scholarly journals Characterization of Full Pore and Stress Compression Response of Reservoirs With Different Coal Ranks

2021 ◽  
Vol 9 ◽  
Author(s):  
Jielin Lu ◽  
Xuehai Fu ◽  
Junqiang Kang ◽  
Ming Cheng ◽  
Zhenzhi Wang
Keyword(s):  
Pore Structure ◽  
Effective Stress ◽  
Coalbed Methane ◽  
Nitrogen Adsorption ◽  
Test Methods ◽  
Low Rank ◽  
Coal Rank ◽  
Structure Characteristics ◽  
Multiple Test

The accurate characterization of coal pore structure is significant for coalbed methane (CBM) development. The splicing of practical pore ranges of multiple test methods can reflect pore structure characteristics. The pore\fracture compressibility is the main parameter affecting the porosity and permeability of coal reservoirs. The difference in compressibility of different coal rank reservoirs and pore\fracture structures with changing stress have not been systematically found. The pore structure characteristics of different rank coal samples were characterized using the optimal pore ranges of high-pressure mercury intrusion (HPMI), low-temperature liquid nitrogen adsorption (LT-N2A), low-pressure carbon dioxide adsorption (LP-CDA), and nuclear magnetic resonance (NMR) based on six groups of different rank coal samples. The compressibility of coal matrix and pore\fracture were studied using HPMI data and NMR T2 spectrum under effective stress. The results show that the more accurate full pore characterization results can be obtained by selecting the optimal pore range measured by HPMI, LT-N2A, and LP-CDA and comparing it with the NMR pore results. The matrix compressibility of different rank coal samples shows that low-rank coal > high-rank coal > medium-rank coal. When the effective stress is less than 6 MPa, the microfractures are compressed rapidly, and the compressibility decreases slowly when the effective stress is more than 6 MPa. Thus, the compressibility of the adsorption pore is weak. Nevertheless, the adsorption pore has the most significant compression space because of the largest proportion in different pore structures. The variation trend of matrix compressibility and pore\fracture compressibility is consistent with the increase of coal rank. The compressibility decreases with the rise of reservoir heterogeneity and mechanical strength. The development of pore volume promotes compressibility. The research results have guiding significance for the exploration and development of CBM in different coal rank reservoirs.

scholarly journals Microscopic Pore Structure Characteristics and Methane Adsorption of Vitrain and Durain

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Fu Yang ◽  
Dongmin Ma ◽  
Zhonghui Duan ◽  
Dazhong Ren ◽  
Tao Tian ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Pore Structure ◽  
Coalbed Methane ◽  
Nitrogen Adsorption ◽  
Ash Content ◽  
Methane Adsorption ◽  
Low Rank ◽  
Reservoir Evaluation ◽  
Structure Characteristics ◽  
Carbon Dioxide Co2

During reservoir evaluation, the microscopic pore structure of low-rank coal is mainly characterized in order to study the coalbed methane diffuse and migration mechanisms and control. The low-rank coals are very different in pore type and size, so it is necessary to use various techniques to describe their pore structure. For vitrain and durain of the Coal Member of the Yan’an Formation from Huanglong Coalfield, their chemical composition and microscopic pore structure characteristics were studied, and the factors of influencing the pore size distribution (PSD) were explored. Obviously, vitrain and durain are different in chemical composition. Vitrain has higher moisture content, volatile yield, and vitrinite group content than durain. Vitrain and durain mainly contain vitrinite and inertinite, respectively. The pore structure characteristics (e.g., pore types and PSD) of vitrain and durain were systematically by mercury intrusion porosimetry (MIP), low-temperature nitrogen adsorption, and carbon dioxide (CO2) adsorption. The vitrain and durain samples with a micropore size of <2 nm were mainly tested on their specific surface area (SSA) and pore volume (PV). The results show that microporous vitrain has larger SSA and PV than microporous durain, while mesoporous and macroporous vitrain has smaller SSA and PV than mesoporous and macroporous durain. SSA is very positively correlated with PV. The ash content is negatively correlated with SSA and PV. The ash content influences microporous vitrain more greatly than microporous durain, but mesoporous and macroporous durain more greatly than mesoporous and macroporous vitrain. SSA is positively correlated with the vitrinite content of durain and negatively correlated with the inertinite and exinite contents of durain. However, SSA is negatively correlated with the vitrinite and exinite contents of vitrain and positively correlated with the inertinite content of vitrain. Vitrain has higher methane adsorption capacity, desorption rate, and recovery ratio than durain. There are parameters that are obviously affected by the micropore characteristics.

scholarly journals Characterization of Pores and Fractures in Soft Coal from the No. 5 Soft Coalbed in the Chenghe Mining Area

Processes ◽  
2018 ◽  
Vol 7 (1) ◽  
pp. 13 ◽  
Author(s):  
Pan Wei ◽  
Yunpei Liang ◽  
Song Zhao ◽  
Shoujian Peng ◽  
Xuelong Li ◽  
...  
Keyword(s):  
Low Temperature ◽  
Pore Structure ◽  
Pore Volume ◽  
Fractal Dimensions ◽  
Nitrogen Adsorption ◽  
Mining Area ◽  
Hard Coal ◽  
Structure Characteristics ◽  
Soft Coal

The characteristics of the pore structure and gas migration in soft coalbeds are the premise of evaluating gas discharge in soft coalbeds. To explore the pore structure characteristics of soft coal masses, the No. 5 soft coalbed in the eastern zone of Chenghe Mining Area, was investigated and compared with the No. 5 hard coalbed in the western zone. By using a mercury intrusion method, low-temperature liquid nitrogen adsorption, and scanning electron microscopy (SEM), the pore structure characteristics of the No. 5 coalbed were explored. Moreover, based on fractal theory, the pore structure of coal was characterized. The results showed the pores in soft coal mainly appeared as small pores and micropores in which the small pores accounted for nearly half of the total pore volume. Mesopores and macropores were also distributed throughout the soft coal. The mercury-injection and mercury-ejection curves of soft coal showed significant hysteresis loops, implying that pores in coal samples were mainly open while the mercury-injection curve of hard coal was consistent with its mercury-ejection curve, showing no hysteresis loop while having an even segment, which indicated that closed pores occupied the majority of the pore volume in the coal samples. The curves of low-temperature nitrogen adsorption of soft coal all follow an IV-class isotherm. Moreover, the fractal dimensions of soft coal are respectively larger than the fractal dimensions of hard coal. It can be seen that the characterization of pores and fractures of the soft coal was different from the hard coal in the western distinct of the old mining area. The gas prevention and control measures of soft coal should be formulated according to local conditions.

Evaluation Shale Pore Size Spectrum Using Mercury Porosimetry and Nitrogen Adsorption Experiment: A Case Study from the Longtan Formation Shale, Southeastern Hunan, China

2014 ◽  
Vol 962-965 ◽  
pp. 34-40
Author(s):  
Ning Yang ◽  
Shu Heng Tang ◽  
Song Hang Zhang ◽  
Jun Jie Yi
Keyword(s):  
Pore Structure ◽  
Parallel Plate ◽  
Mercury Porosimetry ◽  
Nitrogen Adsorption ◽  
Size Spectrum ◽  
Adsorption Experiment ◽  
Structure Characteristics ◽  
Gas Shales ◽  
Strong Ability

Gas shales have a complex pore structure. Using mercury porosimetry and nitrogen adsorption experiment on shale of Longtan Formation in southeastern of Hunan, the pore structure characteristics were contrast analyzed, influencing factors and its impact on reservoir-forming were discussed. Longtan Formation shale is composed of nanopores, include the cylinder pores with two ends open and parallel-plate pores with four sides open. The efficiency of mercury ejection ranges 31.45%~63.82%, 51.94% on average, pores uniformity is well. The size of nanopores is 5~30nm, taking up 94.74% of the total volume and 98.08% of specific surface area. Brittle minerals content is high, as an important parameter influencing pore development. The nanopores have a strong ability to absorb gas, methane molecule exist in a structured way.

Variation in Pore Structure Characteristics with Composition in the High Volatile Bituminous Coal of Binchang Area

2014 ◽  
Vol 962-965 ◽  
pp. 890-898
Author(s):  
Jin Ping Li ◽  
Da Zhen Tang ◽  
Ting Xu Yu ◽  
Gang Sun
Keyword(s):  
Low Temperature ◽  
Pore Structure ◽  
Parallel Plate ◽  
Bituminous Coal ◽  
Nitrogen Adsorption ◽  
Bet Surface Area ◽  
Test Results ◽  
Structure Characteristics ◽  
Desorption Isotherms ◽  
Adsorption Desorption

Pore structure characteristics and the effect of lithotype and maceral on pore for three types of high-volatile bituminous coals from Binchang area were investigated by combined low-temperature nitrogen adsorption/desorption, nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and maceral analysis. The low temperature N2 adsorption/desorption test results show that: micropores are more abundant than transitional pores with high BET surface area; two types of pore structures can be identified by adsorption/desorption isotherms; Pore morphology is mainly represented by well-connected, ink-bottled, cylindrical and parallel plate pores. NMR T2 distributions at full saturated condition are apparent or less obvious trimodal and three types of T2 distributions are identified; Seepage pores are better developed when compared with the middle-high rank coal. Further research found that the three coal lithotypes are featured by remarkably different pore structure characteristics and maceral contents of coal are linearly correlated to some of pore structure parameters.

scholarly journals Characterization of Coal Porosity for Naturally Tectonically Stressed Coals in Huaibei Coal Field, China

2014 ◽  
Vol 2014 ◽  
pp. 1-13
Author(s):  
Xiaoshi Li ◽  
Yiwen Ju ◽  
Quanlin Hou ◽  
Zhuo Li ◽  
Mingming Wei ◽  
...  
Keyword(s):  
Surface Area ◽  
Pore Volume ◽  
Coalbed Methane ◽  
Nitrogen Adsorption ◽  
Ductile Deformation ◽  
Macromolecular Structure ◽  
Coal Field ◽  
Nanopore Structure ◽  
The Relationship

The enrichment of coalbed methane (CBM) and the outburst of gas in a coal mine are closely related to the nanopore structure of coal. The evolutionary characteristics of 12 coal nanopore structures under different natural deformational mechanisms (brittle and ductile deformation) are studied using a scanning electron microscope (SEM) and low-temperature nitrogen adsorption. The results indicate that there are mainly submicropores (2~5 nm) and supermicropores (<2 nm) in ductile deformed coal and mesopores (10~100 nm) and micropores (5~10 nm) in brittle deformed coal. The cumulative pore volume (V) and surface area (S) in brittle deformed coal are smaller than those in ductile deformed coal which indicates more adsorption space for gas. The coal with the smaller pores exhibits a large surface area, and coal with the larger pores exhibits a large volume for a given pore volume. We also found that the relationship betweenSandVturns from a positive correlation to a negative correlation whenS>4 m2/g, with pore sizes <5 nm in ductile deformed coal. The nanopore structure (<100 nm) and its distribution could be affected by macromolecular structure in two ways. Interconversion will occur among the different size nanopores especially in ductile deformed coal.

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.

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