不同压力下冻土区水合物法封存CO2的实验研究

Experimental study of CO2 storage using hydrate method under various pressures in permafrost region

关键词:  冻土区  水合物  CO₂  封存  注气压力 

Key words:  permafrost region  hydrate  CO₂  storage  injection pressure

摘要:

目的水合物法封存CO₂稳定性良好、储气密度高,是一种极具潜力的碳封存方式,利用冻土区的地层条件更具独特优势,将CO₂气体注入冻土区地层中,在一定的温度和压力条件下,形成固态CO₂水合物实现封存。 方法依据国内冻土地区地层深度对应的温度和压力条件,选取不同地层深度(150 m和200 m)对应温度(1.27 ℃和2.72 ℃)和有效孔隙含水率(40%),研究不同注气压力(3.5 MPa、4.5 MPa和5.5 MPa)下的封存特征。分析封存过程的温度和压力变化、封存速率、最终水转化率和最终封存率等动力学规律。 结果封存压力越高,水合物法封存所需的诱导时间越短,压力降幅越大。较高的封存压力导致初期封存速率较慢,缓慢封存期的持续时间减少,且封存压力越高,封存率、最终水转化率和水合物相饱和度越高。封存温度越高,压力对封存率的影响效果越明显。 结论在地层深度150 m(对应地层平均温度1.27 ℃)、5.5 MPa及有效孔隙含水率(40%)的条件下,CO₂封存效果最佳。 

Abstract:

ObjectiveCO₂ storage via the hydrate method is one of the potential carbon storage methods because of its stability and high gas storage capacity. The use of formation conditions in permafrost region has more unique advantages. CO₂ is injected into the permafrost region, and solid-state CO₂ hydrate is formed under specific temperature and pressure conditions to achieve long-term stable storage. Methods According to the temperature and pressure conditions of the formation in the permafrost region of China, the temperature (1.27 °C and 2.72 °C) and effective pore water content (40%) corresponding to different formation depths (150 m and 200 m) and different initial injection pressures (3.5 MPa, 4.5 MPa and 5.5 MPa) were selected. The characteristics of kinetic parameters such as temperature and pressure changes, storage rate, final water conversion rate and final storage ratio in the CO₂ storage process via the hydrate method were analyzed. ResultsThe results of the CO₂ hydrate storage process under different initial injection pressures show that the higher the initial injection pressure, the shorter the induction time required for hydrate storage and the larger the pressure drop. Higher injection pressure results in a slower storage rate at the initial stage and a reduced duration of the slow storage period. The higher the injection pressure, the higher the hydrate storage ratio, the final water conversion rate, and the hydrate phase saturation at the end of the reaction. The higher the storage temperature, the more obvious the effect of pressure on the gas storage ratio. ConclusionsThe best CO₂ storage effect was achieved under 40% water content at the depth of 150 m (the average temperature of the formation is 1.27 ℃) and 5.5 MPa.