Progress of coal fines agglomeration and settlement mechanism based on high efficiency coalbed methane drainage

Significant low-yield and inefficient wells seriously hinder the development of China’s coalbed methane (CBM) industry, and the coal fractures and production pipes blocking caused by the coal fines settlement are the key influencing factors. This paper systematically investigates the latest research progress in the composition, generation mechanism, suspension transport and output control of coal fines produced by coalbed methane wells at home and abroad, summarizes the control mechanism and key issues of coal fines agglomeration-settlement and dispersion behavior, and proposes research prospects. The coal fines problem accompanies the entire process of CBM exploration and development, involving all aspects of geological selection evaluation, engineering fracturing construction, and drainage management control. The coal fines include the primary fines generated by the destruction of the coal body structure and the secondary fines formed by the engineering construction. The fines produced from the CBM wells are mainly a mixture of organic debris and clay minerals, with some samples of high clay minerals content. The suspended migration of coal fines is controlled by coal structure and surface properties, nm-μm coal particles interaction, the role of organic matter and clay minerals, and the flow of gas and water in the channel. The moderate and stable output of coal fine is the key to the management and control of drainage, involving the influences and mechanism of formation water environment on coal fines wettability, surface electrical properties and steric effects; and effect of dispersant ion addition on the desorption and seepage capacity of CBM. Focusing on “whole process experimental simulation of coal fines adhesion-wetting-agglomeration-settlement” and “optimization of coal fines dispersion stability and its moderate drainage”, accurate characterization of the physical and chemical properties of coal fines, the mechanism of agglomeration and settlement, the boundary conditions of the scattering behavior are carried out. Then the flow rate suitable for the stable migration control of coal fine is put forward to form the basic basis for maintaining the suspended production of coal fines, which provides theoretical and technical support for ensuring the stable and efficient output of methane-water-coal fines.