Establishing an effective displacement
system for conventional water flooding development in low-permeability
reservoirs is difficult, with generally low liquid and oil production
and a worse water flooding effect. Imbibition oil recovery technology
has received increasing attention from oil development workers because
of its simple operation, low cost, and good oil increase effect. To
explore the method and mechanism to further improve the effect of
imbibition oil recovery, we study the imbibition and oil recovery
effect and its influencing factors in a low-permeability reservoir
in the Dagang Oilfield based on evaluation indexes of the adhesion
work reduction factor, ratio of capillary force to gravity
N
B
–1
, regression analysis of
the recovery rate of imbibition, proportional relationship with spontaneous
imbibition, and dynamic imbibition effect in crack rocks. Results
show that reducing the interfacial tension of the surfactant on the
imbibition process has a dual effect. The selection of the surfactant
for fractured tight reservoirs should not excessively pursue ultralow
interfacial tension, and it should consider the surface wettability
environment favorable for imbibition to ensure that a sufficient driving
force can be provided. In the initial imbibition stage, the capillary
force is large, the velocity of water imbibition in pores is fast,
and the oil recovery rate is high; the holding time of the imbibition
process is important to imbibition recovery. With the increase in
imbibition time, the capillary force weakens, and the imbibition speed
decreases to zero. With the increase in injection volume, reservoir
pressure, pressure holding time, and imbibition cycles, the oil recovery
increases, but the amplification of oil recovery decreases. From the
technical and economic viewpoints, the optimal slug size, throughput
cycle, and pressure holding time of the target reservoir are recommended
as follows: 0.5 PV,three3 rounds, and greater than 96 h, respectively.
