OIL RESERVOIR DRIVE

MECHANISMS Presented by :

Moklesur Rahman Moupiya Mallick

Natra Kamal HazarikaNayan Jyoti Sabhapandit

Nishal GohainParardha Sabhapandit.

4th SEMESTER, PETROLEUM ENGINEERING, DUIET

INTRODUCTIONEach Reservoir is a unique combination of :

GEOMETRIC FORM

Each Drive Mechanism has typical performance characteristics:

ULTIMATE RECOVERY FACTOR

PRESSURE DECLINE RATE

GAS-OIL RATIO

WATER PRODUCTION

GEOLOGICAL ROCK PROPERTIES

PRIMARY DRIVE MECHANISMS

FLUID CHARACTERISTICS

PRIMARY RECOVERY MECHANISMSThe term refers to the production of hydrocarbons from a

reservoir without the use of any process like fluid injection, to supplement the natural energy of the reservoir.

SIX OIL RESERVOIR DRIVING MECHANISMS:

ROCK & LIQUID EXPANSION DRIVE

DEPLETION DRIVE

GAS-CAP DRIVE

WATER DRIVE

GRAVITY DRAINAGE DRIVE

COMBINATION DRIVE

It exists in under saturated oil reservoir (i.e. Pr >Pb )

The only materials present in an under saturated oil reservoir are-* Crude oil * Connate water* Rock

As the reservoir pressure declines, the rock and fluids expand due to their individual compressibilities.

The reservoir rock compressibility is the result of two factors:

• Expansion of the individual rock grains • Formation compaction

ROCK AND LIQUID EXPANSION DRIVE

FLUIDS

ROCKS

ROCKS

ROCKS

ROCKS

ROCKS

ROCKS

WELLBORE

WELLBORE

WELLBORE

Res. Pr Decreases Rocks Expand Pore Volume Reduces Fluids force out of the pore space to the wellbore

PERFORMANCE CHARACTERISTICS

RESERVOIR PRESSURE :

GAS-OIL RATIO:

WATER PRODUCTION :

RECOVERY

EFFICIENCY:

DECLINE RAPIDLY & CONTINUOSLY

REMAINS LOW & CONSTANT

NIL

1 - 10 %, Average 3 %

DEPLETION DRIVE MECHANISM :

Also known as :

SOLUTION GAS DRIVE,DISSOLVED GAS DRIVE & INTERNAL GAS DRIVE

Principal source of energy Gas liberation from the crude oil & the subsequent expansion of the solution gas as the reservoir pressure is reduced.

Production data of a depletion drive

PERFORMANCE CHARACTERISTICS :

RESERVOIR PRESSURE :

GAS-OIL RATIO :

WATER PRODUCTION :

RECOVERY EFFICIENCY :

DECLINE RAPIDLY & CONTINUOSLY

FIRST LOW, THEN RISES TO MAXIMUM & THEN DROPS

NIL

5 - 35 %, Average 20 %

GAS-CAP DRIVE MECHANISM

It can be identified by the presence of a gas cap with little or no water drive

Due to the ability of the gas cap to expand, these reservoirs are characterized by a slow decline inthe reservoir pressure.

The natural energy available to produce crude oil comes from :

• Expansion of the gas-cap gas• Expansion of the solution gas as it

is liberated

PERFORMANCE CHARACTERISTICS :

DECLINE SLOWLY & CONTINUOSLY

RISES CONTINUOSLY IN UP DIP WELLS

NIL

20-40%, Average 25 %

WATER DRIVE MECHANISM

Many reservoirs are bounded by water bearing rocks called AQUIFERS

The reservoir may be outcropped at one or more places where it may be replenished by surface water as shown in the figure

BOTTOM WATER occurs directly beneath the oil and EDGE WATER occurs off the flanks of the structure at the edge of the oil as illustrated in the figure

WATER DRIVE is the result of water moving into the pore spaces originally occupied by oil, replacing the oil and displacing it to the producing wells

PERFORMANCE CHARACTERISTICS :

REMAINS HIGH & IS SENSITIVE TO THE RATE OF OIL, GAS & WATER PRODUCTION

REMAINS LOW IF THE PRESSURE IS HIGH

DOWN DIP WELLS PRODUCE WATER EARLY & WATER PRODUCTION INCREASES35-80%, Average 50 %

GRAVITY DRAINAGE DRIVE MECHANISM

This mechanism occurs as a result of difference in densities of the reservoir fluid

The fluids in petroleum reservoirs have all been subjected to the forces of gravity, as evidenced by the relative positions of the fluids, i.e., gas on top, oil underlying the gas and water underlying oil as shown in the figure

If the reservoir fluids are in equilibrium, then the gas-oil & oil-water contacts should be essentially horizontal

PERFORMANCE CHARACTERISTICS :

DECLINES RAPIDLY & CONTINUOSLY

REMAINS HIGH IN UP DIP WELLS & LOW IN DOWN DIP WELLS

ABSENT OR NEGLIGIBLE

40-80%, Average 60 %

In operating a gravity-drainage reservoir, it is essential that the oil saturation in the vicinity of the wellbore must be maintained as high as possible

There are two basic reasons for this requirement :

• A high oil saturation means a higher oil flow rate• A high oil saturation means a lower gas flow rate

In order to have maximum conservation of the reservoir gas in a gravity-drainage mechanism, wells should be located as structurally low as possible

COMBINATION DRIVE MECHANISM

This drive mechanism is most commonly encountered where both water & free gas are available in some degree to displace the oil towards the producing wells

Here, two combinations of driving force can be present :

• Depletion drive & a weak Water drive

• Depletion drive with a small gas cap & a weak Water drive

PERFORMANCE CHARACTERISTICS :

DECLINE RAPIDLY

REMAINS LOW IN DOWN DIP WELLS

NEGLIGIBLE

DEPLETION DRIVE < % < WATER DRIVE

CHARACTERISTIC COMPARISON TABLE

SL.

NO.

DRIVE

MECHANISMS

CHARACTERISTICS RESRVOIR PRESSURE

GAS-OIL RATIO

WATER PRODUCTION

RECOVERY EFFICIENCY

1. Rock and liquid expansion

Decline rapidly &

continuously

Remains low & constant

Nil

1-10% Average 3%

2.

Depletion

drive

Decline rapidly &

continuously

First low, then rises to maximum & then

drops

Nil

5-35% Average 20%

3.

Gas-cap drive

Decline slowly &

continuously

Rises continuously in up dip wells

Nil

20-40% Average 25%

4.

Water drive

Remains high & is sensitive to the rate of

oil, gas & water

production

Remains low if the pressure is high

Down dip wells produce water early & water

production increases

35-80% Average 50%

5. Gravity

drainage drive

Decline rapidly &

continuously

Remains high in up dip wells & low in

down dip wells

Absent or Negligible

40-80% Average 60%

6.

Combination drive

Decline rapidly Remains low in down dip wells

Negligible

Greater than Depletion drive & less than Water

drive

CONCLUSION

After studying the six driving mechanisms under primary recovery, it is clear that each drive mechanism has typical performance characteristics in terms of Ultimate Oil Recovery, Pressure decline rate, Gas-oil ratio and Water production. These driving mechanisms provide the natural energy necessary for recovery of the oil from the reservoir and without the use of any external processes like fluid injection etc..

SOURCES & REFERENCES

Reservoir Engineering Handbook by Tarek Ahmed

INTERNET

OUR SPECIAL THANKS TO :

Master Pranjit Borah, 4th semester, Petroleum Engineering, DUIET

Master Manas Kalita, 4th semester, Electronics & Communication Engineering, DUIET

Master Jyotirmoy Sharma, 2nd semester, Mechanical Engineering, DUIET