A series of in situ imbibition imaging experiments were carried out by using the self-developed nanofluid SNF-SL to study the imbibition effects and oil drainage imaging characteristics of nanofluids in ultra-low permeability core. Based on the influence of nanofluids on factors such as core wettability, oil-water interfacial tension, and viscosity, the synergistic effects of nanofluids on the power and resistance of imbibition were analyzed, and the mechanical mechanism of nano-enhanced imbibition was expounded. The results showed that the imbibition recovery rate of nanofluids in fractured cores with ultra-low permeability was 2.63% and 5.75% higher than that of nanofluids in hydrophilic cores. Nanofluid with concentration ranging from 0.15% and 0.3% could reduce the oil-water interfacial tension by 59% and 65% and the contact angle of the core surface from 73.8- to 9.5- and 6.6-, and the reduction rate of viscosity could reach 39% and 48%. Therefore, the capillary force of imbibition was increased by 24% and 44.6%. The adhesion work of crude oil was reduced by 99.2% and 99.7%. The internal friction resistance was reduced by 39% and 48%. The results demonstrated that the vertical fractures had the best imbibition effect, followed by the horizontal fractures, which were higher than the recovery rate of the matrix core. The reason lay in the fact that the fractures increased the action area between the nanofluid and the core and shortened the oil drainage distance of transverse imbibition, and the oil drainage speed was accelerated by the vertical fractures based on gravity differentiation. The higher concentration or temperature of the nanofluid led to a higher oil drainage efficiency of imbibition. The synergistic effects of improving the power of imbibition and reducing the internal and external friction resistance occured through the dual action of the nanofluid on the core and crude oil, improving the oil drainage effects of imbibition, which reflected the mechanical mechanism of the nanofluid to enhance imbibition.
XUE Peiyu
,
GU Chunyuan
,
LI Yuhua
,
ZHU Junjie
. Enhanced imbibition effect of nanofluids and driving characteristics of oil drainage in fractured ultra-low permeability reservoirs[J]. Journal of Shanghai University, 2026
, 32(1)
: 54
-66
.
DOI: 10.12066/j.issn.1007-2861.2617
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