Peak Gas Production Research Articles

Effect of water occurrence in coal reservoirs on the production capacity of coalbed methane by using NMR simulation technology and production capacity simulation

The occurrence of gas and water is a critical factor affecting the production capacity of coalbed methane. Therefore, occurrence and dynamic interaction between gas and water in coal reservoirs need to be studied. T2 spectrum of all the samples were studied by NMR technique at 0, 5, 9, and 28 h of natural evaporation. Then, multifractal model was used to characterize water distribution heterogeneity, and a novel evaluation coefficient was proposed to characterize distribution heterogeneity of water content, the correlation among evaluation coefficient, water distribution heterogeneity and pore structure parameters was analyzed. The results are as follows. In the saturated state, the moisture distribution of three types is heterogeneous. Type A of adsorption pore-developed exhibits strong moisture variation heterogeneity of small pores, in contrast to the uniform moisture variation in large pores. Type B of fracture-developed has the highest coefficient of variation in moisture distribution. The coefficient of variation A1 for moisture content can determine the speed of moisture transport and evaporation in the pore structure. A lower A1 indicates a greater moisture transport volume and faster moisture transport rate over the same time. The coefficient of variation A2 for moisture distribution represents the heterogeneity of moisture content variation in the pore structure. That is, a smaller A2 indicates better heterogeneity in the distribution of moisture content in the pore structure. Numerical simulation indicates the average gas production and the peak gas production time increase and decrease with the initial moisture content (Sgrw) increases, respectively. These findings provide practical guidance for coalbed methane development, especially in optimizing coalbed methane production capacity prediction and improving recovery efficiency.

The gas production characteristics and catastrophic hazards evaluation of thermal runaway for LiNi0.5Co0.2Mn0.3O2 lithium-ion batteries under different SOCs

Lithium-ion batteries (LIBs) are widely used as electrochemical energy storage systems in electric vehicles due to their high energy density and long cycle life. However, fire accidents present a trend of frequent occurrence caused by thermal runaway (TR) of LIBs, so it is especially important to evaluate the catastrophic hazards of these LIBs. This study conducted the adiabatic TR test coupled gas production test, Gas Chromatography-Mass Spectrometry test, and explosion limit test on a commercial LIB with Ni0.5Co0.2Mn0.3 as the cathode material at different states of charge (SOCs). The results show that the TR temperature and the maximum temperature at low SOC are lower compared to that at a high SOC. The probability of LIBs TR at less than SOC = 50 % is small and also causing less harm. For the gas production characteristics, the lower the SOC of the battery, the lower the gas production volume. The peak and steady-state gas production increase with the increase of SOC. For the mixed gases generated during TR, the content of CO2 shows a trend of decreasing with the increasing of battery SOC, while that of H2 and CO increase with the increasing of SOC. For the explosion limit of the mixed gas, the lower explosion limit and upper explosion limit decrease and increase with the increasing of SOC, respectively. Finally, based on the seven parameters related to the TR gas production of LIBs and so on, the analytic hierarchy process method was used to establish a LIB TR disaster-causing hazard evaluation system. The evaluation system can quantitatively evaluate the thermal safety of a LIB. This is instructive for establishing a comprehensive quantitative evaluation method for battery safety in practical engineering applications.

Extreme massive hydraulic fracturing in deep coalbed methane horizontal wells: A case study of the Linxing Block, eastern Ordos Basin, NW China

Deep coal seams show low permeability, low elastic modulus, high Poisson’s ratio, strong plasticity, high fracture initiation pressure, difficulty in fracture extension, and difficulty in proppants addition. We proposed the concept of large-scale stimulation by fracture network, balanced propagation and effective support of fracture network in fracturing design and developed the extreme massive hydraulic fracturing technique for deep coalbed methane (CBM) horizontal wells. This technique involves massive injection with high pumping rate + high-intensity proppant injection + perforation with equal apertures and limited flow + temporary plugging and diverting fractures + slick water with integrated variable viscosity + graded proppants with multiple sizes. The technique was applied in the pioneering test of a multi-stage fracturing horizontal well in deep CBM of Linxing Block, eastern margin of the Ordos Basin. The injection flow rate is 18 m3/min, proppant intensity is 2.1 m3/m, and fracturing fluid intensity is 16.5 m3/m. After fracturing, a complex fracture network was formed, with an average fracture length of 205 m. The stimulated reservoir volume was 1 987×104 m3, and the peak gas production rate reached 6.0×104 m3/d, which achieved efficient development of deep CBM.

Influence of depressurization mode on natural gas hydrate production characteristics: One-dimensional experimental study

The latest research suggests that using depressurization methods and their enhancements could be the most effective way to produce natural gas hydrates efficiently in marine areas. Therefore, it's crucial to investigate the gas production behavior and the changes in temperature and pressure within natural gas hydrate reservoirs under different depressurization methods. In this paper, the self-developed one-dimensional natural gas hydrate production simulation test system was utilized to conduct one-dimensional depressurization production tests during two depressurization modes of significant depressurization and slow depressurization. The findings indicated that the minimum temperature increment-depressurization rate curves in significant depressurization tests exhibited irregular patterns, primarily due to the frequency and intensity of hydrate reformation, while the smaller the depressurization rate, the larger the minimum temperature increment and the smaller the maximum dissociation rate under slow depressurization. In addition, when maintaining a fixed hydrate saturation level, the peak gas production rate showed a decline with decreasing depressurization rate. However, the exact correlation between the peak gas production rate and the depressurization rate remained uncertain due to the unpredictable nature of the “armoring” effect.

Gas production decline trends for Longmaxi shale under thermally stimulated conditions

Recently, thermal treatment has emerged as a promising technology to enhance shale gas recovery efficiency by promoting gas desorption. However, the understanding of gas desorption characteristics from heterogeneous shale matrix under thermal stimulation remains inadequate, which constrains the development of thermal recovery technology. In this study, on-site canister desorption tests were employed to investigate the shale gas desorption patterns of four distinct shale cores, sourced from four various production zones, under two heating stages (50 °C and 110 °C). Additionally, low-temperature N2 adsorption experiments and infrared examination were used to study the microstructure characteristics of shale before and after thermal treatments. The canister desorption tests revealed that the gas production rates increased for all shales under heating conditions, particularly when transitioning from 50 °C to 110 °C. However, the peak gas production rates at the two heating stages exhibited different trends: nearly identical for Shale-1 and Shale-2, decreasing for Shale-3 and increasing for Shale-4. This can be attributed to the different quantities of adsorbed gas present in shale samples, with Shale-4 containing approximately 0.0088 m3, compared to the markedly lower volumes in Shale-1 (0.0053 m3), Shale-2 (0.0040 m3), and Shale-3 (0.0041 m3). Furthermore, the gas production rates followed distinct decline trends at different temperatures: exponentially at 50 °C and following a power law at 110 °C, indicating varying gas desorption dynamics under different thermal conditions. Moreover, the findings from low-temperature N2 adsorption experiments and infrared examination indicated that combustion increased the pore volume and induced thermal cracks and fractures, thereby enhancing shale permeability. These insights highlight the potential of combustion fracturing as a technology to improve gas recovery efficiency.

Modeling of gas production during pyrolysis of biomass with triple gaussian function

To address the limitations of the inability to monitor the internal processing environment of pyrolysis, a triple Gaussian model was developed to effectively describe gas production during biomass pyrolysis at different dwelling temperatures and ramping rates. A CO2 and H2 gas sensor array was constructed to collect gas production data during the biomass pyrolysis which was fitted to the three gas production ranges of the triple Gaussian model, carbonization, gasification, and activation. The amplitude A (peak gas production), mean µ (time at gas production peak), and standard deviation σ (rate of gas production) components of the triple Gaussian function were studied for the three ranges. The results showed that as both ramping rate and dwelling temperature increased, the production of CO2 increased, while the H2 production decreased. The analysis of A, σ, and μ Gaussian components of the model showed that in the carbonization range, the peak CO2 increased and H2 production decreased. In the gasification range, the CO2 production decreased, while more H2 production happened as the ramping rate and dwelling temperature increased. The components of both H2 and CO2 models were compared. These relationships between Gaussian components and ramping rate and dwelling temperature, showed clear linear trends. The results showed that the carbonization and gasification ranges of the two models were inversed. ESEM was performed on the resulting carbons which showed that more degradation in the carbon structure occurred at higher temperatures and lower ramping rate.

Effects of Functional Groups in Coal with Different Vitrinite/Inertinite Ratios on Pyrolysis Products.

Maceral composition is one of the key factors affecting the liquefaction and gasification of coal, which has attracted extensive attention of researchers working on coal chemical industry. To elucidate the impact of vitrinite and inertinite in coal on pyrolysis products, vitrinite and inertinite were extracted from a single coal sample and mixed to create six samples with varying vitrinite/inertinite ratios. The samples were subjected to thermogravimetry coupled online with mass spectrometry (TG-MS) experiments, and the Fourier transform infrared spectrometry (FITR) experiment was used to determine the macromolecular structures before and after the TG-MS experiments. The results show that the maximum mass loss rate is proportional to the vitrinite content and inversely proportional to the inertinite content, and increased vitrinite content accelerates the pyrolysis process and shifts the pyrolysis peak to low temperatures. Based on FTIR experiments, the sample's CH2/CH3 content, representing the length of aliphatic side chains, decreases significantly after pyrolysis, and the greater the loss of CH2/CH3, the greater the intensity of organic molecule production, indicating that aliphatic side chains are likely to yield organic molecule products. The aromatic degree (I) of samples rises sharply and steadily with increasing inertinite content. After high-temperature pyrolysis, the polycondensation degree of aromatic rings (DOC) and relative abundance of aromatic and aliphatic hydrogen (Har/Hal) within the sample increased significantly, indicating the thermal degradation rate of aromatic hydrogen content is much lower than that of aliphatic hydrogen. When the pyrolysis temperature is lower than 400 °C, the higher the inertinite content, the easier it is to produce CO2, whereas an increase in vitrinite leads to an increase in CO production. At this stage, the "-C-O-" functional group is pyrolyzed to produce CO and CO2. When the temperature exceeds 400 °C, the CO2 output intensity of vitrinite-rich samples is much higher than that of inertinite-rich samples, while the CO output intensity of vitrinite-rich samples is lower, and the higher the vitrinite content, the higher the peak temperature of CO gas production of samples, indicating that when the temperature exceeds 400 °C, the increase of vitrinite inhibits CO production and promotes CO2 production. At this stage, the reduction of each sample's "-C-O-" functional group after pyrolysis is positively correlated with the maximum CO gas production intensity, and the reduction of each sample's "-C=O" functional group after pyrolysis is positively correlated with the maximum CO2 gas production intensity. As a result, the "-C-O-" functional group is more likely to produce CO, whereas the "-C=O" functional group is more likely to be pyrolyzed to CO2. Hydrogen is primarily produced during the polycondensation and aromatization processes, and its production is proportional to the dynamic DOC values after pyrolysis. The higher the I value after pyrolysis, the lower the maximum gas production peak intensity of CH4 and C2H6, which indicates that increasing the aromatic proportion is detrimental to CH4 and C2H6 production. This work is expected to provide theoretical support of the liquefaction and gasification of coal with different vitrinite/inertinite ratios.

Effects of biogas slurry reflux mode and reflux rate on methane production by mixed anaerobic digestion of corn straw and pig manure

Biogas slurry reflux is a promising method to realize biogas slurry reduction and improve biogas production performance of anaerobic digestion. The purpose of this study was to investigate the effects of reflux mode and reflux ratio on mixed anaerobic digestion of corn straw and pig manure to obtain the best biogas slurry reflux process. The influence of reflux mode and reflux ratio on the internal environment during anaerobic digestion were clarified by kinetic analysis. The results showed that compared with the control group, the degree of substrate hydrolysis in the hydrolysis phase reflux (HPR) and two-phase synergistic reflux (TPSR) treatment groups increased, and the initial concentration and peak value of volatile fatty acids (VFAs) increased by 20.35%–85.81% and 24.72%–74.37%, respectively. The modified Gompertz model fitting results that the three biogas slurry reflux modes all significantly shortened the lag period of anaerobic digestion (17.29%–48.32%) and increased the peak gas production (7.54%–88.07%). And the maximum daily gas production (65.82 mL/(g VS∙d)), methane production (422.86 mL/g VS) and biodegradation rate (83.65%) were obtained under the TPSR mode with reflux ratios of 75% and 100%. This study provides a theoretical basis for the development of biogas slurry reflux technology in the mixed anaerobic digestion of corn straw and pig manure, and realizes the reduction and resource utilization of biogas slurry.

Transient modeling of plunger lift with check valve for gas well deliquification in horizontal well

ABSTRACT To improve the plunger gas lift efficiency, a modified plunger was developed by adding a check valve to the downhole positioner in the Changqing Gas Field. However, the transient flow behavior of the plunger lift with check valve is unclear owing to the lack of a reliable method. Therefore, in this study, a simplified transient mechanistic model based on the law of conservation of momentum and mass is proposed to simulate the comprehensive dynamic process of a plunger-lift system. The results of the proposed method exhibited a high coincidence with that of the accumulated gas and liquid production of gas Well-1 in one cycle, and the relative errors were 2.11% and 4.29%, respectively. The calculation results demonstrate that the plunger lift with check valve can effectively prevent the flow of liquid to the bottom of the well, reduce the bottom hole flow pressure, and increase the productivity of gas well during the shut-in period. The efficiency of the plunger lift with check valve was enhanced with an increase in the volume of the accumulated liquid unloaded from the bottom of gas wells. Additionally, for the plunger lift with check valve, the production peak value was higher and the instantaneous gas production peak value was lower in comparison with the conventional plunger. After the plunger reached the wellhead, the instantaneous fluid production of the conventional plunger was relatively unstable than that of the plunger lift with check valve. A certain distance should be maintained from the bottom of the well in the case of the positioner with check valve. If the positioner is placed at the bottom of the tubing, the difference between the lift efficiency of the plunger with check valve and conventional plunger is small, and lower than that of the conventional plunger. The installation position of the downhole positioner in a gas well should be below the accumulated liquids level and should maintain a certain distance between the positioner and bottom of the well (200 m). The results of this study enhance the understanding of the operation mechanism of the plunger lift with check valve, and unloading of the accumulated liquids from the bottom of gas wells.

Numerical simulation of gas extraction from marine hydrate sediments using sodium chloride injection

The inhibitor injection method is an important method for natural gas hydrate development and sodium chloride (NaCl) is a cheap and clean inhibitor. In this study, a new three-dimensional three-phase, four-component numerical model is developed to consider the effect of inhibitors. The focus is on the production dynamics of hydrate development by using inhibitor injection method, and the effects of different injection salt mass fraction, temperatures, and pressures are investigated. The results show that the inhibitor injection method has higher gas production rates, higher peak gas production, and shorter extraction development period compared to conventional extraction methods in challenging hydrate reservoirs. In addition, higher inhibitor concentrations increase peak gas production rates and shorten the development period. Injected pressure at 20 MPa is reasonable. The results of the global sensitivity analysis of the production parameters indicate that the mass fraction of salt in the injected water has a significant positive effect on extraction. In summary, the inhibitor injection method can be an effective method for developing challenging hydrate-bearing sediments

Enhancing Biogas Production of Corn Stover by Biogas Slurry Reflux Based on Microfiltration Membrane Filtration and Biochar Adsorption

Reflux of biogas slurry is an effective way to reduce the discharge of wastewater. In order to improve the utilization efficiency of reflux fluid and reduce ammonia inhibition in an anaerobic digestion (AD) system, biogas slurry was pretreated by microfiltration membrane and biochar adsorption. In this study, the suspension solid (SS), biochemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) were investigated, as well as the gas production effect of the reflux of biogas slurry in AD, so as to evaluate the filtration effect of the microfiltration membrane with different pore sizes and the adsorption effect of biochar with different dosages. The results showed that 0.65 μm microfiltration had the best interaction effect and 7 g/L biochar had the best adsorption effect. The results of anaerobic co-digestion of the biogas slurry and corn stover showed the peak gas production of the pretreated reflux fluid was advanced by 1 day, and the maximum daily methane production and maximum cumulative methane production reached 39.20 mL·g−1 VS and 137.14 mL·g−1 VS, respectively. These results indicated that the combined treatment of biogas slurry by microfiltration membrane and biochar could have potential applications for the treatment and recycling of biogas slurry.

The Influence of Fracturing Fluid Volume on the Productivity of Coalbed Methane Wells in the Southern Qinshui Basin

Hydraulic fracturing is the main technical means for the reservoir stimulation of coalbed methane (CBM) vertical wells. The design of fracturing fluid volume (FFV) is mainly through numerical simulation, and the numerical simulation method does not fully consider the water block damage caused by the leakage of fracturing fluid into the reservoir. In this work, the variance analysis method was used to analyze the production data of 1238 CBM vertical wells in the Fanzhuang block and Zhengzhuang block of the Qinshui Basin, to clarify the relationship between the FFV and the peak gas production (PGP) under the different ratios of critical desorption pressure to reservoir pressure (Rc/r), and to reveal the controlling mechanism of fracturing fluid on CBM migration. The results show that both the FFV and Rc/r have a significant impact on gas production. When Rc/r < 0.5, the PGP decreases with the increase of the FFV, and the FFV that is beneficial to gas production is 200–500 m3. When Rc/r > 0.5, the PGP increases first and then decreases with the increase of FFV. Specifically, the FFV that is favorable for gas production is 500–700 m3. Excessive FFV does not significantly increase the length of fractures due to leaks in the coal reservoir. Instead, it is more likely to invade and stay in smaller pores, causing water block damage and reducing gas production. Reservoirs with high Rc/r have larger displacement pressure, which can effectively overcome the resistance of liquid migration in pores, thereby reducing the damage of the water block. Therefore, different reservoir conditions need to match the appropriate fracturing scale. This study can provide guidance for the optimal design of hydraulic fracturing parameters for CBM wells.

The effects of time variable fracture conductivity on gas production of horizontal well fracturing in natural gas hydrate reservoirs

AbstractHydrate reservoirs in the South China Sea belong to muddy silt‐type hydrate reservoirs with low permeability. Horizontal well fracturing is one of the main stimulation methods for low‐permeability oil and gas reservoirs. For muddy silt‐type hydrate reservoirs, the stability and effectiveness of hydraulic fractures may be a severe problem due to poor reservoir cementation, reservoir deformation, and sand production. In this paper, the time variability of fracture conductivity is considered for the first time. According to the geological data at offshore gas hydrate production test site in the South China Sea, a multilayer hydrate reservoir model was established, and the influence of the time variable fracture conductivity on the production behavior in the process of horizontal well fracturing was analyzed. The simulation results show that, compared with the case of constant fracture conductivity, the gas production rate with the case of time variable fracture conductivity is greatly reduced, and the 5‐year cumulative gas production is reduced by 49.9%. Sensitivity analysis shows that the larger the initial fracture conductivity, the higher the peak gas production rate; the larger the attenuation magnitude of the fracture conductivity, the lower the gas production rate in the late production period; the larger the decline rate coefficient of the fracture conductivity, the higher the gas production rate in the early production period. The analysis of the orthogonal experimental design shows that the influence of the attenuation magnitude of fracture conductivity, the initial conductivity of fracture, and the decline rate coefficient of fracture conductivity on the cumulative gas production decreases in order. The actual production process should try to avoid excessive attenuation magnitude of fracture conductivity, while improving the initial fracture conductivity as much as possible to ensure high cumulative gas production.

Coalbed methane reservoir dynamic simulation comparisons using the actual steeply inclined model and ideal steeply inclined model

Numerical simulation is an efficient method to quantitatively describe the reservoir dynamics of coalbed methane (CBM) reservoirs. The ideal steeply inclined model (ISIM), assumed to be a steeply inclined plate, has been widely applied in steep coalbed methane reservoir modeling, although the ISIM cannot accurately reflect the actual reservoir geological conditions. In this paper, the dynamics of CBM production and reservoirs using the ISIM and actual steeply inclined model (ASIM) were compared, taking the steep coal in the Fukang mining area located in northwestern China as an example, with the purpose of revealing the differences and applicability of the ASIM and ISIM. The ASIM and ISIM were established by Petrel software, and CBM production was matched and predicted by Eclipse software. Data reflecting reservoir dynamics, such as water saturation, reservoir pressure, and gas content, were extracted. The dynamic changes in the reservoir physical properties of the ASIM and ISIM were also compared. The results showed that: 1) multiple gas production peaks occurred in both ASIM and ISIM. The maximum daily gas production of ASIM occurred earlier than the maximum daily gas production of ISIM. The peak gas production and cumulative gas production of ASIM were both greater than the peak gas production and cumulative gas production of ISIM. 2) Due to the variations in grid shape and dip angle with each grid in the ASIM, the production effect of the ASIM was better than the production effect of the ISIM in the third stage (4–10 years) of drainage. 3) In the third stage (4–10 years) of drainage, the decrease rate of reservoir pressure of ASIM was larger than the decrease rate of reservoir pressure of ISIM because of the relatively better production performance of ASIM. 4) Differentiation of gas and water dominated the variation trend of gas content, and in the third stage (4–10 years) of drainage, the ASIM has higher recovery efficiency compared with ISIM. Compared with ISIM proposed by previous scholars, the ASIM was more helpful to monitor the dynamic behavior of coal reservoirs, and ASIM can provide a more reliable basis for guiding coalbed methane development.

Biohythane production from swine manure and pineapple waste in a single-stage two-chamber digester using gel-entrapped anaerobic microorganisms

A mixture of swine manure and pineapple waste was used to check the feasibility of producing biohythane in a newly-developed single-stage anaerobic fermentation system that having immobilized H2 and CH4-producing microbes in a two-chamber digester. Tested hydraulic retention times (HRT) were from 96 h to 6 h. HRT 6 h resulted in peak gas production performance with hydrogen production rate 1240 and methane production rate 812 mL/L-d. Besides, the synergistic function of generation and consumption of volatile fatty acids in this hybrid biosystem had a significant impact on biohythane composition with acetate and butyrate being the dominant liquid metabolites. Chemical oxygen demand and ammonium removal efficiencies were 52.4 and 78.8%, respectively during steady-state conditions. Based on the experimental findings, prospects for field applications of single-stage biohythane fermentation were suggested.

Gas production analysis for hydrate sediment with compound morphology by a new dynamic permeability model

Hydrate sediments usually have both pore-filling and grain-coating morphology, but current permeability models consider either pore-filling or grain-coating morphology. This paper proposes a dynamic permeability model for compound morphology in hydrate sediment with rough capillary. After it is verified with permeability experiments and existing permeability models, this dynamic permeability model is incorporated into our thermal-hydraulic-mechanical-chemical fully coupling model for hydrate decomposition. This fully coupling model is verified by the analytical solution of Terzaghi's one-dimensional consolidation and the Masuda's hydrate decomposition experiment. The simulation results showed that the difference between phase equilibrium pressure and reservoir dynamic pressure is an important indicator to ensure the stable and efficient production of hydrate. Capillary roughness mainly affects gas production peak rate during gas hydrate decomposition. Greater capillary roughness will make smaller gas production peak rate appear at later time. Cumulative gas production and sediment dynamic permeability increase with increase of the volume fraction of grain-coating hydrate.

Study on biogas production from corn straw pretreated by compound microorganisms

The pretreated corn straw is pretreated by Fomes fomentarius, Trichoderma adaptatum and the compound microbial agent of Fomes fomentarius and Trichoderma adaptatum under the same conditions. Then biogas was produced by anaerobic fermentation of pretreated straw. According to the experimental results, it has been found that the straw pretreatment with complex microorganisms can not only promote the process of straw anaerobic fermentation biogas production, but also improve the gas production and gas production efficiency, among which the compound microbial agent pretreatment shows the best effect. Compared with the untreated straw, the degradation of lignin and cellulose in straw pretreated with compound microbial agent is much higher, and the lignin content is decreased from 16.6% to 6.8%, and the cellulose content is decreased from 32.3% to 19.8%. Besides, the gas production of compound microbial agent pretreatment has increased by 14.86%, the gas production time is 6 d earlier, the gas production peak is 17 d earlier, the volume gas production rate reaches 2.008 mL/(mL⋅d), and the gas production rate of raw materials reaches 526.66 mL/g. The straw pretreatment with only Fomes fomentarius also has a good effect. However, the effect of straw pretreatment by Trichoderma adaptatum is poor, which has indicated that straw pretreatment by lignin-degrading strain plays an important role in improving the anaerobic fermentation efficiency of straw.

Effects of Organic Maceral on Biogenic Coalbed Gas Generation from Bituminous Coal.

Clarifying the effect of organic maceral on biogenic coalbed gas generation is important to understand the mechanism of biogenic coalbed gas generation and to develop bioengineering of coalbed gas. Bituminous coals in the Huainan mining area of China were selected as the research object, and the organic macerals were enriched through manual separation and floatation–sedimentation experiments first. Then, the simulated biogas generation experiments were carried out by using raw coal, single vitrinite, and inertinite, respectively. The results showed that all the bituminous coal, vitrinite, and inertinite could be biodegraded to generate biogas. The gas production yield of vitrinite was11.5 mL/g, which was more than that of raw coal (9.8 mL/g) and inertinite (6.26 mL/g). The production processes showed the stage characteristics of rapid increase and continuous decrease, but the gas production peak of inertinite lagged behind that of raw coal and vitrinite. Vitrinite content was positively correlated with total gas production, while inertinite could inhibit biogas production. CH4 composition in simulated biogas from vitrinite was the most, and that from inertinite was the least, while there was a positive correlation between vitrinite content and CH4 composition. The above evidence showed that vitrinite in bituminous coal is more easily biodegradable. There were significant positive correlations between chloroform bitumen “A”, H, and H/C to total gas production, and they can be used as important indicators to evaluate the output of coalbed biogas.

Effects of Increasing Concentrations of Enrofloxacin on Co-Digestion of Pig Manure and Corn Straw

Enrofloxacin (ENR) is one of the most commonly used antibiotics in pig farms. In this study, using fresh pig manure and corn straw powder as substrates, the effects of different concentrations of ENR (2.5, 10, and 20 mg/L) on anaerobic digestion in completely mixed anaerobic reactors were investigated. A relatively low concentration of ENR (2.5 mg/L) increased methane production by 47.58% compared with the control group. Among the volatile fatty acids (VFAs) in the reactors, the propionic acid content was the lowest, and the concentrations of acetic acid kinase and coenzyme F420 were highest in the first seven days during peak gas production. However, methane production in the reactors with 10 mg/L and 20 mg/L ENR decreased by 8.59% and 20.25%, respectively. Furthermore, the accelerated hydrolysis of extracellular polymeric substances causes a significant accumulation of VFA levels. The microbial community in anaerobic reactors was analyzed by 16S rRNA sequencing. Proteiniphilum was the dominant bacterial genus. In addition, ENR at 2.5 mg/L effectively increased the abundance and diversity of anaerobic microorganisms, whereas a high concentration of ENR (10 and 20 mg/L) significantly decreased these parameters. This study demonstrated that different concentrations of ENR had significantly different effects on anaerobic digestion.

China's natural gas production peak and energy return on investment (EROI): From the perspective of energy security

China has to make full use of natural gas for a long period due to its cleanness and economy. To ensure energy security and promote natural gas development, it is necessary to reasonably predict natural gas peak under the background of unconventional natural gas replacing conventional natural gas in the long term. Based on Hubbert's peak theory, this paper forecasts that China's natural gas production will reach 196.7–582.5 billion cubic meters when considering the contribution of unconventional natural gas. The upper value is an optimistic scenario that fully considers the impact of technological progress and development investment on unconventional natural gas exploration. In an optimistic scenario, China can achieve energy security and a Nationally Determined Contribution plan by controlling the foreign dependence on natural gas within 40%. This paper also analyzes the internal mechanism between resource scarcity, natural gas peak and energy transformation from an energy return on investment. China's EROI in the oil and gas industries has experienced a U-shaped fluctuation process; in an optimistic scenario; EROI will continue to rise until natural gas production reaches its peak and effectively make natural gas the bridging fuel for the transformation from fossil energy to renewable energy.