Comprehensive understandings of the influences of negative pressure on air-leakage and its driving mechanism are critical for controlling methane concentration during coal seam gas extraction. Laboratory experiments were conducted using an integrated apparatus to study the air-leakage process of coal seam gas extraction under different negative pressures. In addition, a coupled computational fluid dynamics-discrete element approach was used to simulate the process of air flow and particle transport in a natural coal fracture to understand the influential mechanism of negative pressure on air-leakage at the mesoscale. Experimental results show that with an increase in the absolute value of negative pressure, the air-leakage experiences three stages of increase, decrease and increase at Stage I, Stage II and Stage III, respectively. It is reported for the first time and in good agreement with field test data. From experimental and numerical results, at Stage I the air-leakage increases with the absolute value of negative pressure because there is no blockage in fractures around borehole. At Stage II, the further increased absolute value of negative pressure contributes to particles motion in fractures. It gradually leads to the formation of blockage structure composed of aggregated particles in fractures, and the decrease of fracture conductivity and air velocity. With the absolute value of negative pressure rising continuously, the contact forces between the aggregated particles increase. Therefore, the balance of the blockage structure tends to be broken, which helps to understand the air-leakage increase with the absolute value of negative pressure at Stage III. Between Stage II and Stage III, there is a valley point corresponding to the minimum air-leakage, which is important to the improvement of gas extraction performance. The contact forces on the aggregated soft particles are larger than those on the aggregated hard particles under the same negative pressure. Therefore, the blockage structure consisting of soft particles is much easier to be broken than that formed by hard particles. This explains why the absolute value of negative pressure corresponding to the valley point for hard coal model is larger than that for the soft coal model.

全面了解负压对漏气的影响及其驱动机理对于控制煤层气开采过程中的甲烷浓度至关重要。使用集成设备进行实验室实验，以研究在不同负压下抽采煤层气的漏气过程。此外，采用耦合计算流体动力学离散元方法模拟天然煤裂缝中的气流和颗粒运移过程，以了解负压对中尺度漏气的影响机理。实验结果表明，随着负压绝对值的增加，漏气在第一，第二和第三阶段分别经历了增加，减少和增加的三个阶段。首次报告，并且与现场测试数据高度吻合。从实验和数值结果来看，在第一阶段，由于井眼周围的裂缝没有阻塞，漏气量随负压的绝对值而增加。在第二阶段，负压的绝对值进一步增加有助于裂缝中的颗粒运动。它逐渐导致裂缝中聚集颗粒组成的堵塞结构的形成，并降低了裂缝的电导率和空气流速。随着负压的绝对值连续增加，聚集颗粒之间的接触力增加。因此，堵塞结构的平衡趋于被破坏，这有助于理解在阶段III处随着负压绝对值的漏气增加。在第II阶段和第III阶段之间，有一个对应于最小空气泄漏的谷点，这对于提高气体提取性能非常重要。在相同的负压下，聚集的软颗粒上的接触力大于聚集的硬颗粒上的接触力。因此，由软颗粒组成的阻塞结构比由硬颗粒形成的阻塞结构更容易破裂。这解释了为什么硬煤模型对应于谷点的负压绝对值比软煤模型更大。在相同的负压下，聚集的软颗粒上的接触力大于聚集的硬颗粒上的接触力。因此，由软颗粒组成的阻塞结构比由硬颗粒形成的阻塞结构更容易破裂。这解释了为什么硬煤模型对应于谷点的负压绝对值比软煤模型更大。在相同的负压下，聚集的软颗粒上的接触力大于聚集的硬颗粒上的接触力。因此，由软颗粒组成的阻塞结构比由硬颗粒形成的阻塞结构更容易破裂。这解释了为什么硬煤模型对应于谷点的负压绝对值比软煤模型更大。