高CO2含量天然气偏差因子影响研究

天然气偏差因子是天然气物性参数和地质储量计算的基础，其不仅受温度压力的影响，也是天然气组分与组成的函数。目前，对低含量CO₂的天然气偏差因子计算方法精度较高，但对以DF气田典型代表的高含CO₂天然气偏差因子，其计算精度难以得到保障。针对不同CO₂含量天然气采用PVT实验方法，分析了CO₂含量对天然气偏差因子的影响规律，并以实验结果为基础，用麦夸特法及通用全局优化法修正了DAK计算天然气偏差因子经验公式。结果表明，与重烃（乙烷、丙烷）对天然气偏差因子的影响规律相似，CO₂的存在明显降低了天然气的偏差因子，且影响幅度随CO₂含量增加而逐渐增大；当CO₂含量较低时，DAK经验公式能够较准确计算天然气偏差因子，而当CO₂含量大于50%时，应用修正的DAK经验公式能够获得满意的效果。

Study on Influence of High CO2 Content on Gas Deviation Factor of Natural Gas

The gas deviation factor of natural gas is the basis for the calculation of the physical parameters and geological reserves of natural gas. It is affected by temperature and pressure and is also a function of natural gas composition and its components. At present, a high-precision calculation method of gas deviation factor suitable for natural gas with low CO₂ content already exists. However, its calculation precision is not guaranteed when applied to the calculation of gas deviation factor for natural gas with high CO₂ content, typically found in DF Gas Field. Targeting this problem, the influence of CO₂ content on the gas deviation factor of natural gas was analyzed using the PVT experimental method. Based on the experimental results, the empirical formula of the DAK method for calculating the gas deviation factor of natural gas was modified using the Levenberg-Marquardt algorithm and the general global optimization method. The results show that, similar to the effects of heavy hydrocarbons (ethane and propane), the presence of CO₂ significantly reduces the gas deviation factor of natural gas, and the magnitude of this influence gradually increases as CO₂ content increases. When CO₂ content is low, the DAK empirical formula can calculate the gas deviation factor of natural gas relatively accurately, whereas if CO₂ content becomes larger than 50%, the corrected DAK empirical formula can lead to satisfactory results.