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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