考虑CO_(2)吸附和滑脱效应影响的页岩渗透率演化机制研究

Study of gas seepage law by considering the influence of adsorption and slippage

为探究气体吸附以及滑脱效应对页岩渗透率的影响规律,利用自主研制的渗流装置,开展了CO_(2)的脉冲衰减渗流试验。试验结果表明:在低孔隙压力下,CO_(2)吸附对渗透率计算结果影响较大,随着孔隙压力增大,CO_(2)吸附对渗透率的影响逐渐减小;通过修正后的滑脱效应渗流公式对渗透率进行拟合,发现修正后的滑脱效应公式与渗透率变化趋势更加贴合;利用滑脱效应贡献率量化分析滑脱效应对渗透率的影响规律,孔隙压力为2.5MPa~4MPa时,滑脱效应对渗透率影响较大,贡献率达到27.78%,随着孔隙压力的增大,贡献率逐渐下降至8.44%,在低孔隙压力条件下,滑脱效应影响更加明显,随着孔隙压力的增大,滑脱效应影响呈指数形式逐渐减小。

In order to investigate the influence of CO_(2) on shale permeability,the pressure pulse seepage test of CO_(2)was carried out by using the self-developed seepage device.The test results show that:at low pore pressure,the effect of CO_(2) adsorption on the permeability is greater,and with the increase of pore pressure,the effect of CO_(2) adsorption on the permeability decreases gradually;The permeability is fitted by the modified slippage effect seepage formula,and it is found that the modified slippage effect formula is more in line with the permeability trend.The effect of slippage effect on permeability was quantitatively analyzed by the contribution rate of slippage effect.When the pore pressure was in the range of 2.5MPa~4MPa,the slippage effect had a great influence on the permeability,and the contribution rate reached 27.78%.With the increase of pore pressure,the contribution rate gradually dropped to 8.44%.Under the condition of low pore pressure,the slippage effect is more obvious,and the slippage effect decreases exponentially with the increase of pore pressure.