Effects of nano-pore system characteristics on CH4 adsorption capacity in anthracite

This study aims to determine the effects of nanoscale pores system characteristics on CH4 adsorption capacity in anthracite.A total of 24 coal samples from the southern Sichuan Basin,China,were examined systemically using coal maceral analysis,vitrinite reflectance tests, proximate analysis,ultimate analysis,low-temperature N2 adsorption-desorption experiments,nuclear magnetic resonance (NMR)analysis,and CH4 isotherm adsorption experiments.Results show that nano-pores are divided into four types on the basis of pore size ranges:super micropores (<4 nm),micropores (4-10 nm),mesopores (10-100 nm),and macropores (>100 nm).Super micropores,micropores,and mesopores make up the bulk of coal porosity,providing extremely large adsorption space with large intemal surface area.This leads us to the conclusion that the threshold of pore diameter between adsorption pores and seepage pores is 100 nm.The "ink bottle"pores have the largest CH4 adsorption capacity, followed by semi-opened pores,whereas opened pores have the smallest CH4 adsorption capacity which indicates that anthracite pores with more irregular shapes possess higher CH4 adsorption capacity.CH4 adsorption capacity increased with the increase in NMR porosity and the bound water saturation.Moreover,CH4 adsorption capacity is positively correlated with NMR permeability when NMR permeability is less than 8 ×10^-3 md.By contrast,the two factors are negatively correlated when NMR permeability is greater than 8 × 10^-3 md.

Sedimentary and diagenetic facies of tidal flat in epeiric sea and its related descriptive method-a case of Ma51-4 submember in Jingbian gas field of Ordos basin,China

The Ma5_(1-4)submembers of Jingbian gas field in Ordos basin of China belongs to epeiric sea evaporative carbonate tidal flat facies.Supratidal zone of gypsum nodule dolostone and upper part of intertidal zone of gypsum crystal dolostone are most favorable reservoir.The carbonate rocks of Ma5_(1-4)had undergone complex diagenesis.Penecontem-poraneous dolomitization and gypsification provided the material foundation of the reservoir.Epidiagenesis selective dissolution of gypseous dolostone constructs the origin shape of pore structure.The dissolution and filling of various minerals in the burial period determine whether the early dissolution pores can be preserved,and the final state of the reservoir.Burial dissolution and filling of various minerals determined the preservation of early dissolved pores and the final condition of the reservoir.The concept of“minus cement porosity”directly reflects that sedimentary facies have great influence on the growth of reservoir in Ma5_(1-4).Combined with sedimentary microfacies and diagenetic facies,a concise numerical symbol is used to express semiquantitatively sed-imentary microfacies and diagenesis facies.This descriptive method has great benefit in reservoir evaluation and prediction.