多场耦合作用下页岩渗透特性实验研究

页岩气开采过程,其储层页岩渗透率受多重因素的影响。采用自主研发的多场耦合作用下不同相态CO₂致裂驱替CH₄实验装置,实验研究了有效应力、孔隙压力、温度以及吸附膨胀效应等因素对裂隙页岩体与型岩渗透特性的影响。结果表明:(1)页岩渗透率随有效应力增加呈负指数关系减小,且型岩对于有效应力变化具有更强的敏感性;(2)在相同应力状态下,由于吸附引起的差异性膨胀效应会降低页岩渗透率,不同气体作用下测得的页岩渗透率表现为He＞N₂＞CO₂。(3)两种页岩中渗透率随孔隙压力变化规律具有差异性。SC-CO₂致裂页岩在低压条件下Klingkenberg效应不明显,渗透率随平均孔隙压力的增大而增大,型岩在低压阶段由于Klingkenberg效应对渗透率变化起主导作用,随着孔隙压力增加,其渗透率降低,在达到极小值后,随着孔隙压力的增加,Klingkenberg效应减弱,有效应力起主导作用,渗透率随孔隙压力增加而增加;(4)温度作用通过改变页岩的孔隙结构、力学性质等控制页岩渗透率的变化,随着温度增加,页岩渗透率降低。因此,在页岩气开采过程以及CO₂强化页岩气开采过程需要考虑多因素耦合作用对页岩渗透率的影响。

Experiment Study on the Coupling Multi-field Effect on the Dynamic Variation of Permeability in Shale

During the exploitation of shale gas, the permeability of reservoirs influenced by multiple factors. Using the self-developed experimental device for displacing CH₄ by different phase of CO₂ in multi-field coupling conditions, the study of the percolation mechanism of shale, which can be influenced by effective stress, pore pressure, temperature and swell/shrinkage effect, are done. The experimental results show that: (1) With the effective stress increased, the permeability decreased as negative exponent relation; and the influence law of permeability with different loading path of effective stress is different. (2) In the stage of low pore pressure, Klinkenberg effect is remarkable for moulded shale; on the contrary, with pore pressure increase, the permeability of fractured shale increase. (3) The permeability of shale is sensitive to temperature which could transform pore structure and mechanical properties. (4) The permeability of shale decrease because of the matrix swelling, and there is otherness of adsorption swelling for different kinds of gas; and the matrix adsorption swelling impact the permeability together with effective stress and temperature The experiment results is instructive for the study of percolation mechanism and exploitation of shale gas.