GAS RELATIVE PERMEABILITY HYSTERESIS DURING IMMISCIBLE WATER ALTERNATING GAS INJECTION

Although WAG (Water Alternating Gas) has been studied and implemented widely
for hydrocarbon recovery improvement, still there are some uncertainties regarding
the three-phase flow. One of the most important uncertainty areas is modeling the
three-phase relative permeability for three-phase flow. Commercial simulators by
using currently implemented three-phase models cannot capture all of the features
behind three-phase flow.
Hysteresis is one of the crucial features of three-phase flow which IS still
remained controversial in three-phase relative permeability and needs to be
elaborated. Some of the current relative permeability models have accounted for this
phenomenon and in some of them, hysteresis is lacking. Two-phase models usually
fail to predict the actual behavior of the hysteresis in three-phase flow. Some of the
three-phase models also take in to account some of the features of hysteresis but not
all of them. In the simulation process of water alternating gas, hysteresis modeling is a
corner stone of the workflow. If this work step is not done properly and not elaborated
seriously, the results of the simulation will not really help to understand different
aspects of the WAG injection scenario for field application.
In this study, first a literature survey has been done on recovery definition and
WAG history. Then fundamentals of displacement process and trapping mechanisms
in porous media have been addressed. Hysteretic in two and three-phase relative
permeability models have been reviewed and the comparison has been made in terms
of the applicability for simulating immiscible WAG (I-WAG) injection. The more
applicable model which is commercially implemented in the reservoir simulator was
selected and model prediction versus selected experimental data was shown and
discrepancies are highlighted.