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Eor Course 2012 Lecture#2 Eor Methods (1)
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Transcript of Eor Course 2012 Lecture#2 Eor Methods (1)
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ENHANCED OIL RECOVERY
PE 510
DR. MOHAMED EL HOUNI
FALL 2013
EOR
METHODS
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Methods to Improve Recovery Efficiency
D I S C O V E R Y
Artificial Lift
Methods to Improve
Recovery Efficiency
Enhanced Oil Recovery Production/Injection Control
Natural Flow
Strategic Wellbore Placement
Conventional
Oil Recovery
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EOR methods
Waterflooding
Thermal methods: steam stimulation, steamflooding,
hot water drive, and in- situ combustion
Chemical methods: polymer, surfactant, caustic, andmicellar/polymer flooding.
Miscible methods: hydrocarbon gas, CO2, and
nitrogen (flue gas and partial miscible/immiscible gas
injection may also be considered)
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Miscible gasChemicalThermalWaterflood
Reduces Sorw by
developing miscibilitywith the oil through a
vaporizing or
condensing gas
drive process.
Reduces Sorw by
lowering water-oilinterfacial tension, &
increases volumetric
sweep efficiency by
reducing the water-oil
mobility ratio.
Reduces Sorw by
steam distillation &reduces oil viscosity
Maintains reservoir
pressure & physicallydisplaces oil with
water moving through
the reservoir from
injector to producer.
EOR methods
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Objective of EOR
The goal of any enhanced oil recovery process is tomobilize "remaining" oil.
This is achieved by enhancing oil displacement andvolumetric sweep efficiencies.
Oil displacement efficiency is improved by reducing oilviscosity (e.g., thermal floods) or by reducing capillaryforces or interfacial tension (e.g., miscible floods).
Volumetric sweep efficiency is improved by developing amore favorable mobility ratio between the injectant andthe remaining oil-in-place (e.g., polymer floods,
wateralternating- gas processes). It is important to identify remaining oil and the
mechanisms that are necessary to improve recoveryprior to implementing an EOR process.
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Waterflooding
Description
Waterflooding consists of injecting water into the
reservoir. Most widely used post-primary recovery
method. Water is injected in patterns or along theperiphery of the reservoir.
Mechanisms that Improve Recovery Efficiency
Water drive
Increased pressure
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Waterflooding
Limitations
High oil viscosities result in higher mobilityratios.
Some heterogeneity is acceptable but avoidextensive fractures.
Challenges Poor compatibility between the injected water
and reservoir may cause formation damage
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Screening Parameters
Gravity >25API
Viscosity 10% mobile oil
Formation type sandstone/carbonate
Net thickness not critical
Average permeability not critical Transmissibility not critical
Depth not critical
Temperature not critical
Waterflooding
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Chemical oil recovery methods
To increase ultimate oil production beyondthat achievable with primary and secondarymethods, there are a few steps to undertake.
First, an improvement of the sweep efficiencymust ensue. This is then followed byareduction of the amount of residual oil in theswept zone. Thirdly, there must be an
increase in the displacement efficiency. Andfinally, there must be a reduction in theviscosity of thick oils.
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Surfactant / Polymer Flooding
Description
Surfactant / polymer flooding consists of injecting
slug that contains water, surfactant, electrolyte (salt),
usually a co-solvent (alcohol), followed by polymer-thickened water.
Mechanisms that Improve Recovery Efficiency
Interfacial tension reduction (improves displacement
sweep efficiency). Mobility control (improves volumetric sweep efficiency).
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Surfactant / Polymer Flooding
Limitations
An areal sweep of more than 50% for
waterflood is desired.
Relatively homogeneous formation.
High amounts of anhydrite, gypsum, or clays
are undesirable.
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Surfactant / Polymer Flooding
Challenges
Complex and expensive system.
Possibility of chromatographic separation of
chemicals. High adsorption of surfactant.
Interactions between surfactant and polymer.
Degradation of chemicals at high temperature.
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Screening Parameters
Gravity >25API
Viscosity 20% PV
Formation type sandstone
Net thickness >10 ft
Average permeability > 20 md
Transmissibility not critical Depth
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Polymer Flooding
Description
Polymer augmented waterflooding consists of adding
water soluble polymers to the water before it is
injected into the reservoir.
Mechanisms that Improve Recovery Efficiency
Mobility control (improves volumetric sweep
efficiency).
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Polymer Flooding
Limitations
High oil viscosities require a higher polymer
concentration.
Results are normally better if the polymer flood isstarted before the water-oil ratio becomes
excessively high.
Clays increase polymer adsorption.
Some heterogeneity is acceptable, but avoidextensive fractures.
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Polymer Flooding
Challenges
Lower injectivity than with water can
adversely affect oil production rates in the
early stages of the polymer flood.
Xanthan gum polymers cost more, are subject
to microbial degradation, and have a greater
potential for wellbore plugging.
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Miscible Gas Flooding
(CO2Injection)
Description
CO2flooding consists of injecting large quantities ofCO2(15% or more hydrocarbon pore volumes) in thereservoir to form a miscible flood.
Mechanisms that Improve Recovery Efficiency
Components from the oil, and, if the pressure is high
enough, develops miscibility to displace oil from thereservoir.
Viscosity reduction / oil swelling.
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Miscible Gas Flooding
(CO2Injection)
Limitations
Very low viscosity of CO2results in poor
mobility control.
Availability of CO2
Surface facilities
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Miscible Gas Flooding
(CO2Injection)Challenges
Early breakthrough of CO2causes problems.
Corrosion in the producing wells.
The necessity of separating CO2from saleablehydrocarbons. Repressuring of CO2forrecycling.
A large requirement of CO2
per incrementalbarrel produced.
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Miscible Gas Flooding
(Hydrocarbon Injection)
Description
Hydrocarbon gas flooding consists of injecting light
hydrocarbons through the reservoir to form amiscible flood.
Mechanisms that Improve Recovery Efficiency
Viscosity reduction / oil swelling / condensing orvaporizing gas drive.
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Miscible Gas Flooding
(Hydrocarbon Injection)
Limitations
Minimum depth is set by the pressure needed to
maintain the generated miscibility. The required
pressure ranges from about 1,200-5000 psi for thehigh pressure Gas Drive, depending on the oil.
A steeply dipping formation is very desirable-
permits gravity stabilization of the displacement that
normally has an unfavorable mobility ratio.
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Miscible Gas Flooding
(Hydrocarbon Injection)
Challenges
Viscous fingering results in poor vertical and
horizontal sweep efficiency.
Large quantities of expensive products are
required.
Solvent may be trapped and not recovered.
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Nitrogen / Flue Gas Flooding
Description
Nitrogen or flue gas injection consists of injectinglarge quantities of gas that may be miscible orimmiscible depending on the pressure and oil
composition. Large volumes may be injected, because of the low
cost.
Nitrogen or flue gas are also considered use as
chase gases in the hydrocarbon-miscible and CO2floods.
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Nitrogen / Flue Gas Flooding
Mechanisms that Improve Recovery Efficiency
Vaporizes the lighter components of the crude oil
and generates miscibility if the pressure is highenough.
Provides a gas drive where a significant portion of
the reservoir volume is filled with low-cost gases.
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Nitrogen / Flue Gas Flooding
Limitations
Miscibility can only be achieved with light oilsat high pressures; therefore, deep reservoirsare needed.
A steeply dipping reservoir is desired topermit gravity stabilization of the
displacement, which has a very unfavorablemobility ratio.
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Nitrogen / Flue Gas Flooding
Challenges
Viscous fingering results in poor vertical and
horizontal sweep efficiency.
Flue gas injection can cause corrosion.
Non hydrocarbon gases must be separated
from saleable gas.
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Thermal (Steamflooding)
Description
Steamflooding consists of injecting about
80% quality steam to displace oil.
Normal practice is to precede and
accompany the steam drive by a cyclic
steam simulation of the producing wells
(called Huff and Puff).
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Thermal (Steamflooding)
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Thermal (Steamflooding)
Mechanisms that Improve Recovery Efficiency
Viscosity reduction / steam distillation. Thermal expansion.
Supplies pressure to drive oil to the producing
well.
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Thermal (Steamflooding)
Limitations
Application to viscous oil in massive, highpermeability sandstones or unconsolidated sands.
Oil saturations must be high, and pay zones shouldbe > 20 feet thick to minimize heat losses toadjacent formations.
Steamflooded reservoirs should be as shallow aspossible, because of excessive wellbore heatlosses.
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Thermal (Steamflooding)
More Limitations
Steamflooding is not normally done incarbonate reservoirs.
Since about 1/3 of the additional oil recoveredis consumed to generate the required steam,the cost per incremental barrel of oil is high.
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Thermal (Steamflooding)
More Limitations
A low percentage of water-sensitive clays isdesired for good injectivity.
Challenges
Adverse mobility ratio and channeling ofsteam.
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Thermal (IN SITU COMBUSTION
or "Fireflooding")
This method is sometimes applied to reservoirs
containing oil too viscous or "heavy" to be produced by
conventional means. Burning some of the oil in situ (inplace), creates a combustion zone that moves through
the formation toward production wells, providing a steam
drive and an intense gas drive for the recovery of oil.
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