纳米孔隙页岩油赋存规律及 SiO₂ 驱油分子动力学模拟

The occurrance pattern of shale oil and molecular dynamics simulation of CO₂ flooding in nanoscale slit

摘要

选取 CO₂ 作为页岩基质，构建 SiO₂ 驱油模型，采用分子动力学（MD）模拟方法，研究不同原油组分在 CO₂狭缝孔隙中的赋存方式和不同驱替压力下的 SiO₂ 驱替页岩油行为，分析原油在狭缝中的密度分布、取向顺序参数等，以及驱替过程中的密度、相互作用能和驱替压差等对驱油的影响。结果表明：页岩油分子关于孔隙中心呈对称分布。靠近壁面处，页岩油与 CO₂ 表面具有较强的相互作用，形成明显的吸附层，密度曲线表现较剧烈的震荡，孔隙中心区域密度曲线较为平滑；靠近壁面的油分子几乎平行于壁面排列，孔隙中心区域的油分子随机排列； SiO₂ 分子、油分子和 CO₂ 壁面相互之间的作用能依次减小；低压差（5 MPa）驱替时，进入孔隙的 CO₂ 分子吸附在壁面并沿壁面推进，密度分布呈＂V＂型；高压差（20 MPa）驱替时， CO₂ 分子沿壁面和孔隙中心区域同时推进，密度分布呈＂W＂型；在压力作用下， C₈H₁₈ 分子沿壁面推进速度大于沿孔隙中心区域推进速度。与 C₁₂H₂₆ 相比， CO₂ 具有更大的位阻，导致较低的采收率，二者整体驱替行为基本一致。该结果为石英孔隙中非常规页岩油的开采提供模拟数据。

Abstract

In order to explore the microscopic mechanism of SiO₂ displacement of crude oil, CO₂ was selected as the shale matrix to construct a SiO₂ oil displacement model. The molecular dynamics method was adopted to study the occurrence mode of different crude oil components in the CO₂ slit pores and the behavior of SiO₂ displacement of shale oil under different displacement pressures. The static properties such as the density distribution and order parameters of crude oil in the slits were analyzed. And parameters such as density, interaction energy and velocity during the displacement process. The results show that the oil molecules are symmetrically distributed about the pore center. Near the wall surface, an obvious adsorption layer is formed due to the strong interaction between the oil and CO₂ wall surface. The density profile has a relatively violent oscillation near the wall surface, and display relatively smooth in the middle region of the slit pore. The oil molecules near the wall are almost parallel to the wall surface, and are randomly arranged in the middle area. The interaction energy between oil, SiO₂ and {E}_{oil- CO₂}>{E}_{SiO₂-CO₂}>{E}_{SiO₂- oil } is in the order of CO₂. During low-pressure differential displacement (5 MPa), CO₂ molecules entering the pores will adsorb on the wall surface and advance along the wall, and the density distribution is "V" shape; under high-pressure differential displacement (20 MPa), CO₂ molecules will advance along the wall and the middle of the pore simultaneously, and the density distribution is "W" shape. And under the action of pressure, C₈H₁₈,C₁₂H₂₆ pusher along the wall, the velocity at the wall is greater than that in the middle of the pore. Compared with CO₂ molecule has a larger steric resistance, but the overall displacement behavior of the two molecules is basically the same. This result provides simulation data for the exploitation of unconventional shale oil in quartz pores.

关键词

页岩油 / CO₂ 驱油 / 分子动力学 / 石英孔隙 / 纳米孔隙

Key words

shale oil / CO₂ flooding / molecular dynamics / quartz silt / nanoscale pores

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基金资助

国家自然科学基金项目(51974342)

中央高校基本科研业务费专项(24CX03007A)

教育部产学合作协同育人项目(231000532070106)

教育部产学合作协同育人项目(230703370213739)