Occurrence characteristics of deep coal-measure gas in Junggar Basin and a quantitative characterization method for free gas saturation

doi:10.3969/j.issn.1006-6535.2026.01.003

Abstract

Abstract: In view of the inadequate understanding of the pore structure refined characterization and gas occurrence mechanism in deep coal-measure gas reservoirs of the Junggar Basin,a quantitative characterization method for free gas saturation was proposed based on pore types and gas occurrence space.A correspondence was established between different pore types in coal rock(micropores,mesopores and macropores)and different gas occurrence states(adsorbed gas,free gas).The adsorption space do minated by micropores and the free gas space composed of mesopores-macropores are quantitatively delineated,overco ming the limitation of traditional methods lacking targeted linkage between pore types and gas occurrence states.By integrating measured gas content,isothermal adsorption,overburden porosity-permeability and other experimental data,targeted corrections were made for the bias in free gas content caused by dynamic adsorption-desorption-diffusion changes in measured total gas,as well as for the compression effect on free space under reservoir conditions.This achieved accurate quantification of in-situ free gas space and the space occupied by in-situ free gas,and ultimately established a calculation model for free gas saturation.This method,for the first time,systematically couples pore types with gas occurrence states and introduces free gas saturation as a key evaluation parameter.Application results show that in Dimei Well and Caimei Well areas,free gas saturation is below 35%,belonging to the model of moderate gas generation capacity-relatively strong storage space-relatively low free gas saturation;in Qixin Well area,despite lower pore development,free gas saturation is mostly above 75%,belonging to the model of strong gas generation capacity-moderate storage space-high free gas saturation.This method effectively reveals the controlling mechanism of different pore types on gas occurrence,deepens the understanding of gas occurrence and production mechanisms.The combined evaluation model of gas generation capacity-gas storage capacity-free gas saturation can provide a basis for optimizing future development plans and improve the production efficiency of coal-measure gas.

Key words: coal-measure gas, gas occurrence, adsorption space, free gas space, free gas saturation, gas generation capacity, gas storage capacity

CLC Number:

TE132.2

YANG Xiao, HU Zhengzhou, PAN Tuo, YAO Weijiang, CHEN Guohui, XIE Fei, FU Jiyou. Occurrence characteristics of deep coal-measure gas in Junggar Basin and a quantitative characterization method for free gas saturation[J]. Special Oil & Gas Reservoirs, 2026, 33(1): 22-32.

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