The interaction between shale and CO2 is of great significance to CO2 storage and shale gas production; however, there are few reports on chemical changes after CO2 injection into shale reservoirs. We used Fourier transform infrared spectroscopy to study the chemical structure changes of shale samples before and after CO2 injection. In this paper, self-developed high-temperature and high-pressure vessels were used to examine CO2 treatment of shale to simulate the stratigraphic environment and infrared was used to study the influence of changes in pressure and temperature on the chemical interaction between shale and CO2. These results showed that: (1) after shale CO2 treatment, the number of functional groups remained unchanged, though the content and structure of the shale did change; (2) pressure increases reduced hydroxyl and aliphatic group levels in the shale; the branched-chain and aromaticity indexes of the shale were reduced by 81.5% and 53.8%, respectively, relative to untreated samples; (3) below 60°C, free water in the shale increased with temperature increases and dissolution of the shale increased; however, above 60°C, dissolution was inhibited which resulted in precipitation; (4) the dissolution degree of shale carbonate minerals positively correlated with CO2 pressure and temperature, while silicate minerals were unchanged CO2 pressure and temperature. Finally, the change of CO2 pressure had a more significant influence on the chemical structure of shale. These results provide a basis for the continuing study of the influence of chemical structure change of shale caused by CO2 on shale wettability and enhance the theoretical level of CO2 shale mining.

中文翻译：

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超临界二氧化碳引起海相页岩化学结构变化

页岩与 CO2 相互作用对 CO2 封存和页岩气生产具有重要意义；然而，关于页岩储层注入 CO2 后化学变化的报道很少。我们使用傅里叶变换红外光谱研究了 CO2 注入前后页岩样品的化学结构变化。本文利用自主研发的高温高压容器研究页​​岩CO2处理模拟地层环境，利用红外线研究压力和温度变化对页岩与CO2化学相互作用的影响。 . 这些结果表明：（1）页岩CO2处理后，虽然页岩的含量和结构发生了变化，但官能团数量保持不变；(2) 压力增加降低了页岩中羟基和脂肪族基团的含量；与未处理样品相比，页岩的支链和芳香性指数分别降低了81.5%和53.8%；(3) 60℃以下，页岩中的游离水随着温度的升高而增加，页岩的溶解度增加；但在60°C以上，溶解受到抑制，导致沉淀；(4)页岩碳酸盐矿物的溶解程度与CO2压力和温度呈正相关，而硅酸盐矿物的CO2压力和温度不变。最后，CO2 压力的变化对页岩化学结构的影响更为显着。