tertiary recovery methods

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Tertiary recovery

So our well has been drilled and production has started.

We have produced using the wells natural momentum, pressure andtemperature.Our reservoir driveshave helped produce via dissolved gas, gas cap and waterdrive.

We then use our primary methods.

We will artificially help our reservoir via pumps and gas lift.

We then used our secondary methods.

We will inject our wells with gas and water.

Once reservoir drives, primary and secondary methods have been exhausted,we have our final option which will be our tertiary methods.

These methods do not have to be used last or even when all other methodshave finished therefore, they will be called enhanced oil recovery (EOR).EOR methods can increase productivity up to 75% of the oil in place, so cantake about 5-20% itself.

But this extra % comes with a much higher price tag then the previous methods

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These methods unlike our previous do not just try and push the hydrocarbonsthrough the well but they try to alter the oil properties.

So they do not only provide pressure but also try to increase flow.

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Tertiary recovery types

There are three main types of enhanced oil recovery including:

Chemical

Miscible Displacement

Thermal

As already said, these methods are quite expensive so a lot of research has togo in to this to ensure money is not wasted

Chemical recovery

Chemical recovery is in form of chemical injection or chemical flooding

Chemical injection

In this method, chemicals are injected into the reservoir to reduce capillarypressure to allow oil to flow more easily.

In fluids, capillary pressure is the pressure difference betweentwo immiscible fluids

Pcapillary = Pnon-wetting phase Pwetting phase

In an oil-water reservoir, water is the wet phase and in gas-oil reservoirs, oil is

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In chemical injection method, chemicals (surfactants) are pumped in to othereservoir to lower surface tension to allow the reservoir to be more free flowing.

Polymers can also be injected to increase the water flooding/water injection. Inthis case the injection process will be as below:

Reservoir fluid is pumped inThen the surfactant which has caused the oil to form droplets in the water isinjected

Finally, polymers are injected.

Chemical injection works best in sandstone as clay and limestone can absorbthe surfactants, so injection wells must be drilled in the correct location and inthe ideal beds

Chemical injection can increase recovery by up to 40%.

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Miscible displacement

Miscible displacement is pumping liquid petroleum, gas, CO2 or Nitrogen topush against the reservoir fluid into the wellbore.

The gas is expanded and pushed through the reservoir or mixed/dissolved in

the oil to decrease viscosity and allow better flow.

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CO2 is either pumped in from a CO2 well, bought in liquefied or in storagecontainers in a gas state.

Some of this gas can then be re-injected into the well once separated from theoil.

Air cannot be used instead of CO2.

CO2injection is the most common injection method as CO2is a by product fromthe industry and it is very cheap.

Nearly 50% of EOR in the USA is CO2injection.

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Thermal recovery

Thermal recovery is a method of injecting heat into reservoir.

The heat allows the oil to flow more freely by reducing viscosity.

Thermal recovery is very widely used especially on very viscous oil.

Thermal recovery can be split in to three main groups:

Hot injections including steam flood and cycle steam injection

Hot water flooding

Combustion

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Hot fluid injection

Steam injection to reduce viscosity or a cycle which starts off by injecting steaminto the reservoir, then shutting the well for a few days to allow the steam tospread out evenly and then produce the oil out,

This process can be done over and over again.

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Combustion

In this method, gas and air are injected into the reservoir and then a device islowered in to ignite a fire.

Heat is generated by the heavy oil burning and vaporization of the lighter oil,gas and reservoir water forming steam and hot water.The fire moves and the burning front pushes the gases, steam and hot waterwhich will then reduce oil viscosity and displace oil toward production wells.

Hot water flooding

Also known as hot water injection, this works in the same way as steaminjection in that it reduces the viscosity of the oil, however, it is not as successfulas steam because it is not as hot

Thermal recovery can recover between 25-70% of oil in place.

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Microbial recovery

In this method, biology is used to break down the hydrocarbon to make it easierto recover or enhance the micro-organisms already down there.

Microbial technology can cause a chain of reactions which release gas andtherefore increase pressure.

This method breaks down the heavy oil into lighter oil i.e. reduces viscosity

It also produces natural surfactants

This type of recovery is not used too much as it is still a new and expensivetechnology and prices are very high

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tertiary recovery methods

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