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Acidizing Sandstone Reservoirs Using Different Acid Systems
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AlCl₃ has been long used as a retarding agent for mud acid, its applications studied in the lab and tested in the field. The theory and mechanism of AlCl₃ retardation have been investigated in many projects involving mud acidizing and reservoir permeability enhancement. This dissertation advances this investigation by using 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. To enhance the acid performance and to minimize formation damage, this study provides a systematic investigation of the interactions between the Al-based retarded mud acid and clay minerals in sandstone reservoirs. 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 while the Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) techniques were used to identify the reaction products and detect any precipitation. This study shows that AlCl₃ can retard the reaction of HF with kaolinite, bentonite, or illite at 75 and 200°F in Al-based retarded mud acid. Even with 5 wt% AlC₃∙6H₂O added to the acid system, no AlF₃ precipitate was observed in any of the solubility tests. Coreflood tests showed significant permeability improvement in the Berea sandstone when Al-based retarded mud acid was used. The enhancement diminished when the temperature increased to 300°F. 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. Based on these results, new mechanisms were developed to better understand the reaction of Al-based retarded mud acid and clay minerals. Field tests were followed in this study. The optimal acidizing plan was found for the Katz field after a series of coreflood experiments. This study provides the guidelines for designing the acidizing jobs in the Katz field.
Ji, Qin (2017). Acidizing Sandstone Reservoirs Using Different Acid Systems. Doctoral dissertation, Texas A & M University. Available electronically from