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Impact of Connate Brine Chemistry on In Situ Wettability and Oil Recovery: Pore-Scale Experimental Investigation
journal contribution
posted on 2020-03-25, 17:38 authored by Yun Xie, Mahdi Khishvand, Mohammad PiriIn this study, we
present the results of micro- and macroscale
core-flooding experiments performed on reservoir and outcrop sandstone
core samples to investigate the impact of connate brine salinity on
wettability and oil recovery. Numerous core samples were fully saturated
with connate brines of varying salinities and then subjected to a
dynamic wettability restoration (aging) process. The miniature core
samples were imaged at high resolutions, and the images were used
to measure in situ contact angles and evaluate the wettability alteration.
Subsequently, some of the core samples were flooded with identical
injection brine to examine
the interrelationship between connate brine salinity and oil recovery
potentials. The experimental observations demonstrate an ascending
trend of initial oil–water contact angles with increases in
brine salinity. We believe that brine film thickness, controlled by
the DLVO interactions and initial cation-water bridging, is responsible
for this wettability sensitivity. The equilibrium wettability state
is found to shift toward reduced water-wetness when the connate brine
salinity increases, which could be associated with improved oil−mineral
bonding at higher salinities. Furthermore, using an ultralow salinity
connate brine in the aging process results in a heterogeneous equilibrium
wettability state including 46% of weakly water- and neutral-wet pores.
It is believed that the ultralow salinity brine preserves stable brine
films on some of the pore walls, prevents direct oil−mineral
contact, and consequently reduces the degree of wettability alteration
during the aging process. The subsequent waterflooding experiments
on the aged samples indicated favorable oil recovery from media with
heterogeneous equilibrium wettability compared to the weakly oil-wet
samples. This was due to the existence of water- and neutral-wet pores
that reduced the entry pressures of water-displacing-oil events and
enhanced the accessibility of water to the oil-wet pore elements,
which in turn improved the oil displacement efficiency.
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Numerous core samplesoil-wet pore elementsconnate brine salinityconnate brine salinity increasesultralow salinity connate brineequilibrium wettability statemacroscale core-flooding experimentsoutcrop sandstone core samplesConnate Brine Chemistryoil recoveryultralow salinity brineoil recovery potentialsoil displacement efficiencycore samplesneutral-wet poresDLVOwettability alterationbrine film thickness
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