Summary Aluminum chloride (AlCl3) has been used as a retarding agent for mud acid for a long time; its applications are studied in the laboratory and tested in the field. The theory and mechanism of AlCl3 retardation were investigated in many works involving mud acidizing and reservoir-permeability enhancement. This paper furthers this investigation with solubility tests, coreflood tests, and 19F nuclear magnetic resonance (NMR) to better understand the mechanism of AlCl3 working as a retarding agent in mud acid. The reactivity of Al-based retarded mud acid (15 wt% HCl, 1.5 wt% HF, and 5 wt% AlCl3·6H2O) with clay minerals and sandstones at different conditions has not been examined fully. To enhance the acid performance and to minimize formation damage, a systematic investigation of the interactions between the Al-based retarded mud acid and clay minerals in sandstone reservoirs is provided in this study. Furthermore, for the first time, 19F NMR spectroscopy was used to follow the reactions of Al-based retarded mud acid with clay minerals. Solubility tests were performed to evaluate the retardation of the Al-based retarded mud acid when reacted with kaolinite, bentonite, and illite. Inductively coupled plasma (ICP) and 19F NMR were used to analyze the concentrations of key cations and components in the supernatant, whereas the scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques were used to identify the reaction products and to explore the possibility of the presence of any precipitation. Coreflood tests of sandstone cores were also conducted. This study shows that AlCl3 can retard the reaction of hydrofluoric acid (HF) with kaolinite, bentonite, or illite at 75 and 200 °F in Al-based retarded mud acid. Even with 5 wt% AlCl3·6H2O added in the acid system, no AlF3 precipitate was observed in any of the solubility tests. 19F NMR results showed that AlF4− and AlF3 were the only Al-F species existing in the spent Al-based retarded mud acid. H2SiF6 and HSiF5 were also identified. Coreflood tests showed significant permeability improvement to Berea sandstone when Al-based retarded mud acid was used, and the enhancement diminished when the temperature increased to 300 °F. Computed-tomography (CT) scan showed deeper penetration of Al-based retarded mud acid than mud acid at 75 °F, and the penetration reduced when temperature increased to 200 °F. On the basis of these results, new mechanisms were developed to better understand the reaction of Al-based retarded mud acid and clay minerals.
Coal gasification wastewater, as a typical industrial wastewater has poor biodegradability and high toxicity. In this paper, simple anaerobic shaker test was conducted to investigate the degradation of hydroquinone in coal gasification wastewater. Anaerobic sludge shaker test were run for 27, 50 and 73 days, the phenol concentration were adjusted to 300 mg/L and 500 mg/L with pH 7.5, respectively. The experimental results also showed that this system could effectively deal with COD and phenol removal and remain in a stable level when the operational parameters altered while the hydrolysis acidification at 45h is appropriate. Organics degradation and transformation of anaerobic coal gasification wastewater samples at 12h, 24h, 36h, 48h, and 60h were analyzed by GC/MS and it was found that hydrolysis acidification played an important role in degradation of methyl phenol, hydroquinone and refractory compounds. Therefore, the results illustrated that the simple anaerobic shaker process is an easy way for pollutant degradation and treat coal gasification wastewater effectively.
AlCl 3 has been used as a retarding agent for regular mud acid. It has been studied in the lab and tested in the field. However, the mechanism of AlCl 3 retardation has never been determined and the reactions of fines control acid (15 wt% HCl, 1.5 wt% HF, and 5 wt% AlCl 3 ·6H 2 O) with clay minerals and sandstones at different conditions have never been fully examined. To enhance the acid performance and to minimize formation damage, a systematic investigation to the interactions between the fines control acid and clay minerals in sandstone reservoirs has been provided in this study. Also, for the first time, 19 F Nuclear Magnetic Resonance (NMR) spectroscopy was used to determine the reaction of fines control acid with clay minerals.Solubility tests were performed to evaluate the retardation of the fines control acid when reacted with kaolinite, bentonite and illite. Inductively Coupled Plasma (ICP) and 19 F NMR were utilized to analyze the concentrations and ratios of key cations and components in the supernatant while the Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) techniques were used to identify the reaction products and explore the possibility of the presence of any precipitations. Coreflood tests on sandstone cores featured with different mineralogy were also conducted at different conditions. The core effluent samples were analyzed by ICP to determine the concentrations of Si, Al, Ca, Fe, and Mg.This study showed AlCl 3 can retard the reaction of HF with kaolinite, bentonite or illite at 75°F in fines control acid. Even with 5 wt% AlCl 3 ·6H 2 O added into the acid system, no AlF 3 precipitate was observed in any of the solubility tests. 19 F NMR results showed several aluminum fluorides species that were not identified before. H 2 SiF 6 and HSiF 5 were also recognized in the spent fines control acid. Based on these new results, new mechanisms were developed to better understand the retarding effect of this acid system, and how this acid reacts with different clays.
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