Water-Alternating-Gas Injection Simulation - Best Practices

Abstract

Water-Alternating-Gas injection is one of the most applicable EOR techniques in oil reservoirs worldwide. To optimize the WAG injection projects, numerical simulation is the best available tool to aid with such objective. In this paper, we are looking into the simulation process (from core-scale to reservoir-scale) in more details to understand the challenges and try to suggest best practices and guidelines. The first part of this paper will discuss the role of hysteresis in WAG injection based on the results of several three-phase Water-Alternating-Gas injection experiments. Then the significance of three-phase hysteresis in simulating WAG injection will be highlighted. After establishing a good understanding of the role of three-phase hysteresis in WAG injection simulation, the second part will present sensitivity study at reservoirs-scale to identify the main differences in the simulation results. Finally, towards the end of the paper, WAG injection's best practices guideline will be suggested. Currently, the common practice is to estimate three-phase hysteresis parameters (Land trapping parameter [C], secondary drainage gas relative permeability reduction exponent [alpha], residual oil modification factor [a], and three-phase water relative permeability [krw3ph]) from coreflood experiments. Based on several three-phase WAG injection experiments conducted at Heriot-Watt University, we came up with several conclusions. These conclusions are: If the pressure drop (DP) during the three-phase water injection experiment is significantly higher than the DP during two-phase water injection, then a lower three-phase water relative permeability is essential to match the three-phase WAG injection experimental data.If the pressure drop (DP) at the end of two-phase gas injection is lower than the DP at the end of three-phase gas injection, then alpha [α] is critical to match the three-phase WAG injection experimental data.If the experimental results showed significant gas trapping [Sgt] during water injection after gas injection, then Land's trapping parameter is essential to model such trapping behaviour at any scale.These parameters should be obtained from experiments starting with gas injection (GAW) to fit with the definitions accepted into the numerical simulations. Many studies in the literature either ignores the effect of hysteresis in WAG injection or use invalid WAG hysteresis parameters. In this paper, we highlighted the role of hysteresis in WAG injection and clarified the confusion on the procedures to obtain the correct hysteresis parameters. Also, we provided an easy guideline to help the industry in making accurate predictions for WAG injection projects.

Evaluation of the use of Water Alternated Gas Injection for Enhanced Oil Recovery

“…It was also probably conducted in gas phase modification by applying Foam assisted water alternating gas injection (FAWAG) or water alternating high-pressure air injection (WAHPAI)) as well as in operating conditions by employing miscible or immiscible WAG. Since the processes are characterized by a strong cyclic hysteresis effect which is directly correlated from the pressure drop behavior between the three and two-phase water injection experiments, the use of restart option in Eclipse-100 should be performed (Alzayer & Sohrabi, 2018). Furthermore, the cyclic hysteresis essential at the core scale should be incorporated in full reservoir scale simulations to enhance performance prediction accuracy.…”

Comparative numerical study for polymer alternating gas (PAG) flooding in high permeability condition

“…Despite the success of CO 2 -WAG, the challenge is achieving the field incremental recovery, which is between 5 and 10% OOIP [6]. This low production is due to gravity segregation effect, water blocking phenomena and WAG mobility control [7]. Also, the method faced significant challenge in improving sweep efficiency in high permeable zones.…”

Advances in Raw Material Industries for Sustainable Development Goals

“…Scientists (Hoare & Coll 2018, Kumar et al 2017, Khorsandi et al 2017Alzayer & Sohrabi 2018) note the influence of hysteresis relative permeability on the effectiveness of WAG. It is often expected that the gas phase will show large hysteresis effects (Hoseini et al 2011).…”