Tao Shu, Tang Dazhen, Xu Hao, Li Song
School of Energy Resources, China University of Geosciences (Beijing), Beijing, 100083, PR China.
Coal Reservoir Laboratory of National Engineering Research Center of CBM Development & Utilization, Beijing, 100083, PR China.
Sci Rep. 2017 Oct 26;7(1):14124. doi: 10.1038/s41598-017-14295-y.
Coal samples were cut into cores to perform a flow velocity sensitivity (FVS) analysis under varying initial permeability, confining pressures, injection volumes, and injection intensities. The results show that the permeability and the output of the coal fines decrease with an increase in confining pressures at a constant displacement velocity. A critical flow velocity exists for the migration of relatively large coal fines. Below this critical flow velocity, very small coal fines can be transported out of the coal by the fluid, slightly increasing the coal permeability. However, larger coal fines are transported at a higher flow velocity, which may block the effective seepage paths and reduce coal permeability, inducing FVS. Moreover, as the flow velocity and the injection volume increase, the permeability damage rate increases, but the rate of increase in the permeability damage decreases. The damage to the permeability due to FVS mainly occurs in the early stage of coal fines migration, and an abrupt increase in the flow velocity can damage reservoirs and induce substantial coal fines generation. Thus, maintaining a stable effective strength and a controlled depressurization rate during drainage can effectively constrain coal fines output and decrease permeability damage within coal reservoirs.
将煤样切割成岩芯，以在不同的初始渗透率、围压、注入量和注入强度下进行流速敏感性（FVS）分析。结果表明，在恒定驱替速度下，渗透率和煤粉产出量随围压的增加而降低。相对较大的煤粉运移存在一个临界流速。低于该临界流速时，非常小的煤粉可被流体带出煤体，使煤的渗透率略有增加。然而，较大的煤粉以较高的流速运移，这可能会堵塞有效渗流通道并降低煤的渗透率，从而引发流速敏感性。此外，随着流速和注入量的增加，渗透率损害率增加，但渗透率损害的增加速率降低。流速敏感性对渗透率的损害主要发生在煤粉运移的早期阶段，流速的突然增加会损害储层并导致大量煤粉产生。因此，在排水过程中保持稳定的有效强度和可控的降压速率，可以有效地抑制煤粉产出并降低煤储层内的渗透率损害。
