旬邑中低熟页岩油热解特征与自生热裂解可行性研究

Study on pyrolysis characteristics and feasibility of autothermal pyrolysis for low-medium maturity shale oil from Xunyi

摘要:

鄂尔多斯盆地长7段蕴藏着丰富的中低熟页岩油资源，其中旬邑地区资源丰富，具备良好的原位开发潜力，但自生热反应的热动态特征、反应门槛温度及产物演化规律尚未明晰。针对这一问题，本文以旬邑地区延长组长7段中低熟页岩为研究对象，综合采用热重-红外联用分析、热解实验、元素分析、族组分分析及气相色谱-质谱联用分析等手段，系统研究了热解气氛与预热温度对其氧化辅助热解特征的影响。结果表明：氧化气氛显著增强有机质反应活性，触发低温氧化-热解协同反应，使其初始分解温度显著降低，同时在高温阶段能够促进重质组分的氧化分解；氧化气氛对中低熟页岩油的热解反应具有化学促热作用，空气气氛下热解的表观活化能为167 kJ/mol，较氮气气氛降低约30%，呈现“热裂解-氧化耦合”特征；230~390 ℃为氧化辅助热解的适宜预热温度区间，可有效激发自生热反应，促进烃类轻质化，而温度过高则导致部分油气过度氧化，造成油产率下降并改变产物组成；当热解温度≤530 ℃时，热解生成的残碳氧化放热可维持体系能量平衡，证实了自生热原位转化的可行性。本研究明确了关键工艺参数控制区间，为中低熟页岩油高效原位开发提供了理论支撑。

Abstract:

The Chang 7 Member of the Ordos Basin contains abundant low-to medium-maturity shale oil resources， with the Xunyi area exhibiting rich reserves and favorable potential for in-situ development. However， the thermal dynamic characteristics， reaction threshold temperature， and product evolution patterns of autothermal reactions in this reservoir remain unclear. To address this， low-medium maturity shale samples from the Chang 7 Member of the Yanchang Formation in the Xunyi area were investigated using thermogravimetry-Fourier transform infrared spectroscopy （TG-FTIR）， pyrolysis experiments， elemental analysis， SARA analysis， and gas chromatography-mass spectrometry （GC-MS）. The effects of pyrolysis atmosphere and preheating temperature on oxidation-assisted pyrolysis characteristics were systematically studied. Results show that an oxidative atmosphere significantly enhances organic matter reactivity， triggering a low-temperature oxidation-pyrolysis synergy that markedly reduces the initial decomposition temperature and promotes oxidative cracking of heavy components at high temperatures. The oxidative atmosphere exerts a chemical heat-promoting effect on the pyrolysis of low-medium maturity shale oil， with the apparent activation energy under air being 167 kJ/mol—about 30% lower than under nitrogen-indicating a distinct "pyrolysis-oxidation coupling" mechanism. The suitable preheating temperature range for oxidation-assisted pyrolysis is 230~390 ℃， which effectively activates the autothermal reaction and promotes hydrocarbon lightening. Excessive temperatures， however， lead to over-oxidation of some oil and gas， reducing oil yield and altering product composition. Thermodynamic analysis confirms that when the pyrolysis temperature is ≤530 ℃， the exothermic oxidation of residual carbon can maintain system energy balance， demonstrating the feasibility of autothermal in-situ conversion. This study clarifies the control ranges for key process parameters and provides theoretical support for the efficient in-situ development of low-medium maturity shale oil.