基于Ono-Kondo格子模型的页岩气超临界吸附机理探讨

周尚文; 王红岩; 薛华庆; 郭伟; 李晓波

doi:10.3799/dqkx.2017.543

基于Ono-Kondo格子模型的页岩气超临界吸附机理探讨

doi: 10.3799/dqkx.2017.543

周尚文^1,2,3,,
王红岩^1,2,3,
薛华庆^1,2,3,
郭伟^1,2,3,
李晓波^1,2,3

1.
中国石油勘探开发研究院, 北京 100083
2.
国家能源页岩气研发(实验)中心, 河北廊坊 065007
3.
中国石油非常规油气重点实验室, 河北廊坊 065007

基金项目:

国家重点基础研究发展计划（973计划）项目 2013CB2281

详细信息

作者简介:
周尚文(1987-), 男, 工程师, 主要从事页岩气实验方法和技术研究

中图分类号: P624.7
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出版历程
- 收稿日期: 2017-01-22
- 刊出日期: 2017-08-15

Discussion on the Supercritical Adsorption Mechanism of Shale Gas Based on Ono-Kondo Lattice Model

Zhou Shangwen^{1,2,3
,},
Wang Hongyan^1,2,3,
Xue Huaqing^1,2,3,
Guo Wei^1,2,3,
Li Xiaobo^1,2,3

1.
Petro China Research Institute of Petroleum Exploration & Development, Beijing 100083, China
2.
National Energy Shale Gas R & D(Experiment) Center, Langfang 065007, China
3.
Key Laboratory of Unconventional Oil & Gas, CNPC, Langfang 065007, China

摘要

摘要: 页岩气吸附机理的研究对于页岩气成藏和储量评价具有重要意义.甲烷在地层温度和压力条件下处于超临界状态，页岩气的吸附实际上为超临界吸附，但其机理目前尚不明确.在建立Ono-Kondo格子模型的基础上，结合低温氮气吸附和高压甲烷等温吸附实验，对龙马溪组页岩的微观孔隙结构和超临界吸附曲线进行了分析.结果表明，页岩中发育的孔隙尺度较小，比表面积较大，吸附气主要赋存于微孔和中孔中；页岩的等温吸附曲线在压力较大时，必然存在下降的趋势，这并非异常现象，而是超临界甲烷过剩吸附量的本质特征.Ono-Kondo格子模型对页岩高压等温吸附曲线的拟合效果很好，相关系数均在0.99以上，说明该模型可以表征页岩纳米孔隙中超临界甲烷的吸附特征.基于拟合得到的吸附相密度可将过剩吸附量转换为绝对吸附量，并直接计算地层温度和压力下甲烷的吸附分子层数，计算层数均小于1，表明甲烷分子并没有铺满整个孔隙壁面.因此受流体性质、吸附剂吸附能力和孔隙结构3个方面的影响，页岩气的吸附机理为单层吸附，不可能为双层甚至多层吸附.
- 页岩气 /
- Ono-Kondo模型 /
- 超临界 /
- 吸附机理 /
- 过剩吸附量 /
- 单层吸附
Abstract: Studies on the adsorption mechanism of shale gas are of great significance to shale gas accumulation and reserves evaluation. Methane is in supercritical state at conditions under formation temperature and pressure, so the adsorption of shale gas is supercritical adsorption, however, its mechanismis still controversial. Based on Ono-Kondo lattice model, micropore structure and supercritical adsorption curves of Longmaxi shales were analyzed, combining with low temperature N₂ adsorption and high pressure CH₄ adsorption experiments. The results show that its pore size is small but specific surface area is large, and adsorbed gas may mainly exist in the micro-mesopores. The excess adsorption capacity will reach a maximum value when the pressure reaches about 10 MPa, and then the excess adsorption capacity decreases with the increase of pressure. The decreasing phenomenon is not abnormal, but the essential characteristics of excess adsorption capacity of supercritical methane. The fitting effect of the high pressure isothermal adsorption curves by Ono-Kondo lattice model is very good with its correlation coefficient above 0.99, indicating that the model can characterize the process of supercritical methane adsorption. Based on the fitted absorbed phase density of methane, the excess adsorption was converted into absolute adsorption. Then the number of adsorbed molecular layers under formation temperature and pressure was calculated and they are all less than 1, showing that the methane molecules are not entirely covered on the whole pore wall. Considering the influence of supercritical fluid properties, adsorption capacity and pore structure of shale, the adsorption mechanism of shale gas should be monolayer adsorption instead of two-layer or multilayer adsorption.
- shale gas /
- Ono-Kondo model /
- supercritical /
- adsorption mechanism /
- excess adsorption /
- monolayer adsorption

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图 1 甲烷在狭缝孔隙中吸附的格子模型

Fig. 1. The sketch of lattice model for methane adsorption in slit pores

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图 2 低温氮气吸附实验结果分析

Fig. 2. Analysis of experimental results of nitrogen adsorption at low temperature

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图 3 高压等温吸附曲线实验测试结果

Fig. 3. Experimental results of high pressure isothermal adsorption curve

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图 4 Ono-Kondo格子模型曲线拟合结果

Fig. 4. High pressure isothermal adsorption curve fitting results by Ono-Kondo lattice model

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图 5 吸附相体积、吸附分子层数和吸附气比例计算结果

Fig. 5. Calculation results of the adsorbed phase volume, the number of adsorbed layers and the proportion of adsorbed gas

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表 1 样品比表面和孔体积分析结果

Table 1. Analysis results of specific surface area and pore volume of shale samples

样品编号	TOC(%)	S_total(m²/g)	S_micro(m²/g)	S_meso(m²/g)	V_total(cm³/g)	V_micro(cm³/g)	V_meso(cm³/g)
X3-1	3.1	9.83	2.22	7.64	0.023 05	0.001 15	0.021 84
X3-2	4.3	11.81	3.22	8.91	0.023 14	0.001 68	0.021 72
X3-3	3.7	12.17	3.64	8.81	0.022 84	0.001 91	0.021 25
X3-4	3.5	11.90	3.45	8.78	0.024 18	0.001 80	0.022 66
注：S_total为BET方程计算的样品总比表面积，m²/g；S_micro为t-plot方法计算的微孔比表面积，m²/g；S_meso为BJH方程计算的中孔比表面积，m²/g；V_total为BET方程计算的样品总孔体积，cm³/g；V_micro为t-plot方法计算的微孔体积，cm³/g；V_meso为BJH方程计算的中孔体积，cm³/g.

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表 2 Ono-Kondo格子模型参数拟合结果

Table 2. Results of parameter fitting by Ono-Kondo lattice model

样品编号	a_m (mmol/g)	ε_s/ kT	ρ_mc (g/cm³)	n_abs-f (mmol/g)	相关系数 R²
X3-1	0.038 2	-3.234	0.263 7	0.069 52	0.996
X3-2	0.045 5	-3.496	0.305 1	0.084 65	0.993
X3-3	0.043 8	-3.369	0.284 5	0.079 64	0.994
X3-4	0.039 1	-3.536	0.318 7	0.074 16	0.997
注：n_abs-f为地层压力条件下的页岩绝对吸附量.

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