低渗孔隙介质的渗透率应力敏感性及气体滑脱效应实验研究:以鄂尔多斯盆地延长组第7段泥/页岩为例

Permeability stress sensitivity and gas-slippage effect of low-permeability porous media: An experimental case study of mudstone/shale of Chang 7 Member of Yanchang Formation in the Ordos Basin

气体渗透率作为重要的孔隙介质属性,是页岩气开发的重要参数。在纳米孔隙介质中,气体渗透率很大程度上受分子滑脱效应的影响。当孔隙大小和分子自由程达到了可比较的程度,单个气体分子与孔壁之间的相互作用更加明显,气体传输不再遵循达西定律。本次研究采用压力脉冲衰减技术测量了鄂尔多斯盆地延长组第7段泥岩(YK-108)和页岩(YK-81)的气体渗透率,通过Klinkenberg校正求得了样品的固有渗透率,建立了样品的渗透率应力敏感性,定量表征了分子滑脱效应的相对贡献并探讨了其影响因素,最后讨论了地质条件下的分子滑脱效应及其地质意义。研究发现,矿物组成影响渗透率应力敏感性,分子滑脱效应对表观渗透率有显著贡献,测试样品中气体主要通过滑脱流和转换流传输,不属于达西流范畴。

As an important pore-medium property,gas permeability is an important parameter in shale-gas development.In nanopore media,gas permeability is largely affected by the molecular-slippage effect.When the pore size and molecular free path reach a comparable degree,the interaction between a single gas molecule and the pore wall becomes more obvious,and the gas transport does not follow the Darcy’s law.In this study,the gas permeability of the Chang 7 Member of the Yanchang Formation mudstone(YK-108)and shale(YK-81)in Ordos Basin was measured using the pressure pulse-decay technique.The intrinsic permeability values of the samples were obtained using Klinkenberg calibration,and the permeability sensitivity of the samples was established.The relative contribution of the molecular slippage was quantitatively characterized,and its influencing factors were discussed.Finally,the molecular-slippage effect under geological conditions and its geological significance were discussed.The results showed that the permeability stress sensitivity was influenced by mineral composition,the molecular-slippage effect significantly contributed to the apparent permeability,and the gas in the tested samples was mainly transmitted via slip and transition flows,which did not belong to the Darcy-flow category.