A preliminary study of oxidant stimulation for enhancing coal seam permeability: Effects of sodium hypochlorite oxidation on subbituminous and bituminous Australian coals

Abstract

A preliminary study of oxidant stimulation for enhancing coal seam permeability: Effects of sodium hypochlorite oxidation on subbituminous and bituminous Australian coals. Cogel (2018),

Oxidant stimulation of coal seams to increase coal seam permeability

“…In this study, the majority of the new fractures and the void space were produced in the bright coal bands. The massive change occurred in the bright coal in this study conflicts with our previous finding that NaClO prefers to attack the dull coal than the bright coal when it flowed through the artificial cleats across both bright coal and dull coal [179]. To examine this confliction, the void space fractions for each coal before and after oxidation were analysed and we found that the NaClO oxidation seems to occur at the locations where high void space exists.…”

“…This tendency has been observed by researchers who tried to generate valuable organic acids from coal through NaClO oxidation [17,21]. The different reaction behaviours with different coal types were hypothesized to be related to key features in coal molecular structures and NaClO oxidative mechanisms [150]. Regarding coal molecular structure differences, the lower rank coals have been proposed to contain longer aliphatic side chains and more oxygen functional groups, while the higher rank coals are more aromatic with more poly-condensed structures [31,[122][123][124].…”

“…Our previous research showed that coal S could react more vigorously than coal B when in contact with NaClO [179]. Firstly coal S dissolved 10 times more than coal B in NaClO and secondly, artificial channels in coal S could be etched more by NaClO than coal B [179].…”

Permeability Enhancement via Acetic Acid (CH3COOH) Acidizing in Coals Containing Fracture-Filling Calcite

“…The majority of pore spaces in coals were micropores (less than 2 nm) and mesopores (2–50 nm), indicating that coal seam permeability is mainly controlled by fractures at different scales. Therefore, the stimulation methods focused on generating artificial fractures, − oxidative dissolution of coal organic matter to improve natural fracture aperture, − and mineral dissolution to remove occlusion and improve connectivity of natural fracture systems. − Hydraulic fracturing and hydraulic slotting are the most common physical methods for generating fractures in coal seam. During the injection of high-pressure fluids and proppants for hydraulic fracturing, however, massive coal fines were always produced and may block the artificial fractures, , resulting in a serious reduction of fracture permeability. , The numerous fractures induced by stress release during hydraulic slotting have been proved to play a key role in improving methane extraction in underground coal mines.…”

Dissolution behaviour of different rank coals in L‐glutamic acid N, N‐diacetic acid chelating agent: Implications to enhance coalbed methane recovery by acid stimulation

“…[12] Fluoride precipitation can occur easily in the presence of Ca and Mg ions. [13] Alternatively, Jing et al [3,14,15] proposed using a NaClO oxidant to increase the pore system connectivity or generate micro-structures in the matrix by dissolution. Such practice has also been reported by Yang et al [16,17] for enhancing permeability of shale formation.…”