基于分子动力学模拟的致密储层CO<sub>2</sub>/N<sub>2</sub>换油机理研究

陈汉钊; 吴正彬; 李轩; 舒坤; 蒋恕; 陈掌星

doi:10.19509/j.cnki.dzkq.tb20230456

基于分子动力学模拟的致密储层CO₂/N₂换油机理研究

doi: 10.19509/j.cnki.dzkq.tb20230456

陈汉钊^1,,
吴正彬^{1, 2, ,},
李轩³,
舒坤⁴,
蒋恕¹,
陈掌星²

1.
中国地质大学（武汉）油气勘探开发理论与技术湖北省重点实验室，武汉 430074
2.
Department of Chemical and Petroleum Engineering, University of Calgary, Calgary T2N 1N4, Alberta, Canada
3.
中国石油长庆油田分公司第九采油厂，银川 750006
4.
中国石油吐哈油田公司勘探开发研究院，新疆哈密 839009

基金项目: 国家自然科学基金项目（52404046；42130803）；湖北省自然科学基金项目（2024AFD385）；武汉市知识创新专项-曙光计划项目

详细信息

作者简介:
陈汉钊：E-mail：hanzhaochen@cug.edu.cn

通讯作者:
E-mail：wuzb@cug.edu.cn

中图分类号: TE357.45
计量
- 文章访问数: 412
- PDF下载量: 64
- 被引次数: 0
出版历程
- 收稿日期: 2023-05-11
- 录用日期: 2023-11-24
- 修回日期: 2023-11-20
- 网络出版日期: 2023-12-17

Mechanism of CO₂/N₂ oil exchange in tight reservoirs based on molecular dynamics simulation

1.
Hubei Key Laboratory of Oil and Gas Exploration and Development Theory and Technology, China University of Geosciences (Wuhan), Wuhan 430074, China
2.
Department of Chemical and Petroleum Engineering, University of Calgary, Calgary T2N 1N4, Alberta, Canada
3.
No. 9 Oil Production Plant, CNPC Changqing Oilfield Company, Yinchuan 750006, China
4.
Research Institute of Exploration & Development, PetroChina Tuha Oilfield Company, Hami Xinjiang 839009, China

More Information

Author Bio:
E-mail：hanzhaochen@cug.edu.cn

Corresponding author: E-mail：wuzb@cug.edu.cn

摘要

摘要:
利用分子动力学模拟来研究致密油的赋存状态以及CO₂置换致密油的机理。采用蒙特卡洛法和分子动力学模拟算法，建立了不同相对分子质量烷烃在岩石壁面的赋存状态模型，研究了烷烃分子在不同岩石壁面的赋存特征，分析了CO₂和N₂置换致密油的微观机理。模拟温度和压力条件（343.13 K、20 MPa）选取四川盆地致密储层的温度和压力条件。测得石英壁面和方解石壁面中，C₇在CO₂中的扩散系数分别为1.88×10⁻⁵ m/s²和1.83×10⁻⁵ m/s²，在N₂中分别为6.4×10⁻⁶ m/s²和9.01×10⁻⁶ m/s²。结果将CO₂置换致密油的效果明显好于N₂。随着相对分子质量的增加，烷烃分子从岩石壁面置换的难度增大，方解石壁面对烷烃分子的吸附作用要强于石英壁面。根据本研究模拟结果将CO₂置换机理大致分为4个阶段：分子扩散阶段、竞争吸附阶段、乳化溶解阶段以及混相阶段（低相对分子质量烷烃）。
- 致密油 /
- CO₂ /
- N₂ /
- 赋存状态 /
- 驱油机理 /
- 分子动力学模拟
Abstract: Objective
This research aims to investigate the storage state of tight oil and the mechanism of its replacement by CO₂ through molecular dynamics simulations.
Methods
The Monte Carlo method and molecular dynamics simulation algorithms were utilized to model the storage state of alkanes with varying molecular weights on rock surfaces. These models facilitate the examination of the storage characteristics of alkane molecules on different types of rock surfaces and analyze the micromechanisms of tight oil replacement by CO₂ and N₂. The simulated temperature and pressure conditions (343.13 K and 20 MPa) were chosen to reflect the conditions in tight reservoirs of the Sichuan Basin.
Results
The diffusion coefficients of C₇ in CO₂ were measured at 1.88×10⁻⁵ m/s² and 1.83×10⁻⁵ m/s² for the quartz and calcite surfaces, respectively. In contrast, the coefficients in N₂ were lower, measuring 6.4×10⁻⁶ m/s² and 9.01×10⁻⁶ m/s² for the same surfaces.
Conclusion
These findings indicate that CO₂ is significantly more effective than N₂ in displacing tight oil. The challenge of displacing alkane molecules from rock surfaces increases with the relative molecular weight of the alkane. In addition, alkane molecule adsorption on the calcite surface is greater than on the quartz surface. Based on the experimental results presented in this paper, the CO₂ replacement mechanism can be broadly categorized into four stages: molecular diffusion, competitive adsorption, emulsification and dissolution, and a mixed-phase stage (involving low-molecular-weight alkanes).
- tight oil /
- CO₂ /
- N₂ /
- occurrence state /
- oil displacement mechanism /
- molecular dynamics simulation

HTML全文

图 1 模型结构示意图

a. α-石英壁面；b. 方解石壁面；c. 致密油赋存模型（C₇）；d. α-石英致密油置换模型（红色为CO₂、白色为C₇）；e. 方解石致密油置换模型（红色为CO₂、白色为C₇）

Figure 1. Structure diagram of molecular models

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图 2 烷烃分子径向相对浓度分布图

Figure 2. Radial density distribution of alkane molecules

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图 3 α-SiO₂-CO₂模型模拟结果示意图

Figure 3. Simulation results of the α-SiO₂-CO₂ model

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图 4 CaCO₃-CO₂模型模拟结果示意图

Figure 4. Simulation results of the CaCO₃-CO₂ model

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图 5 α-SiO₂-N₂模型结果示意图

Figure 5. Simulation results of the α-SiO₂-N₂ model

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图 6 CaCO₃-N₂模型模拟结果示意图

Figure 6. Simulation results of the CaCO₃-N₂ model

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图 7 MSD分布曲线图

Figure 7. Distribution of the MSD

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图 8 α-石英模型中流体分子质心随模拟时长变化曲线图

Figure 8. Centroid displacement of components in different α-SiO₂ models

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图 9 C₇在CO₂氛围中的扩散（黄色为H原子、红色为O原子、灰色为C原子）

Figure 9. C₇ diffusion in CO₂ (hydrogen in yellow, oxygen in red, and carbon in grey)

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图 10 C₇和CO₂在α-石英壁面竞争吸附（黄色为H原子、红色为O原子、灰色为C原子）

Figure 10. Competitive adsorption of C₇ and CO₂ on the quartz wall (hydrogen in yellow, oxygen in red, and carbon in grey)

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图 11 C₇（a）、C₂₂（b）烷烃在CO₂中呈乳化状态（黄色为H原子、红色为O原子、灰色为C原子）

Figure 11. Emulsification conditions of alkaness: C₇ (a) and C₂₂ (b) (hydrogen in yellow, oxygen in red, and carbon in grey)

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图 12 C₇（a）、C₂₂（b）烷烃与CO₂呈混相状态（黄色为H原子、红色为O原子、灰色为C原子）

Figure 12. Miscibility conditions of alkanes: C₇ (a), C₂₂ (b) and CO₂ (hydrogen in yellow, oxygen in red, and carbon in grey)

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表 1 α-石英壁面体系参数

Table 1. Parameters of the quartz system

体系成分	温度/ K	压力/ MPa	X方向/ nm	Y方向/ nm	Z方向/ nm	密度/ （g·cm⁻³）	分子数
真空层	343.15	20	3.4	5.4	1.5	—	—
封盖层					0.8	1.50	300
CO₂					9.0	0.65	1500
N₂					9.0	0.18	1500
C₇					2.0	0.66	140
C₁₂					2.0	0.73	100
C₁₅					2.0	0.75	80
C₁₈					2.0	0.76	70
C₂₂					2.0	0.80	60
α-SiO₂					2.4	—	—

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表 2 方解石壁面体系参数

Table 2. Parameters of the calcite systems

体系成分	温度/ K	压力/ MPa	X方向/ nm	Y方向/ nm	Z方向/ nm	密度/ （g·cm⁻³）	分子数
真空层	343.15	20	3.2	5.5	1.5	—	—
封盖层					0.8	1.50	300
CO₂					9.0	0.65	1500
N₂					9.0	0.18	1500
C₇					2.0	0.66	135
C₁₂					2.0	0.73	95
C₁₅					2.0	0.75	75
C₁₈					2.0	0.76	65
C₂₂					2.0	0.80	55
CaCO₃					2.3	—	—

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表 3 不同模型扩散系数统计表

Table 3. Diffusion coefficient of components in different models 扩散系数/(m·s⁻²)

模型	C₇	C₁₂	C₁₅	C₁₈	C₂₂
α-SiO₂-CO₂	1.88×10⁻⁵	1.38×10⁻⁵	6.43×10⁻⁶	3.93×10⁻⁶	3.65×10⁻⁶
α-SiO₂-N₂	6.40×10⁻⁶	2.02×10⁻⁶	1.50×10⁻⁶	9.29×10⁻⁷	7.00×10⁻⁷
CaCO₃-CO₂	1.83×10⁻⁵	9.29×10⁻⁶	8.32×10⁻⁶	4.22×10⁻⁶	3.74×10⁻⁶
CaCO₃-N₂	9.01×10⁻⁶	2.88×10⁻⁶	1.57×10⁻⁶	1.02×10⁻⁶	8.70×10⁻⁷

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