Adhesion behavior and influencing factors of crude oil on rock surface in ultra-deep tight reservoir- insights from molecular dynamics

Abstract

The development of ultra-deep tight reservoirs is paramount to the global energy supply. However, their unique conditions hindering efficient development. This study focuses on ultra-deep tight reservoirs in Shunbei Oilfield, leveraging molecular dynamics simulation to establish a crude oil adhesion model. We delve into the adhesion dynamics, relative concentration, interaction energy, and morphology to understand the distribution of crude oil on rock surfaces. Utilizing different component models, we clarify the adhesion mechanisms and distribution of different oil components on rock surface. Finally, the effects of temperature and pressure on adhesion were investigated. Notably, the adhesion of crude oil components is governed by their composition and polarity strength, with resin and asphaltene being strongly polar, aromatic weakly polar, and saturated non-polar. Surprisingly, saturated adhere fastest to rock surface, whereas asphaltenes adhere slowest due to their strong polar interactions that hinder detachment from crude oil droplet. During adhesion, the electrostatic force (−7115.85 kJ/mol) significantly outweighs the van der Waals force (−1753.72 kJ/mol). For non-polar components, van der Waals interactions prevail, while electrostatic potential dominates for polar components. The robust interaction between polar components and rock surface enhances their stable adhesion, with asphaltene exhibiting the strongest adhesion, followed by resin, aromatic, and saturated. Temperature exerts a notable influence on crude oil adhesion, while pressure’s impact is relatively minor. Rising temperatures boost molecular activity, facilitating initial adhesion but weakening long-term interactions with rock surface, ultimately diminishing the final adhesion state. Despite pressure variations influencing adhesion dynamics, the final adhesion efficiency (85 %-90 %), interaction energy (9000–9500 kJ/mol), relative concentration peaks (around 13), adhesion morphology (1.75–1.85 nm), and mean square displacement (40 nm²) remain largely consistent.