Oxidant stimulation of coal seams to increase coal seam permeability

Abstract

Low permeability renders a significant fraction of coal seam gas (CSG) resources subeconomic. An effective permeability enhancement strategy is thereby crucial in monetising low permeability CSG resources. Though employed in a number of coal basins, conventional low permeability stimulation treatments have not been ubiquitously successful. The natural cleat system of coal is the primary conduit for gas flow and low permeability is in many cases attributed to low cleat porosity and connectivity. Cleat demineralisation by acid has been addressed previously with mixed results. This thesis explores the possibility that coal cleats could be etched and the cleat aperture could be widened by use of oxidants. It could have high potential to increase the cleat porosity and connectivity, thus enhancing the coal permeability in the near well bore region where high permeability is critical. Two coal samples, from the Bowen (coal B) and Surat (coal S) basins in Queensland, Australia were selected. A screening method was designed based on time-lapse photography to assess the extent of coal particle size change immersed in potential oxidants, including sodium hypochlorite (NaClO), potassium permanganate (KMnO4), hydrogen peroxide (H2O2), and potassium persulfate (K2S2O8). Results show coal solubilisation and the propensity to swell in all the oxidants as well as coal breakage in specific oxidants (NaClO and KMnO4). Both coals react vigorously with NaClO and KMnO4, where massive coal solubilisation occurs, but react only slightly with K2S2O8 and H2O2. Given the solid products of the KMnO4 reaction (MnO2), NaClO is selected as the most promising oxidant stimulant. After NaClO treatment, the total accessible pore volume of both coals increases. Pore size distributions indicate that oxidation can enlarge the pores, particularly for coal S, which was confirmed by scanning electron microscopy (SEM). A microfluidic cleat flow cell (CFC) was used to inject NaClO into artificial channels scribed on polished coal samples, and measured an increase in the widths of the channels after NaClO treatment. The channel aperture increase indicates that coal solubilisation/etching is a more dominant mechanism than coal swelling when coal is confined in coal cleats. The channel aperture of coal S increases more than coal B.

Coal-Derived Activated Carbon for Electrochemical Energy Storage: Status on Supercapacitor, Li-Ion Battery, and Li–S Battery Applications

“…Coal has many distinct advantages among the bioresources such as high abundance, low material and processing costs, high carbon content ranging from 65 to 90% depending on rank or grade of coal, and a high-density three-dimensional cross-linked skeleton . High-grade coal has a greater amount of cyclic and aromatic carbon units linked through short aliphatic and ether linkages, which can be beneficial for producing graphene-like structures; − on the other hand, low-grade coal has a high amount of oxygen-containing functional groups (carboxyl, phenolic, quinone, ether, furan, etc. ), hetero atom S and N containing groups (thiol, thiophene, aniline, pyrrole, pyridine, etc.)…”

“…), hetero atom S and N containing groups (thiol, thiophene, aniline, pyrrole, pyridine, etc.) along with other inorganic impurities. − The wide varieties of macromolecular properties in different types of coal have attracted researchers around the world to explore it as a precursor porous carbon material for diverse applications. − …”