CH4在原油体系中溶解规律及影响机理

为了研究甲烷（CH₄）在原油体系中的溶解过程，本文采用CH₄溶解度测试和分子模拟相结合的方式，系统研究了不同温度、压力条件下CH₄在原油体系中的溶解行为。以正庚烷为基础油，蜡、胶质、沥青质含量为影响因素，按照L₁₆(4³)正交表构建相应的原油体系，并构建胜利原油和南阳原油两种特定比例的原油体系，共18种原油体系。利用分子动力学方法模拟了CH₄分子在不同原油体系中的溶解过程，并利用试验结果验证了模拟的可靠性。结果表明：在泡点压力范围内，随着溶气压力的增加，CH₄溶解量逐渐增大，但其溶解位置可能发生变化；当溶气压力较低时，CH₄分子较为分散地分布在原油体系中，随着CH₄溶解量的增多，部分CH₄分子会发生聚集；CH₄在原油体系中的溶解为物理溶解过程，且CH₄溶解过程中范德华力为主要的力学作用方式；原油体系自由体积分数越大，能够为CH₄提供的溶解空间越大；原油大分子对CH₄溶解量影响程度依次为：蜡<胶质<沥青质，且原油大分子未改变CH₄溶解的力学作用方式，并通过力学模型揭示了相互作用能与原油体系体积变化量的线性关系，促进对CH₄在原油体系中溶解的分子级理解。

Dissolution of CH4 in the crude oil system: behaviors and mechanisms

In order to study the dissolution process of methane (CH₄) in the crude oil system, the dissolution behavior of CH₄ in crude oil systems at different temperatures and pressures was systematically studied by means of CH₄ solubility test and molecular simulation. Taking n-heptane as the base oil, wax, colloid, and asphaltene content as influencing factors, the corresponding crude oil system was constructed according to L₁₆ (4³) orthogonal table. Two specific proportion crude oil systems of Shengli crude oil and Nanyang crude oil were constructed, with a total of 18 crude oil systems. The molecular dynamics method was used to simulate the dissolution of CH₄ in different crude oil systems. The reliability of the simulation was verified by experimental results. The results show that in the range of bubble point pressure, with the increase of dissolved gas pressure, the amount of CH₄ dissolved gradually increases, but the position of CH₄ dissolved may change. When the dissolved gas pressure is low, CH₄ molecules are more dispersed in the crude oil system, and with the increase of CH₄ dissolved amount, some CH₄ molecules will accumulate. The dissolution of CH₄ in crude oil system is a physical dissolution process, and the Van der Waals force is the main mechanical action in the process of CH₄ dissolution. The larger the free volume fraction of crude oil system is, the larger the dissolution space can be provided for CH₄. The influence of crude oil macromolecules on CH₄ dissolution is wax < colloid < asphaltene and the mechanical action mode of CH₄ dissolution is not changed by crude oil macromolecules. The linear relationship between the interaction energy and the volume change of crude oil system is revealed by mechanical model, which promotes the understanding on the dissolution of CH₄ in crude oil system molecular-level.