Abstract
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.
Highlights
Coalbed methane (CBM) is a type of unconventional natural gas, which is characterized by self-generation and self-accumulation in coals
Moisture associated with a CBM project involves three forms: inherent moisture, adherent moisture, and chemically bound moisture (Rogers et al, 1994)
The moisture content of coals in the Anhe coalfield ranges from 0.42% to 2.68% with an average of 1.16% (Table 1), and the coals in the shallow west part have a higher moisture content than that of coals in the deep eastern Anhe coalfield
Summary
Coalbed methane (CBM) is a type of unconventional natural gas, which is characterized by self-generation and self-accumulation in coals. The adsorption characteristics of methane in coal are key factors in both affecting the gas content of coal and determining the recovery of CBM (He et al, 2016; Li et al, 2016; Perera et al, 2012). The methane adsorption characteristics are influenced by the internal factors of coal and external factors (Rogers et al, 1994). Internal factors include coal rank, ash yield, moisture content, coal macerals, and pore structure (Chalmers and Bustin, 2007; Crosdale et al, 2008; Gensterblum et al, 2016; Li et al, 2016). Pressure, and coal particle size (Gensterblum et al, 2016; Krooss et al, 2002; Pan et al, 2012; Perera et al, 2012)
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