College of Mining Engineering, Taiyuan University of Technology
Key Laboratory of In-situ Property-improving Mining of Ministry of Education, Taiyuan University of Technology

将CO2注入到深部不可采煤层是实现CO2地质封存的有效途径之一，但CO2在高压、高温作用下会处于超临界状态，为了探究超临界CO2作用对煤系储层结构的影响，基于自主研发的超临界CO2浸泡实验系统，结合声发射测试系统及RFPA3D数值模拟，研究了3种煤层厚度和3种顶底板岩性的“岩−煤−岩”(RCR)组合试件在超临界CO2作用下的力学损伤特性及其裂隙扩展演化规律。研究结果表明：① 超临界CO2作用后，随煤厚增加RCR组合体抗压强度劣化幅度逐渐增大，弹性模量劣化幅度逐渐降低，而当岩煤强度比不同时，抗压强度和弹性模量劣化幅度基本一致，未呈现较大差异；② 超临界CO2作用会促进煤体塑性破坏，加剧RCR组合体由拉伸劈裂破坏向剪切塑性破坏转变的趋势，RCR组合体塑性破坏程度与煤厚和岩煤强度比均成正相关关系；③ 超临界CO2浸泡作用促使RCR组合体更早进入弹性变形阶段，且经历更为短暂的弹性变形后发生失稳破坏，煤厚越大影响越大，而岩煤强度比影响较小；④ RCR组合体失稳态势与煤厚成正比、与岩煤强度比成反比，破坏时动力显现强度与煤厚成反比，与岩煤强度比成正比；⑤ RCR组合体总能量、耗散能、弹性能、盈余能随煤体厚度增加而逐渐降低，随岩煤强度比的增大而逐渐增大，超临界CO2作用会使RCR组合体试件弹性能占比降低，耗散能占比升高，盈余能占比降低。综合上述研究成果可知，煤层越厚的地层越容易发生失稳，顶底板岩层强度越高的地层越不容易发生失稳，地层失稳破坏时动力显现强度与煤厚成反比、与岩煤强度比成正比。故在满足CO2注入封存量前提的一定区域地层内，应选择顶底板岩层强度较高、煤层厚度较薄的区域地层封存CO2安全性更高。该研究成果可为CO2注入到深部不可采煤层进行地质封存的安全性提供一定的理论借鉴。

The injection of CO2 into deep unrecoverable coal seams is one of the effective ways to achieve CO2 geological sequestration, but CO2 will be in a supercritical state under the action of high pressure and high temperature. In order to investigate the effect of supercritical CO2 action on coal reservoir structure, based on the self-developed supercritical CO2 immersion experimental system, combined with acoustic emission test system and RFPA3D numerical simulation, we studied the three coal seam thicknesses and three top and bottom lithologies of the mechanical damage characteristics and the fracture extension evolution of “Rock-Coal-Rock” (RCR) composite specimens under the action of supercritical CO2 were investigated. The results show that: ① After the action of supercritical CO2, the degradation of compressive strength and elastic modulus of the RCR composite gradually increases and decreases with the increase of coal thickness, while the degradation of compressive strength and elastic modulus are basically the same when the strength ratios of rock and coal are different and do not show large differences; ② The action of supercritical CO2 will promote the plastic damage of the coal body and intensify the transformation of the RCR composite from tensile splitting damage to shear plastic damage, and the degree of plastic damage of RCR assemblage is positively correlated with both coal thickness and rock-to-coal strength ratio; ③ The supercritical CO2 immersion promoted the RCR assemblage to enter the elastic deformation stage earlier, and the destabilization damage occurred after a more brief elastic deformation, the greater the coal thickness, the greater the influence, while the rock-to-coal strength ratio has less influence; ④ The instability potential of RCR assemblage is proportional to coal thickness and inversely proportional to rock-coal strength ratio, and the power intensity of damage is inversely proportional to coal thickness and proportional to rock-coal strength ratio; ⑤ The total energy, dissipative energy, elastic energy and surplus energy of RCR assemblage gradually decrease with the increase of coal thickness and gradually increase with the increase of rock-coal strength ratio, and the supercritical CO2 effect will cause the elastic energy ratio of RCR assemblage specimens to decrease, the dissipative energy ratio to increase and the surplus energy ratio to decreases. Combining the above research results shows that the thicker the coal seam is, the more likely it is to be destabilized, and the higher the strength of the top and bottom rock layer is, the less likely it is to be destabilized, and the dynamic strength of the seam destabilization is inversely proportional to the coal thickness and positively proportional to the rock-to-coal strength ratio. Therefore, in a certain area of stratum that meets the premise of CO2 injection and storage, the area of stratum with higher top and bottom rock strength and thinner coal seam thickness should be selected to store CO2 with higher safety. The research results can provide some theoretical reference for the safety of geological storage of CO2 injected into deep unmineable coal seams.

国家自然科学基金资助项目(52104097，51974194)；山西省基础研究计划资助项目(20210302124352)

张小强，王文伟，姜玉龙，等. 超临界CO2作用下煤岩组合体力学特性损伤及裂隙演化规律[J]. 煤炭学报，2023，48(11)：4049−4064.

ZHANG Xiaoqiang，WANG Wenwei，JIANG Yulong，et al. Mechanical properties and fracture damage law of coal-rock composition under the action of supercritical CO2[J]. Journal of China Coal Society，2023，48(11)：4049−4064.