Eor Course 2012 Lecture#2 Eor Methods

7/27/2019 Eor Course 2012 Lecture#2 Eor Methods

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ENHANCED OIL RECOVERY

PE 510

DR. MOHAMED EL-HOUNI

FALL 2013

E O R

M E T H O D S



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





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)



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



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.



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



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



Screening Parameters

Gravity >25ºAPI

Viscosity <30cp

Composition not critical

Oil saturation >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



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 by areduction 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.



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.


Interfacial tension reduction (improves displacement

sweep efficiency). Mobility control (improves volumetric sweep efficiency).




Limitations

An areal sweep of more than 50% for

waterflood is desired.

Relatively homogeneous formation.

High amounts of anhydrite, gypsum, or clays

are undesirable.




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.



Screening Parameters

Gravity >25ºAPI

Viscosity <20cp

Composition light intermediate Oil saturation >20% PV

Formation type sandstone

Net thickness >10 ft

Average permeability > 20 md

Transmissibility not critical Depth <8000 ft

Temperature 225 ºF

Salinity of formation brine <150,000 ppm TDS




Polymer Flooding

Description

Polymer augmented waterflooding consists of adding

water soluble polymers to the water before it is

injected into the reservoir.


Mobility control (improves volumetric sweep

efficiency).





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.



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.



Miscible Gas Flooding

(CO2 Injection)

Description

CO2 flooding consists of injecting large quantities of CO2 (15% or more hydrocarbon pore volumes) in thereservoir to form a miscible flood.


Components from the oil, and, if the pressure is high

enough, develops miscibility to displace oil from thereservoir.

Viscosity reduction / oil swelling.






(CO2 Injection)

Limitations

Very low viscosity of CO2 results in poor

mobility control.

Availability of CO2

Surface facilities




(CO2 Injection)Challenges

Early breakthrough of CO2 causes problems.

Corrosion in the producing wells.

The necessity of separating CO2 from saleablehydrocarbons. Repressuring of CO2 for recycling.

A large requirement of CO2

per incrementalbarrel produced.




(Hydrocarbon Injection)

Description

Hydrocarbon gas flooding consists of injecting light

hydrocarbons through the reservoir to form amiscible flood.


Viscosity reduction / oil swelling / condensing or vaporizing gas drive.







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.





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.



Nitrogen / Flue Gas Flooding

Description

Nitrogen or flue gas injection consists of injectinglarge quantities of gas that may be miscible or immiscible 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 CO2 floods.





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.






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.




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.



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).








Viscosity reduction / steam distillation. Thermal expansion.

Supplies pressure to drive oil to the producing

well.




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.




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.




More Limitations

A low percentage of water-sensitive clays isdesired for good injectivity.

Challenges

Adverse mobility ratio and channeling of steam.



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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Eor Course 2012 Lecture#2 Eor Methods

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