scholarly journals Application of a Modified Low-Field NMR Method on Methane Adsorption of Medium-Rank Coals

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Xiaozhen Chen ◽  
Taotao Yan ◽  
Fangui Zeng ◽  
Yanjun Meng ◽  
Jinhua Liu
Keyword(s):  
Adsorption Capacity ◽  
Coalbed Methane ◽  
Gas Adsorption ◽  
Vitrinite Reflectance ◽  
Methane Adsorption ◽  
Coal Rank ◽  
Nmr Method ◽  
Low Field ◽  
Low Field Nmr ◽  
The Absolute

Methane adsorption capacity is an important parameter for coalbed methane (CBM) exploitation and development. Traditional examination methods are mostly time-consuming and could not detect the dynamic processes of adsorption. In this study, a modified low-field nuclear magnetic resonance (NMR) method that compensates for these shortcomings was used to quantitatively examine the methane adsorption capacity of seven medium-rank coals. Based on the typical T 2 amplitudes obtained from low-field NMR measurement, the volume of adsorbed methane was calculated. The results indicate that the Langmuir volume of seven samples is in a range of 18.9–31.85 m3/t which increases as the coal rank increases. The pore size in range 1-10 nm is the main contributor for gas adsorption in these medium-rank coal samples. Comparing the adsorption isotherms of these coal samples from the modified low-field NMR method and volumetric method, the absolute deviations between these two methods are less than 1.03 m3/t while the relative deviations fall within 4.76%. The absolute deviations and relative deviations decrease as vitrinite reflectance ( R o ) increases from 1.08% to 1.80%. These results show that the modified low-field NMR method is credible to measure the methane adsorption capacity and the precision of this method may be influenced by coal rank.

scholarly journals Methane adsorption characteristics and its influencing factors of the medium-to-high rank coals in the Anyang-Hebi coalfield, northern China

2018 ◽  
Vol 37 (1) ◽  
pp. 60-82 ◽  
Author(s):  
Sheng Zhao ◽  
Longyi Shao ◽  
Haihai Hou ◽  
Yue Tang ◽  
Zhen Li ◽  
...  
Keyword(s):  
Adsorption Capacity ◽  
Influencing Factors ◽  
Coalbed Methane ◽  
Vitrinite Reflectance ◽  
Negative Relationship ◽  
Methane Adsorption ◽  
High Rank ◽  
Gas Content ◽  
Coal Rank ◽  
Adsorption Characteristics

The variation of coal rank in the Anyang-Hebi (Anhe) coalfield has the phenomenon of anti-Hilt law, which makes the coalfield distinctive for coalbed methane exploration research. The methane adsorption characteristics and influencing factors of the medium-to-high rank coal samples of the Shanxi Formation in this coalfield were analyzed. The results indicate that the Langmuir volume ( VL) of coals in the shallow western part of the Anhe coalfield is generally higher than that in the deep eastern part. The coal rank and the coal macerals are the dominant factors that influence the methane adsorption capacity of coals in this anti-Hilt law area. The methane adsorption capacity, represented by VL, first increases and then decreases with the coal rank, and the highest VL value corresponds to the maximum vitrinite reflectance of ∼2.1%. The adsorption capacity has a positive correlation with the vitrinite and the moisture content, a negative relationship with the inertinite content. In general, the adsorption capacity of coal samples shows a “V-shaped” change with the ash yield, and the lowest VL value corresponds to the ash yield of ∼9%. A prediction model of the gas content of the Anhe coalfield was proposed based on changes of the methane adsorption capacity and principal component analysis. Areas with a critical depth ranging from 400 m to 700 m are suggested to be methane enrichment regions for coalbed methane exploration in the Anhe coalfield.

scholarly journals Changes in Pore Structure of Coal Caused by CS2 Treatment and Its Methane Adsorption Response

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Run Chen ◽  
Yong Qin ◽  
Pengfei Zhang ◽  
Youyang Wang
Keyword(s):  
Pore Structure ◽  
Adsorption Capacity ◽  
Gas Adsorption ◽  
Recovery Process ◽  
Micropore Volume ◽  
Methane Adsorption ◽  
Coal Bed ◽  
Methane Recovery ◽  
Before And After ◽  
Key Issues

The pore structure and gas adsorption are two key issues that affect the coal bed methane recovery process significantly. To change pore structure and gas adsorption, 5 coals with different ranks were treated by CS2 for 3 h using a Soxhlet extractor under ultrasonic oscillation conditions; the evolutions of pore structure and methane adsorption were examined using a high-pressure mercury intrusion porosimeter (MIP) with an AutoPore IV 9310 series mercury instrument. The results show that the cumulative pore volume and specific surface area (SSA) were increased after CS2 treatment, and the incremental micropore volume and SSA were increased and decreased before and after Ro,max=1.3%, respectively; the incremental big pore (greater than 10 nm in diameter) volumes were increased and SSA was decreased for all coals, and pore connectivity was improved. Methane adsorption capacity on coal before and after Ro,max=1.3% also was increased and decreased, respectively. There is a positive correlation between the changes in the micropore SSA and the Langmuir volume. It confirms that the changes in pore structure and methane adsorption capacity due to CS2 treatment are controlled by the rank, and the change in methane adsorption is impacted by the change of micropore SSA and suggests that the changes in pore structure are better for gas migration; the alteration in methane adsorption capacity is worse and better for methane recovery before and after Ro,max=1.3%. A conceptual mechanism of pore structure is proposed to explain methane adsorption capacity on CS2 treated coal around the Ro,max=1.3%.

scholarly journals Geologic characterization of a lower Cambrian marine shale: Implications for shale gas potential in northwestern Hunan, South China

2018 ◽  
Vol 6 (3) ◽  
pp. T635-T647 ◽  
Author(s):  
Zhenghui Xiao ◽  
Jisong Liu ◽  
Jingqiang Tan ◽  
Rongfeng Yang ◽  
Jason Hilton ◽  
...  
Keyword(s):  
Adsorption Capacity ◽  
South China ◽  
Lower Cambrian ◽  
Gas Adsorption ◽  
Vitrinite Reflectance ◽  
Mean Value ◽  
Hunan Province ◽  
Quartz Content ◽  
Gas Potential

We have investigated the geologic features of the lower Cambrian-aged Niutitang Shale in the northwestern Hunan province of South China. Our results indicate that the Niutitang Shale has abundant and highly mature algal kerogen with total organic carbon (TOC) content ranging from 0.6% to 18.2%. The equivalent vitrinite reflectance (equal-Ro) value is between 2.5% and 4.3%. Mineral constituents are dominated by quartz and clay. The average quartz content (62.8%) is much higher than that of clay minerals (26.1%), and this suggests a high brittleness index. Organic-matter pores, interparticle pores, intraparticle pores, interlaminated fractures, and structural fractures are all well developed. The porosity ranges from 0.6% to 8.8%, with an average of 4.8%, whereas the permeability varies from 0.0018 to [Formula: see text] (microdarcy) (averaging [Formula: see text]). The porosity of TOC- and clay-rich shale samples is generally higher than that of quartz-rich shale samples. The gas adsorption capacity of the Niutitang Shale varies from 2.26 to [Formula: see text], with a mean value of [Formula: see text]. The TOC content appears to significantly influence gas adsorption capacity. In general, TOC-rich samples exhibit a much higher adsorption capacity than TOC-poor samples.

scholarly journals Variation of Petrophysical Properties and Adsorption Capacity in Different Rank Coals: An Experimental Study of Coals from the Junggar, Ordos and Qinshui Basins in China

Energies ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 986 ◽  
Author(s):  
Yingjin Wang ◽  
Dameng Liu ◽  
Yidong Cai ◽  
Xiawei Li
Keyword(s):  
Adsorption Capacity ◽  
Vitrinite Reflectance ◽  
Inhibitory Effect ◽  
Proximate Analysis ◽  
Methane Adsorption ◽  
Low Rank ◽  
Petrophysical Properties ◽  
Isothermal Adsorption ◽  
Variation Rule ◽  
Moisture Absorbent

The petrophysical properties of coal will vary during coalification, and thus affect the methane adsorption capacity. In order to clarify the variation rule and its controlling effect on methane adsorption, various petrophysical tests including proximate analysis, moisture measurement, methane isothermal adsorption, mercury injection, etc. were carried out on 60 coal samples collected from the Junggar, Ordos and Qinshui basins in China. In this work, the boundary values of maximum vitrinite reflectance (Ro,m) for dividing low rank, medium rank and high rank coals are set as 0.65% and 2.0%. The results show that vitrinite is the most abundant maceral, but the maceral contents are controlled by sedimentation without any relation to coal rank. Both the moisture content and porosity results show higher values in the low ranks and stabilized with Ro,m beyond 1%. Ro,m and VL (daf) show quadratic correlation with the peak located in Ro,m = 4.5–5%, with the coefficient (R2) reaching 0.86. PL decrease rapidly before Ro,m = 1.5%, then increase slowly. DAP is established to quantify the inhibitory effect of moisture on methane adsorption capacity, which shows periodic relationship with Ro,m: the inhibitory effect in lignite is the weakest and increases during coalification, then remains constant at Ro,m = 1.8% to 3.5%, and finally increases again. In the high metamorphic stage, clay minerals are more moisture-absorbent than coal, and the inherent moisture negatively correlates with the ratio of vitrinite to inertinite (V/I). During coalification, micro gas pores gradually become dominant, fractures tends to be well oriented and extended, and clay filling becomes more common. These findings can help us better understand the variation of petrophysical properties and adsorption capacity in different rank coals.

scholarly journals Effect of Kerogen Thermal Maturity on Methane Adsorption Capacity: A Molecular Modeling Approach

Molecules ◽  
2020 ◽  
Vol 25 (16) ◽  
pp. 3764 ◽  
Author(s):  
Saad Alafnan ◽  
Theis Solling ◽  
Mohamed Mahmoud
Keyword(s):  
Molecular Modeling ◽  
Adsorption Capacity ◽  
Gas Adsorption ◽  
Material Balance ◽  
Methane Adsorption ◽  
Source Rocks ◽  
Thermal Maturity ◽  
Reserve Estimation ◽  
Adsorbed Gas ◽  
Key Factor

The presence of kerogen in source rocks gives rise to a plethora of potential gas storage mechanisms. Proper estimation of the gas reserve requires knowledge of the quantities of free and adsorbed gas in rock pores and kerogen. Traditional methods of reserve estimation such as the volumetric and material balance approaches are insufficient because they do not consider both the free and adsorbed gas compartments present in kerogens. Modified versions of these equations are based on adding terms to account for hydrocarbons stored in kerogen. None of the existing models considered the effect of kerogen maturing on methane gas adsorption. In this work, a molecular modeling was employed to explore how thermal maturity impacts gas adsorption in kerogen. Four different macromolecules of kerogen were included to mimic kerogens of different maturity levels; these were folded to more closely resemble the nanoporous kerogen structures of source rocks. These structures form the basis of the modeling necessary to assess the adsorption capacity as a function of the structure. The number of double bonds plus the number and type of heteroatoms (O, S, and N) were found to influence the final configuration of the kerogen structures, and hence their capacity to host methane molecules. The degree of aromaticity increased with the maturity level within the same kerogen type. The fraction of aromaticity gives rise to the polarity. We present an empirical mathematical relationship that makes possible the estimation of the adsorption capacity of kerogen based on the degree of polarity. Variations in kerogen adsorption capacity have significant implications on the reservoir scale. The general trend obtained from the molecular modeling was found to be consistent with experimental measurements done on actual kerogen samples. Shale samples with different kerogen content and with different maturity showed that shales with immature kerogen have small methane adsorption capacity compared to shales with mature kerogen. In this study, it is shown for the first time that the key factor to control natural gas adsorption is the kerogen maturity not the kerogen content.

Evaluation of Methane Dynamic Adsorption–Diffusion Process in Coals by a Low-Field NMR Method

2020 ◽  
Vol 34 (12) ◽  
pp. 16119-16131
Author(s):  
Zhentao Li ◽  
Dameng Liu ◽  
Songbin Xie ◽  
Xianglong Fang ◽  
Guangyao Si ◽  
...  
Keyword(s):  
Diffusion Process ◽  
Dynamic Adsorption ◽  
Nmr Method ◽  
Low Field ◽  
Low Field Nmr

scholarly journals Study on the Effect of Soft and Hard Coal Pore Structure on Gas Adsorption Characteristics

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Xun Zhao ◽  
Tao Feng ◽  
Ping Wang ◽  
Ze Liao
Keyword(s):  
Pore Structure ◽  
Adsorption Capacity ◽  
Residence Time ◽  
Coalbed Methane ◽  
Gas Adsorption ◽  
Nitrogen Adsorption ◽  
Hard Coal ◽  
Research Results ◽  
Adsorption Characteristics ◽  
Soft Coal

In order to grasp the effect of soft and hard coal pore structure on gas adsorption characteristics, based on fractal geometry theory, low-temperature nitrogen adsorption and constant temperature adsorption test methods are used to test the pore structure characteristics of soft coal and its influence on gas adsorption characteristics. We used box dimension algorithm to measure the fractal dimension and distribution of coal sample microstructure. The research results show that the initial nitrogen adsorption capacity of soft coal is greater than that of hard coal, and the adsorption hysteresis loop of soft coal is more obvious than that of hard coal. And the adsorption curve rises faster in the high relative pressure section. The specific surface area and pore volume of soft coal are larger than those of hard coal. The number of pores is much larger than that of hard coal. In particular, the superposition of the adsorption force field in the micropores and the diffusion in the mesopores enhance the adsorption potential of soft coal. Introducing the concept of adsorption residence time, it is concluded that more adsorption sites on the surface of soft coal make the adsorption and residence time of gas on the surface of soft coal longer. Fractal characteristics of the soft coal surface are more obvious. The saturated adsorption capacity of soft coal and the rate of reaching saturation adsorption are both greater than those of hard coal. The research results of this manuscript will provide a theoretical basis for in-depth analysis of the adsorption/desorption mechanism of coalbed methane in soft coal seams and the formulation of practical coalbed methane control measures.

scholarly journals Contribution of Ash Content Related to Methane Adsorption Behaviors of Bituminous Coals

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Yanyan Feng ◽  
Wen Yang ◽  
Wei Chu
Keyword(s):  
Adsorption Capacity ◽  
Coalbed Methane ◽  
Textural Properties ◽  
Isosteric Heat ◽  
Micropore Volume ◽  
Ash Content ◽  
Heat Of Adsorption ◽  
Methane Adsorption ◽  
Adsorbed Phase ◽  
Adsorption Processes

Methane adsorption isotherms on coals with varying ash contents were investigated. The textural properties were characterized by N2adsorption/desorption isotherm at 77 K, and methane adsorption characteristics were measured at pressures up to 4.0 MPa at 298 K, 313 K, and 328 K, respectively. The Dubinin-Astakhov model and the Polanyi potential theory were employed to fit the experimental data. As a result, ash content correlated strongly to methane adsorption capacity. Over the ash range studied, 9.35% to 21.24%, the average increase in methane adsorption capacity was 0.021 mmol/g for each 1.0% rise in ash content. With the increasing ash content range of 21.24%~43.47%, a reduction in the maximum adsorption capacities of coals was observed. In addition, there was a positive correlation between the saturated adsorption capacity and the specific surface area and micropore volume of samples. Further, this study presented the heat of adsorption, the isosteric heat of adsorption, and the adsorbed phase specific heat capacity for methane adsorption on various coals. Employing the proposed thermodynamic approaches, the thermodynamic maps of the adsorption processes of coalbed methane were conducive to the understanding of the coal and gas simultaneous extraction.

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