(NITROGEN INJECTION FOR RESERVOIR ENHANCED OIL RECOVERY.)

Emerging Applications in Cryogenics

The life of an oil well goes through three distinct phases

Primary recovery Secondary recovery Tertiary recovery

Primary recovery

Secondary recovery

Tertiary recovery

Enhanced Oil Recovery (EOR) they can substantially improve

extraction efficiency Much of these oils would be

recovered by various EOR methods which involve the injection of a fluid, or series of fluids

Three major EOR methods

Thermal injection Chemical injection Gas injection

Thermal injection

Chemical injection

Gas injection

Natural gas -limited availability -increasing value of natural gas Inert nitrogen-less expensive substitutes-provides a higher reservoir displacement

volume per standard volume of nitrogen-provides the lowest volume requirement for

pressure maintenance. -non corrosive.

Cryogenic processes

can produce 99.999% pure nitrogen Cryogenic processes can produce

very pure end products the most cost-effective choice Are more energy efficient

Non-cryogenic processes

employ membranes or adsorbents (PSA/VPSA) to remove the unwanted components of air

They produce nitrogen which is typically 95 to 99.5% oxygen-free

Non-cryogenic plants are less energy efficient than cryogenic plants

Non-cryogenic plants are relatively quick and easy to start up

The cost of nitrogen is depending upon the pressures, quantities and location

Because of increasing cost of natural gas, nitrogen injection is becoming more popular and attractive

In 1983-over 500 million cubic feet per day was being injected into thirty oil or gas reservoir

In 1985-becomes 600 million cubic feet per dayIn 1990-this number grew to 800 million cubic

feet per day in forty oil gas reservoir

EOR METHODS

With varying degrees of success, for the recovery of light and heavy oils.

Two major types of EOR methodThermal methods -supply heat to the reservoir, and vaporize

some of the oil. -the major mechanisms involve a large

reduction in viscosity, and hence mobility ratio.

-best suited for heavy oils and tar sands.

Non-thermal methods -are best suited for light oils.-applicable to moderately viscous oils,

which are not suitable for thermal methods

Objective:Lowering the interfacial tension and

improving the mobility ratio

There are two types of non-thermal EOR gas injection

miscible gas injection -the gas is injected at or above

minimum miscibility pressure immiscible gas injection-flooding by the gas is injected below

MMP

Comparison of nitrogen with other gas injectant

Hydrocarbon gas-require less treatment than other

gases-a corrosion problem-increasing natural gas priceMajor factor limiting CO2 injection-availability-the cost to build pipelines to carry

Advantage of carbon dioxide flooding

-miscibility can be attained at low pressures

-useful over a wider range of crude oils than hydrocarbon

Disadvantage of using CO2-availability of carbon dioxide resources-transportation cost-poor sweep and gravity segregation

and corrosion

Nitrogen-most available and cheapest universal

gas-no pipeline are required-no incremental cost and required for

corrosion control

Nitrogen application for EOR In 1970- it was first introduced In 1970 to 1977-almot all of the

nitrogen for the EOR projects was taken from onsite inert gas plants

In 1980-most of the EOR projects was supplied by onsite air separation plants

Offshore Cantarell oilfield in the gulf of Mexico

The largest oilfield in Mexico and one of the largest in the world

PEMEX heavy oilfield Have high productivity due to

presence of a gigantic natural gas cap

Rank second fastest producing oil field in the world behind Ghawar field in Saudi Arabia

Cantarell oilfield

Factor affecting the cost of nitrogen

The cost of energy necessary to produce and compress nitrogen

The air compressors for generating nitrogen can be operated with motors, gas turbines or gas diesel engines

Membrane produced nitrogen can be used in plants where natural gas is unavailable

Advantage of a membrane plant-compactness-simplicity-reliabilityResulting is low capital cost at smaller

capacitiesAnd moderate purities

CONCLUDING REMARKS: Recent advances in technology and the current

economic climate have resulted an increased interest in EOR, especially [N.sub.2] gas injection in the petroleum reservoirs for improved recovery. While the use of Thermal and Chemical EOR methods are decreasing, Gas injection method in EOR is increasing. Because cryogenic air separation plants can be constructed at or

near the field and no pipelines are required, nitrogen gas injection is rapidly increasing both in onshore and offshore application for reservoir enhanced oil recovery. The inert and non-corrosive nature makes it a preferred choice over other gases (i.e. [CO2.sub.2], Natural gas etc.). The long term supply security of nitrogen also makes preferable and reliable than other unsecured gases.

Nitrogen injection is believed to yield high recovery of the lightest hydrocarbon components. Nitrogen use in the oil field continues to grow as new opportunities are recognized, the demand being mainly satisfied with large scale cryogenic nitrogen plants. Perhaps the greatest task of the cryogenic industry is to develop more cost effective nitrogen producing plants and means for its effective injection to the reservoirs. In the mean time the Petroleum Industry needs to study the long term effect of Nitrogen on the reservoirs, including determining any side effects the nitrogen injection may have on the sustainability of the enhanced recovery. One important factor may be the study of the effect of nitrogen purity, as well as consideration for injection of a mixture of gases vs. pure nitrogen.