Characterization of fines produced during drainage of coalbed methane reservoirs in the Linfen block, Ordos Basin

Abstract

Coal fines produced during drainage of coalbed methane reservoirs can affect the permeability of the coal reservoir and damage production facilities such as downhole pumps, shafts, and valves. Thus, to clarify the mechanism of coal fines output is very important to high production of coalbed methane. The characteristics of coal fines can be used to identify the sources of the coal fines and to develop reasonable means of controlling coal fines output. In this study, different coal fines characteristics were investigated to reveal the output mechanism of coal fines. The coal fines samples were collected from 16 coalbed methane wells, which located in Eastern Ordos Basin of China. And the wells are in different drainage stages. The coal fines samples were analyzed by using transmission light microscopy, reflection polarized optical microscopy, laser particle size analysis, X-ray diffraction, and scanning electron microscopy with energy dispersive X. The results show that the concentration of coal fines is in the range of 3–8% (volume percent). The sizes of the coal fine particles tended to be below 200 µm. The main components of pulverized coal are vitrinite and inorganic minerals and the average content of inorganic minerals account for 50.56% and the standard deviation is 0.0685. The morphology analysis results show that the shape of coal fines is different in different parts of the coalbed methane wells. The coal fines concentration increases with the increase in the thickness of the deformed coal, and decreases with the increase in the burial depth. The concentration of coal fines becomes higher with the increase of casing pressure and coal fines concentration increases with the increase of the variation of bottom hole pressure.