Influencing effects of different types of dispersants on the permeability levels of Coal-Bearing propped fractures in coalbed methane reservoirs

Abstract

This study investigated how to effectively discharge deposited pulverized coal particles in coal-bearing propped fractures and improve the permeability levels of the propped fractures in order to enhance coalbed methane production. Four types of dispersants were selected to carry out wettability and permeability tests, including sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), dodecyl dimethyl betaine (BS-12), and alkyl poly glycoside dodecyl glucoside (APG). The results showed reductions in surface tension of 63.71 to 69.75 %, and reductions in contact angles of 40.08 to 60.46 %, when compared with water injections alone. In addition, under the same closure pressure conditions, the dispersant solutions had increased the permeability of the propped fractures by 76.67 to 123.34 % when compared with that of the water injections, and the pulverized coal discharge rates were increased by 1.44 to 2.41 times. The decreases in closure stress also contributed to the enhancement of the permeability of the propped fractures, with increases of between 11.24 and 29.18 % observed. This study found that for the four tested dispersants, the order of the effective wetting of the pulverized coal particles and enhancement of the permeability of the propped fractures were (from strong to weak) as follows: SDS > BS-12 > APG > SDBS. Among the tested dispersants, the 6 mmol/L SDS dispersant solution was found to be the most effective for improving the wettability of the pulverized coal particle surfaces and achieved the highest permeability improvement of the propped fractures.