eor screening
TRANSCRIPT
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EOR Screening
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Learning Objectives
Describe the main methods which can be usedto improve reservoir recovery efficiency.
For each method, state whether it can improve
displacement, vertical or areal sweep efficiencyand explain how it works.
Describe screening criteria for enhanced oilrecovery methods.
Use a systematic decision analysis approach forselecting an alternative to improve reservoirrecovery efficiency.
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1. The goal of any enhanced oil recovery process is to
mobilize "remaining" oil. This is achieved by enhancing oildisplacement and volumetric sweep efficiencies. Oil displacement efficiency is improved by reducing oil
viscosity (e.g., thermal floods) or by reducing capillary
forces or interfacial tension (e.g., miscible floods). Volumetric sweep efficiency is improved by developing
a more favorable mobility ratio between the injectantand the remaining oil-in-place (e.g., polymer floods,water-alternating-gas processes).
2. It is important to identify remaining oil and the mechanismsthat are necessary to improve recovery prior toimplementing an EOR process.
Goal of EOR Techniques
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Fig.1-2. EOR methods
EOR Methods
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CLASSIFICATION OF ENHANCED RECOVERY BY THEMACN MECHANISM OF OIL DISPLACEMENT
Solvent Extraction or Miscible-Type Processes Hydrocarbon Miscible Methods
Carbon Dioxide Flooding
Nitrogen and Flue Gas
Alcohol Flooding or other Liqufied Solvent Flooding
Solvent Extraction of Mined, Oil-Bearing Ore
Interfacial Tension Reduction Processes Surfactant Flooding
Surfactant/Polymer (Micellar) Flooding (sometime including miscible-typeflooding above)
Alkaline Flooding
Viscosity reduction (of oil) or viscosity increase (of driving fluid) Steam Flooding
Fire Flooding
Polymer Flooding
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Chemical EOR Methods
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Polymer Flooding
Description
Polymer augmented waterflooding consists of adding watersoluble polymers to the water before it is injected into thereservoir.
Mechanisms That Improve Recovery Efficiency:
Increasing the viscosity of water.Decreasing the mobility of water.
Contacting a larger volume of the reservoir.
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Polymer Flooding Limitations:
High oil viscosities require a higher polymer concentration. Results are normally better if the polymer flood is started before the
water-oil ratio becomes excessively high.
Clays increase polymer adsorption.
Some heterogeneity is acceptable, but avoid extensive fractures. If
fractures are present, the crosslinked or gelled polymer techniquesmay be applicable.
Challenges: Lower injectivity than with water can adversely affect oil production
rates in early stages of polymer flood Acrylamide-type polymers loose viscosity due to sheer degradation,
or it increases in salinity & divalent ions
Xanthan gum polymers cost more, are subject to microbialdegradation, & have greater potential for wellbore plugging
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Polymer Flooding Screening parameters
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DescriptionSurfactant / polymer flooding consists of injecting a slug that
contains water, surfactant, electrolyte (salt), usually a co-solvent
(alcohol), and possibly a hydrocarbon (oil), followed by polymer-
thickened water.
Mechanisms That Improve Recovery Efficiency
Lowering the Interfacial tension between oil and water.
Solubilization of oil.
Emulsification of oil and water.
Mobility enhancement.
Surfactant/Polymer Flooding
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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.
Limitations: An areal sweep of more than 5O% for waterflood is desired.
Relatively homogeneous formation is preferred.
High amounts of anhydrite, gypsum, or clays are undesirable.Available systems provide optimum behavior within a narrow setof conditions.
With commercially available surfactants, formation water chloridesshould be < 20,000 ppm and divalent ions (Ca++ and Mg++) < 500ppm.
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Surfactant/Polymer Flooding Screening parameters
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Alkaline Flooding
Description Best result are obtained if the alkaline material reacts with the crude oil; the oil
should have an acid number of more that 0.2 mg KOH/g of oil. The interfacial tension between the alkaline solution and the crude oil should be
less than 0.001 dyne/cm. At high temperatures and in some chemicals environments, excessive amounts
of alkaline chemicals may be consumed by reaction with clays, mineral or silicain the sandstone reservoir
Carbonates are ussualy avoided because they often contain anhydrite orgypsum, which interact adversely with the caustic chemical.
Mechanisms That Improve Recovery Efficiency A reduction of interfacial tension resulting from produced surfactants. Changing wettability from oil-wet to water-wet.
Changing wettability from water wet to oil-wet. Emulsification and entrainment of oil. Emulsification and entrapment of oil to aid mobility control. Solubilization of rigid oil films at oil-water interfaces
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Alkaline Flooding
Limitations
Alkaline or caustic flooding involves the injection ofchemical such as sodium hydroxide, sodium silicate,
or sodium carbonate. These chemicals react withorganic petroleum acids in certain crudes to createsurfactants in situ and also react with reservoir rock tochange wettability.
Challenges Scaling and plugging in the producing wells. High caustic consumption.
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Alkaline Flooding Screening parameters
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Gas Floodings
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Miscible Gas Flooding (CO2 Injection)
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Miscible Gas Flooding (CO2 Injection)
Description
CO2 flooding consists of injecting large quantities ofCO2 (15% or more hydrocarbon pore volumes) in thereservoir to form a miscible flood.
EOR Mechanisms
CO2 extracts the light-to-intermediate components fromthe oil, and, if the pressure is high enough, developsmiscibility to displace oil from the reservoir (vaporizinggas drive).
Viscosity reduction / oil swelling.
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Miscible Gas Flooding (CO2 Injection)
Limitations
Very low Viscosity of CO2 results in poor mobilitycontrol.
Availability of CO2 Challenges
Early breakthrough of CO2 causes problems.
Corrosion in producing wells.
The necessity of separating CO2 from saleablehydrocarbons. Repressuring of CO2 for recycling.
A large requirement of CO2 per incremental barrelproduced.
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Miscible Gas Flooding (CO2 Injection)
Screening Parameters
Gravity > 27 API
Viscosity 30% PV Formation type sandstone/carbonate
Net thickness relatively thin
Average permeability not critical
Transmissibility not critical
Depth > 2,300 feet
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HYDROCARBON MISCIBLE FLOODING
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HYDROCARBON MISCIBLE FLOODING
Limitations
Minimum depth is set by the pressure needed tomaintain the generated miscibility. The
required pressure ranges from about 1,200 psi for theLPG process to 3,000-5,000 psi for the High PressureGas Drive, depending on the oil.
Challenges
Viscous fingering results in poor vertical andhorizontal sweep efficiency.
Large quantities of expensive products are required.
Solvent may be trapped and not recovered.
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HYDROCARBON MISCIBLE FLOODING
Screening Parameters
Gravity >27 API
Viscosity 30% PV Formation type sandstone/carbonate
Net thickness relatively thin
Average permeability not critical
Transmissibility not critical Depth >2,000 feet (LPG)
>5,000 feet (lean gas)
Temperature
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NITROGEN ANO FLUE GAS FLOODING
Description Nitrogen or flue gas injection consists of injecting large 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 for use as chase gases in
hydrocarbonmiscibl and CO2 floods.
Mechanisms that Improve Recovery Efficiency
Vaporizes the lighter components of the crude oil and generatesmiscibility if the pressure is high enough.
Provides a gas drive where a significant portion of the reservoir
volume is filled with lowcos gases.
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NITROGEN ANO FLUE GAS FLOODING
Limitations
Miscibility can only be achieved with light oils at high pressures;therefore, deep
reservoirs are needed.
A steeply dipping reservoir is desired to permit gravitystabilization of the displacement,
which has a very unfavorable mobility ratio.
Challenges
Viscous fingering results in poor vertical and horizontal sweepefficiency.
Flue gas injection can cause corrosion.
Nonhydrocarbon gases must be separated from saleable gas.
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NITROGEN ANO FLUE GAS FLOODING
Screening Parameters Gravity >24 API (35 for nitrogen)
Viscosity 30% PV Formation type sandstone/carbonate
Net thickness relatively thin (not critical for pressure
maintenance)
Average permeability not critical
Transmissibility not critical
Depth >4,500 feet
Temperature not critical
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Thermal (Steamflooding)
Description
Steamflooding consists of injecting 80% qualitysteam to displace oil.
Normal practice is to precede and accompany thesteam drive by a cyclic steam stimulation of theproducing wells (called huff and puff).
EOR Mechanisms
Viscosity reduction / steam distillation.
Supplies pressure to drive oil to the producing well.
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Thermal (Steamflooding) Limitations
Applicable to viscous oils in massive, high permeability sandstones or
unconsolidated sands.
Oil saturations must be high, and pay zones should be > 20 feet thick tominimize heat losses to adjacent formations.
Less viscous crude oils can be steamflooded if they don't respond towater.
Steamflooded reservoirs should be as shallow as possible, because ofexcessive
wellbore heat losses.
Steamflooding is not normally done in carbonate reservoirs.
Since about 1/3 of the additional oil recovered is consumed to generate
the required steam, the cost per incremental barrel of oil is high.
A low percentage of water-sensitive clays is desired for good injectivity.
Challenges
Adverse mobility ratio and channeling of steam.
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Thermal (Steamflooding)
Screening Parameters
Gravity 20 cp (10-5,000 cp)
Composition not critical Oil saturation >500 bbl/acre-ft (>40-50% PV)
Formation type sandstone
Net thickness >20 feet
Average permeability >200 md Transmissibility >100 md ft / cp
Depth >200-5,000 feet
Temperature not critical
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Cost of EOR
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Cost of Chemicals
As the oil prices rise, so does the cost of chemicals,but not in the same proportion
Typical Costs:
Polymer - $3/lb Surfactant - $1.20/lb
Caustic - $0.60/lb
Isopropanol - $20/gallon
Micellar slug - $25/bbl
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EOR Recovery Processes
Typical
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EOR Recovery Processes
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Estimated Cost of a Barrel of EOR Injectant
Taber, 1990
EOR S i C it i
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EOR Screening Criteria
EOR S i
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EOR Screening
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Chemical Floods Worldwide
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Incremental Oil
Recovery Evaluation
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Incremental Oil Recovery (IOR)
Oil (HC) produced in excess ofexisting (conventional) operations
Difficulties.
Comingled productionOil from outside project
Inaccurate decline estimates
IOR recovery efficiency = 100 IOROOIP
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Decline Curve Analysis
a 1qdqdt[]time1Decline rate:
Np q()d0tCumulativeoil produced:
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Decline Curve Analysis
Decline rate:
Decline rate
types:
a ai qqi
b
b 0 Exponential0 b 1 Hyperbolic1 Harmonic
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Decline Curve Analysis
Exponential decline:
Rate-time
q qieat
q qi aNp Rate-cumulative
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Rate-Time...
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Rate-Cumulative...
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Accelerated Production...
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Increased Mobile Oil...
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Deaccelerated Production...
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Accelerated Production...
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IOR Example