Prediction of thermophysical properties for natural gas mixtures close to the mixture's critical point and cricondenbar (the maximum pressure at which two fluid phases can co-exist) is challenging but important as often natural gas processes operate close to these conditions. Here we present a comprehensive study of the viscosity of (CH₄ + C₃H₈ + C₇H₁₆) mixtures with heptane fractions up to 15 mol%. Accurate measurements of saturated-phase and compressed-fluid (single phase) viscosities, at temperatures from 200 K to 423 K and pressures up to 35 MPa, are presented. The collected data were compared with the prediction of the extended corresponding states (ECS) model, with relative deviations spanning between (−20 to 11) % from the model. Additionally, pure component parameters needed for the residual entropy scaling (RES) model were fit to literature data and then applied predictively to mixtures viscosity without any additional fit parameters. The relative deviation of the measured viscosities from values calculated with the RES model is generally within 15%. This work demonstrates that no current model satisfactorily predict mixtures viscosity, and that high quality experimental data are needed to anchor the methods used to design and optimize natural gas processing.

预测接近混合物临界点和临界点（两种流体相可以共存的最大压力）的天然气混合物的热物理性质具有挑战性，但很重要，因为天然气过程通常在接近这些条件下运行。在这里，我们对 (CH ₄  + C ₃ H ₈  + C ₇ H ₁₆) 庚烷馏分高达 15 mol% 的混合物。提供了在 200 K 到 423 K 的温度和高达 35 MPa 的压力下对饱和相和压缩流体（单相）粘度的准确测量。将收集到的数据与扩展对应状态 (ECS) 模型的预测进行比较，相对偏差范围在（-20 到 11）% 之间。此外，残差熵标度 (RES) 模型所需的纯组分参数适合文献数据，然后预测性地应用于混合物粘度，无需任何额外的拟合参数。测量的粘度与使用 RES 模型计算的值的相对偏差通常在 15% 以内。这项工作表明，目前没有任何模型可以令人满意地预测混合物粘度，