Study On The Micro-mechanism Of The Effect Of Crude Oil Components On The Calcite Surface Wettability

Carbonate reservoir is one of the most important part in the world engry system,its discovered amount account for 50% of the world's total reserves,and its production occupy 60% of the world's production.Nowadays the gap between energy supply and demand is more and more apparent,hence,the exploration and development of carbonate reservoirs are in the ascendant all over the world.However,the recovery of carbonate reservoirs is generally low,wettability as the basic property of reservoirs has an important impact on it.The micro-mechanism of wettability,that is,the crude oil-water-minerals surface interaction is still unclear,which directly hinders the optimization of many enhanced oil recovery technologies.Therefore,it is very necessary to systematically study the formation and alteration mechanism of carbonate wettability at atomic and molecular scales.This study combines molecular dynamics simulation with density functional theory and assists with physical experiments to explore the formation and alteration mechanism of calcite surface wettability at atomic and molecular scales.Meanwhile,the roles of different polar crude oil components are also systemically analyzed.This study consists three parts:?1?Molecular dynamic simulation studies on the formation,alteration process and mechanism of calcite surface wettability at molecular scale;?2?Density functional theory explores the adsorption mechanism of water molecule and crude oil components on calcite surface at atomic scale;?3?Density functional theory studys the intermolecular interaction of different polar crude oil components at atomic scale.Results show that:?1?The higher the polar components in crude oil,the more stable the oil-wet calcite surface;the higher the non-polar components in crude oil,the easier the oil-wet calcite surface will be destroyed.The stronger the crude oil molecules polarity,the stronger the adsorption on calcite surface.The interaction between polar crude oil molecules and calcite surface are mainly electrostatic force and hydrogen bond.While,Van der Waals force is dominant in the non-polar components adsorption.Crude oil molecules can be miscible with each other,and the closer the polarity is,the stronger the miscibility.Van der Waals force is the main force among non-polar components,and electrostatic force is the driving force among polar components.With the increase of polarity difference between crude oil molecules,electrostatic force decreases and van der Waals force increases;?2?Ca-O ion bond and H-O hydrogen bond between water and calcite surface are formed during the water adsorption;Ca-O ion bond and H-O covalent bond are formed when benzoic acid molecule adsorb on CaCO₃{104} surface;Ca-N ion bond and H-O covalent bond are exsited between pyridine molecule and CaCO₃{104} surface;There are only weak hydrogen bonds between thiophene,toluene and CaCO₃{104} surface;?3?When hexanoic acid and hexane molecules are jointly adsorbed,hexanoic acid molecules are adsorbed preferentially,and then dragging the hexane molecules to the calcite surface by van der Waals force.The adsorption strength of hexanoic acid molecule decreases,while that of hexane molecule decreases a little.