Experimental Study on Coal Structure Variation and CH₄ Adsorption Properties under the Effect of Cocamidopropyl Betaine

Abstract

Surfactants can be used to improve the coal surface wettability and reduce the CH 4 adsorption capacity of coals, so they are usually added to fracturing fluids to promote coalbed methane (CBM) production. In this work, the impacts of a surfactant cocamidopropyl betaine (CAB) on coal structures and CH 4 adsorption characteristics were investigated. The CAB solutions with five CAB concentrations (0, 0.002, 0.006, 0.008, and 0.01 mol/L) were prepared and used to treat coal samples. The treated coal samples were dried and tested for infrared spectroscopy experiments, liquid nitrogen adsorption experiments, and CH 4 adsorption experiments. The results indicate that the hydrophilicity of the coal samples was enhanced after being treated with CAB solutions; the number of hydroxyl functional groups increased; and some aliphatic, aromatic, and oxygen-containing structures disappeared, which promoted the replacement of CH 4 by H 2 O and reduced the amount of adsorbed CH 4 . Meanwhile, the pore volume of the coal samples increased and the CBM migration rate was improved. Among the five CAB concentrations, 0.008 mol/L CAB was determined to be an optimal concentration to increase the CBM extraction efficiency. Compared to the untreated coal, the amount of adsorbed CH 4 decreased by 13.18% and the CBM migration channel volume increased by 16.74% at 0.008 mol/L CAB. The results reported in this work will offer new insights into the improvement of CBM extraction efficiency using CAB.

Physicochemical Effect on Coal Pores of Hydrocarbon Chain Length and Mixing of Viscoelastic Surfactants in Clean Fracturing Fluids

“…Huang et al 22 suggested that the clean fracturing fluid altered the coal pore structure mainly because the clean fracturing fluid residue entered the coal pore system and adhered to the pore wall or blocked the pore throat. Dong et al 34 In this study, the effects of the hydrocarbon chain length of hydrophobic groups and mixing of VESs on the porosity and pore volume of coal with different levels of hardness were investigated. Then, by conducting elemental analysis of clean fracturing fluids after soaking of coal samples and testing the mineral composition and content in coal samples treated with clean fracturing fluids, the effect of the hydrocarbon chain length of hydrophobic groups and mixing of VESs on mineral NaO 3 , NaSal) was used as a micellar promoter of cationic surfactant, and potassium chloride (KCl) acted as a counterion and antiswelling agent.…”

“…Huang et al 22 suggested that the clean fracturing fluid altered the coal pore structure mainly because the clean fracturing fluid residue entered the coal pore system and adhered to the pore wall or blocked the pore throat. Dong et al 34 indicated that the pore volume of coal samples treated with clean fracturing fluids containing zwitterionic VES increased. At present, there is a lack of research on the laws and mechanisms of the influence of the VES molecular structure and VES mixing on the pores of coal treated with a clean fracturing fluid.…”