Literature Review of Water Alternation Gas Injection

The Water Alternating Gas (WAG) process is a cyclic method of injecting alternating cycles of gas followed by water and repeating this process over a number of cycles. WAG injection is to improve oil recovery, by both increasing the macroscopic and microscopic sweep efficiency and to help maintain the reservoir pressure. Also, WAG injection is to postpone the gas breakthrough. The WAG process provides mobility control in fast zones which extends gas project life and oil recovery. This paper provided a comprehensive literature study about WAG injection. This paper has collected most of the requirements of the petroleum engineers that has to know about the WAG injection started from basic concepts until the design parameter for WAG injection. Keywords: Enhanced oil recovery, WAG injection

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Numerical Optimization of WAG Injection in a Sandstone Field using a Coupled Surface and Subsurface Model

10.2118/207449-ms ◽

2021 ◽

Author(s):

Thaer I. Ismail ◽

Emad W. Al-Shalabi ◽

Mahmoud Bedewi ◽

Waleed AlAmeri

Keyword(s):

Oil Recovery ◽

Gas Injection ◽

Coupled Model ◽

Sensitivity Study ◽

Mobility Control ◽

Base Case ◽

The North ◽

Injection Process ◽

Interaction Terms ◽

Wag Injection

Abstract Gas injection is one of the most commonly used enhanced oil recovery (EOR) methods. However, there are multiple problems associated with gas injection including gravity override, viscous fingering, and channeling. These problems are due to an adverse mobility ratio and cause early breakthrough of the gas resulting, in poor recovery efficiency. A Water Alternating Gas (WAG) injection process is recommended to resolve these problems through better mobility control of gas, leading to better project economics. However, poor WAG design and lack of understanding of the different factors that control its performance might result in unfavorable oil recovery. Therefore, this study provides more insight into improving WAG oil recovery by optimizing different surface and subsurface WAG parameters using a coupled surface and subsurface simulator. Moreover, the work investigates the effects of hysteresis on WAG performance. This case study investigates a field named Volve, which is a decommissioned sandstone field in the North Sea. Experimental design of factors influencing WAG performance on this base case was studied. Sensitivity analysis was performed on different surface and subsurface WAG parameters including WAG ratio, time to start WAG, total gas slug size, cycle slug size, and tubing diameter. A full two-level factorial design was used for the sensitivity study. The significant parameters of interest were further optimized numerically to maximize oil recovery. The results showed that the total slug size is the most important parameter, followed by time to start WAG, and then cycle slug size. WAG ratio appeared in some of the interaction terms while tubing diameter effect was found to be negligible. The study also showed that phase hysteresis has little to no effect on oil recovery. Based on the optimization, it is recommended to perform waterflooding followed by tertiary WAG injection for maximizing oil recovery from the Volve field. Furthermore, miscible WAG injection resulted in an incremental oil recovery between 5 to 11% OOIP compared to conventional waterflooding. WAG optimization is case-dependent and hence, the findings of this study hold only for the studied case, but the workflow should be applicable to any reservoir. Unlike most previous work, this study investigates WAG optimization considering both surface and subsurface parameters using a coupled model.

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An Improved Three-Phase Relative Permeability and Hysteresis Model for the Simulation of a Water-Alternating-Gas Injection

SPE Journal ◽

10.2118/152218-pa ◽

2013 ◽

Vol 18 (05) ◽

pp. 841-850 ◽

Cited By ~ 15

Author(s):

H.. Shahverdi ◽

M.. Sohrabi

Keyword(s):

Relative Permeability ◽

Oil Recovery ◽

Gas Injection ◽

Phase Flow ◽

Relative Permeabilities ◽

Water Alternating Gas ◽

Three Phase ◽

Three Phase Flow ◽

Oil Water ◽

Wag Injection

Summary Water-alternating-gas (WAG) injection in waterflooded reservoirs can increase oil recovery and extend the life of these reservoirs. Reliable reservoir simulations are needed to predict the performance of WAG injection before field implementation. This requires accurate sets of relative permeability (kr) and capillary pressure (Pc) functions for each fluid phase, in a three-phase-flow regime. The WAG process also involves another major complication, hysteresis, which is caused by flow reversal happening during WAG injection. Hysteresis is one of the most important phenomena manipulating the performance of WAG injection, and hence, it has to be carefully accounted for. In this study, we have benefited from the results of a series of coreflood experiments that we have been performing since 1997 as a part of the Characterization of Three-Phase Flow and WAG Injection JIP (joint industry project) at Heriot-Watt University. In particular, we focus on a WAG experiment carried out on a water-wet core to obtain three-phase relative permeability values for oil, water, and gas. The relative permeabilities exhibit significant and irreversible hysteresis for oil, water, and gas. The observed hysteresis, which is a result of the cyclic injection of water and gas during WAG injection, is not predicted by the existing hysteresis models. We present a new three-phase relative permeability model coupled with hysteresis effects for the modeling of the observed cycle-dependent relative permeabilities taking place during WAG injection. The approach has been successfully tested and verified with measured three-phase relative permeability values obtained from a WAG experiment. In line with our laboratory observations, the new model predicts the reduction of the gas relative permeability during consecutive water-and-gas-injection cycles as well as the increase in oil relative permeability happening in consecutive water-injection cycles.

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Performance Quantification of Enhanced Oil Recovery Methods in Fractured Reservoirs

Energies ◽

10.3390/en14164739 ◽

2021 ◽

Vol 14 (16) ◽

pp. 4739

Author(s):

Riyaz Kharrat ◽

Mehdi Zallaghi ◽

Holger Ott

Keyword(s):

Enhanced Oil Recovery ◽

Oil Recovery ◽

Driving Forces ◽

Fractured Reservoirs ◽

Gas Injection ◽

Capillary Forces ◽

Dimensionless Numbers ◽

Water Alternating Gas ◽

Eor Processes ◽

Wag Injection

The enhanced oil recovery mechanisms in fractured reservoirs are complex and not fully understood. It is technically challenging to quantify the related driving forces and their interaction in the matrix and fractures medium. Gravity and capillary forces play a leading role in the recovery process of fractured reservoirs. This study aims to quantify the performance of EOR methods in fractured reservoirs using dimensionless numbers. A systematic approach consisting of the design of experiments, simulations, and proxy-based optimization was used in this work. The effect of driving forces on oil recovery for water injection and several EOR processes such as gas injection, foam injection, water-alternating gas (WAG) injection, and foam-assisted water-alternating gas (FAWAG) injection was analyzed using dimensionless numbers and a surface response model. The results show that equilibrium between gravitational and viscous forces in fracture and capillary and gravity forces in matrix blocks determines oil recovery performance during EOR in fractured reservoirs. When capillary forces are dominant in gas injection, fluid exchange between fracture and matrix is low; consequently, the oil recovery is low. In foam-assisted water-alternating gas injection, gravity and capillary forces are in equilibrium conditions as several mechanisms are involved. The capillary forces dominate the water cycle, while gravitational forces govern the gas cycle due to the foam enhancement properties, which results in the highest oil recovery factor. Based on the performed sensitivity analysis of matrix–fracture interaction on the performance of the EOR processes, the foam and FAWAG injection methods were found to be more sensitive to permeability contrast, density, and matrix block highs than WAG injection.

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Experimental Investigation of Near-Miscible Water-Alternating-Gas Injection Performance in Water-Wet and Mixed-Wet Systems

SPE Journal ◽

10.2118/145191-pa ◽

2013 ◽

Vol 18 (01) ◽

pp. 114-123 ◽

Cited By ~ 16

Author(s):

S. Mobeen Fatemi ◽

Mehran Sohrabi

Keyword(s):

Relative Permeability ◽

Oil Recovery ◽

Gas Injection ◽

Water Injection ◽

Laboratory Data ◽

Co2 Injection ◽

Water Alternating Gas ◽

Three Phase ◽

The Impact ◽

Wag Injection

Summary Laboratory data on water-alternating-gas (WAG) injection for non-water-wet systems are very limited, especially for near-miscible (very low IFT) gas/oil systems, which represent injection scenarios involving high-pressure hydrocarbon gas or CO2 injection. Simulation of these processes requires three-phase relative permeability (kr) data. Most of the existing three-phase relative permeability correlations have been developed for water-wet conditions. However, a majority of oil reservoirs are believed to be mixed-wet and, hence, prediction of the performance of WAG injection in these reservoirs is associated with significant uncertainties. Reliable simulation of WAG injection, therefore, requires improved relative permeability and hysteresis models validated by reliable measured data. In this paper, we report the results of a comprehensive series of coreflood experiments carried out in a core under natural water-wet conditions. These included water injection, gas injection, and also WAG injection. Then, to investigate the impact of wettability on the performance of these injection strategies, the wettability of the same core was changed to mixed-wet (by aging the core in an appropriate crude oil) and a similar set of experiments were performed in the mixed-wet core. WAG experiments under both wettability conditions started with water injection (I) followed by gas injection (D), and this cyclic injection of water and gas was repeated (IDIDID). The results show that in both the water-wet and mixed-wet cores, WAG injection performs better than water injection or gas injection alone. Changing the rock wettability from water-wet to mixed-wet significantly improves the performance of water injection. Under both wettability conditions (water-wet and mixed-wet), the breakthrough (BT) of the gas during gas injection happens sooner than the BT of water in water injection. Ultimate oil recovery by gas injection is considerably higher than that obtained by water injection in the water-wet system, while in the mixed-wet system, gas injection recovers considerably less oil.

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Investigation of Significance of Critical Components in Optimization of WAG Injection Processes under Uncertainty

10.2118/spe-169940-ms ◽

2014 ◽

Author(s):

C.. Temizel ◽

S.. Purwar ◽

A.. Agarwal ◽

A.. Abdullayev ◽

K.. Urrutia ◽

...

Keyword(s):

Oil Recovery ◽

Large Fraction ◽

Water Injection ◽

Sweep Efficiency ◽

Improved Oil Recovery ◽

Injection Process ◽

Water Alternating Gas ◽

Gas Flooding ◽

Reservoir Simulator ◽

Wag Injection

Abstract Water alternating gas (WAG) injection has been widely used for the last 50 years throughout the world. The typical improved oil recovery (IOR) potential for WAG injection compared with water injection is 5 to 10%. It was originally intended to improve sweep efficiency during gas flooding, with intermittent slugs of water and gas designed to follow the same route through the reservoir. Mechanisms in WAG injection include microscopic effects, particularly in cases where three-phase flow and hysteresis are important for the IOR effect. Injection of gas usually aids an ongoing waterflood, and finding technical and commercial methods to reduce gas costs would be useful. Water injection alone tends to sweep the lower parts of a reservoir, while gas injected alone sweeps more of the upper parts of a reservoir because of gravitational forces. Gas represents a large fraction of the total cost, making WAG injection an expensive method. Thus, optimizing WAG injection is not only crucial in terms of recovery but also economics, especially where gas is expensive and/or limited. In this study, the significance of key components in a WAG injection process on SPE's 5th Comparative Solution Project (CSP) is presented that models the WAG process through a pseudo-miscible formulation by means of coupling a full-physics reservoir simulator with commercial optimization and uncertainty software. The results are analyzed and presented in a comparative manner by means of tornado charts showing the significance of each decision and uncertainty variable.

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Evaluation of Oil Recovery by Water Alternating Gas (WAG) Injection - Oil-Wet & Water-Wet Systems

10.2118/143438-ms ◽

2011 ◽

Cited By ~ 2

Author(s):

Abdulrazag Yusef Zekri ◽

Mohamed Sanousi Nasr ◽

Abdullah AlShobakyh

Keyword(s):

Oil Recovery ◽

Water Alternating Gas ◽

Wag Injection

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Pilot Project Evaluating WAG Efficiency for Carbonate Reservoir in Eastern Siberia

10.2118/206417-ms ◽

2021 ◽

Author(s):

Valentina Zharko ◽

Dmitriy Burdakov

Keyword(s):

Oil Recovery ◽

Gas Injection ◽

Oil Production ◽

Pilot Project ◽

Carbonate Reservoir ◽

Recovery Factor ◽

Eastern Siberia ◽

Water Cut ◽

Wag Injection ◽

Injection Rates

Abstract The paper presents the results of a pilot project implementing WAG injection at the oilfield with carbonate reservoir, characterized by low efficiency of traditional waterflooding. The objective of the pilot project was to evaluate the efficiency of this enhanced oil recovery method for conditions of the specific oil field. For the initial introduction of WAG, an area of the reservoir with minimal potential risks has been identified. During the test injections of water and gas, production parameters were monitored, including the oil production rates of the reacting wells and the water and gas injection rates of injection wells, the change in the density and composition of the produced fluids. With first positive results, the pilot area of the reservoir was expanded. In accordance with the responses of the producing wells to the injection of displacing agents, the injection rates were adjusted, and the production intensified, with the aim of maximizing the effect of WAG. The results obtained in practice were reproduced in the simulation model sector in order to obtain a project curve characterizing an increase in oil recovery due to water-alternating gas injection. Practical results obtained during pilot testing of the technology show that the injection of gas and water alternately can reduce the water cut of the reacting wells and increase overall oil production, providing more efficient displacement compared to traditional waterflooding. The use of WAG after the waterflooding provides an increase in oil recovery and a decrease in residual oil saturation. The water cut of the produced liquid decreased from 98% to 80%, an increase in oil production rate of 100 tons/day was obtained. The increase in the oil recovery factor is estimated at approximately 7.5% at gas injection of 1.5 hydrocarbon pore volumes. Based on the received results, the displacement characteristic was constructed. Methods for monitoring the effectiveness of WAG have been determined, and studies are planned to be carried out when designing a full-scale WAG project at the field. This project is the first pilot project in Russia implementing WAG injection in a field with a carbonate reservoir. During the pilot project, the technical feasibility of implementing this EOR method was confirmed, as well as its efficiency in terms of increasing the oil recovery factor for the conditions of the carbonate reservoir of Eastern Siberia, characterized by high water cut and low values of oil displacement coefficients during waterflooding.

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Pore-Scale Transport Mechanisms and Macroscopic Displacement Effects of In-Situ Oil-in-Water Emulsions in Porous Media

Journal of Energy Resources Technology ◽

10.1115/1.4040200 ◽

2018 ◽

Vol 140 (10) ◽

Cited By ~ 8

Author(s):

Chuan Lu ◽

Wei Zhao ◽

Yongge Liu ◽

Xiaohu Dong

Keyword(s):

Porous Media ◽

Oil Recovery ◽

Heavy Oil ◽

Mobility Control ◽

Pore Scale ◽

Sweep Efficiency ◽

Emulsion Droplets ◽

Oil In Water ◽

Retention Volumes

Oil-in-water (O/W) emulsions are expected to be formed in the process of surfactant flooding for heavy oil reservoirs in order to strengthen the fluidity of heavy oil and enhance oil recovery. However, there is still a lack of detailed understanding of mechanisms and effects involved in the flow of O/W emulsions in porous media. In this study, a pore-scale transparent model packed with glass beads was first used to investigate the transport and retention mechanisms of in situ generated O/W emulsions. Then, a double-sandpack model with different permeabilities was used to further study the effect of in situ formed O/W emulsions on the improvement of sweep efficiency and oil recovery. The pore-scale visualization experiment presented an in situ emulsification process. The in situ formed O/W emulsions could absorb to the surface of pore-throats, and plug pore-throats through mechanisms of capture-plugging (by a single emulsion droplet) and superposition-plugging or annulus-plugging (by multiple emulsion droplets). The double-sandpack experiments proved that the in situ formed O/W emulsion droplets were beneficial for the mobility control in the high permeability sandpack and the oil recovery enhancement in the low permeability sandpack. The size distribution of the produced emulsions proved that larger pressures were capable to displace larger O/W emulsion droplets out of the pore-throat and reduce their retention volumes.

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