Gas content serves as a critical indicator for assessing the resource potential of deep coal mines and forecasting coal mine gas outburst risks.However,existing sampling technologies face challenges in maintaining the...Gas content serves as a critical indicator for assessing the resource potential of deep coal mines and forecasting coal mine gas outburst risks.However,existing sampling technologies face challenges in maintaining the integrity of gas content within samples and are often constrained by estimation errors inherent in empirical formulas,which results in inaccurate gas content measurements.This study introduces a lightweight,in-situ pressure-and gas-preserved corer designed to collect coal samples under the pressure conditions at the sampling point,effectively preventing gas loss during transfer and significantly improving measurement accuracy.Additionally,a gas migration model for deep coal mines was developed to elucidate gas migration characteristics under pressure-preserved coring conditions.The model offers valuable insights for optimizing coring parameters,demonstrating that both minimizing the coring hole diameter and reducing the pressure difference between the coring-point pressure and the original pore pressure can effectively improve the precision of gas content measurements.Coring tests conducted at an experimental base validated the performance of the corer and its effectiveness in sample collection.Furthermore,successful horizontal coring tests conducted in an underground coal mine roadway demonstrated that the measured gas content using pressure-preserved coring was 34%higher than that obtained through open sampling methods.展开更多
The methane adsorption capacity,gas content,and carbon isotope characteristics of coal are crucial parameters that determine the productivity of coalbed methane(CBM)wells and their development potential.In this paper,...The methane adsorption capacity,gas content,and carbon isotope characteristics of coal are crucial parameters that determine the productivity of coalbed methane(CBM)wells and their development potential.In this paper,test analyses of methane adsorption,gas content and carbon isotope of methane were carried out using 89 samples from the No.3 coal seam in the southwestern part of the Qinshui Basin.Their characteristics and correlations were analyzed.A relationship model between methane adsorption,gas content,carbon isotopes,coal metamorphism and material composition were established,and its controlling mechanism was investigated.The results indicate that the distribution patterns of Langmuir volume and Langmuir pressure in No.3 coal seam are mainly determined by the material composition and the thermal evolution level.The methane gas content in coal is mainly affected by the burial depth,microcosmic co mposition,mineral conte nt,moisture content and ash yield,adsorption capacity and metamorphism of the coal.The methane carbon isotope(δ^(13)C_(1))values in the natural desorbed gas from No.3 coal seam range from-26.95%to-57.80‰,with a mean value of-34.53‰.δ^(13)C_(1)in coal shows a two-stage variation pattern with increasing in vitrinite reflectance(R_(max)^(o)).When R_(max)^(o)is blow 3.0%,δ^(13)C_(1)values of methane in coal become progressively heavier with increasing R_(max)^(o).When R_(max)^(o)reaches or exceeds 3.0%,δ^(13)C_(1)values exhibit a lightning trend with furth er increases in R_(max)^(o),which is primarily controlled by the carbon isotope fractionation effects during thermal evolution.展开更多
The Lower Cambrian shales in the Sichuan Basin are considered one of the most promising shale gas resources in China.However,large-scale commercial development has not been achieved due to the relatively low and signi...The Lower Cambrian shales in the Sichuan Basin are considered one of the most promising shale gas resources in China.However,large-scale commercial development has not been achieved due to the relatively low and significantly variable gas contents of the drilled shales.Excitingly,the first major breakthrough in deep and ultra-deep Lower Cambrian shale gas was made recently in the well Z201 in the southern Sichuan Basin,with a gas yield exceeding 73×10^(4)m^(3)/d.The success of well Z201 provides a favorable geological case to reveal the distinct enrichment mechanism of deep and ultra-deep Lower Cambrian shale gas.In this study,at drilling site of well Z201,fresh shale core samples with different gasin-place contents were collected,and their geochemical,pore development and water-bearing characteristics were analyzed systematically.The results showed that the Z201 organic-rich shales reached an overmature stage,with an average Raman maturity of 3.70%.The Z201 shales with high gas-in-place contents are mainly located in the Qiongzhusi 12section and the upper Qiongzhusi 11section,with an average gas-in-place content of 10.08 cm^(3)/g.Compared to the shales with low gas-in-place contents,the shales with high gas-in-place contents exhibit higher total organic carbon contents,greater porosities,and lower water saturations,providing more effective pore spaces for shale gas enrichment.The effective pore structures of the deep and ultra-deep Lower Cambrian shales are the primary factors affecting their gas-in-place contents.Similar to the shales with high gas-in-place contents of well Z201,the deep and ultra-deep Lower Cambrian shales in the Mianyang-Changning intracratonic sag,especially in the Ziyang area,generally developed in deep-water shelf facies with high total organic carbon contents and thick sedimentary thickness,providing favorable conditions for the development and preservation of effective pores.Therefore,they are the most promising targets for Lower Cambrian shale gas exploration.展开更多
Currently,regression prediction methods based on logging data is one of the main methods for analyzing gas content of coal seams.However,the complexity of logging parameters for deep coal seams and the scarcity of mea...Currently,regression prediction methods based on logging data is one of the main methods for analyzing gas content of coal seams.However,the complexity of logging parameters for deep coal seams and the scarcity of measured gas content data signifcantly afects the accuracy and generalizability of data regression models.Accurately predicting the gas content of coal seams under small-sample condition become a difcult point in deep coalbed methane(CBM)exploration.The ModelAgnostic Meta-Learning(MAML)and Support Vector Regression(SVR)algorithms are among the few suitable for smallsample learning,exhibiting strong adaptability under limited sample conditions.In this study,logging parameters are used as input variables to construct MAML and SVR models,and their performance in predicting gas content of deep coal seams across diferent regions and layers is compared.The results demonstrate that the MAML algorithm efectively addresses the complex relationships between gas content of deep coal seam and logging parameters.The prediction errors for test dataset and new samples are merely 3.61%and 4.52%respectively,indicating exceptional adaptability,robust generalization capability,and stable model performance.In contrast,the dependency of SVR model on input parameters restricts its accuracy and generalizability in predicting gas content in deep coal seams with varying geological conditions.Although achieving a test dataset error of 4.71%,the SVR model demonstrates substantially degraded performance when applied to novel samples,with prediction errors escalating to 12.46%.Therefore,the MAML model is selected to predict gas content in the unknown areas of the Baijiahai region.The prediction results reveal that the gas content of coal seams in the Xishanyao formation(J2x)ranges from 1.32 m^(3)/t to 16.11 m^(3)/t,while that in the Badaowan Formation(J1b)varies between 1.73 m^(3)/t and 11.27 m^(3)/t.Notably,the gas enrichment areas are predominantly distributed in well blocks adjacent to fault systems,such as wells C31 and BJ8,etc.,which align with the favorable geological conditions for deep CBM accumulation in the Baijiahai region.These spatial distribution patterns not only corroborate existing geological insights but also further validate the reliability of the MAML model in predicting gas content within deep coal seams.展开更多
Coal seam gas content is frequently measured in quantity during underground coal mining operation and coalbed methane(CBM)exploration as a significant basic parameter.Due to the calculation error of lost gas and resid...Coal seam gas content is frequently measured in quantity during underground coal mining operation and coalbed methane(CBM)exploration as a significant basic parameter.Due to the calculation error of lost gas and residual gas in the direct method,the efficiency and accuracy of the current methods are not inadequate to the large area multi-point measurement of coal seam gas content.This paper firstly deduces a simplified theoretical dynamic model for calculating lost gas based on gas dynamic diffusion theory.Secondly,the effects of various factors on gas dynamic diffusion from coal particle are experimentally studied.And sampling procedure of representative coal particle is improved.Thirdly,a new estimation method of residual gas content based on excess adsorption and competitive adsorption theory is proposed.The results showed that the maximum error of calculating the losing gas content by using the new simplified model is only 4%.Considering the influence of particle size on gas diffusion law,the particle size of the collected coal sample is below 0.25 mm,which improves the measurement speed and reflects the safety representativeness of the sample.The determination time of gas content reduced from 36 to 3 h/piece.Moreover,the absolute error is 0.15–0.50 m^3/t,and the relative error is within 5%.A new engineering method for determining the coal seam gas content is developed according to the above research.展开更多
The key of the direct method of determining coalbed gas content is how to shorten the coal core exposure time in the sampling progress and reduce measuring error of gas content which comes from the calculation of losi...The key of the direct method of determining coalbed gas content is how to shorten the coal core exposure time in the sampling progress and reduce measuring error of gas content which comes from the calculation of losing gas content. The coring tests were carried out in No.24 drilling field of 715 floor gateway in Qinan Coal Mine by using traditional drill core bar- rel sampler and self-designed reversion seal coring equipment. The losing gas content was calculated by power functional method, and the gas content of two coring methods was determined, respectively. Results show that, compared with traditional drill core barrel sampling, the newly seal coring equipment can significantly shorten the coal core exposure time, the 30 min desorption gas content increases obviously, the calculation of losing gas content reduces by 56.99%, the desorption gas content in normal atmosphere increases by 113.24%, and the determining value of gas content increases by 10.06%. The new technol- ogy has much higher accuracy, and it is worthwhile to be popularized.展开更多
The sudden and violent nature of coal and gas outbursts continues to pose a serious threat to coal mine safety in China. One of the key issues is to predict the occurrence of outbursts. Current methods that are used f...The sudden and violent nature of coal and gas outbursts continues to pose a serious threat to coal mine safety in China. One of the key issues is to predict the occurrence of outbursts. Current methods that are used for predicting the outbursts in China are considered to be inadequate, inappropriate or impractical in some seam conditions. In recent years, Huainan Mining Industry Group(Huainan) in China and the Commonwealth Scientific and Industrial Research Organisation(CSIRO) in Australia have been jointly developing technology based on gas content in coal seams to predict the occurrence of outbursts in Huainan. Significant progresses in the technology development have been made, including the development of a more rapid and accurate system in determining gas content in coal seams, the invention of a sampling-while-drilling unit for fast and pointed coal sampling, and the coupling of DEM and LBM codes for advanced numerical simulation of outburst initiation and propagation. These advances are described in this paper.展开更多
The influence of ground stress was quantitatively analyzed on coal seam gas pressure and gas content in this paper.Mining activities in coal mine can result in stress concentration in the coal(rock)body around the min...The influence of ground stress was quantitatively analyzed on coal seam gas pressure and gas content in this paper.Mining activities in coal mine can result in stress concentration in the coal(rock)body around the mining space,but porosity of the coal seam would not change too much.Therefore,gas pressure and gas content in the coal seam are slightly affected.Studies showed that the free gas was gradually transformed into adsorbed gas,and the gas adsorption volume was small,and then gas pressure increases roughly linearly when the porosity decreased because of stress influence.Additionaly,when porosity of coal seam reduced to 40%,the amount of adsorbed gas accounted for no more than 10%of coal seam gas content,and the increase of gas pressure did not exceed 15%of the original gas pressure.展开更多
The methane bubble plume attracts interest because it offers direct evidence of seafloor gas leakage and plays an indirect role in the exploration and identification of natural gas hydrate.In this study,based on estab...The methane bubble plume attracts interest because it offers direct evidence of seafloor gas leakage and plays an indirect role in the exploration and identification of natural gas hydrate.In this study,based on established plume models and their migration sections,three amplitude-class attributes were extracted from three formations for the migration sections of five plumes,and the correlation between the gas content and seismic attribute was obtained.As the gas content increases,the amplitude attribute correspondingly increases,and the linear correlation is relatively good.Moreover,correlation coefficients between gas content and amplitude attributes are close to 1.0.By using linear fitting,the relation model between the gas content of the plume and the seismic attribute was obtained.The relation model was subsequently used to invert the gas content from a real databearing plume.Comparison of the gas content section of the plume with the attribute section and real seismic section reveals common distribution characteristics,namely,the color of the section in the lower right corner is dark.If the amplitude value is large in the seismic section of the real plume,the amplitude attribute value is also large in the corresponding attribute section,and the inverted value of the gas content is also large(because gas content and amplitude are linearly correlated),which indicates that the plume bubbles of the section in the lower right corner is intensively distributed.Finally,the obtained gas content section of the plume can reflect the distribution of the plume bubble content more simply and intuitively,from which the distribution law of seafloor bubbles can be deduced,and this lays a foundation for the further estimation of the gas content of the plume and hydrate reserves.展开更多
The gas content is crucial for evaluating coal and gas outburst potential in underground coal mining. This study focuses on investigating the in-situ coal seam gas content and gas sorption capacity in a representative...The gas content is crucial for evaluating coal and gas outburst potential in underground coal mining. This study focuses on investigating the in-situ coal seam gas content and gas sorption capacity in a representative coal seam with multiple sections (A1, A2, and A3) in the Sydney basin, where the CO_(2) composition exceeds 90%. The fast direct desorption method and associated devices were described in detail and employed to measure the in-situ gas components (Q_(1), Q_(2), and Q_(3)) of the coal seam. The results show that in-situ total gas content (Q_(T)) ranges from 9.48 m^(3)/t for the A2 section to 14.80 m^(3)/t for the A3 section, surpassing the Level 2 outburst threshold limit value, thereby necessitating gas drainage measures. Among the gas components, Q_(2) demonstrates the highest contribution to Q_(T), ranging between 55% and 70%. Furthermore, high-pressure isothermal gas sorption experiments were conducted on coal samples from each seam section to explore their gas sorption capacity. The Langmuir model accurately characterizes CO_(2) sorption behavior, with ft coefcients (R^(2)) greater than 0.99. Strong positive correlations are observed between in-situ gas content and Langmuir volume, as well as between residual gas content (Q_(3)) and sorption hysteresis. Notably, the A3 seam section is proved to have a higher outburst propensity due to its higher Q_(1) and Q_(2) gas contents, lower sorption hysteresis, and reduced coal toughness f value. The insights derived from the study can contribute to the development of efective gas management strategies and enhance the safety and efciency of coal mining operations.展开更多
On the basis of the analysis of coal bed gas pressure in deep mine, and the coal bed permeability ( k ) and the characteristic of adsorption parameter ( b ) changing with temperature, the author puts forward a new cal...On the basis of the analysis of coal bed gas pressure in deep mine, and the coal bed permeability ( k ) and the characteristic of adsorption parameter ( b ) changing with temperature, the author puts forward a new calculating method of gas content in coal seam influenced by in situ stress grads and ground temperature. At the same time, the contrast of the measuring results of coal bed gas pressure with the computing results of coal bed gas pressure and gas content in coal seam in theory indicate that the computing method can well reflect the authenticity of gas content in coal seam,and will further perfect the computing method of gas content in coal seam in theory,and have important value in theory on analyzing gas content in coal seam and forecasting distribution law of gas content in coal seam in deep mine.展开更多
In this study, we selected 9 typical coal samples with different metamorphic grades as the study subjects,measured their initial 30-min gas desorption at 30℃ and different pressure using a self-developed gas adsorpti...In this study, we selected 9 typical coal samples with different metamorphic grades as the study subjects,measured their initial 30-min gas desorption at 30℃ and different pressure using a self-developed gas adsorption/desorption device. Based on the characteristics of gas desorption from coal samples, we proposed a direct fitting method for measurement of gas content in coalbed, analyzed the effects of sampling time on the measurement results and determined the reasonable sampling time of coal samples with different metamorphic grades at different gas adsorption pressure at equilibrium. The results show that (1)the error of gas contents obtained using the direct fitting method relative to that obtained using indirect method is less than 10%, which meets the actual on-site requirements and verifies the feasibility of the direct fitting method;(2) when the relative error is controlled within ±10%, the reasonable sampling time of coal samples is linearly related to the gas adsorption pressure at equilibrium;(3) the reasonable sampling time of coal samples with the same metamorphic grade exhibits a shortening trend with increasing gas adsorption pressure at equilibrium;(4) for coal samples with similar gas adsorption pressure at equilibrium, the reasonable sampling time of coal samples displays a shortening trend with increasing metamorphic grade. Overall, the study provides a basis for improving the measurement accuracy of gas content in coalbed.展开更多
When the gas content of a coal reservoir is calculated,the reservoir pressure measured by well logging and well testing is generally used for inversion calculation instead of gas pressure.However,the calculation resul...When the gas content of a coal reservoir is calculated,the reservoir pressure measured by well logging and well testing is generally used for inversion calculation instead of gas pressure.However,the calculation result is not accurate because the reservoir pressure is not equal to the gas pressure in overpressure environments.In this paper,coal samples of different ranks in Shanxi and Henan are collected for testing the capillary pressure of coal pores.Based on the formation process of CBM reservoirs and the hydrocarbon generation and expulsion history of coal beds,the forming mechanisms of micro-pore overpressure environments in coal reservoirs were analyzed.Accordingly,a new method for calculating the gas content of coal reservoirs with consideration of a micro-pore overpressure environment was developed.And it was used to calculate the gas content of No.1 coal bed of the 2nd member of Lower Permian Shanxi Fm in the Zhongmacun Coal Mine in Jiaozuo,Henan.It is indicated that during the formation and evolution of coals,some solid organic matters were converted into gas and water,and gasewater contact is surely formed in pores.In the end,capillary pressure is generated,so the gas pressure in micro-pores is much higher than the hydrostatic column pressure,which results in a micro-pore overpressure environment.Under such an environment,gas pressure is higher than reservoir pressure,so the gas content of coal reservoirs calculated previously based on the conventional reservoir pressure evaluation are usually underestimated.It is also found that the micro-pore overpressure environment exerts a dominating effect on the CBM content calculation of 3-100 nm pores,especially that of 3-10 nm pores,but a little effect on that of pores>100 nm.In conclusion,this new method clarifies the pressure environment of CBM gas reservoirs,thereby ensuring the calculation accuracy of gas content of coal reservoirs.展开更多
Gas content of the hydraulic system directly affects the rate of pressure change of the hydraulic system. The purpose of this paper is to establish a mathematical model of oil gas content, hydraulic system pressure an...Gas content of the hydraulic system directly affects the rate of pressure change of the hydraulic system. The purpose of this paper is to establish a mathematical model of oil gas content, hydraulic system pressure and pressure rise rate, obtain corresponding oil pressure value when the pressure rise rate of different gas content is maximum, and verify the accuracy of this conclusion by the FLUENT simulation software. On this basis, a rapid pressure building device of the hydraulic system is developed and designed. The above oil pressure value is used as the working cut-off pressure of the rapid pressure building device, and then the hydraulic oil pump continues to pressurize to the highest working pressure required by the system. The research content can replace the hydraulic system from the initial low pressure to the rapid pressure build-up of the oil, thus increasing the construction pressure of the hydraulic system. The research results show that the rapid pressure building device effectively reduces the time for the hydraulic system to establish pressure. Through the analysis of theoretical derivation and the collected experimental data, the error is about 5.9%, which verifies the correctness of the theoretical formula.展开更多
Factors of shale gas accumulation can be divided into the external and internal factors,according to accumulation mechanism and characteristics of shale gas. The internal factors mainly refer to parameters of organic ...Factors of shale gas accumulation can be divided into the external and internal factors,according to accumulation mechanism and characteristics of shale gas. The internal factors mainly refer to parameters of organic geochemistry,mineral components and physical parameters. Six factors were presented in this study,i. e.organic matter,maturity,quartz,carbonate,clay mineral and pore. The external factors mainly refer to geologic environment of shale gas reservoir,including four factors: temperature,pressure,depth and thickness.Based on the experiment results of 26 samples of drilling cores from Wuling fold belt in Lower Paleozoic Silurian of the Upper Yangtze Basin,combined with the integrated analysis of geology,logging and test,the correlation of the gas content of shale gas to the above-mentioned ten factors was concluded. Six important evaluation indicators were preliminarily established in the gas-bearing core area of marine shale in the Upper Yangtze Basin.展开更多
By investigating the evolution of shale gas generation,storage,adjustment and accumulation under different structural settings in superimposed basins,this study elucidates the differential accumulation mechanisms of s...By investigating the evolution of shale gas generation,storage,adjustment and accumulation under different structural settings in superimposed basins,this study elucidates the differential accumulation mechanisms of shale gas.An improved evaluation method of shale gas content evolution in superimposed basins is proposed.This method incorporates the coupling effect of key geological factors such as temperature,pressure,organic matter abundance,maturity,and pore characteristics on the content and occurrence state of shale gas,as well as the configuration relationship between shale gas generation and storage throughout geological history.Using this approach,the gas evolution histories of the Longmaxi Formation shales in wells N201 and PY1 are reconstructed under varying geological conditions.The Longmaxi Formation shales in these wells are dominated by typeⅠkerogen,with original total organic carbon(TOC_(o))contents of 6.20 wt% and 4.92 wt%,respectively,indicating differences in the initial material basis for gas generation.At the maximum burial depth of approximately 5000 m,the Longmaxi Formation shale in well N201 exhibits a formation pressure coefficient of 2.05,an organic matter maturity of 2.2%,and organic pores accounting for 68%of the total porosity.The gas generation quantity(Q_(g))reaches 19.24 m^(3)/t,while the gas storage capacity(Q_(s))is 4.30 m^(3)/t.The actual total gas content(Q_(a)),constrained by Q_(s),is 4.30 m^(3)/t,with free gas comprising 94%.Following relatively moderate tectonic uplift,the Q_(a) in well N201 decreases to 4.03 m^(3)/t,with free gas accounting for 63%.In contrast,the Longmaxi Formation shale in well PY1 reached a maximum burial depth of 6300 m,associated with a formation pressure coefficient of 1.62,organic matter maturity of 2.5%,and organic pore proportion of 67%.Here,Q_(g) is 16.87 m^(3)/t,and both Q_(s) and Q_(a) are 3.65 m^(3)/t,with free gas accounting for 98%.After intense tectonic uplift,Q_(a) declines to 2.72 m^(3)/t,and the proportion of free gas drops to51%.Finally,a four-stage differential accumulation model of shale gas is established:Slow gas generation and only adsorbed gas occur in stageⅠ,which is primarily controlled by TOC content;both adsorbed gas and free gas present in stageⅡ,with free gas becoming dominant;rapid gas generation and free gas predominance are controlled by temperature and porosity in stageⅢ;and gas adjustment and accumulation are primarily controlled by temperature and pressure in stageⅣ.展开更多
Shale gas is being hailed as the green energy of the future due to high heating value,low carbon emissions,and large reserves.Gas content of shale is a key parameter for evaluating the shale gas potential and screenin...Shale gas is being hailed as the green energy of the future due to high heating value,low carbon emissions,and large reserves.Gas content of shale is a key parameter for evaluating the shale gas potential and screening for the shale gas sweet spots.Although the concept of gas content has been well defined,obtaining a reliable gas content data still remains a challenge.A significant barrier is the method for evaluating the gas content.In this paper,we provide a review of the long-established and recently developed gas content evaluation methods.In the first part of this review article,the history of gas content evaluation methods is summarized since 1910s,relied on published and unpublished literatures as well as our own experiences.Then,the fundamental contents and concepts involved in gas content evaluation are introduced to provide a clear theoretical foundation for the methods.In the third part,eleven evaluation methods,including four direct methods and seven indirect methods,are systematically reviewed.In each method,its application to evaluating the gas content is presented,the key advances are highlighted,and the advantages and limitations are discussed.Finally,future directions are discussed to promote creative thinking across disciplines to develop new methods or improve current methods for evaluating the gas content more accurately and efficiently.展开更多
Pore structure characteristics,gas content,and micro-scale gas occurrence mechanisms were investigated in the Shan_(2)^(3)sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin ...Pore structure characteristics,gas content,and micro-scale gas occurrence mechanisms were investigated in the Shan_(2)^(3)sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin using scanning electron microscope images,lowtemperature N_(2)/CO_(2)adsorption and high-pressure mercury intrusion,methane isothermal adsorption experiments,and CH4-saturated nuclear magnetic resonance(NMR).Two distinct shale types were identified:organic pore-rich shale(Type OP)and microfracture-rich shale(Type M).The Type OP shale exhibited relatively well-developed organic matter pores,while the Type M shale was primarily characterized by a high degree of microfracture development.An experimental method combining methane isothermal adsorption on crushed samples and CH4-saturated NMR of plug samples was proposed to determine the adsorbed gas,free gas,and total gas content under high temperature and pressure conditions.There were four main research findings.(1)Marine-continental transitional shale exhibited substantial total gas content in situ,ranging from 2.58 to 5.73 cm^(3)/g,with an average of 4.35 cm^(3)/g.The adsorbed gas primarily resided in organic matter pores through micropore filling and multilayer adsorption,followed by multilayer adsorption in clay pores.(2)The changes in adsorbed and free pore volumes can be divided into four stages.Pores of<5 nm exclusively contain adsorbed gas,while those of 5-20 nm have a high proportion of adsorbed gas alongside free gas.Pores ranging from 20 to 100 nm have a high proportion of free gas and few adsorbed gas,while pores of>100 nm and microfractures are almost predominantly free gas.(3)The proportion of adsorbed gas in Type OP shale exceeds that in Type M,reaching 66%.(4)Methane adsorbed in Type OP shale demonstrates greater desorption capability,suggesting a potential for enhanced stable production,which finds support in existing production well data.However,it must be emphasized that high-gas-bearing intervals in both types present valuable opportunities for exploration and development.These data may support future model validations and enhance confidence in exploring and developing marine-continental transitional shale gas.展开更多
In the municipal solid waste incineration process,it is difficult to effectively control the gas oxygen content by setting the air flow according to artificial experience.To address this problem,this paper proposes an...In the municipal solid waste incineration process,it is difficult to effectively control the gas oxygen content by setting the air flow according to artificial experience.To address this problem,this paper proposes an optimization control method of gas oxygen content based on model predictive control.First,a stochastic configuration network is utilized to establish a prediction model of gas oxygen content.Second,an improved differential evolution algorithm that is based on parameter adaptive and t-distribution strategy is employed to address the set value of air flow.Finally,model predictive control is combined with the event triggering strategy to reduce the amount of computation and the controller's frequent actions.The experimental results show that the optimization control method proposed in this paper obtains a smaller degree of fluctuation in the air flow set value,which can ensure the tracking control performance of the gas oxygen content while reducing the amount of calculation.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51827901,42477191,and 52304033)the Fundamental Research Funds for the Central Universities(No.YJ202449)+1 种基金the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences(No.SKLGME022009)the China Postdoctoral Science Foundation(No.2023M742446).
文摘Gas content serves as a critical indicator for assessing the resource potential of deep coal mines and forecasting coal mine gas outburst risks.However,existing sampling technologies face challenges in maintaining the integrity of gas content within samples and are often constrained by estimation errors inherent in empirical formulas,which results in inaccurate gas content measurements.This study introduces a lightweight,in-situ pressure-and gas-preserved corer designed to collect coal samples under the pressure conditions at the sampling point,effectively preventing gas loss during transfer and significantly improving measurement accuracy.Additionally,a gas migration model for deep coal mines was developed to elucidate gas migration characteristics under pressure-preserved coring conditions.The model offers valuable insights for optimizing coring parameters,demonstrating that both minimizing the coring hole diameter and reducing the pressure difference between the coring-point pressure and the original pore pressure can effectively improve the precision of gas content measurements.Coring tests conducted at an experimental base validated the performance of the corer and its effectiveness in sample collection.Furthermore,successful horizontal coring tests conducted in an underground coal mine roadway demonstrated that the measured gas content using pressure-preserved coring was 34%higher than that obtained through open sampling methods.
基金supported by the National Natural Science Foundation of China(No.42372192)Shanxi Province science and technology plan joint unveiling project(No.20201101002)。
文摘The methane adsorption capacity,gas content,and carbon isotope characteristics of coal are crucial parameters that determine the productivity of coalbed methane(CBM)wells and their development potential.In this paper,test analyses of methane adsorption,gas content and carbon isotope of methane were carried out using 89 samples from the No.3 coal seam in the southwestern part of the Qinshui Basin.Their characteristics and correlations were analyzed.A relationship model between methane adsorption,gas content,carbon isotopes,coal metamorphism and material composition were established,and its controlling mechanism was investigated.The results indicate that the distribution patterns of Langmuir volume and Langmuir pressure in No.3 coal seam are mainly determined by the material composition and the thermal evolution level.The methane gas content in coal is mainly affected by the burial depth,microcosmic co mposition,mineral conte nt,moisture content and ash yield,adsorption capacity and metamorphism of the coal.The methane carbon isotope(δ^(13)C_(1))values in the natural desorbed gas from No.3 coal seam range from-26.95%to-57.80‰,with a mean value of-34.53‰.δ^(13)C_(1)in coal shows a two-stage variation pattern with increasing in vitrinite reflectance(R_(max)^(o)).When R_(max)^(o)is blow 3.0%,δ^(13)C_(1)values of methane in coal become progressively heavier with increasing R_(max)^(o).When R_(max)^(o)reaches or exceeds 3.0%,δ^(13)C_(1)values exhibit a lightning trend with furth er increases in R_(max)^(o),which is primarily controlled by the carbon isotope fractionation effects during thermal evolution.
基金supported by the National Natural Science Foundation of China(41925014).
文摘The Lower Cambrian shales in the Sichuan Basin are considered one of the most promising shale gas resources in China.However,large-scale commercial development has not been achieved due to the relatively low and significantly variable gas contents of the drilled shales.Excitingly,the first major breakthrough in deep and ultra-deep Lower Cambrian shale gas was made recently in the well Z201 in the southern Sichuan Basin,with a gas yield exceeding 73×10^(4)m^(3)/d.The success of well Z201 provides a favorable geological case to reveal the distinct enrichment mechanism of deep and ultra-deep Lower Cambrian shale gas.In this study,at drilling site of well Z201,fresh shale core samples with different gasin-place contents were collected,and their geochemical,pore development and water-bearing characteristics were analyzed systematically.The results showed that the Z201 organic-rich shales reached an overmature stage,with an average Raman maturity of 3.70%.The Z201 shales with high gas-in-place contents are mainly located in the Qiongzhusi 12section and the upper Qiongzhusi 11section,with an average gas-in-place content of 10.08 cm^(3)/g.Compared to the shales with low gas-in-place contents,the shales with high gas-in-place contents exhibit higher total organic carbon contents,greater porosities,and lower water saturations,providing more effective pore spaces for shale gas enrichment.The effective pore structures of the deep and ultra-deep Lower Cambrian shales are the primary factors affecting their gas-in-place contents.Similar to the shales with high gas-in-place contents of well Z201,the deep and ultra-deep Lower Cambrian shales in the Mianyang-Changning intracratonic sag,especially in the Ziyang area,generally developed in deep-water shelf facies with high total organic carbon contents and thick sedimentary thickness,providing favorable conditions for the development and preservation of effective pores.Therefore,they are the most promising targets for Lower Cambrian shale gas exploration.
基金supported by the National Natural Science Foundation of China(42272200)The Science and Technology Major Project of China National Petroleum Corporation(2023ZZ18-03)+1 种基金The Science and Technology Major Project of Changqing Oilfeld(2023DZZ01)The Technology project of Huaneng Group Headquarters(Medium-deep Low-Rank Coalbed Methane Resource Potential Evaluation and Key Development Technologies of Zhalainuoer Coalfeld,HNKJ23-H51).
文摘Currently,regression prediction methods based on logging data is one of the main methods for analyzing gas content of coal seams.However,the complexity of logging parameters for deep coal seams and the scarcity of measured gas content data signifcantly afects the accuracy and generalizability of data regression models.Accurately predicting the gas content of coal seams under small-sample condition become a difcult point in deep coalbed methane(CBM)exploration.The ModelAgnostic Meta-Learning(MAML)and Support Vector Regression(SVR)algorithms are among the few suitable for smallsample learning,exhibiting strong adaptability under limited sample conditions.In this study,logging parameters are used as input variables to construct MAML and SVR models,and their performance in predicting gas content of deep coal seams across diferent regions and layers is compared.The results demonstrate that the MAML algorithm efectively addresses the complex relationships between gas content of deep coal seam and logging parameters.The prediction errors for test dataset and new samples are merely 3.61%and 4.52%respectively,indicating exceptional adaptability,robust generalization capability,and stable model performance.In contrast,the dependency of SVR model on input parameters restricts its accuracy and generalizability in predicting gas content in deep coal seams with varying geological conditions.Although achieving a test dataset error of 4.71%,the SVR model demonstrates substantially degraded performance when applied to novel samples,with prediction errors escalating to 12.46%.Therefore,the MAML model is selected to predict gas content in the unknown areas of the Baijiahai region.The prediction results reveal that the gas content of coal seams in the Xishanyao formation(J2x)ranges from 1.32 m^(3)/t to 16.11 m^(3)/t,while that in the Badaowan Formation(J1b)varies between 1.73 m^(3)/t and 11.27 m^(3)/t.Notably,the gas enrichment areas are predominantly distributed in well blocks adjacent to fault systems,such as wells C31 and BJ8,etc.,which align with the favorable geological conditions for deep CBM accumulation in the Baijiahai region.These spatial distribution patterns not only corroborate existing geological insights but also further validate the reliability of the MAML model in predicting gas content within deep coal seams.
基金the National Natural Science Foundation of China(51774119,51374095,and 51604092)the primary research projects of critical scientific research in Henan Colleges and Universities(19zx003)+1 种基金Program for Innovative Research Team in University of Ministry of Education of China(IRT_16R22)State Key Laboratory Cultivation Base for Gas Geology and Gas Control(Henan Polytechnic University)(WS2018A02)。
文摘Coal seam gas content is frequently measured in quantity during underground coal mining operation and coalbed methane(CBM)exploration as a significant basic parameter.Due to the calculation error of lost gas and residual gas in the direct method,the efficiency and accuracy of the current methods are not inadequate to the large area multi-point measurement of coal seam gas content.This paper firstly deduces a simplified theoretical dynamic model for calculating lost gas based on gas dynamic diffusion theory.Secondly,the effects of various factors on gas dynamic diffusion from coal particle are experimentally studied.And sampling procedure of representative coal particle is improved.Thirdly,a new estimation method of residual gas content based on excess adsorption and competitive adsorption theory is proposed.The results showed that the maximum error of calculating the losing gas content by using the new simplified model is only 4%.Considering the influence of particle size on gas diffusion law,the particle size of the collected coal sample is below 0.25 mm,which improves the measurement speed and reflects the safety representativeness of the sample.The determination time of gas content reduced from 36 to 3 h/piece.Moreover,the absolute error is 0.15–0.50 m^3/t,and the relative error is within 5%.A new engineering method for determining the coal seam gas content is developed according to the above research.
文摘The key of the direct method of determining coalbed gas content is how to shorten the coal core exposure time in the sampling progress and reduce measuring error of gas content which comes from the calculation of losing gas content. The coring tests were carried out in No.24 drilling field of 715 floor gateway in Qinan Coal Mine by using traditional drill core bar- rel sampler and self-designed reversion seal coring equipment. The losing gas content was calculated by power functional method, and the gas content of two coring methods was determined, respectively. Results show that, compared with traditional drill core barrel sampling, the newly seal coring equipment can significantly shorten the coal core exposure time, the 30 min desorption gas content increases obviously, the calculation of losing gas content reduces by 56.99%, the desorption gas content in normal atmosphere increases by 113.24%, and the determining value of gas content increases by 10.06%. The new technol- ogy has much higher accuracy, and it is worthwhile to be popularized.
文摘The sudden and violent nature of coal and gas outbursts continues to pose a serious threat to coal mine safety in China. One of the key issues is to predict the occurrence of outbursts. Current methods that are used for predicting the outbursts in China are considered to be inadequate, inappropriate or impractical in some seam conditions. In recent years, Huainan Mining Industry Group(Huainan) in China and the Commonwealth Scientific and Industrial Research Organisation(CSIRO) in Australia have been jointly developing technology based on gas content in coal seams to predict the occurrence of outbursts in Huainan. Significant progresses in the technology development have been made, including the development of a more rapid and accurate system in determining gas content in coal seams, the invention of a sampling-while-drilling unit for fast and pointed coal sampling, and the coupling of DEM and LBM codes for advanced numerical simulation of outburst initiation and propagation. These advances are described in this paper.
基金Supported by the National Natural Science Foundation of China(Grant Nos.51734007,51704099 and 51604101)Program for Innovative Research Team in University of Ministry of Education of China(IRT_16R22)+1 种基金Key scientific research projects in Colleges and universities in Henan(Grant No.19A440003)the Opening Foundation of State Key Laboratory Cultivation Base for Gas Geology and Gas Control(Grant No.WS2017B14).
文摘The influence of ground stress was quantitatively analyzed on coal seam gas pressure and gas content in this paper.Mining activities in coal mine can result in stress concentration in the coal(rock)body around the mining space,but porosity of the coal seam would not change too much.Therefore,gas pressure and gas content in the coal seam are slightly affected.Studies showed that the free gas was gradually transformed into adsorbed gas,and the gas adsorption volume was small,and then gas pressure increases roughly linearly when the porosity decreased because of stress influence.Additionaly,when porosity of coal seam reduced to 40%,the amount of adsorbed gas accounted for no more than 10%of coal seam gas content,and the increase of gas pressure did not exceed 15%of the original gas pressure.
基金The Innovation and Enhancing School Project of Guangdong Ocean University under contract No.230419096the Joint Research on Exploration and Development Technology of Natural Gas Hydrate under contract No.2018YFE0208200+2 种基金the Teaching Team Project of Guangdong Ocean University under contract No.570220033the National Natural Science Fundation of China under contract Nos 42004103 and 41306050the Fund of Southern Marine Science and Engineering Guangdong Laboratory(Zhanjiang)under contract No.ZJW-2019-08。
文摘The methane bubble plume attracts interest because it offers direct evidence of seafloor gas leakage and plays an indirect role in the exploration and identification of natural gas hydrate.In this study,based on established plume models and their migration sections,three amplitude-class attributes were extracted from three formations for the migration sections of five plumes,and the correlation between the gas content and seismic attribute was obtained.As the gas content increases,the amplitude attribute correspondingly increases,and the linear correlation is relatively good.Moreover,correlation coefficients between gas content and amplitude attributes are close to 1.0.By using linear fitting,the relation model between the gas content of the plume and the seismic attribute was obtained.The relation model was subsequently used to invert the gas content from a real databearing plume.Comparison of the gas content section of the plume with the attribute section and real seismic section reveals common distribution characteristics,namely,the color of the section in the lower right corner is dark.If the amplitude value is large in the seismic section of the real plume,the amplitude attribute value is also large in the corresponding attribute section,and the inverted value of the gas content is also large(because gas content and amplitude are linearly correlated),which indicates that the plume bubbles of the section in the lower right corner is intensively distributed.Finally,the obtained gas content section of the plume can reflect the distribution of the plume bubble content more simply and intuitively,from which the distribution law of seafloor bubbles can be deduced,and this lays a foundation for the further estimation of the gas content of the plume and hydrate reserves.
基金supported by China Scholarship Council(202006430006)the International Postgraduate Tuition Award(IPTA)of the University of Wollongongthe research funding provided by the Mine A,ACARP Project C35015 and Coal Services Health and Safety Trust.
文摘The gas content is crucial for evaluating coal and gas outburst potential in underground coal mining. This study focuses on investigating the in-situ coal seam gas content and gas sorption capacity in a representative coal seam with multiple sections (A1, A2, and A3) in the Sydney basin, where the CO_(2) composition exceeds 90%. The fast direct desorption method and associated devices were described in detail and employed to measure the in-situ gas components (Q_(1), Q_(2), and Q_(3)) of the coal seam. The results show that in-situ total gas content (Q_(T)) ranges from 9.48 m^(3)/t for the A2 section to 14.80 m^(3)/t for the A3 section, surpassing the Level 2 outburst threshold limit value, thereby necessitating gas drainage measures. Among the gas components, Q_(2) demonstrates the highest contribution to Q_(T), ranging between 55% and 70%. Furthermore, high-pressure isothermal gas sorption experiments were conducted on coal samples from each seam section to explore their gas sorption capacity. The Langmuir model accurately characterizes CO_(2) sorption behavior, with ft coefcients (R^(2)) greater than 0.99. Strong positive correlations are observed between in-situ gas content and Langmuir volume, as well as between residual gas content (Q_(3)) and sorption hysteresis. Notably, the A3 seam section is proved to have a higher outburst propensity due to its higher Q_(1) and Q_(2) gas contents, lower sorption hysteresis, and reduced coal toughness f value. The insights derived from the study can contribute to the development of efective gas management strategies and enhance the safety and efciency of coal mining operations.
文摘On the basis of the analysis of coal bed gas pressure in deep mine, and the coal bed permeability ( k ) and the characteristic of adsorption parameter ( b ) changing with temperature, the author puts forward a new calculating method of gas content in coal seam influenced by in situ stress grads and ground temperature. At the same time, the contrast of the measuring results of coal bed gas pressure with the computing results of coal bed gas pressure and gas content in coal seam in theory indicate that the computing method can well reflect the authenticity of gas content in coal seam,and will further perfect the computing method of gas content in coal seam in theory,and have important value in theory on analyzing gas content in coal seam and forecasting distribution law of gas content in coal seam in deep mine.
基金the support of the National Natural Science Foundation of China(Nos.51674158,51604168 and 51504142)the Natural Science Foundation of Shandong Province(No.ZR2016EEQ18)+2 种基金the SDUST Research Fund(No.2015JQJH105)the Qingdao Postdoctoral Applied Research Project(No.2015204)the Taishan Scholar Talent Team Support Plan for Advantaged&Unique Discipline Areas
文摘In this study, we selected 9 typical coal samples with different metamorphic grades as the study subjects,measured their initial 30-min gas desorption at 30℃ and different pressure using a self-developed gas adsorption/desorption device. Based on the characteristics of gas desorption from coal samples, we proposed a direct fitting method for measurement of gas content in coalbed, analyzed the effects of sampling time on the measurement results and determined the reasonable sampling time of coal samples with different metamorphic grades at different gas adsorption pressure at equilibrium. The results show that (1)the error of gas contents obtained using the direct fitting method relative to that obtained using indirect method is less than 10%, which meets the actual on-site requirements and verifies the feasibility of the direct fitting method;(2) when the relative error is controlled within ±10%, the reasonable sampling time of coal samples is linearly related to the gas adsorption pressure at equilibrium;(3) the reasonable sampling time of coal samples with the same metamorphic grade exhibits a shortening trend with increasing gas adsorption pressure at equilibrium;(4) for coal samples with similar gas adsorption pressure at equilibrium, the reasonable sampling time of coal samples displays a shortening trend with increasing metamorphic grade. Overall, the study provides a basis for improving the measurement accuracy of gas content in coalbed.
基金supported by the National Natural Science Foundation of China(No.:41472129,41472127,41502158)Scientific and Technological Key Project for Coal Rank of Shanxi Province in 2014(No.:MQ2014-01)project supported by the CBM Joint Study Foundation of Shanxi Province(No.:2013012004).
文摘When the gas content of a coal reservoir is calculated,the reservoir pressure measured by well logging and well testing is generally used for inversion calculation instead of gas pressure.However,the calculation result is not accurate because the reservoir pressure is not equal to the gas pressure in overpressure environments.In this paper,coal samples of different ranks in Shanxi and Henan are collected for testing the capillary pressure of coal pores.Based on the formation process of CBM reservoirs and the hydrocarbon generation and expulsion history of coal beds,the forming mechanisms of micro-pore overpressure environments in coal reservoirs were analyzed.Accordingly,a new method for calculating the gas content of coal reservoirs with consideration of a micro-pore overpressure environment was developed.And it was used to calculate the gas content of No.1 coal bed of the 2nd member of Lower Permian Shanxi Fm in the Zhongmacun Coal Mine in Jiaozuo,Henan.It is indicated that during the formation and evolution of coals,some solid organic matters were converted into gas and water,and gasewater contact is surely formed in pores.In the end,capillary pressure is generated,so the gas pressure in micro-pores is much higher than the hydrostatic column pressure,which results in a micro-pore overpressure environment.Under such an environment,gas pressure is higher than reservoir pressure,so the gas content of coal reservoirs calculated previously based on the conventional reservoir pressure evaluation are usually underestimated.It is also found that the micro-pore overpressure environment exerts a dominating effect on the CBM content calculation of 3-100 nm pores,especially that of 3-10 nm pores,but a little effect on that of pores>100 nm.In conclusion,this new method clarifies the pressure environment of CBM gas reservoirs,thereby ensuring the calculation accuracy of gas content of coal reservoirs.
基金Support by the National Natural Science Foundation of China(No.51505315)the Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi+1 种基金the Collaborative Innovation Center of Taiyuan Heavy Machinery Equipment Fundedthe Fund for Shanxi“1331 Project”Key Subjects Construction
文摘Gas content of the hydraulic system directly affects the rate of pressure change of the hydraulic system. The purpose of this paper is to establish a mathematical model of oil gas content, hydraulic system pressure and pressure rise rate, obtain corresponding oil pressure value when the pressure rise rate of different gas content is maximum, and verify the accuracy of this conclusion by the FLUENT simulation software. On this basis, a rapid pressure building device of the hydraulic system is developed and designed. The above oil pressure value is used as the working cut-off pressure of the rapid pressure building device, and then the hydraulic oil pump continues to pressurize to the highest working pressure required by the system. The research content can replace the hydraulic system from the initial low pressure to the rapid pressure build-up of the oil, thus increasing the construction pressure of the hydraulic system. The research results show that the rapid pressure building device effectively reduces the time for the hydraulic system to establish pressure. Through the analysis of theoretical derivation and the collected experimental data, the error is about 5.9%, which verifies the correctness of the theoretical formula.
文摘Factors of shale gas accumulation can be divided into the external and internal factors,according to accumulation mechanism and characteristics of shale gas. The internal factors mainly refer to parameters of organic geochemistry,mineral components and physical parameters. Six factors were presented in this study,i. e.organic matter,maturity,quartz,carbonate,clay mineral and pore. The external factors mainly refer to geologic environment of shale gas reservoir,including four factors: temperature,pressure,depth and thickness.Based on the experiment results of 26 samples of drilling cores from Wuling fold belt in Lower Paleozoic Silurian of the Upper Yangtze Basin,combined with the integrated analysis of geology,logging and test,the correlation of the gas content of shale gas to the above-mentioned ten factors was concluded. Six important evaluation indicators were preliminarily established in the gas-bearing core area of marine shale in the Upper Yangtze Basin.
基金funded by the Sinopec Science and Technology Project(No.P23132)the AAPG Foundation Grants-inAid Program(No.18644937)。
文摘By investigating the evolution of shale gas generation,storage,adjustment and accumulation under different structural settings in superimposed basins,this study elucidates the differential accumulation mechanisms of shale gas.An improved evaluation method of shale gas content evolution in superimposed basins is proposed.This method incorporates the coupling effect of key geological factors such as temperature,pressure,organic matter abundance,maturity,and pore characteristics on the content and occurrence state of shale gas,as well as the configuration relationship between shale gas generation and storage throughout geological history.Using this approach,the gas evolution histories of the Longmaxi Formation shales in wells N201 and PY1 are reconstructed under varying geological conditions.The Longmaxi Formation shales in these wells are dominated by typeⅠkerogen,with original total organic carbon(TOC_(o))contents of 6.20 wt% and 4.92 wt%,respectively,indicating differences in the initial material basis for gas generation.At the maximum burial depth of approximately 5000 m,the Longmaxi Formation shale in well N201 exhibits a formation pressure coefficient of 2.05,an organic matter maturity of 2.2%,and organic pores accounting for 68%of the total porosity.The gas generation quantity(Q_(g))reaches 19.24 m^(3)/t,while the gas storage capacity(Q_(s))is 4.30 m^(3)/t.The actual total gas content(Q_(a)),constrained by Q_(s),is 4.30 m^(3)/t,with free gas comprising 94%.Following relatively moderate tectonic uplift,the Q_(a) in well N201 decreases to 4.03 m^(3)/t,with free gas accounting for 63%.In contrast,the Longmaxi Formation shale in well PY1 reached a maximum burial depth of 6300 m,associated with a formation pressure coefficient of 1.62,organic matter maturity of 2.5%,and organic pore proportion of 67%.Here,Q_(g) is 16.87 m^(3)/t,and both Q_(s) and Q_(a) are 3.65 m^(3)/t,with free gas accounting for 98%.After intense tectonic uplift,Q_(a) declines to 2.72 m^(3)/t,and the proportion of free gas drops to51%.Finally,a four-stage differential accumulation model of shale gas is established:Slow gas generation and only adsorbed gas occur in stageⅠ,which is primarily controlled by TOC content;both adsorbed gas and free gas present in stageⅡ,with free gas becoming dominant;rapid gas generation and free gas predominance are controlled by temperature and porosity in stageⅢ;and gas adjustment and accumulation are primarily controlled by temperature and pressure in stageⅣ.
基金supported by the National Natural Science Foundation of China(42202175,41927801,and 42102128)the Open Foundation of State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development(33550000-22-ZC0613-0296)。
文摘Shale gas is being hailed as the green energy of the future due to high heating value,low carbon emissions,and large reserves.Gas content of shale is a key parameter for evaluating the shale gas potential and screening for the shale gas sweet spots.Although the concept of gas content has been well defined,obtaining a reliable gas content data still remains a challenge.A significant barrier is the method for evaluating the gas content.In this paper,we provide a review of the long-established and recently developed gas content evaluation methods.In the first part of this review article,the history of gas content evaluation methods is summarized since 1910s,relied on published and unpublished literatures as well as our own experiences.Then,the fundamental contents and concepts involved in gas content evaluation are introduced to provide a clear theoretical foundation for the methods.In the third part,eleven evaluation methods,including four direct methods and seven indirect methods,are systematically reviewed.In each method,its application to evaluating the gas content is presented,the key advances are highlighted,and the advantages and limitations are discussed.Finally,future directions are discussed to promote creative thinking across disciplines to develop new methods or improve current methods for evaluating the gas content more accurately and efficiently.
基金the Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance,China(No.2020CX030101)the National Natural Science Foundation of China(No.42222209)the Scientific Research and Technological Development Program of CNPC,China(No.2023ZZ0801).
文摘Pore structure characteristics,gas content,and micro-scale gas occurrence mechanisms were investigated in the Shan_(2)^(3)sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin using scanning electron microscope images,lowtemperature N_(2)/CO_(2)adsorption and high-pressure mercury intrusion,methane isothermal adsorption experiments,and CH4-saturated nuclear magnetic resonance(NMR).Two distinct shale types were identified:organic pore-rich shale(Type OP)and microfracture-rich shale(Type M).The Type OP shale exhibited relatively well-developed organic matter pores,while the Type M shale was primarily characterized by a high degree of microfracture development.An experimental method combining methane isothermal adsorption on crushed samples and CH4-saturated NMR of plug samples was proposed to determine the adsorbed gas,free gas,and total gas content under high temperature and pressure conditions.There were four main research findings.(1)Marine-continental transitional shale exhibited substantial total gas content in situ,ranging from 2.58 to 5.73 cm^(3)/g,with an average of 4.35 cm^(3)/g.The adsorbed gas primarily resided in organic matter pores through micropore filling and multilayer adsorption,followed by multilayer adsorption in clay pores.(2)The changes in adsorbed and free pore volumes can be divided into four stages.Pores of<5 nm exclusively contain adsorbed gas,while those of 5-20 nm have a high proportion of adsorbed gas alongside free gas.Pores ranging from 20 to 100 nm have a high proportion of free gas and few adsorbed gas,while pores of>100 nm and microfractures are almost predominantly free gas.(3)The proportion of adsorbed gas in Type OP shale exceeds that in Type M,reaching 66%.(4)Methane adsorbed in Type OP shale demonstrates greater desorption capability,suggesting a potential for enhanced stable production,which finds support in existing production well data.However,it must be emphasized that high-gas-bearing intervals in both types present valuable opportunities for exploration and development.These data may support future model validations and enhance confidence in exploring and developing marine-continental transitional shale gas.
基金supported by the National Natural Science Foundation of China(62373017,62073006)and the Beijing Natural Science Foundation of China(4212032)。
文摘In the municipal solid waste incineration process,it is difficult to effectively control the gas oxygen content by setting the air flow according to artificial experience.To address this problem,this paper proposes an optimization control method of gas oxygen content based on model predictive control.First,a stochastic configuration network is utilized to establish a prediction model of gas oxygen content.Second,an improved differential evolution algorithm that is based on parameter adaptive and t-distribution strategy is employed to address the set value of air flow.Finally,model predictive control is combined with the event triggering strategy to reduce the amount of computation and the controller's frequent actions.The experimental results show that the optimization control method proposed in this paper obtains a smaller degree of fluctuation in the air flow set value,which can ensure the tracking control performance of the gas oxygen content while reducing the amount of calculation.
