二氧化碳在链状烷烃中的溶解性能及膨胀效应

Dissolving capacity and volume expansion of carbon dioxide in chain n-alkanes

选取原油中含量普遍较高的5种链状正构烷烃与不同比例的CO2组成油-气体系。通过体系在不同温度下的恒质膨胀实验,研究CO2在5种链状正构烷烃中的溶解性能及体系膨胀效应。研究表明,链状正构烷烃-CO2体系的压力-体积关系曲线并非是严格意义的两段直线,弯曲程度受温度、压力、CO2含量、正构烷烃类别等因素影响。体系的泡点压力随温度升高呈直线增大趋势,随CO2含量的增加大幅度增大。当压力较低时,CO2在不同链状正构烷烃中溶解度近似相同,而高压时溶解度随烷烃碳原子数增大而减小。CO2溶于链状正构烷烃中可造成体系不同程度的体积膨胀,膨胀系数的大小受温度、压力影响不大,随CO2含量的增加快速增大,随烷烃碳原子数的增大直线下降。体积膨胀作用对油井增产有重要意义。

Five kinds of n-alkanes, which have high proportions in crude oil from China, were mixed with CO2 of different molar fractions forming oil-gas systems. The dissolution of CO2 in the five n-alkanes and the system volume swelling were studied through the constant component expansion （CCE） experiments in different temperatures. The pressure-volume curves of the n-alkanes-CO2 systems are not strictly two-part straight lines. The bending degree is affected by the parameters of temperature, pressure, CO2 molar fraction and n-alkanes. Saturation pressure and the temperature of the oil-CO2 system is a linear relationship. Besides, as the CO2 fraction increases, the saturation pressure goes up largely. There is a fact that the CO2 solubility in different kinds of alkanes is nearly the same in low pressure condition, while the solubility is inversely proportional to the carbon number in high pressure. The dissolution of CO2 may swell the system, and temperature and pressure are not the main reasons. However, the swelling factor increases quickly as the CO2 molar fraction goes up, and lowers with the carbon number increase. The oil swelling has a great significance for oilfield development and well production.