International Journal of Earth Sciences and Engineering

Youhong Sun ¹, Pengfei Jiang ¹, Wei Guo ¹, Sunhua Deng ¹

Affiliations
1 College of Construction Engineering, Jilin University, No.6 Ximinzhu Str., Changchun-130026, CN

Abstract

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.

Keywords

Oil Shale, Gelled Acid, Micropore, Pyrolysis, Oil Yield.

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Pengfei Jiang ¹, Youhong Sun ¹, Wei Guo ¹, Qiang Li ¹

Affiliations
1 College of Construction Engineering, Jilin University, No.6 Ximinzhu Str., Changchun-130026, CN

Abstract

In light of the pilot project on the in situ conversion of the Nong’an oil shale and the actual geological condition of the area, this study proposed a new in situ pyrolysis method that combines fracturing and nitrogen injection and introduced the corresponding ground equipment. In building the mathematical model, the technology parameters related to the in situ pyrolysis method were optimized through numerical simulation. This optimization was aimed at reaching the highest possible heat transfer efficiency between the high-temperature nitrogen and the oil shale layer. Simulation results revealed an optimal nitrogen injection flow of 30 m³/h and a high energy utilization ratio that can reach 62.7%. Heating time was set to 125 d to sufficiently pyrolyze the oil shale stratum between the injection-heating well and the production well.

Keywords

Oil Shale, In Situ Pyrolysis, High-Temperature Nitrogen, Injection Flow Rate, Heat Transfer Efficiency.

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