation methods. The effects of the nickel-cobalt metal content and the reaction temperature on both the hydrogen production and the quality of the CNTs were investigated. The deposited carbonaceous products were characterised to analyse their external appearance, internal structure, oxidation stability and graphitisation degree. The results indicated that the catalyst containing 20% Ni and 30% Co showed the highest activity. When reaction temperature was 800°C, the instantaneous volume fraction of hydrogen was close to 43.5 vol% and the content of hydrogen in the gas product was close to 66.5 vol%. A few multi-walled CNTs having a small diameter and some CNTs with an open-topped structure were deposited on 10%Ni-40%Co/SBA-15 and 30%Ni-20%Co/SBA-15, respectively. Thermogravimetric analysis and Raman spectroscopic analysis indicated that all CNTs showed high oxidation stability and a high degree of graphitisation.     

Regulated effect of organic small molecular doped in carbon nitride skeleton for boosting photocatalytic hydrogen evolution

Organic small molecules doping in polymer carbon nitride (PCN) skeleton can dramatically improve photocatalytic performance owing to its effective regulation effect on molecular and electronic structure. Here, a new PCN-based photocatalyst is obtained via polymerization of urea with 1-benzyl-3-phenylthiourea (BPT). The doping effect of BPT in PCN skeleton directly adjusts the hybridization states and delocalization of molecular orbitals, so that the visible light harvest ability, adsorption capacity, charge separation efficiency and transfer kinetics are improved significantly. Consequently, the photocatalytic hydrogen evolution reaction (HER) rate reaches to 125.0 μmol h⁻¹ over the optimal PCN-BPT₁₅ photocatalyst, which is as 13.9 times as PCN (9.0 μmol h⁻¹). Noteworthily, a high apparent quantum efficiency (AQE) of 24.2% is achieved at 420 nm for photocatalytic HER. This work enriches the functionalized investigations of PCN-like photocatalysts by insight into regulated effect of organic small molecules in the skeleton for photocatalytic applications.     

生物油-甲醇催化重整制氢的氢产率及碳转化率的研究

采用生物油-甲醇催化重整制氢。在微型固定反应装置上通过正交法试验设计,对生物油甲醇混合比例、反应温度、水碳比、进样流速等因素进行了系统的试验。在选择的最佳反应条件下,氢气产率和碳转化率分别为34.89%及63.34%。     

A new numerical simulation method of hydrogen and carbon compounds in shale reservoir

Hydrogen energy can be produced by the decomposition of hydrogen and carbon compounds. A numerical analysis method of accuracy and efficiency provides important reference value for optimizing development plans and predicting production performance of hydrogen and carbon compounds. In this work, embedded discrete fracture model (EDFM) is used to study the production performance of hydrogen and carbon compounds under non-liner seepage under the threshold pressure gradient and complex fracture systems consist of the hydraulic fractures, secondary fractures, natural fractures. A dual-permeability model of the same case is also constructed as a comparison study to analyze the development of hydrogen and carbon compounds. On this basis, the influence of threshold pressure gradient on production of hydrogen and carbon compounds is quantitatively evaluated in this paper to modify the numerical model and a novel method for the simulation of fractured hydrogen and carbon compounds reservoirs is provided. Through model comparison, the impact of fractures in the reservoir on production can reach 289.1%. A dual-permeability model of the same case is also constructed as a comparison study to analyze the development of the reservoir and the result shows a 7.9% distinction on the cumulative production. It is analyzed that when the threshold pressure gradient is increased from 0.1 MPa/m to 0.6 MPa/m, the output decline of different models ranges from 6% to 15% and a novel method improving model fidelity for the simulation of fracture reservoirs is provided.     

Inhibition of carbon deposition using iron ore modified by K and Cu in chemical looping hydrogen generation

Chemical looping hydrogen generation based on iron is an innovative method to produce high purity hydrogen and capture CO₂ simultaneously. However, carbon deposition of iron ore limits the development. The iron ore modified by K and Cu was employed to suppress the carbon deposition. Experiments were carried out to investigate the effects of the additive amount on carbon deposition and hydrogen purity via carbon release characteristics in a batch fluidized bed. The carbon deposition ratio decreased monotonically with the increasing amount of potassium, but the excess copper loading led to a rise in the ratio of carbon deposition instead. The carbon deposition ratio decreased by up to 84% after adding K and Cu, which is speculated to be closely related to the weight ratio of Fe on the oxygen carrier surfaces. The experimental results at different temperatures demonstrated that 850°C was suitable for the inhibition of carbon deposition and sintering. In addition, the mechanism of inhibition of carbon deposition was proposed in detail and illustrated that it was correlated to the covering of active sites and the reactivity enhancement. Moreover, the carbon deposition ratio of the modified oxygen carrier maintained stable during the cyclic experiments. Therefore, it is feasible to employ the iron ore modified by K and Cu as oxygen carrier to suppress carbon deposition in the chemical looping hydrogen generation.     

Techno-economic analysis of alternative processes for alcohol-assisted methanol synthesis from carbon dioxide and hydrogen

The novel methanol production from carbon dioxide (CO₂) and hydrogen (H₂) called alcohol-assisted process is simulated. Although the alcohol-assisted process allows the reduction in operating temperature and pressure, the subsequent product purification is complicated. Comparative studies between the conventional CO₂ hydrogenation and the alcohol-assisted processes are carried out (case I–V). The alcohol-assisted processes present the opportunity of increasing the CO₂ conversion per-pass and reducing 25% of the hydrogen consumption, the barriers in the conventional process. However, the product purifications remain challenging due to the azeotrope of methanol and by-products. Energy consumptions decrease in the feed and reaction sections of the alcohol-assisted processes but significant increase in the product purifications. The formation of by-products and the sequence of purification units affect process performance and economics. The obtained results indicate that the product purification and the catalyst development to increase methanol selectivity and produce an easy-separated by-product play key roles in the enhancement of the process feasibility.     

Comparison of hydrogen absorption in metallic and semiconductor single-walled Ge- and GeO2-doped carbon nanotubes

First-principles calculations were carried out to compare hydrogen absorption in pristine metallic and semiconductor carbon nanotubes (CNTs) with the situation in their Ge- and GeO₂-doped counterparts. We found out that the pristine carbon nanotubes have low absorption efficiency (?1.53 eV in the metallic, and ?2.06 eV in the semiconductor carbon nanotube). When Ge was doped into both carbon nanotubes, the hydrogen absorption was enhanced to ?5.29 eV in the metallic and ?3.99 eV in the semiconductor carbon nanotubes. Investigating the Partial density of states proved that there was considerable overlap between Ge 4p and hydrogen 1s orbitals in both CNTs. When CNTs were doped with GeO₂, hydrogen atoms were bound to oxygen atoms, due to high electronegativity of oxygen atom. The hydrogen absorption was found to be increased remarkably in the metallic carbon nanotube (?6.59 eV). In order to compare the binding energy of Ge and GeO₂ doped metallic and semiconductor carbon nanotubes, the partial density of states and the magnetization of the samples were studied.     

On the nature, capability and reversibility of hydrogen storage in novel carbon nanomaterials for mobile power units

On the basis of the thermodynamic analysis of most representative recent data on hydrogen storage in graphite and novel carbon-based nanomaterials of sp² hybridization, the open questions have been studied of the nature, capability and reversibility of such storage, particularly, for mobile power units. For an interpretation of the thermodynamic and kinetic (diffusion) characteristics obtained in such a way, the known results have been used of ‘ab initio’ molecular orbital study of adsorption of atomic hydrogen on graphite and carbon nanostructures.     

The hydrogen sorption and desorption behavior in spherical powder of pure titanium used for additive manufacturing

The hydrogen sorption and desorption behavior in spherical powder of pure titanium used for additive manufacturing have been investigated. The dependencies of oxide dissolution time and hydrogen sorption rate on pressure and temperature have been obtained. The main regularities of phase formation in titanium powder during hydrogenation until hydrogen concentration 4 wt% have been showed. The peculiarities of hydrogen desorption from the spherical powder of titanium with hydrogen concentration 4 wt% have been demonstrated.     

Transient reaction and exergy analysis of catalytic partial oxidation of methane in a Swiss-roll reactor for hydrogen production

Catalytic partial oxidation of methane (CPOM) is a promising method for hydrogen production with autothermal reaction. To figure out the unsteady reaction characteristics of CPOM in a Swiss-roll reactor along with heat recirculation, a numerical method is employed to simulate the transient reaction dynamics, with emphasis on energy recovery using exergy analysis. Three different gas hourly space velocities (GHSVs) of 5000, 10,000 and 50,000 h⁻¹ with the condition of atomic O/C ratio of 1 are considered. The predictions indicate that increasing GHSV substantially shortens the transient period of chemical reactions; however, it also reduces the methane conversion, as results of more reactants sent into the reactor and shorter residence time of the reactants in the catalyst bed. Within the investigated range of GHSV, the methane conversion with energy recovery at the steady state is larger than 80%, much higher than the reaction without heat recovery. The selectivities of H₂ and CO in the product gas are always larger than 90%. The exergy recovery is in the range of 66–80%, implying that over two-third useful work contained in the product gas can be reused to preheat the reactants in the reactor, thereby enhancing the performance of CPOM.     

Techno-economic optimization of PV system for hydrogen production and electric vehicle charging stations under five different climatic conditions in India

India is one of the most populous countries in the world, and this has implications for its energy consumption. The country's electricity generation and road transport are mostly dominated by fossil fuels. As such, this study assessed the techno-economics and environmental impact of a solar photovoltaic power plant for both electricity and hydrogen production at five different locations in India (i.e., Chennai, Indore, Kolkata, Ludhiana, and Mumbai). The hydrogen load represents a refueling station for 20 hydrogen fuel cell vehicles with a tank capacity of 5 kg for each location. According to the results, the highest hydrogen production occurred at Kolkata with 82,054 kg/year, followed by Chennai with 79,030 kg/year. Ludhiana, Indore, and Mumbai followed with 78,524 kg/year, 76,935 kg/year and 74,510 kg/year, respectively. The levelized cost of energy (LCOE) for all locations ranges between 0.41 and 0.48 $/kWh. Mumbai recorded the least LCOH of 3.00 $/kg. The total electricity that could be generated from all five cities combined was found to be about 25 GWh per annum, which translates to an avoidable emission of 20,744.07 metric tons of CO₂e. Replacing the gasoline that could be used to fuel the vehicles with hydrogen will result in a CO₂ reduction potential of 2452.969 tons per annum in India. The findings indicate that the various optimized configurations at the various locations could be economically viable to be developed.     

Use of lower grade coals in IGCC plants with carbon capture for the co-production of hydrogen and electricity

This paper investigates the potential use of lower grade coals in an IGCC-CCS plant that generates electricity and produces hydrogen simultaneously with carbon dioxide capture and storage. The paper underlines one of the main advantages of gasification technology, namely the possibility to process lower grade coals, which are more widely available than the high-grade coals normally used in European power plants. Based on a proposed plant concept that generates about 400 MW net electricity with a flexible output of 0–50 MW_th hydrogen and a carbon capture rate of at least 90%, the paper develops fuel selection criteria for coal fluxing and blending of various types of coal for optimizing plant performance e.g. oxygen consumption, hydrogen production potential, specific syngas energy production per tonne of oxygen consumed, etc. These performance indicators were calculated for a number of case studies through process flow simulations. The main conclusion is that blending of coal types of higher and lower grade is more beneficial in terms of operation and cost performance than fluxing high-grade coals.     

川西地区老井挖潜选井评层标准研究

老井挖潜以其"投资少、见效快、周期短"的优点,成为油气藏勘探开发中增储上产、增收节支、降本增效的重要举措。以新场气田为例,针对致密砂岩气藏复杂的地质特征,通过建立地震识别原则、录井地质综合指标评价标准和测井电性标准,结合储层改造工艺的特点,形成老井挖潜选井评层研究的思路与方法,实现挖潜选井评层标准由定性向定量化的转变。就新场气田而言,目前阶段,蓬莱镇组气藏"强波峰、低频率"和沙溪庙组气藏"低频率、强振幅"的特征作为老井挖潜选井评层的地震识别原则及标准是适用的;在对挖潜获得成功的含气层的测井响应及解释资料归纳总结,并与蓬莱镇组、沙溪庙组历年挖潜获得成功的气层的测井响应特征结合的基础上,建立的挖潜选井评层测井电性标准、特别是给出的储层电性特征推荐值是可靠的,可以为老井挖潜选井选层提供参考。