基于格子理论模型页岩储层气-固吸附分子动力学分析

利用格子理论模型探讨了甲烷在页岩中的吸附特征。该模型基于不同假设可发生一定转变,利用该理论预测甲烷吸附量的精度较高,绝对误差小于0.004 2mmol/g,预测精度随着温度的升高而略升;模型中确定的理论单层饱和吸附密度Г₀及吸附质分子与微孔表面之间的接触势能ε_s等参数可用来指示温压对甲烷吸附特征的影响及页岩中纳米级微孔发育程度。随着温度的升高|ε_s|减小,|ε_s|与温度间的变化近乎线性;Г₀<Г_max,Г₀可以大体表征分子吸附状态,甲烷在页岩中吸附的Г₀和|ε_s|值比富含纳米级微孔的多孔活性炭小得多。同时讨论了所定义参数Y与X之间的线性关系,进而对微孔中吸附质分子间平均作用势ε_a进行了估算,结果表明|ε_a|<|ε_s|;在测试温压范围内,随着温度的升高|ε_a|先升高后降低;温度较低时ε_s/ε_a倍率较大(7.05倍),随着温度升高,该倍率减小并逐渐趋于稳定(平均约3.37倍)。利用该理论对不同地区及不同类型页岩在更宽尺度温压范围内对页岩微观结构表征或真实含气量关系研究具参考价值。 

Molecular Dynamics Analysis of Shale Reservoir Gas-Solid Adsorption Based on the Lattice Theory Model

This paper describes pure methane's adsorption characteristics based on the lattice theory model.The model can make a difference based on different assumptions.This model has a high precision on predicting the adsorption quantity with the absolute error of less than 0.0042 mmol/g.The determined parameters such as Г₀ and ε_s can be used to indicate the influence of temperature-pressure of methane adsorption characteristics and the development degree of micropores.The value of |ε_s| decreases with the increase of temperature,with the relationship being almost linear, Г₀ <Гmaxand Г₀ can roughly characterize the molecular adsorption state,with the value of Г₀ and |ε_s| of methane adsorption in the shale much smaller than that of the activated carbon rich in micro-pores.The discussion of the linear relationship of Y and X and the calculation of the value of ε_a show that the value of |ε_a| is smaller than |ε_s|, within the scope of P and T in this paper,|ε_a| gets alittle rise first and then decrease with the increasing temperature,at a lower temperature the ratio of ε_s and and ε_a is larger(7.05 times),but as the temperature increases,the ratio decreases and gradually becomes stable(3.37 times).The study of different types of shale on a wider scale temperature and pressure with this theory has a great significance for the shale microstructure characterization.