enhanced oil recovery.docxs

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Enhanced Oil Recovery

EOR Introduction

EORis a method that use to recover the oil content when the general oil production method no

longer efficient

Oil recovery methods

1. Primary recovery:a. When the natural reservoir energy has been depleted, it becomes necessary to

augment the natural energy with an external source.

2. Secondary recoverya. When water injection is the secondary recovery process, the process is referred to

as waterflooding. The main purpose of either a natural gas or a water injection

process is to repressurize the reservoir and then to maintain the reservoir at a highpressure. Hence the term pressure maintenanceis sometimes used to describe asecondary recovery process.

b. When gas is used as the pressure maintenance agent, it is usually injected into azone of free gas (i.e., a gas cap) to maximize recovery by gravity drainage. Theinjected gas is usually natural gas produced from the reservoir in question. This,

of course, defers the sale of that gas until the secondary operation is completed

and the gas can be recovered by depletion.


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c. No compositional or temperature changes take place in the reservoir exceptpressure and displacement

d. Its suitable for light oil, low viscosity oil and low pressure reservoirs

3.

Tertiary recovery or EORa. The term enhanced oil recovery (EOR) was introduced and has become popular inreferring to, in general, any recovery process that enhances the recovery of oil

beyond what primary and secondary production would normally be expected to

yield.b. Appropriate selection and design are important.c. Sometimes Tertiary Recovery Methods called EOR Methods. But this does not

mean that EOR Methods have to be applied after Secondary Recovery. In some

cases, EOR Methods could be applied after Primary or even at discovery.

Typical Recovery Factors:

Natural or Primary Methods:o Heavy oil 05 - 15%o Light oil:

solution gas drive 10 - 25% water drive, gas cap 20 - 40% gravity drainage 30 - 45%

Secondary Methodso Water flood 20 - 45%o Immiscible Gas flood 15 - 40%

Tertiary or EOR Methodso Laboratory tests 70 - 90%o Field applications 45 - 75%


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EOR Technical Concepts:

EOR is the recovery method technic to improving the performance of existing oil fields ,

also to access reserves that were previously unattainable due to geology or expense.

EOR is chiefly concerned with affecting the mobility of the oil , primarily by injecting fluids

either a natural gas or water. These processes can result in 30-60 % or more of the reservoirs

original oil being extracted, compared to just 20-40% using primary or secondary recovery

methods.

The overall recovery efficiency Eof any fluid displacement process is given by the product of

the volumetric (macroscopic), displacement efficiency Ev, and the microscopic displacement

efficiency Ed.

The macroscopic (volumetric) displacement efficiencyis a measure of how well the displacing

fluid has come in contact with the oil-bearing parts of the reservoir.

The macroscopic (volumetric) displacement efficiency is made upof two other terms,theareal, Esand vertical Ei,Sweep efficiencies:Ev = Es . Ei

When using water, consideration of the mobility of the fluids is an important factor whendetermining the area and vertical sweep efficiencies. This would help to determine the mobility

ratio.

The microscopic displacement efficiency is a measure of how well the displacing fluid

mobilizes the residual oil once the fluid has come in contact with the oil.

If M is less than one (M1), the displacing fluid has greater mobility than the displaced

fluid. Also the position of the water injection and the flooding patterns would go a long way todetermining the recovery patterns.

The oil recovery is to direct the injection wells around the production well.As the mobility

ratio increases, the sweep efficiency decreases. Once a channel of water exists between theinjector and the producer, then little additional oil would be recovered.

Permeability varies in a vertically direction can create an irregular vertical fluid front and

this is as a result of the differing permeability and the mobility ratio.

Displacement efficiency is the fraction of oil that is swept from unit volume of reservoir upon

injection. This depends on the mobility ratio, the wettability of the rock and the pore geometry.


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The wettability is determined by the absorption of the grains to oil over water.

Enhanced oil recovery processes can be classified into four categories:1. Miscible flooding processes:

o Miscible displacement includes:- Single contact and Multiple-contact miscible processes.

2. Chemical flooding processes Polymer, Micellarpolymer, and Alkaline flooding.

3. Thermal flooding processes Hot water, steam cycling, steam drive, and In-situ combustion.

4. Microbial flooding processesIn general, thermal processes are applicable in reservoirs containing heavy crude oils,

whereas chemical and miscible displacement processes are used in reservoirs containing

light crude oils.

Microbial processes use microorganisms to assist in oil recovery.

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