煤体层理方向对液态CO2致裂效果的影响规律

Influence of Bedding Planes in Coal Mass on Fracturing Effect when Cyclically Injecting Liquid CO2

煤体原生层理裂隙对煤岩的性质有明显的影响,为研究液态CO2致裂煤体的各向异性,对5种不同层理方位的煤岩进行注入液态CO2致裂实验,借助超声波检测仪与低场核磁共振设备,分析其波速变化、孔隙分布及渗流空间演化规律.研究结果表明:不同层理方位的煤体致裂效果具有明显的各向异性.纵波波速变化与层理角度负相关,不同孔径的孔隙变化与层理角度正相关,且中、大孔径(渗流孔)相对于微小孔的层理方向效应更高.孔隙度与层理角度呈二次函数关系.该研究对现场注入液态CO2致裂增透高效抽采瓦斯具有一定的指导意义.

Primary bedding fractures in coal mass exhibit a significant influence on the properties of a coal-rock mass.To explore the anisotropy of liquid CO2 in fracturing coal mass,five types of coal-rock mass with different bedding orientations were subjected to fracturing experiment by injecting liquid CO2.On this basis,by using an ultrasonic detector and a low-field nuclear magnetic resonance(LF-NMR)apparatus,the changes in wave velocity,pore distribution,and seepage space in coal-rock mass were analyzed.The research results showed that the fracturing effects of coal masses with different bedding orientations delivered significant anisotropy.The change of velocity of longitudinal waves is negatively correlated with the bedding angle while the change of pores with different sizes show a positive correlation with the bedding angle.Moreover,mesopores and macropores(seepage pores)exhibited a more significant directivity effect on bedding planes compared with micropores.The relationship between porosity and bedding angle is a quadratic function.The research exerts guidance on fracturing coal and increasing permeability of coal mass to extract coalbed methane(CBM)efficiently by injecting liquid CO2 in situ.