Effect of Gelled Acid Fracturing Fluid on the Structure and Pyrolysis Behavior of Oil Shale

This paper simulates the application of gelled acid fracturing in the in-situ conversion of oil shale. Oil shale samples with sizes of 3-5 mm were immersed in and treated with gelled acid fracturing fluid. The samples were tested by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) before and after the acid treatment. The results show that the mineral compositions and distribution of the porosity were significantly different in the treated samples (OST) and the raw samples (OSR). SEM images show that the OST surfaces were rough and porous. The MIP analysis determined a porosity of 0.142 for the OST samples, whereas the porosity of the OSR samples was only 0.050. Thermogravimetric analysis (TGA) showed that the OST samples had a significantly higher thermal weight loss rate than the OSR samples. The Fischer assay showed that the oil yield increased from 26% to 29.2% after treatment with the acid fracturing fluid. Gas chromatography-mass spectrometry (GC-MS) analysis showed that the shale oil which was obtained from the OST samples contained higher levels of low molecular weight products. The OSR and OST samples had different thermal decomposition kinetic parameters, the thermal decomposition activation energies at 420°C-480°C were 131 KJ/mol and 127 KJ/mol, respectively, which indicates that the acid treatment slightly decreased the thermal decomposition activation energy.