Immiscible water-alternating-gas (WAG) flooding
is an EOR technique that has proven successful for
water drive reservoirs due to its ability to improve displacement
and sweep efficiency. Nevertheless, considering
the complicated phase behavior and various multiphase
flow characteristics, gas tends to break through early in
production wells in heterogeneous formations because of
overriding, fingering, and channeling, which may result in
unfavorable recovery performance. On the basis of phase
behavior studies, minimum miscibility pressure measurements,
and immiscible WAG coreflood experiments, the
cubic B-spline model (CBM) was employed to describe the
three-phase relative permeability curve. Using the Levenberg–
Marquardt algorithm to adjust the vector of unknown
model parameters of the CBM sequentially, optimization of
production performance including pressure drop, water cut,
and the cumulative gas–oil ratio was performed. A novel
numerical inversion method was established for estimation
of the water–oil–gas relative permeability curve during the
immiscible WAG process. Based on the quantitative
characterization of major recovery mechanisms, the proposed
method was validated by interpreting coreflood data
of the immiscible WAG experiment. The proposed method
is reliable and can meet engineering requirements. It
provides a basic calculation theory for implicit estimation
of oil–water–gas relative permeability curve.