Water Flooding A-Z Reservoir Life Cycle Infill Drilling Water Flooding A-Z Waterflooding increases...
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1 Water Flooding A-Z Describing Waterflooding 2 Water Flooding A-Z Objectives Definition Objectives Candidates Patterns Oil, water, and gas saturations Fractional flow Performance measures Practices and problems Reservoir monitoring 3 Water Flooding A-Z Reservoir Life Cycle 4 Water Flooding A-Z Infill Drilling
Transcript of Water Flooding A-Z Reservoir Life Cycle Infill Drilling Water Flooding A-Z Waterflooding increases...
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Water Flooding A-Z
Describing Waterflooding
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Objectives
Definition Objectives Candidates Patterns Oil, water, and gas saturations Fractional flow Performance measures Practices and problems Reservoir monitoring
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Reservoir Life Cycle
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Infill Drilling
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Infill Drilling
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Waterflooding
Injection of water into a reservoir• Increases reservoir energy• Sweeps oil towards producing wells
Most widely applied secondary recovery method
Accounts for about 50% of U.S. oil production
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History of Waterflooding
1865
~ ~
1920 1930 1940 1950 1960 1970 1980 1990
Waterflood projects in Oklahoma and Texas
Widescale waterflood implementation
Infill drilling
Tertiary recovery
* First recorded waterflood in Pennsylvania.
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Goal of Waterflooding
The primary goal of waterflooding is to displace oilwith water in an efficient manner that maximizes theprofitable recovery of oil from a reservoir.
History of Waterflooding
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Waterflooding increases the amount of oil recoveredfrom a reservoir in two ways.
• Pressure maintenance (Maintain high wellproductivity)
• Displacement of oil with water
History of Waterflooding
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Reasons for Water Injection
Pressure Maintenance
Maintain pressure above the bubble point to prevent:1. Gas breakout which reduce shrinkage factor andmaintain oil of low viscosity2. Relative permeability: Gas saturation increases3. IPR?
Water Drive
Push water towards the production wells, usually donewhen peripheral wells cease to be productive Shift waterfrom low permeability regions
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Pressure Maintenance
Oil
Sealing Fault
Water Treatment Plant
ProductionWell
WaterInjection
Gas
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Displace Oil With Water
Use injector producer patterns to sweep oil from thereservoir.
• Primary recovery not very efficient.
• Waterflooding yields additional production.
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Primary Drive Mechanisms
Most applicable:• Solution-gas drive• Gas-cap drive• Weak water drive
Not applicable• Strong water drive
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Primary Drive Mechanisms• Solution-gas drive reservoirs are some of the best
candidates for waterflooding.• Gas-cap drives benefit from waterflooding but require
careful attention to prevent 1) water injection losses into the gas cap2) oil being pushed up into the gas cap.
• A weak water drive that cannot maintain reservoir pressure can be supplemented by water injection.
• Strong water drive reservoirs generally do not need any water injection.
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Proposed and Conditions of Gas and Water Injection
Advantage:1- Readily available at low cost (economics)2- Recovery efficiency of the water flood process is
generally high because of the favorable mobility ratio,3- Most reservoir rocks are water wet
Water entry into the smaller pores.Effective permeability to water is lower
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5- Pumping of water to increase injection pressure abovethe hydraulic head is relatively inexpensive.
6- Water formation volume factor is about one. Hence,volume of water required to replace reservoir voidageis relative low.
7- Spreads well throughout the formation
Proposed and Conditions of Gas and Water Injection
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Disadvantages:1- Scaling in wellbores and facilities due to water
incompatibility.2- Injection well plugging due to suspended solids and
entrapped oil.3- Corrosion in wellbores and surface facilities.4- Production, handling, separation, and disposal of
produced water.
Proposed and Conditions of Gas and Water Injection
A typical water flood projectThe essential components of a water flood project, described below:1- Water source and its treatment
sufficiency, treatment, compatibility, transport to the injectors2- Water injectors
Pressure rating, mechanical integrity, injector/reservoir connectivity,3- Reservoir
Reservoir characteristics, fluid distribution and saturations, and reservoir/producer connectivity.
4- ProducersPressure rating, mechanical integrity, Reservoir monitoring
5- Water oil separation / water conditioning plantsSize, efficiency of oil separation, efficiency of disposal water conditioning
6- Disposal wellsAquifer or reservoir characteristics, injection pressure rating, and safety / environmental related concerns. 20
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A Typical Water Flood Project
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Source WatersSeawater3.5% salinity pH 8.2 – 8.4 Oxygen saturatedHigh in bacteria
Aquifer WaterSalinity from 1,000 to 300,000 ppmMay contain carbon dioxide and/or hydrogen sulphidepH acidicOxygen freeFree of bacteria (usually)
Produced WaterWill need to be supplemented for pressure maintenanceMay contain carbon dioxide and/or hydrogen sulphidepH acidicOxygen free
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Main Sources of Injection Water
1- Shallow aquifers, particularly if their waters cannot be used fordomestic or agricultural consumption- Amounts of dissolved salts
i. Formation finesii. Precipitation productsiii. Corrosion productsiv. Bacteria / algae products
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Main Sources of Injection Water
2- Surface water from a lake, river, or sea- Amounts of dissolved salts- Amount of dissolved gases
i. Oxygenii. Carbon dioxideiii. Hydrogen sulfide
- Quantity and nature of suspended solids
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Injection Water
3- Produced water Amounts of oil in suspension & dissolved solids
Water quality requirements for injection are:1- Compatibility with reservoir rock & formation water2- Least corrosive to injector / producer / facilities.3- Environment friendly.
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A Typical Water Flood Project
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Crude Oil Dehydration Emulsion Stability caused by
• Presence of solids• High viscosity crude• Presence of surface active chemicals• High shear forces• Small volumes of dispersed phase
Emulsions resolved by• High temperature• Electrostatic fields• Use of chemical demulsifier
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Difficult Emulsions
High viscosity High solids content (inc. corrosion product) Low pH Waxy
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Produced Water ManagementDisposal Options To Sea
• Environmental restraints - Water quality To Producing Reservoir
• Compatibility - Water quality - Treating/fracturing• Long term effects
To Water Aquifer• Compatibility - Water quality - Long term effects• Effect on shallow water aquifers
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Produced Water Management
Produced water in a waterflooding project comes fromtwo sources:
1. 'DESIRABLE' water - it flows through the reservoir whilepushing or dragging oil with it. It increases continuouslyas the flood progresses.
2. 'UNDESIRABLE' water - it moves through the reservoirwithout pushing or dragging oil with it. It also increasescontinually with the maturity of the flood.
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The project economics will warrant reducing cost ofwater production.
One must make an effort to reduce if not totallyeliminate the 'undesirable' water.
Also, an effort must be made to reduce the 'desirable'water. Mobility Ratio
Produced Water Management
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1. High cost of injection.2. High cost of production - reducing well rate due to
increasing flowing bottom hole pressure, scaling,corrosion, facilities modification for oil-waterseparation and water disposal.
3. Environmental concerns
Produced Water Management
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The first requirement for' water management is theidentification of the nature of water produced and itspossible cause's.
The success of the remedial action will depend upon itscorrect identification and the choice of the rightcorrective procedure.
Produced Water Management
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Typical Water Quality Criteria
Oil content Oil characteristics Dissolved chemicals Suspended solids Scaling propensity Asphaltenes
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Treatment of Water for Waterflooding
Bacteria Check the compatibility with the formation rock Quantity
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pH of Natural Waters
Alkaline soil run off 10 Seawater 8 - 9 River water 7 Rain water 6 Peat and organic waters 4 Mine waters 3 Mineral springs 1 - 2
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Waterflood Performance Measurements
Economic success of a waterflood project depends onthe additional recovery obtained.
The cost of the water, injection wells, and surfacetreatment facilities must be less than the value of theadditional oil recovered.
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Waterflood Performance Measurements
Before an economic evaluation can be made, thereservoir engineer must predict the followingwaterflood performance indicators.• Oil Production Rate (STB/day)• Water Injection Rate (STB/day)• Water-Oil Production Ratio (STB/STB)
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Water Flood Planning in an Economic Perspective
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Optimum Timing for a Water Flood
As a rule of thumb, a water flood project is initiated at atime prior to reservoir declining to a level of 10-200 psihigher that the saturation pressure.
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Key Questions in Designing a Water Flood
1- What does the reservoir look like?
• External configuration.
• Internal continuity of pore space and layers.
2- Natural water drive?
• Aquifer type, shape, size and continuity.
• Aquifer strength.
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Key Questions in Designing a Water Flood
3- Is the reservoir floodable with water?
• Current oil saturation & distribution.
• Oil and water viscosity and mobility ratio.
• Optimum timing for flood.
• Need of a pilot – when & where.
• Development plan
- Well pattern – peripheral or in-field.
- Well locations
- Well completion philosophy.
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4- How much incremental oil?• Oil, water and gas production rates profile.• Profitability
5- Other pertinent matters?• Facilities modification & additional facilities.• Performance concerns.• Risk mitigation plans.• Water handling and disposal.
Key Questions in Designing a Water Flood
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• Sweep monitoring program.• Flood optimization plan.• Enhance oil recovery (EOR) scheme.• Current pressure.• Production oil only or oil+water+gas.• Water source.
Key Questions in Designing a Water Flood
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Water Injection to Sweep Oil
Five - spot
Production wellInjection wellFuture inj. well
Injector/producer patterns sweep oil from injectors to producers more effectively as they increase reservoir pressure.
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Pattern Configurations
Waterflooding patterns are characterized by theconfiguration of the injection and production wells.
Several basic flood patterns will be presented in thissection.
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Peripheral or Repeating Pattern Flood
Two basic types: peripheral and repeating patternflooding.
The reservoir engineer must decide which toimplement.
The reservoir boundaries & physical rock characteristicshelp to determine which flooding approach is mostappropriate.
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Peripheral or Repeating Pattern Flood
A narrow, long reservoir may perform better ifwaterflooded from end to end. This is especially truefor a dipping reservoir where gravity segregation canbe used to assist in the displacement.
A large surface area reservoir is often more suited to aregular spaced repeating geometric pattern ofinjection and production wells.
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Peripheral Flood
Consists of injecting water into wells along the edge ofthe reservoir
Generally yields maximum oil recovery with minimumof produced water
Due to small number of injection wells in peripheralflood, recovery response will occur after a long timedelay.
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Peripheral Flood
If peripheral waterflood is implemented, when floodfront from injection wells breaks through at productionwells, these wells are often converted to injectionwells.
Oil will continue to be produced from wells ahead offront and overall water rates are kept as low aspossible.
A reservoir that pinches out along edges with lowpermeability and thus low productivity would not be agood edge drive reservoir since the injectors wouldhave low injectivity resulting in poor waterfloodperformance.
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Waterflood Patterns
Peripheral (At the edge or periphery of the reservoir)
Advantages: Better areal sweep, increasedisplacement efficiency, for partial water drivereservoir.
Disadvantage: The response to the water injection islimited to the producers, not respond quickly
Uses: in smaller reservoirs or combination with pattern
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Waterflood Patterns
Pattern (irregular and regular repeating patterns)
Injector/Producer Ratio
Direct & Staggered Line Drive: Ratio is 1/1
4-spot, 5-spot, 7-spot and 9-spot patterns: injector/producer ratio and concept
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Repeating Pattern Flood
Repeating pattern floods use injection-production wellpattern to cover all or part of reservoir.
This pattern is an element of symmetry and has,theoretically, “no flow” boundaries.
The pattern can be studied to determine itsperformance during waterflooding and this informationis used to predict field wide waterflood performance.
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Repeating Pattern Flood
Number of injectors in field developed suing repeatingpatterns is greater than for peripheral developmentplan.
As a result, the response time is shorter due toincreased injection capacity.
Increase injection capacity also results in increasedproduction capacity.
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Basic Flood Patterns
Repeatable flood patterns• Line drive• 4-spot• 5-spot• 7-spot• 9-spot
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Basic Flood Pattern Guidelines
Patterns are often referred to as regular or inverted• Regular patterns have only one production well per
pattern• Inverted patterns have only one injection well per
pattern
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Peripheral Flooding
Injectors
Producers
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Optimum water flood patternPeripheral floodAll injection wells are located at or below the oil watercontact, while all producers are located structurallyhigher locations.
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Pattern floodsWells are drilled to form a repeating pattern. Manypatterns have been used, but the 5-spot and 9-spotpatterns are the most popular.
Optimum Water Flood Pattern
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Line Drive Patterns
Direct Drive Staggered Drive
Injection Well
ProductionWell
No-flowBoundary
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5-Spot Pattern
Injection well
Productionwell
No-flowboundary
• 1 : 1 injector-to-producer ratio • Most common pattern• Uniform well spacing• High sweep efficiency• Regular & inverted 5-spot are identical• Special case of a staggered line drive
with square drilling pattern
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7-Spot Pattern
InvertedNormal
Injection Well
ProductionWell
No-flowBoundary
• Not commonly used due to irregular spacing• If used, inverted pattern preferred - has more production than injection wells• May be used for pilot floods in normal pattern form because it results in good
control of flow during a test flood
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9-Spot Pattern
NormalNine - Spot
InvertedNine - Spot
Injection Well
ProductionWell
No-flowBoundary
• Second most common pattern used in waterflooding • In inverted patterns, the difference in distance of the corner wells and the side wells from the
injector causes difficulties with breakthrough as corner wells see less fluid from the injector.• Inverted pattern preferred - more production than injection wells • Uniform well spacing developed from square drilling pattern• Good sweep
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5-Spot 4-S pot 9-Spot
Direct Line Drive 7-S pot
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Factors in Pattern Selection
Current well locations Fracture azimuths Permeability anisotropy Field geometry Injectivity Infill drilling plans Casing integrity of conversion injection candidates Adjacent lease considerations
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Factors Affecting Pattern Selection
Following criteria, presented by Craig, are commonlyused.• Provide desired oil production rate• Provide sufficient water injection capacity to yield
desired oil production rate• Maximize oil recovery with minimum water
production
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Factors Affecting Pattern Selection
Following criteria, presented by Craig, are commonlyused.• Take advantage of reservoir non-uniformities such
as fractures, permeability trends, dip, etc.• Be compatible with existing well pattern and
require a minimum of new wells• Be compatible with flooding operations on adjacent
leases
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Factors Affecting Pattern Selection
Comparison of the economics of possible floodingschemes is used to determine final selection ofspacing, pattern type and orientation of the pattern.
Waterflooding is a secondary recovery process.Pattern selection is often controlled by well locationsthat result from primary field development. The costof drilling new wells frequently dictates that existingwells be used and that few if any additional wells bedrilled.
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Factors Affecting Pattern Selection
In order to prevent early breakthrough due to waterchanneling from injection to production wells, the lineconnecting adjacent injectors should be made parallelto the direction of maximum permeability or fracturetrend.
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Physical Restrictions:
Geographical Directional Permeability Directional Fractures Existing Wells Reservoir Geometry
Factors Affecting Pattern Selection
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Legal Considerations:
Minimum Spacing
Adjacent Leases
Factors Affecting Pattern Selection
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Process Considerations:
Injection Rate Response Time Production Rate Mobility Ratio Flood Life
Factors Affecting Pattern Selection
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Economic Considerations:
Cost Revenue Rate of Return
Factors Affecting Pattern Selection
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Design Aspects
1. Design Process2. (Quality- Compatibility-Recycling of Produced Water)3. Water Injection Rate Volume Requirements4. Optimum Timing5. Optimum Pressure Level6. Fluid Saturation at Start of WF7. Residual Oil Saturation at End of WF
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8. Optimum Well Pattern9. Injection Philosophy10.Injection Well Requirement11.A Pilot Project12.Surface Facilities13.Generalized Response to a Typical WF
Design Aspects
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Conceptual Planning
Data gatheringLocation of the field (offshore, onshore)Field terrain and accessibilityShape of the reservoirVolumes of in place hydrocarbonsi- Initially and at present.ii- Oil, gas and water saturations and their
distributions
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Conceptual Planning
Reservoir characterizationi- Rock and fluid propertiesii- Vertical and areal variationsiii- Zonal continuity, fractures and faultsiv- Formation dipv- directional permeabilityvi- Gas cap & aquifer: size and connectivity
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1- Conceptual Planning
Previous reservoir development
i- Number and type of wells.
ii- Well productivity and completions
iii- Location of wells
iv- Gathering and separation facilities
v- Production practices – natural flow or lift.
vi- Production history – oil, gas and water.
vii- Problems – reservoir, environment and well related.
viii- Studies – development and economics related
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2- Preliminary Designs
These designs will provide most of the followinginformation:
1- Phase or full development2- Project life3- Initial oil rate (decline rate considerations)4- Production rate forecasts5- Water injection rate6- Waterflood lay-out and well spacing7- Sources of injection water
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2- Preliminary Designs
8- Disposal of produced water9- Preliminary facilities design10- CAPEX and OPEX estimates11- Economic analysis13- Risk and mitigation plans14- Reservoir / well monitoring programs15- Logistics and infra structure16- Additional data requirement
