The WAG injection process aims to squeeze more oil out of a reservoir
It was originally intended to improve sweep efficiency during gas flooding, with intermittent slugs of water and gas designed by and large to follow the same route through the reservoir
Variants include injecting gas as a supplement to water or vice versa, primarily to reach other parts of the reservoir. In the case of supplementary water injection, it also saves on valuable injection ga
A distinction can often be drawn between miscible and immiscible WAG injection, and the water and gas can be injected simultaneously (SWAG) rather than intermitten
Adding a foaming agent to the injection water can also improve the gas sweep
Present position
WAG injection has been widely applied since the late 1950s.
Statoil has used it to varying degrees on quite a few fields, including most of the larger developments operated by the group on the Norwegian continental shelf.
These include Snorre, Statfjord, Gullfaks, Heidrun, Norne, Veslefrikk and Siri.
The group has also been pursuing research and development activities for many years to improve understanding of relevant mechanisms and to improve predictive capability.
WAG injection accordingly represents a well-established technology in Statoil today.
The typical improved oil recovery (IOR) potential for WAG injection when compared with water injection is quoted in the literature at 5-10%.
Gas represents a large fraction of the total cost, making WAG injection a fairly expensive method except in cases where a gas surplus is available.
Challenges related to WAG injection being addressed in Statoil’s R&D work primarily concern:
Mechanisms: understanding microscopic effects, particularly in cases where three-phase flow and hysteresis are important for the IOR effect. Capillary phenomena and wettability are important properties for low-permeable rock and may be taken advantage of or manipulated for IOR gains.
Predictions.
Use of foam (foam-assisted WAG or FAWAG).
Gas costs: gas injection is usually seen as supplementary to an on-going waterflood, and finding technical and commercial ways to reduce gas costs would prove beneficial.
The WAG injection process aims to squeeze more oil out of the reservoirs. It is well known that remaining (residual) oil in the flooded rock may be lowest when three phases – oil, water and gas – have been achieved in this volume.
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 owing to gravitational forces.
Three-phase gas, oil and water flow is better at displacing residual oil in the pore system than two-phase flow. WAG and SWAG thus improve the efficiency of both microscopic and macroscopic displacement. The challenge is to achieve sufficient sweep in the reservoirs.
A consistent three-phase model for capillary pressure and relative permeability has been implemented in compositional eclipse in an effort to improve the ability to model hysteresis and miscibility effects.
The model permits the use of primary drainage, imbibition and secondary drainage data for both gas-oil and oil-water systems.
Carbon dioxide is usually injected in a WAG mode. Although carbon injection is treated as a separate technology in this strategy work, all the above-mentioned challenges are also relevant for the greenhouse gas.
These technologies are key to optimising WAG injection procedures and to improving forecasts, and thereby to creating value by improving oil recovery.
It was originally intended to improve sweep efficiency during gas flooding, with intermittent slugs of water and gas designed by and large to follow the same route through the reservoir
Variants include injecting gas as a supplement to water or vice versa, primarily to reach other parts of the reservoir. In the case of supplementary water injection, it also saves on valuable injection ga
A distinction can often be drawn between miscible and immiscible WAG injection, and the water and gas can be injected simultaneously (SWAG) rather than intermitten
Adding a foaming agent to the injection water can also improve the gas sweep
Present position
WAG injection has been widely applied since the late 1950s.
Statoil has used it to varying degrees on quite a few fields, including most of the larger developments operated by the group on the Norwegian continental shelf.
These include Snorre, Statfjord, Gullfaks, Heidrun, Norne, Veslefrikk and Siri.
The group has also been pursuing research and development activities for many years to improve understanding of relevant mechanisms and to improve predictive capability.
WAG injection accordingly represents a well-established technology in Statoil today.
The typical improved oil recovery (IOR) potential for WAG injection when compared with water injection is quoted in the literature at 5-10%.
Gas represents a large fraction of the total cost, making WAG injection a fairly expensive method except in cases where a gas surplus is available.
Challenges related to WAG injection being addressed in Statoil’s R&D work primarily concern:
Mechanisms: understanding microscopic effects, particularly in cases where three-phase flow and hysteresis are important for the IOR effect. Capillary phenomena and wettability are important properties for low-permeable rock and may be taken advantage of or manipulated for IOR gains.
Predictions.
Use of foam (foam-assisted WAG or FAWAG).
Gas costs: gas injection is usually seen as supplementary to an on-going waterflood, and finding technical and commercial ways to reduce gas costs would prove beneficial.
The WAG injection process aims to squeeze more oil out of the reservoirs. It is well known that remaining (residual) oil in the flooded rock may be lowest when three phases – oil, water and gas – have been achieved in this volume.
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 owing to gravitational forces.
Three-phase gas, oil and water flow is better at displacing residual oil in the pore system than two-phase flow. WAG and SWAG thus improve the efficiency of both microscopic and macroscopic displacement. The challenge is to achieve sufficient sweep in the reservoirs.
A consistent three-phase model for capillary pressure and relative permeability has been implemented in compositional eclipse in an effort to improve the ability to model hysteresis and miscibility effects.
The model permits the use of primary drainage, imbibition and secondary drainage data for both gas-oil and oil-water systems.
Carbon dioxide is usually injected in a WAG mode. Although carbon injection is treated as a separate technology in this strategy work, all the above-mentioned challenges are also relevant for the greenhouse gas.
These technologies are key to optimising WAG injection procedures and to improving forecasts, and thereby to creating value by improving oil recovery.
