To clarify the dynamic wettability changes during CO2 injection in unconventional reservoirs,molecular dynamics simulations were performed of water droplets wetting hydroxylated quartz and methylated quartz surfaces at various CO2 pressures.The study shows that hydroxylated quartz is initially strongly hydrophilic,while methylated quartz is initially weakly CO2-affine;as CO2 pressure increased,the water wettability of both decreased,with smaller changes for hydroxylated quartz and larger changes for methylated quartz.With higher CO2 pressure,CO2 and water molecules co-adsorbed on the methylated quartz surface,forming a discontinuous CO2 adsorption film that reduced non-bonded interactions and led to lower hydrophilicity until at 44.96 MPa the water contact angle reaches to 180.00°.As CO2 pressure increases,the number of water molecules in the contact line region decreased and their motion space is compressed,reducing water molecular jump frequency and increasing jump distance.Compared with methylated quartz,hydroxylated quartz remains more hydrophilic with higher water molecule jump frequency and shorter jump distance.This study revealed the dynamic mechanisms of contact angle change for hydroxylated vs. methylated quartz under varying CO2 pressures,established relationships between contact angle,relative permeability and CO2 pressure and then a more accurate description of capillary pressure is proposed.These results provide new theoretical support for nanoscale fluid flow and a more reliable basis for reservoir evaluation,productivity prediction, and development strategy.
YAN Zhiming
,
WANG Fengjiao
,
LIU Yikun
,
CHU Mingxuan
,
REN Mengyao
. Molecular dynamics study of CO2 pressure effects on dynamic wettability of hydroxylated and methylated quartz[J]. Special Oil & Gas Reservoirs, 2026
, 33(1)
: 75
-83
.
DOI: 10.3969/j.issn.1006-6535.2026.01.009
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