3- oil recovery methods

7/29/2019 3- Oil Recovery Methods

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Oil Recovery Methods:

1) Primary Recovery: Oil is transported to the surface by a naturally driving force.Solution gas drive

Gas cap drive

Water drive2) Secondary Recovery: Pressure is maintained by injecting a fluid into the reservoir to

replenish the fluid that is produced.

Water floodingGas flooding

3) Tertiary (enhanced) Recovery: This method uses a chemical-based technique to

produced oil. These methods are often used in conjunction with gas or water flooding.

A) Non-thermalMiscible flooding

Polymer flooding

Surfactant flooding

B) ThermalSteam injection

Steam floodingSteam assisted gravity drainage (SAGD)

In-situ combustion

Primary Recovery: Oil is transported to the surface by a naturally driving

force. There are three primary driving forces:

1) Solution Gas Drive : Oil contains dissolved gases that will be liberated

with the reduction in pressure that occurs with oil production. The gas

fraction increases as oil travels from the reservoir to the well head.

Bouyant forces cause the gas bubbles to rise. Oil is entrained with the

gas phase (gas lift). The oil recovery efficiency with this mechanism is 5

to 30 % of the original oil in place (OOIP).

Rapid decline in reservoir pressure.

Producing GOR(gas oil ratio) starts low.

then increases to a max and finally drops (reservoir blow-down).

Negligible water production.

Artificial lift needed in early production life.



2) Gas Cap Drive :

With this mechanism, the gas cap applies enough pressure to the oil phase to

cause it to naturally flow through the well. The volume of the gas cap must

be comparable to the volume of oil so that the reservoir pressure is not

significantly reduced when the gas expands into the volume in the reservoir

left by the produced oil. Oil recovery efficiencies of 20 to 40 % of the OOIP

are typical.

As P drops due to production, gas cap expands down.

P support from gas cap depends on its size.

Slow decline in reservoir P.

Continuous rise in producing GOR.

Negligible water production.



Depending on size of gas cap and P support schemes, well can flow

naturally longer.

Water Drive:

When the water phase within a reservoir is linked with an aquifer, it can

provide pressure to drive the oil from the reservoir to the well head. In this

case, the water phase will replenish the reservoir volume left by the

produced oil. Typical oil recovery efficiencies are 35 to 75% of the OOIP.

Common types of aquifer: bottom and edge.

Reservoir P remains high (depends on aquifer strength).

Producing GOR is unchanged until reservoir P declines below bubble point.

Water production starts early.

Water disposal costs can be high.

Estimation of primary recovery

By: Guthrie and Greenberger

ER :Sw:

μ0:

k:

Φ:

h:

11403.00003488.0538.1log1355.0255569.0log2719.0 0 +−−−−= hS k E W R

φ µ



Secondary Recovery: Pressure is maintained by injecting a fluid into the

reservoir to replenish the fluid being produced.

1) Water Flooding :

This is the most common method of secondary recovery. Holes are

strategically drilled such that injected water drives oil toward the production

well. A specific geometry is typically used to drill the injection and well

holes.

Water is cheapest flooding agent.

The need to dispose of produced water.

Easy and safe to inject.

Proven technology.

Hole Patterns:



2) Gas Flooding :

Gas flooding is similar to water flooding except that the driving fluid is

natural gas rather than water.

Tertiary (Enhanced) Recovery: This method uses a chemical-based

technique to produce oil. These methods are often used in conjunction with

gas or water flooding.

A) Non-Thermal Methods :

1) Miscible Flooding:

A specific volume or slug of solvent is injected, which is followed by water

or gas flooding. The solvent acts to reduce the viscosity of the oil, which

reduces its resistance to flow. Typical solvents include C3H8, LPG (liquefied



petroleum gas: C2 to C4), or CO2. They combine with the oil phase to

become a single fluid phase.

2) Polymer Flooding:

Similar to water flooding where a slug of immiscible fluid is injected

followed by water flooding. The high viscosity injected fluid pushes the oil

phase through the reservoir resulting in higher recovery levels. Typical

polymers are xantham gum or hydrolyzed polyacrylamide. Polymers are

mixed with water to prepare the injection fluid.

3) Surfactant Flooding: This technique is very similar to water flooding.

The action of the surfactant can change the wetting properties of the

reservoir rock from oil-wetting to water-wetting. This frees the oil which is

attached to the rock resulting in higher oil recovery. Surfactants, in some

cases, will help to stabilize oil/water mixtures resulting in a lower viscosity

mixture. This further enhances recovery.



B) Thermal Methods : These methods are commonly used to produce

heavy oil.

1) Steam Injection :

Heat is supplied by steam to the heavy oil to reduce its viscosity. In the case

of steam injection, a single well is used to first inject the steam. After a finite

period of time, oil is produced from the same well. This steam stimulation

method, where injection and production are cycled, is known as “Huff and

Puff”.

2) Steam Flooding:

One well is used to inject steam and a second well is used to produce the oil.

3) Steam assisted gravity drainage (SAGD):



A steam chamber is formed in a horizontal injector well. Oil is produced

from a parallel horizontal well below the injector.

Flow is caused by gravity

Large oil recovery (50-60% of OOIP)

Low steam/oil ratio (SOR)

High productivity (0.25-0.5 m3/d/m)

m:

4) In-situ Combustion (Fire Flooding):

This in-situ (ie. within reservoir) method is initiated by causing combustion of the

petroleum underground. This is followed by the introduction of air to the reservoir tosustain combustion. The combustion process provides heat, steam and gases which

reduce the oil viscosity, resulting in higher production rates from the well.

Even with all the different recovery techniques, only about 30% of the total amount of

Western Canadian Original Oil in Place can be produced.

3- oil recovery methods

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