water flooding m.tech
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T. SANTHOSHINI PRIYAENHANCED OIL RECOVERY
ANNA UNIVERISTY
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SECONDARY RECOVERY PROCESS
When oil production declines because of the hydrocarbon
production from the formation, the secondary oil recovery
process is employed to increase the pressure required to drive
the oil to production wells.
The mechanism of secondary recovery oil is similar to that of
the primary oil recovery except that more than one well bore is
involved, and the pressure of petroleum reservoir is augmented
or maintained artificially to force oil to the production wells.
Secondary Recovery Process 2
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Secondary Recovery Process 3
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SECONDARY RECOVERY PROCESS
The process includes the appli cation of a vacuum to a well ,
the injection of gas, air, water, and/or aqueous solutions of
caustic and polymer .
The decrease of pressure in the reservoir during primary oil
recovery may be restored partially by injecting a gas into the
reservoir to achieve a high pressure
Secondary Recovery Process 4
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WHY WATERFLOODING?
Most widely used fluid injection process
It’s a “mature” technology
Water availability is generally good
Proven method to increase oil recovery
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WATER FLOODING
Water is injected for two reasons:
1) For pressure support of the reservoir (also known as void age
replacement).
2) To sweep or displace the oil from the reservoir, and push it
towards an oil production well.
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WHEN TO WATER FLOODDefine your objectives
Maximum oil recovery
Highest investment efficiency
Maximize net present value
Minimize risk
Perform economics for various start up times, considering:
Revenue stream (oil & gas)
Injection requirements
Cost of fluid handling & treatment
Cost of facilities
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WATER FLOODING
Water flooding is utilized primarily as a secondary recovery
technique, where the primary drive mechanism used to producethe oil (dissolved gas) is depleted.
The injected water is discharged in the aquifer through several
injection wells surrounding the production well and the
injected water creates a bottom water drive on the oil zone
pushing the oil upwards. Water is recovered from the water
table and injected into the reservoir, displacing the oil towards
the target production wells.
Because of the limited amount of dissolved gas remaining in
solution, pumps are used to bring the oil to surface. 8
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WATER FLOODING
The selection of injection water method depends upon the
mobility rate between the displacing fluid (water) and the
displaced fluid (oil).
The water injection however, has some disadvantages:
Reaction of injected water with the formation water can
cause formation damage.
Corrosion of surface and sub-surface equipment.
Secondary Recovery Process 9
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SELECTION OF FLOODING PATTERNS
The objective is to select the proper pattern that will provide
the injection fluid with the maximum possible contact with
the crude oil system.
This selection can be achieved by
1. Converting existing production wells into injectors.
2. Drilling infill injection wells.
Secondary Recovery Process 10
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TYPES OF WELL ARRANGEMENTS
Essentially four types of well arrangements are used in
fluid injection projects:
Irregular injection patterns
Peripheral injection patterns
Regular injection patterns
Crestal and basal injection patterns
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DISPLACEMENT OF OIL THROUGH RESERVOIR
ROCKS BY WATER FLOODING (FIVE SPOT
PATTERN)
For water flooding the most common pattern of injection and
production wells is a five-spot configuration
Secondary Recovery Process 12
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IRREGULAR INJECTION PATTERNS
Surface or subsurface topology and/or the use of slant-hole
drilling techniques may result in production or injection wells
that are not uniformly located.
Some small reservoirs are developed for primary production
with a limited number of wells and when the economics are
marginal, perhaps only few production wells are converted into
injectors in a non uniform pattern.
Faulting and localized variations in porosity or
permeability may also lead to irregular patterns.
Secondary Recovery Process 13
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PERIPHERAL INJECTION PATTERNS
Secondary Recovery Process 14
The injection wells
are located at the
external boundary of
the reservoir and the
oil is displaced
toward the interior of the reservoir.
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CRESTAL AND BASAL INJECTION PATTERNS
In crestal injection, as thename implies, the injectionis through wells located atthe top of the structure. Gasinjection projects typically
use a crestal injection pattern.
In basal injection, the fluidis injected at the bottom of the structure. Many water-
injection projects use basalinjection patterns withadditional benefits beinggained from gravitysegregation.
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REGULAR INJECTION PATTERNS
Due to the fact that oil leases are divided into square miles and
quarter square miles, fields are developed in a very regular
pattern.
The most common patterns are:
The patterns termed inverted have only one injection well per
pattern. This is the difference between normal and inverted
well arrangements.
(Note: Four spot and inverted seven spot patterns are
identical) Secondary Recovery Process 16
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DIRECT LINE DRIVE The lines of injection and
production are directly
opposed to each other
The pattern is
characterized by two
parameters
a=distance between wellsof the same type
d=distance between lines
of injectors and producers
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STAGGERED LINE DRIVE
The wells are in lines as in
the direct line, but the
injectors and producers are
no longer directly opposed
but laterally displaced by a
distance of a/2
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FIVE SPOT
Special case of staggered
line, i.e., a=2d
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SEVEN SPOTThe injection wells are located at the corner of a hexagon with
a production well at its centre
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NINE SPOT
Similar to five spot but with an extra injection well drilled at
the middle of each side of the square
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REGULAR
INJECTION
PATTERNS
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RECOVERY EFFICIENCY
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OVERALL RECOVERY EFFICIENCYThe overall recovery factor (efficiency) RF of any secondary or
tertiary oil recovery method is the product of a combination of three
individual efficiency factors as given by the following generalized
expression:
R F=ED EA EV NP= NS ED EA EV
Where
RF = Overall recovery factor
NS = Initial oil in place at the start of the flood, STBNP = Cumulative oil produced, STB
ED = Displacement efficiency
EA = Areal sweep efficiency
EV = Vertical sweep efficiencySecondary Recovery Process 24
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OVERALL RECOVERY EFFICIENCY
The areal sweep efficiency EA
Is the fractional area of the
pattern that is swept by the
displacing fluid.
The major factors determining
areal sweep are:
Fluid mobility's
Pattern type
Areal heterogeneity
Total volume of fluid
injected
The vertical sweep efficiency EV
Is the fraction of the vertical
section of the pay zone that iscontacted by injected fluids.
The vertical sweep efficiency
is primarily a function of:
Vertical heterogeneity Degree of gravity
segregation
Fluid mobility's
Total volume injectionSecondary Recovery Process 25
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OVERALL RECOVERY EFFICIENCY- AREAL SWEEP
EFFICIENCY
Fluid mobilities
Pattern type
Areal heterogeneity
Total volume of fluid injected
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OVERALL RECOVERY EFFICIENCY- VERTICAL
SWEEP EFFICIENCY
Vertical heterogeneity
Degree of gravity segregation
Fluid mobilities
Total volume injection
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OVERALL RECOVERY EFFICIENCY-
DISPLACEMENTEFFICIENCY
The displacement efficiency ED is the fraction of movable oil
that has been displaced from the swept zone at any given time
or pore volume injected. Because an immiscible gas injection
or water flood will always leave behind some residual oil, ED
will always be less than 1.0.
All three efficiency factors (i.e., ED, EA, and EV) are variables
that increase during the flood and reach maximum values at
the economic limit of the injection project
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DISPLACEMENT EFFICIENCY
Mathematically, the displacement efficiency is expressed as:
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DISPLACEMENT EFFICIENCY
Secondary Recovery Process 30
Where,
Soi = Initial oil saturation at start of flood
Boi = Oil at start of flood, bbl/STBŜo = Average oil saturation in the flood pattern at a
particular point during the flood
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DISPLACEMENT EFFICIENCY
Assuming a constant oil formation volume factor during the
flood life.
The above equation is reduced to
Where the initial oil saturation is given by
However, in the swept area, the gas saturation is considered
zero, thus
So=1−Sw
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DISPLACEMENT EFFICIENCYThe displacement efficiency ED can be expressed
more conveniently in terms of water saturation by
substituting the above relationships into
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DISPLACEMENT EFFICIENCY
Where,
S W =average water saturation in the swept area
S gi = initial gas saturation at the start of the flood
S wi = initial water saturation at the start of the flood
If no initial gas is present at the start of the flood, Equation is
reduced to
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DISPLACEMENT EFFICIENCY
The displacement efficiency ED will continually increase at
different stages of the flood, i.e., with increasing Sw.
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FACTORS TO CONSIDER IN WATERFLOODING
1. Reservoir Geometry
2. Lithology, Porosity, Permeability
3. Reservoir Depth
4. Continuity of Rock Properties5. Fluid Saturations & Distributions
6. Fluid Properties
7. Relative Permeability
8. Other Considerations
9. Primary Drive Mechanism(s)
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1. RESERVOIR GEOMETRY
The areal geometry of the reservoir will influence the location of
wells and, if offshore, will influence the location and number of
platforms required.
If a water-drive reservoir is classified as an active water drive,
injection may be unnecessary.
Secondary Recovery Process 37
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2. LITHOLOGY AND ROCK PROPERTIES
Reservoir lithology and rock properties that affect flood ability and
success are:
- Porosity - Permeability
- Clay content - Net thickness
The clay minerals present in some sands may clog the pores by
swelling and deflocculating when water flooding is used, no exact data are
available as to the extent to which this may occur.
Tight (low-permeability) reservoirs or reservoirs with thin net thickness
possess water-injection problems in terms of the desired water injection
rate or pressure.
Secondary Recovery Process 38
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3. RESERVOIR DEPTH
Reservoir depth has an important influence on both the technical
and economic aspects of a secondary or tertiary recovery project.
Maximum injection pressure will increase with depth. The costs of
lifting oil from very deep wells will limit the maximum economic
water – oil ratios that can be tolerated, thereby reducing the ultimaterecovery factor and increasing the total project operating costs.
In waterflood operations, there is a critical pressure
(approximately 1 psi/ft of depth) that, if exceeded, permits theinjecting water to expand openings along fractures or to create
fractures
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3. RESERVOIR DEPTH
Drilling costs a function of depth
Dual porosity systems
Temperature gradient
Oil viscosity Vs. temperature
If primary operations were extensive
Fracturing (max. injection pressure vs. depth)
Fracture type (vertical vs. horizontal)
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4. RESERVOIR UNIFORMITY AND PAY
CONTINUITY
Substantial reservoir uniformity is one of the major physical
criterions for successful waterflooding. For example, if the
formation contains a stratum of limited thickness with a veryhigh permeability rapid channeling and bypassing will
develop.
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5. FLUID SATURATIONS In determining the suitability of a reservoir for water flooding,
a high oil saturation that provides a sufficient supply of
recoverable oil is the primary criterion for successful flooding
operations.
Note that higher oil saturation at the beginning of flood
operations increases the oil mobility that, in turn, gives higher
recovery efficiency.
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6. FLUID PROPERTIES
The physical properties of the reservoir fluids have pronounced
effects on the suitability of a given reservoir for further
development by water flooding.
The oil viscosity has the important effect of determining the
mobility ratio that, in turn, controls the sweep efficiency.
Secondary Recovery Process 43
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7. RELATIVE PERMEABILITY
Shape of relative permeability curves impacts oil bank
formation
End point relative permeability to water may impact injectivity
Relative permeability from depletion doesn’t apply to water
flooding
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8. OTHER CONSIDERATIONS
• Pressure.
• Keep average reservoir pressure high for improved well.
• Hydraulics equipment costs are higher for increasing pressures.
• Water floods should always be evaluated; while considering the
project life-cycle with other EOR methods in mind.
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9.PRIMARY RESERVOIR DRIVING
MECHANISMSSix driving mechanisms basically provide the natural energy
necessary for oil recovery:
1. Rock and liquid expansion 2. Solution gas drive 3. Gas
cap drive. 4. Water dri ve 5. Gravity drainage drive 6.
Combination dr ive
The primary drive mechanism and anticipated ultimate oil
recovery should be considered when reviewing possible water
flood prospects.
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9. Primary Reservoir Driving Mechanisms cont.
The approximate oil recovery range is tabulated below for various
driving mechanisms.
Note that these calculations are approximate and, therefore, oil
recovery may fall outside these ranges.
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WATER FLOODAt the scale of field, the main factors governing the efficiency
of a water flood are
The Mobil i ty Ratio,
Reservoir heterogeneity,
Gravity.
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MOBILITY RATIO
Mobility, k/µ, is defined as
permeability of a porous
material to a given phase
divided by the viscosity of that
phase
Mobility ratio, M , is defined as
mobility of the displacing
phase divided by the mobility
of the displaced phase.
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MOBILITY RATIO
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MOBILITY
In general, the mobility of any fluid λ is defined as the ratio of
the effective permeability of the fluid to the fluid viscosity
Secondary Recovery Process 52
where,
λ o, λ w, λ g = mobility of oil, water, and gas, respectively
k o
, k w
, k g
= effective permeability to oil, water, and gas,
respectively
k ro, k rw= relative permeability to oil, water, and gas,
respectively
k = absolute permeability
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MOBILITY RATIO
Secondary Recovery Process 53
Substituting for λ :
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OPTIMUM TIME TO WATERFLOODThe most common procedure for determining the optimum time to start
water flooding is to calculate:
Anticipated oil recovery
Fluid production rates
Monetary investment
Availability and quality of the water supply
Costs of water treatment and pumping equipment
Costs of maintenance and operation of the water installation facilities
Costs of drilling new injection wells or converting existing production
wells into injectors
Secondary Recovery Process 54
FACTORS TO DETERMINE THE RESERVOIR
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FACTORS TO DETERMINE THE RESERVOIR
PRESSURE (OR TIME) TO INITIATE A SECONDARY
RECOVERY PROJECT
Reservoir oil viscosity
Water injection should be initiated when the reservoir
pressure reaches its bubble-point pressure since the oil
viscosity reaches its minimum value at this pressure. The
mobility of the oil will increase with decreasing oil
viscosity, which in turns improves the sweeping efficiency.
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FLOOD PATTERNS
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Stages of
water
flooding.
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OIL FIELD WATERPetroleum formed from the organic matter deposited with the
sediments, migrated from what it is usually called the source
rock into more porous and permeable sedimentary rock
(reservoir rock).
Petroleum, i.e., oil and gas is less denser than water; therefore
it tends to float to the top of a water body regardless whether
the water is on the surface or in the subsurface.
Water associated with the petroleum in subsurface reservoir is
called oilfield water. (i.e., any water associated with a
petroleum deposit). Secondary Recovery Process 58
CHEMICAL AND PHYSICAL PROPERTIES OF
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CHEMICAL AND PHYSICAL PROPERTIES OF
OILFIELD WATERAnalyzed for various chemical and physical properties.
Most oilfield water contains organic and inorganic compounds.
Secondary Recovery Process 59
Inorganicconstituents
Cations
Anions
Physicalproperties
Dissolvedgases
Stableisotopes
Organicconstituents
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OIL FIELD WATER
Must be considered in all Enhanced Oil Recovery Operations
(EOR)
There are seven major EOR techniques
1. Steam injection
2. In-situ combustion
3. Carbon dioxide injection
4. Surfactant- polymer injection
5. Polymer injection
6. Alkaline (caustic) injection
7. Injection of petroleum miscible hydrocarbons
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OIL FIELD WATER Importance of water in EOR technology becomes obvious
when one considers the amount of water necessary to recover
one barrel of oil.
The water quality required may vary from excellent to poor.
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SECONDARY RECOVERY PROCESS –
GAS INJECTION
Gas injection methods can be subdivided into three categories:
1) Pressure restoration
2) Pressure maintenance
3) Gas drive
depending upon the way in which the gas is injected into thereservoir.
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PRESSURE RESTORATION
The gas is injected into productive formation through one well
while the other wells are closed until the pressure is restored
throughout the reservoir.
This may take as long as a year or more.
When the desired reservoir pressure is reached , gas injection is
stopped and all of the wells start producing oil under the
influence of the artificially developed pressure.
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PRESSURE MAINTENANCE METHOD
In this method, gas from producing well is recompressed and
injected into the selected wells before the reservoir pressure is
totally exhausted.
In this method, some wells are operated as injection wells,
whereas others are operated as production wells.
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GAS DRIVE METHOD Gas is injected into the reservoir under pressure and a
continuous gas flow is maintained from injection wells to
producing wells.
The moving gas drives the oil in the form of a film, or gas
bubbles ahead of the gas, toward the producing wells.