water flooding m.tech

8/19/2019 Water Flooding M.tech

1/65

T. SANTHOSHINI PRIYAENHANCED OIL RECOVERY

ANNA UNIVERISTY


2/65

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


3/65



4/65

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



5/65

WHY WATERFLOODING?

Most widely used fluid injection process

It’s a “mature” technology

Water availability is generally good

Proven method to increase oil recovery



6/65

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.



7/65

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



8/65

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


9/65

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.



10/65

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.



11/65

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



12/65

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



13/65

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.



14/65

PERIPHERAL INJECTION PATTERNS


The injection wells

are located at the

external boundary of

the reservoir and the

oil is displaced

toward the interior of the reservoir.


15/65

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.



16/65

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


17/65

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



18/65

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



19/65

FIVE SPOT

Special case of staggered

line, i.e., a=2d



20/65

SEVEN SPOTThe injection wells are located at the corner of a hexagon with

a production well at its centre



21/65

NINE SPOT

Similar to five spot but with an extra injection well drilled at

the middle of each side of the square



22/65

REGULAR

INJECTION

PATTERNS



23/65

RECOVERY EFFICIENCY



24/65

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


25/65

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


26/65

OVERALL RECOVERY EFFICIENCY- AREAL SWEEP

EFFICIENCY

Fluid mobilities

Pattern type

Areal heterogeneity

Total volume of fluid injected



27/65

OVERALL RECOVERY EFFICIENCY- VERTICAL

SWEEP EFFICIENCY

Vertical heterogeneity

Degree of gravity segregation

Fluid mobilities

Total volume injection



28/65

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



29/65

DISPLACEMENT EFFICIENCY

Mathematically, the displacement efficiency is expressed as:



30/65



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


31/65


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



32/65

DISPLACEMENT EFFICIENCYThe displacement efficiency ED can be expressed

more conveniently in terms of water saturation by

substituting the above relationships into



33/65


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



34/65


The displacement efficiency ED will continually increase at

different stages of the flood, i.e., with increasing Sw.



35/65



36/65

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)



37/65

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.



38/65

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.



39/65

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



40/65

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)



41/65

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.



42/65

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.



43/65

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.



44/65

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



45/65

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.



46/65

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.



47/65

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.



48/65

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.



49/65

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.



50/65

MOBILITY RATIO



51/65



52/65

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


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


53/65

MOBILITY RATIO


Substituting for λ :


54/65

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


FACTORS TO DETERMINE THE RESERVOIR


55/65

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.



56/65

FLOOD PATTERNS



57/65

Stages of

water

flooding.



58/65

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


59/65

CHEMICAL AND PHYSICAL PROPERTIES OF

OILFIELD WATERAnalyzed for various chemical and physical properties.

Most oilfield water contains organic and inorganic compounds.


Inorganicconstituents

Cations

Anions

Physicalproperties

Dissolvedgases

Stableisotopes

Organicconstituents


60/65

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



61/65

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.



62/65

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.



63/65

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.



64/65

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.



65/65

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.

water flooding m.tech

Documents