In the process of shale coring, the drilling fluid and its solid-phase immersion inevitably cause core pollution, thereby increasing the flow resistance of the gas inside the core and leading to inaccurate calculations of the loss of shale gas. To study the changes in the seepage resistance and the amount of gas lost while the shale is immersed in the drilling fluid, an experimental study on the effects of immersion pressure on the permeability of fractured shale and matrix shale was carried out. The changes in the permeability due to reservoir fluid changes and the swelling deformation due to soaking in the drilling fluid significantly affected the shale gas loss. In this study, the shale samples were analyzed by varying the immersion time (12, 24, 48, 72, 96 and 120 h) and pressure (4, 8, 12, and 16 MPa). For each saturation cycle, the permeability of the shale samples was measured using the transient method under various injection pressures (1–6 MPa). The results showed that the permeability of the shale samples decreased significantly after immersing in the drilling fluid, and the decrease rate increased with the increase in the immersion time. Compared with the matrix shale samples, the fractured shale samples exhibited better pore micro-fractures and higher hydrophilicity, so the fractured samples exhibited a greater reduction in the permeability than the matrix shale samples. Shale permeability had a negative exponential relationship with the effective stress, and its stress sensitivity increased with increasing immersion time. Importantly, during the shale coring process, under the actions of the effective stress, drilling fluid, and its solid-phase pollution, the gas escape rate on the core surface even changed by an order of magnitude. In the case of serious drilling fluid pollution, the core desorption rate was close to zero, in which case the shale gas loss may be easily underestimated.

页岩取心过程中，钻井液及其固相浸入不可避免地造成岩心污染，从而增加岩心内气体的流动阻力，导致页岩气流失量计算不准确。为研究页岩浸入钻井液中渗流阻力和失气量的变化，开展了浸没压力对裂缝性页岩和基质页岩渗透率影响的实验研究。储层流体变化引起的渗透率变化和钻井液浸泡引起的膨胀变形对页岩气流失有显着影响。在本研究中，通过改变浸泡时间（12、24、48、72、96 和 120 小时）和压力（4、8、12 和 16 MPa）来分析页岩样品。对于每个饱和周期，页岩样品的渗透率是在各种注入压力（1-6 兆帕）下使用瞬态法测量的。结果表明，页岩样品浸入钻井液后渗透率显着下降，且下降率随着浸入时间的增加而增大。与基质页岩样品相比，裂缝性页岩样品表现出更好的孔隙微裂缝和更高的亲水性，因此与基质页岩样品相比，裂缝性页岩样品的渗透率降低幅度更大。页岩渗透率与有效应力呈负指数关系，其应力敏感性随着浸泡时间的增加而增加。重要的是，在页岩取心过程中，在有效应力、钻井液及其固相污染的作用下，核心表面的气体逸出率甚至发生了一个数量级的变化。在钻井液污染严重的情况下，岩心解吸率接近于零，很容易低估页岩气损失。