Influence of Hysteresis on Relative Permeability of Immiscible Water- Alternating-Gas (WAG) Injection of Real Reservoir

The purpose of this project is to study the influence of hysteresis on the relative
permeability with the emphasis on immiscible water-alternating-gas (WAG) injection.
This analysis is focused on the use of simulation software which is ECLIPSE Black Oil
Reservoir Simulator where the input or data is obtained from the Angsi Field reservoir.
Before studying the hysteresis effect, some sensitivity studies on WAG parameters are
conducted to find the optimum values. These parameters include water/gas injection rate,
WAG cycle period as well as WAG ratio. From the sensitivity studies, it is found that the
optimum value for water/gas injection rate is 13000 (stb/day and Mscf/day) meanwhile the
optimum WAG cycle period is found to be 6 months. Although high gas injection rate is
preferable prior to water flooding, however low gas injection rate is more desirable since it
requires less facilities for the WAG process. Therefore 1: 1 ratio is the best ratio for the
WAG process. After all optimum values of the WAG parameters have been determined,
then the hysteresis will be considered in the simulation. Here, the results between the
hysteretic and non-hysteretic models will be compared in order to prove the theory in the
conceptual study which is done by previous researches is valid or not. Based on the results,
it is found that the hysteretic model gives higher recovery factor compared to nonhysteretic
model (base case) as much as 7.3%. Although the increment is not really
significant, it should be reminded that the simulation only considers a portion of the whole
Angsi reservoir. If the whole reservoir is considered, definitely the increment will be
higher. Therefore, it is proved that by considering hysteresis in WAG simulation, the oil
recovery is higher compared to non-hysteretic model and thus the conceptual study done is valid