CO2相态变化致裂对煤层吸附性影响机理研究

doi:10.13809/j.cnki.cn32-1825/te.2024.06.019

摘要/Abstract

摘要：

液态CO₂相变致裂技术（LCPTF）是一种能够提高煤层气采收率的新型无水压裂技术。为了研究CO₂相变致裂前后的煤体吸附性变化特征，选取余吾煤矿3号煤层为实验对象，开展高压压汞、低温液氮吸附实验和CH₄等温吸附实验，分析液态CO₂相变致裂技术对煤体吸附性的影响。研究结果表明：液态CO₂相变致裂后，煤体吸附孔孔容和吸附孔孔比表面积减小；煤体渗流孔孔比表面积减小，渗流孔孔容增大。液态CO₂相变致裂技术能够通过改变煤体的孔隙结构进而影响煤体Langmuir（朗缪尔）吸附常数的变化。液态CO₂相变致裂后，Langmuir吸附常数a值降低、吸附常数b值增加，表明液态CO₂相变致裂作用对煤体具有吸附能力降低、解吸速率增强作用。研究为液态CO₂相变致裂技术的改进和现场应用优化提供了理论指导。

关键词: 煤层瓦斯, 煤体吸附性, 煤体孔隙结构, 液态CO₂相变致裂, 游离态瓦斯

Abstract:

Liquid CO₂ phase transition fracturing（LCPTF） technology is a novel water-free fracturing technique that can enhance coalbed methane recovery. To study the changes in coal adsorption characteristics before and after CO₂ phase transition fracturing, the No. 3 coal seam from the Yuwu coal mine was selected for experimentation. High-pressure mercury intrusion, low-temperature liquid nitrogen adsorption experiments, and CH₄ isothermal adsorption tests were conducted to analyze the impact of liquid CO₂ phase transition fracturing on coal adsorption. The results showed that after liquid CO₂ phase transition fracturing, the pore volume and specific surface area of adsorption pores in coal decreased; the specific surface area of seepage pores decreased while the pore volume of seepage pores increased. The liquid CO₂ phase transition fracturing technique could influence the change in the Langmuir adsorption constant of coal by altering the pore structure. After liquid CO₂ phase transition fracturing, the Langmuir adsorption constant “a” value decreased and the “b” value increased, indicating that the fracturing process reduced the coal’s adsorption capacity and enhanced the desorption rate. This study provides theoretical guidance for the improvement and optimization of liquid CO₂ phase transition fracturing technology for field applications.

Key words: coalbed methane, adsorption, pore structure of coal, liquid CO₂ phase transition fracturing, free gas

中图分类号:

TE372

王志坚. CO₂相态变化致裂对煤层吸附性影响机理研究[J]. 油气藏评价与开发, 2024, 14(6): 967-974.

WANG Zhijian. Mechanism study on effect of CO₂ phase transition fracturing on methane adsorption in coal[J]. Petroleum Reservoir Evaluation and Development, 2024, 14(6): 967-974.

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煤样	工业分析/%			R_max/%
煤样	M_ad	A_ad	V_daf	R_max/%
原煤	0.89	13.19	11.20	2.20

样品	a/(cm³/g)	a均值/(cm³/g)	a均值的变化率/%	b/(MPa^-1)	b均值/(MPa^-1)	b均值的变化率/%
YW-R1	24.062 8	24.622 35	-25.45	0.828 6	0.839 5	43.24
YW-R2	25.181 9	24.622 35		0.850 4	0.839 5
YW-F1	18.908 5	18.354 95		1.133 9	1.202 5
YW-F2	17.801 4	18.354 95		1.271 1	1.202 5

样品	渗流孔孔容/(cm³/g)	渗流孔孔比表面积/（m²/g）
YW-R1	0.050 7	0.048 4
YW-R2	0.046 9	0.043 5
YW-F1	0.061 8	0.027 3
YW-F2	0.058 1	0.021 4

样品	孔容/(cm³/g)	孔比表面积/（m²/g）	平均孔径/nm
YW-R1	0.000 915	0.483 97	14.78
YW-R2	0.000 883	0.572 76	15.12
YW-F1	0.000 600	0.216 40	16.46
YW-F2	0.000 593	0.321 12	16.88

CO₂相态变化致裂对煤层吸附性影响机理研究

Mechanism study on effect of CO₂ phase transition fracturing on methane adsorption in coal

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