Jiangsu Key Laboratory of Coal-based Greenhouse Gas Control and Utilization, China University of Mining and Technology
Carbon Neutrality Institute, China University of Mining and Technology
School of Resources and Geosciences, China Universityof Mining and Technology
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University

During the hydraulic fracturing of coalbed methane (CBM) well, the deposition of coal fines in propped fracturesand the migration of coal fines in cleats will damage the permeabilities of propped fractures and cleats, consequently affecting the hydraulic fracturing and the subsequent drainage of CBM well. For the purpose of dredging propped fracturesand avoiding the clogging of cleats effectively, a novel method for the control of coal fines in propped fractures andcleats during hydraulic fracturing was proposed by optimizing the salinity of fracturing fluid. With the salinity decreasingstepwise, the experiments on the migration of coal fines in propped fractures and cleats were conducted on quartz sandpackedcolumns and anthracite coal plugs, respectively, to investigate the response characteristics of the migration of coalfines to the change of salinity. Additionally, the migration of coal fines was simulated by using the extended DLVO method,to elucidate the influence mechanisms of salinity on the migration of coal fines. On this basis, the optimal salinityrange that takes into account the control of coal fines in propped fractures and cleats was explored. The results indicatedthat there existed a critical salt concentration (CSC) for the migration of coal fines in both propped fractures and cleats.When the salinity was lower than the CSC, the permeability of propped fractures abruptly increased while that of cleats decreasedsharply, accompanied by a large amount of coal fines produced. The value of the CSC for the migration of coalfines in propped fractures was higher than that in cleats, which can be attributed to the fact that the surface electronegativityof proppants was stronger than that of cleats, while the hydrophobicity was weaker than that of cleats. With the gradualdecrease of salinity, the electric double layer (EDL) repulsive force between coal fines and channel increased continuously.When the salinity decreased to the CSC, the EDL repulsion started to be greater than the sum of Lifshitz-van derWaals attraction and Lewis acid-base attraction, resulting in the migration of coal fines. Both the values of the predictedCSCs for the migration of coal fines in propped fractures and cleats were consistent with experimental data, indicating theeffectiveness of the model. During hydraulic fracturing, the salinity of fracturing fluid can be designed between the CSCsfor the migration of coal fines in propped fractures and cleats. In that case, the production of coal fines in propped fracturesis promoted while the migration of coal fines is inhibited in cleats, so as to achieve the dual purposes of coal finescontrol in propped fractures and cleats.

国家自然科学基金资助项目(42002182，42030810，41727801)

皇凡生，桑树勋，刘世奇，等. 压裂液矿化度对支撑裂缝及裂隙内煤粉运移的影响[J]. 煤炭学报，2023，48(4)：1622−1633

HUANG Fansheng，SANG Shuxun，LIU Shiqi，et al. Impact of salinity of fracturing fluid on the migration of coal fines in propped fractures and cleats[J]. Journal of China Coal Society，2023，48(4)：1622−1633