石油与天然气地质2025，Vol.46Issue(3)：983-994,12.DOI:10.11743/ogg20250319
超临界CO2浸泡中阶煤岩力学性能劣化特性及其机制
Degradation of the mechanical properties of medium-rank coals under supercritical CO2 soaking and its mechanisms
摘要
Abstract
Exploring the mechanical properties of coals subjected to supercritical carbon dioxide(SC-CO2)soaking holds great significance for enhanced hydraulic fracturing performance of deep coalbed methane(CBM)reservoirs and CO2 geological sequestration.Using tri-axial compression tests,mineralogical analysis,and porosity and permeability measurements,we systematically reveal the SC-CO2 soaking-induced degradation mechanisms of the macroscopic mechanical properties of medium-rank coals under varying confining pressures.The results indicate that SC-CO2 soaking leads to more pronounced initial compaction and residual failure characteristics in the stress-strain curves of coals,accompanied by a significant reduction in peak stress.This can effectively diminish the strength enhancement of coals caused by confining pressure.After reaching peak strength,coals experience rapid instability and failure,with a higher confining pressure associated with more rapid failure.SC-CO2 soaking induces more significant degradation of the compressive strength of coals compared to their elastic modulus.With an increase in the confining pressure,both the compressive strength and elastic modulus of coals trend upward before and after SC-CO2 soaking;however,the degrees of their degradation gradually decrease.Under low confining pressure,SC-CO2 soaking induces particularly prominent degradation of the mechanical properties of coals.Regarding the degradation mechanisms,SC-CO2 undergoes physicochemical reactions with mineral components in coals,leading to the dissolution of carbonate minerals.This process alters the pore structure and promotes the formation and propagation of micropores.As a result,both the porosity and permeability of coals increase significantly,accompanied by the breakdown of the coals'surface structures.Compared to active water soaking,SC-CO2 soaking causes more severe degradation of coals.Under the same confining pressure,the degrees of degradation of coals'compressive strength and elastic modulus caused by SC-CO2 soaking increase by 7.7%to 36.7%and 1.7%to 19.4%,respectively,compared to those induced by active water soaking.SC-CO2 soaking degrades the mechanical properties of coals primarily through chemical dissolution,while active water soaking induces degradation mainly via physical dispersion.This difference is due to the greater permeability and chemical reactivity of SC-CO2.It has been demonstrated that the chemical and physical synergistic degradation mechanism of SC-CO2 can significantly weaken the strength of coals while enhancing their permeability.The application of SC-CO2 soaking to the well involved in deep CBM tests in the Jixi Basin,Heilongjiang Province,has successfully reduced the fracturing pressure by 6 MPa and enabled a stable CBM production exceeding 1000 m3/d.Therefore,the degradation of coal properties induced by SC-CO2 soaking plays a significant role in promoting deep CBM production via volume fracturing.关键词
力学特性/渗透率/孔隙结构/超临界CO2/深层煤层气/鸡西盆地Key words
mechanical property/permeability/pore structure/supercritical CO2(SC-CO2)/deep coalbed methane(CBM)/Jixi Basin分类
能源科技引用本文复制引用
迟焕鹏,毕彩芹,宛东平,魏呈祥,蔡承政,田守嶒,郑凡石,王天宇..超临界CO2浸泡中阶煤岩力学性能劣化特性及其机制[J].石油与天然气地质,2025,46(3):983-994,12.基金项目
中国地质调查局油气资源调查中心科创基金项目(2023YC07) （2023YC07）
中国地质调查局地质调查项目(DD20240051,DD20230044,DD20190101). （DD20240051,DD20230044,DD20190101）
