Characterization of Coal Fines and their Production Controlling Factors: A Case Study from Southern Qinshui Basin, China

It is essential to formulate coalbed methane (CBM) drainage in order to improve gas production as well as to characterize coal fines and determine factors controlling its production. Some coal fines samples were collected from CBM wells in the Shizhuang block, Qinshui Basin, China. Through application of several characterization methods (i.e., composition testing, particle size measurement, and mass concentration monitoring), the samples of coal fines from various stages of gas production were characterized, and the geological factors affecting coal fines production were discussed. The produced coal fines were found to have greater minerals content than the primary coal fine samples. The organic composition of the coal fines was dominated by vitrinite (51.58-67.00%) followed by inertinite (10-34.74%) and inorganic minerals (4.21-28%). The coal fines samples were dominated by clay minerals, pyrite, and quartz. The particle sizes of coal fines (PZCF) ranged from 0.4 to 3300 mu m with a wide size distribution. The particles' shapes were mainly columnar, spherical, flaky, flat, and lumpy. During CBM drainage, the PZCF decreased, and the average mass concentration of the coal fines (AMCCF) first increased and then decreased. As the floor curvature increased, the AMCCF increased and then plateaued. As the cumulative thickness of the granulated and mylonitized coals increased, the AMCCF first increased, reached a maximum in the range of 1.5-2.0 m, and then decreased. The AMCCF was correlated positively with the initial reservoir pressure gradient. The study can provide some guidance for controlling coal fines production.

Automated summary

Coal fines samples from CBM wells in the Shizhuang block, Qinshui Basin, China were characterized using various methods, and the factors controlling coal fines production were discussed. The study found that the produced coal fines had higher mineral content than the primary samples, and the organic composition was dominated by vitrinite followed by inertinite and inorganic minerals. The coal fines were mainly composed of clay minerals, pyrite, and quartz, with a wide range of particle sizes. During CBM drainage, the average mass concentration of the coal fines first increased and then decreased, and it was positively correlated with the initial reservoir pressure gradient.