超临界CO_2提高煤层渗透性的增透规律研究

Study on increased permeability law of coal seam by supercritical CO_2

基于Peng-Robinson状态方程,考虑了CO2在不同温压下密度和黏度的变化对超临界CO2在低渗透煤层中渗透性的影响,利用自制三轴渗透仪进行不同温压条件下超临界CO2的增透实验,增透实验前后分别进行甲烷的渗透率测试.结果表明:超临界CO2作用后,煤体对甲烷的渗透率较增透实验前提高了一个数量级;超临界CO2的密度和黏度随孔隙压力的增加均呈指数递增的变化规律;在恒定温度下,超临界CO2的渗透率随着孔隙压力的增加呈指数递增的变化趋势;煤体微观孔隙、裂隙的CT扫描图显示超临界CO2作用后,煤体微观孔隙、裂隙较增透前尺寸明显增大、密度增加、连通性提高,说明由于超临界CO2的作用,进一步促进了煤层微观孔隙、裂隙的有效发育,增大了渗流空间,提高了煤层的渗流能力.

Based on the Peng-Robinson equation of state, the effect of changes of CO2 density and viscosity on permeability of supercritical CO2 in low permeability coal seam was considered under different temperature and pressure, the increasing permeability experiment was conduc- ted under different temperature and pore pressure conditions by the homemade three-axis per- meameter, and the permeability of methane was tested before and after the increasing permea- bility experiment, respectively. The results show that the permeability of methane is increased by one order of magnitude than that before increasing permeability experiment, respectively. The density and viscosity of supercritical CO2 present exponential increasing trend with the in- crease of pore pressure. The permeability of supercritical CO2 presents exponential increaseing trend with the increase of at constant temperature; The CT scanning images of microcosmic pore and fissure show that after the effect of supercritical CO2, the size of coal pore and fissure increases significantly than that before increasing permeability experiment, the density increa- ses and the connectivity improves, which explains that, for the effect of supercritical CO2, coal seam microcosmic pore and fissure develop effectively, seepage space increases and the seepage ability of coal seam improves.