TY  - EJOU
AU  - Li, Zheng 

TI  - Molecular	Simulation	of	Multiphase	Interface	Characteristics	and	 Microscale	Flow	Mechanisms	of	Oil	and	Brine	in	Carbonate	Reservoir
T2  - The International Conference on Computational \& Experimental Engineering and Sciences

PY  - 2023
VL  - 26
IS  - 3
SN  - 1933-2815

AB  - Pore	structures	of	carbonate	reservoirs	are	complicated	leading	 to	 the	indistinguishable	 two-phase	 flow	
mechanisms	of	oil	and	brine.	This	work	from	the	molecular	perspective	investigates	the	interfacial	tension	
of	oil-brine	two-phase	system,	the	contact	angle	of	oil-brine-carbonatite	three-phase	system,	as	well	as	the	
microscale	flow	mechanisms	of	oil	and	brine	in	carbonate	nanopores,	especially	focusing	on	the	effects	of	
ion	species,	salinity,	and	carbonate	surface.	The	following	conclusions	can	be	drawn.	(1)	Oil-brine	interfacial	
tension	increases	with	salinity	for	the	same	ion	species,	and	increases	in	the	order	of	KCl,	NaCl, CaCl2 and	
MgCl2 for	 the	 same	 salinity. The	 cation	 mainly	 affects	 the	 interfacial	 tension,	 and	 a	 larger	 cation	 size	
corresponds	 to	a lower	interfacial	 tension.	(2)	The	neutral	carbonate	surface	is	super-hydrophilic	with	a	
water	 film	between	oil	droplet	and	carbonatite.	As	 the	salinity	increases	 from	0	mol/L	 to	3.8	mol/L,	 the	
thickness	of	the	water	film	increases	from	0.6	nm	to	1.05	nm, and	the	contact	angle	of	oil	droplet	increases	
from	145°	to	170°. For	the	same	salinity,	both	the	water	film	thickness	and	the	contact	angle	in	CaCl2 brine	
system	 are	 larger	 than	 those	 in	 NaCl	 brine	 system.	 The	 charged	 carbonate	 surface	 makes	 the	 water	
molecules	oriented,	stretching	the	oil	droplet	vertically,	even	with	the	tendency	to	strip	the	oil	droplet	from	
the	carbonatite. For	CaCl2 and	NaCl	brine	systems,	there	are	critical	salinities	of	0.82	mol/L	and	1.23	mol/L,	
respectively.	The	cross	section	of	the	oil	droplet	is	oval	when	the	salinity	is	smaller	than	the	critical	value,	
while	it	becomes	circular	when	the	salinity	exceeds	the	critical	value. (3)	In	neutral	carbonate	nanopores,	
water	film	forms	near	the	nanopore	wall	which	cannot	flow,	while	oil	prefers	the	nanopore	center	which	
will	flow	under	the	pressure	gradient.	Increasing	the	salinity	will	decrease	the	velocity.	In	charged	carbonate	
nanopores,	both	oil	and	water	adsorb	on	the	nanopore	wall.	There	is	no	velocity	slip	on	the	nanopore	wall.	
Increasing	 the	 salinity	 will	 strip	 the	 oil	 droplet	 and	 a	 water	 film	 will	 form	 between	 the	 oil	 droplet	 and	
carbonatite.	Besides,	the	velocity	will	be	enhanced.	This	work	can	provide	microscale	understanding	and	
theoretical	basis	for	enhancing	carbonate	reservoir	recovery	factors.
KW  - 

DO  - 10.32604/icces.2023.09141