X-ray μCT investigations of the effects of cleat demineralization by HCl acidizing on coal permeability

Balucan, Reydick D.; Turner, Luc G.; Steel, Karen M.

doi:10.1016/j.jngse.2018.05.007

Cited by 63 publications

(24 citation statements)

References 11 publications

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“…Naphthenic and other aliphatic structures contribute to the NMR parameter and thus could also influence the NMR parameter for the average aliphatic chain length [161]. According to the calculated / values, aliphatic chains for coal S (6.71) were longer than that for coal B (3.00) as shown in Table 5 13 C NMR structural and derived lattice parameters of the studied coal samples.…”

Section: Molecular Structure Comparison Between Coal S and Coal Bmentioning

confidence: 90%

“…Vasyuchkov (1985) reported aqueous HCl (2, 4 and 6%) solutions could enhance the coal permeability dramatically from less than 0.1 mD to over 15.1 mD [12] There was clear evidence for cleat opening via mineral dissolution as well as mineral mobilization-accumulation. Based on the X-ray microcomputed tomography (μCT) image analyses, they conducted flow simulation and reported that acidizing could enhance permeability not only in the vertical direction but also in the lateral or horizontal direction [13]. Similarly, Ramandi et al (2018) applied the μCT and numerical simulation to investigate the effect of dissolution of syngenetic and epigenetic minerals on coal permeability and they reported that coal permeability increase depends significantly on epigenetic mineral dissolution, and secondarily on syngenetic mineral dissolution [14].…”

Section: Acid Stimulationmentioning

confidence: 99%

“…The solid state 13 The coal samples' structural parameters were determined from the integral values of 13 C NMR spectra, while the lattice parameters were calculated, according to the methods proposed by Solum and co-workers [32].…”

Section: Solid State 13 C Nmrmentioning

confidence: 99%

“…13 C NMR has been widely applied in the study of carbon structures in coal and oil shale both qualitatively and quantitatively [32,163,164,176]. In this work, 13 C NMR was used to analyse the coal molecular structures and calculate various structural parameters defined by Solumn et al (1989,2001) [163,176] . ppm) and an aromatic region (100 to 200 ppm) [32,177].…”

Section: C Nmrmentioning

confidence: 99%

“…To chemically interpret the various NaClO oxidation effects on different coals, molecular structures of the two studied coals and their oxidised residues (coal So and coal Bo) were examined using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and solid state 13 C nuclear magnetic resonance spectroscopy ( 13 C NMR). The results qualitatively and quantitatively illustrate that NaClO preferentially reacts with aliphatic chains and oxygen functional groups.…”

mentioning

confidence: 99%

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Oxidant stimulation of coal seams to increase coal seam permeability

Jing¹

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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.

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Section: Molecular Structure Comparison Between Coal S and Coal Bmentioning

confidence: 90%

Section: Acid Stimulationmentioning

confidence: 99%

Section: Solid State 13 C Nmrmentioning

confidence: 99%

Section: C Nmrmentioning

confidence: 99%

mentioning

confidence: 99%

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Oxidant stimulation of coal seams to increase coal seam permeability

Jing¹

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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

et al. 2021

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Acid stimulation is a promising method in improving coal seam permeability by demineralization in coal cleats. However, using conventional acids such as HCl and mud acid (12 wt.% HCl + 3 wt.% HF) may cause clay breakage, migration, and precipitation, leading to formation damage. In this study, we investigated the effect of L‐glutamic acid N, N‐diacetic acid (GLDA) chelating agent treatment on the dissolution behaviour of lignite (Coal L) and anthracite (Coal A), collected from Er′Lian Basin and Qinshui Basin, China. Characteristics of the raw and acid treated coal samples, including mercury intrusion porosimetry (MIP) results as well as metal elements distribution analysis of reacted leachates, micromorphology, mineral composition, and mass change were taken into consideration. It was found that high‐rank Coal A is more suitable for chemical stimulation. For both Coal L and Coal A, 5 wt.% GLDA solution is preferred to avoid sticking reaction products. Total porosities of Coal L and Coal A were increased by 3.9 and 1.1 times, respectively. Based on the water chemistry analysis of the reacted solutions, we found that acidic condition is beneficial for clay minerals and carbonates dissolution, while alkaline condition is favourable for the dissolution of quartz. Besides, the dissolution of minerals can trigger the release of trace elements, which is a potential environmental risk that needs to be taken into consideration before its in‐situ application in coal fields.

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Experimental study on improving coalbed methane extraction by chemical treatment using acetic acid or ammonium persulfate

Wang

Chen

2022

Energy Science & Engineering

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Ad‐/desorption and diffusion processes are the key factors controlling methane production from coal. The experiments used samples from methane‐producing coal seams with different contents of carbonate mineral and different ranks. Acid treatment using 1.0 mol/L acetic acid (CH3COOH) and oxidant treatment using 1.0 mol/L ammonium persulfate ((NH4)2S2O8) were conducted on these coal samples to observe the changes in surface functional groups that act as primary sorption sites and pore structure that determines diffusivity by Fourier transform infrared spectrometer, in situ scanning electron microscopy (SEM) imaging and energy dispersive spectroscopy. The results showed that the acidizing‐related mass loss of coal samples is in the range of 3.78%–7.57% due to the complete dissolution of pore‐ and fracture‐filling carbonate minerals. For the coal samples after oxidizing treatment, dissolution evidence can be observed in both carbonate minerals and organic matter, with a mass loss ranging from 2.01% to 3.0%. Acidizing or oxidizing induced dissolution can destroy aliphatic functional groups and the cross‐linked structure of coal, resulting in a decrease in methane adsorption capacity that is beneficial to methane desorption. More opened pores and interconnected fractures can be observed in SEM images due to the dissolution of carbonate minerals, suggesting an alteration of methane diffusion pathways in the coal matrix. Although only some of the carbonate minerals were dissolved following oxidant treatment, coal organic matter is partially oxidized and generates some dissolution pores, which provides more methane diffusion pathways in the coal matrix. Therefore, all the treated coal samples showed a reduction in methane adsorption capacity and an enhancement of desorption capacity and diffusivity. This result suggests that chemical treatment in coal seams using acetic acid or oxidant has the potential to improve coalbed methane extraction.

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X-ray μCT investigations of the effects of cleat demineralization by HCl acidizing on coal permeability

Cited by 63 publications

References 11 publications

Oxidant stimulation of coal seams to increase coal seam permeability

Oxidant stimulation of coal seams to increase coal seam permeability

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

Experimental study on improving coalbed methane extraction by chemical treatment using acetic acid or ammonium persulfate

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