ABSTRACT

Understanding methane adsorption kinetic is of great significance for reserve evaluation and gas production forecast. In order to investigate the kinetic behavior of shale-gas adsorption on shale, multiple-step high-pressure adsorption kinetic experiments are conducted using the volumetric method. We analyze the kinetic characteristics of methane adsorption on Longmaxi shale at nine different pressures. The results show that the adsorption amount increases quickly in the initial time and slowly in the late period, and becomes constant at last. The pressure decreases fast at the beginning and slowly at late, and reaches stable finally. Moreover, we fit the experimental data using Pseudo-first-order (PFO) model, Pseudo-second-order (PSO) model, and Bangham model. To optimize the kinetic model, we calculated and compared correlation coefficients of models and average relative errors between experimental data and calculation, and analyzed the effect of equilibrium pressure on the adsorption rate constant of three models. The results show that the averages of correlation coefficients for nine equilibrium pressure points using three kinetic models (PFO, PSO, and Bangham) respectively, are 0.9766, 0.9999, and 0.9483. Furthermore, the averages of average relative errors for nine equilibrium pressure points using three kinetic models are 49.37%, 3.54%, and 0.49%, respectively. Bangham kinetic model is most suitable for describing the adsorption kinetic of methane on shale in terms of the correlation coefficients, averages of average relative errors, and the trends between the fitting curve and experimental data. This will be very helpful for understanding the adsorption mechanism of shale gas in the Longmaxi formation and forecasting the shale-gas-well production rate.

摘要

了解甲烷的吸附动力学对储量评估和天然气产量预测具有重要意义。为了研究页岩气在页岩上的吸附动力学行为，采用体积法进行了多步高压吸附动力学实验。我们分析了Longmaxi页岩在9种不同压力下甲烷吸附的动力学特征。结果表明，吸附量在开始时迅速增加，在后期缓慢增加，最后保持恒定。压力在开始时快速降低，在后期缓慢降低，最终达到稳定。此外，我们使用伪一阶（PFO）模型，伪二阶（PSO）模型和Bangham模型拟合实验数据。为了优化动力学模型，我们计算并比较了模型的相关系数和实验数据与计算之间的平均相对误差，并分析了平衡压力对三种模型吸附速率常数的影响。结果表明，使用三种动力学模型（PFO，PSO和Bangham），九个平衡压力点的相关系数平均值分别为0.9766、0.9999和0.9483。此外，使用三个动力学模型得出的九个平衡压力点的平均相对误差的平均值分别为49.37％，3.54％和0.49％。Bangham动力学模型最适合根据相关系数，平均相对误差的平均值以及拟合曲线和实验数据之间的趋势来描述甲烷在页岩上的吸附动力学。