Yue Ma

The accumulation of dissolved species during the in situ leaching (ISL) of uranium can lead to ore-layer blockage and reduced production capacity. Clay minerals, including montmorillonite, chlorite, kaolinite, and illite, are the primary cementing and filling materials in sandstone-hosted uranium deposits in China. However, previous studies have predominantly focused on the leaching behavior of uranium minerals, while systematic investigations into the dissolution mechanism of clay minerals under CO₂+O₂ conditions remain scarce. In this study, laboratory dissolution experiments, scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), computed tomography (CT) scanning, and field verification were conducted to systematically investigate the dissolution behavior of major clay minerals and their contribution to ore-layer blockage under CO₂+O₂ leaching conditions. The results indicate the following: (1) Montmorillonite exhibited the most significant dissolution, with granular deposits rich in Ca and Si formed on its surface, which were inferred to be Ca-Si-rich precipitates. (2) Obvious changes in both microstructure and macroscopic physical properties of clay minerals were observed before and after leaching, with porosity decreasing by approximately 12.96% and permeability decreasing by approximately 10.16%. (3) Field verification revealed that the scale in the ore layer, filter cloth blockage, and resin surface caking were primarily composed of silica gel and hydroxide/carbonate precipitates of Al, Ca, and Fe, which are closely related to the dissolution and leaching of clay minerals. This study confirms that montmorillonite is the main source of clogging substances, and long-term closed circulation of injection and extraction leads to the accumulation of precipitates, exerting a significant impact on the uranium-leaching system. The findings provide a theoretical basis for anti-clogging and permeability enhancement in CO₂+O₂ ISL operations.

In this study, oil sludge from Jilin Petrochemical of China was selected to carry out the Fischer assay and proximate analysis. According to the properties of the Jilin oil sludge and its pyrolysates, the material and heat balance of the pyrolysis process was deduced theoretically based on 1000 kg of received base oil sludge. The results show that the solid heat carrier method can be used in the pyrolysis of oil sludge, and a new process flow is proposed. According to the heat required and heat provided in the rotary reactor and in the fluidized bed, 5940 kg of ash was needed as a solid heat carrier, and 25 kg of liquefied petroleum gas was needed as a supplementary fuel besides the semi-coke and retorting gas. The total input heat and output heat were 13.65 GJ and 10.04 GJ. The loss was 3.61 GJ and the thermal efficiency was 73.6%.

Pyrolysis of crude oil is an important way to generate natural gas. However, the current analysis of pyrolysis gas carbon isotopes and the study of gas generation dynamics are not unified, and the genesis and accumulation of gas reservoirs are needed to conduct in-depth discussions. Therefore, Tarim crude oil samples in China were selected to perform thermal simulation experiments using an autoclave. The pyrolysis hydrocarbon production yield, carbon isotope characteristics and gas-generation process of crude oil samples in Tarim Basin were studied by GC-MS, FT-IR and carbon isotope analysis, respectively. The compositions of the Tarim Oilfield were determined, including the 83.69% content of hydrocarbons, the 14.08% content of aromatic compounds, and lower than 3% content of heteroatom compounds. The non-monotonic linear relationship of C_2-5 isotopes may be due to the complexity of crude oil, and the formation of gaseous hydrocarbons can be divided into three stages. The results showed that the δ¹³C distribution range of C_2-5 hydrocarbons was −40.5% to −10.5%, and the δ¹³C distribution of methane was −53.3% to −27.4%. The lowest δ¹³C value for methane occurs at 350 °C, and the corresponding carbon isotope value is −53.3%. When the pyrolysis temperature range is 250–300 °C, crude oil undergoes volatilization and preliminary pyrolysis, and the C_4-5 output exceeds 95%. When the temperature rises to 300–500 °C, the aliphatic hydrocarbon chain in crude oil begins to crack, the side and branch chains of aromatic and heteroatomic compounds are broken, and C₄-₅ begins to crack to form C_1-3. Finally, the temperature rises to 500–600 °C, and C_3-5 begins to deeply crack into C_1-2, and eventually all is converted to methane.