a review on research areas in enhanced oil recovery_platform eor

7/28/2019 A Review on Research Areas in Enhanced Oil Recovery_platform EOR

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A Review on Research Areas in Enhanced oil recoveryAbstract

Enhanced oil recovery (EOR) spans a wide area of research to increase oil reserves and production. This

article is a general review on enhanced oil recovery (EOR) and research problems. Although the focus ofEOR is to inject fluid or fluids to reduce surface tension and increase the swept area, a multitude of

problems are faced when processes are to be applied to reservoirs which are usually complex in

structure and located in increasingly harsh areas. Using current EOR technology, extraction of oil

approaches 50% of the oil in place. More research is needed to find methods that are effective and

cheap.

Keywords: Enhanced oil recovery, drive mechanisms, surface tension, water injection, research

Background

Although claims that the Chinese and other

old civilisations had used some kind of fluidfrom the ground for fuel a long time ago, the

industry as is known today has its beginning in

Titusville, a small town in Pennsylvania, where

the first oil well was drilled in 1859 by the Drake

oil company. [1] At 69.5 feet, it was just as deep

as many water wells in some countries today.

Although in the sixties, the price of oil was in

the one or two USD range, in 1795-1800, crude

oil was quoted as USD16. [1] If the price were

to be compared with the price of gold, which

was about USD19 per ounce in 1800 [2], then

the price of oil today at more than USD100 per

barrel is undervalued since the price of gold was

USD914 in January 2008 . However, the aim of

this paper is not to predict the price of oil,

which has never followed predictions, but to

review enhanced oil recovery (EOR) and present

research opportunities either directly or

indirectly related to EOR processes.

Nevertheless in any industry, the economic

viability of a process is just as important as the

results it delivers. Therefore EOR discussion will

always be related to the price of oil.

The oil industry has always operated in

remote regions, and small towns often

mushroomed with the industry. Those were the

times of what is now termed 'easy oil' when

reservoirs are large, shallow and, if offshore,

shallow water. For example the Ghawar field in

Saudi Arabia found in 1948 is 230 km by 30 km

with reservoirs reaching 1300 ft thick. [3]

Nowadays, fields are found in even more

uninhabitable places such as Sakhalin where the

temperatures are below zero for most of theyear. Reservoirs off the Brazilian coast and east

coast of Sabah are found where water depths

are one to two km. It is therefore not surprising

that the cost of one well can be as high as

USD120 million. Enhanced oil recovery is an

attractive alternative to finding new sources

since at least 50% of oil still remains in the

ground after a reservoir has been produced.

The challenge is to produce at an economical

rate.

Oil Production and Drives

Before any process to produce oil or gas is

chosen, the characteristics of a reservoir must

be identified since production depends on the

type of reservoir. Reservoirs are porous media

mostly made of sandstone and carbonates. Oil

reservoirs containing only oil and water in the

pores exist when the reservoir pressure is

higher than the bubble point pressure and is

known as undersaturated reservoirs. When oil

is produced from this type of reservoir, the

reduced reservoir pressure causes liquid to

expand thereby causing the oil to be pushed to

the well. If the pressure drops below the bubble

point, gas that exists as dissolved gas in the oil

and water phases is liberated, providing more

force but at the same time will be removed with

the oil. This driving force or drive mechanism is

weak and usually less than 5% of oil can be


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recovered under expansion drive. Under water

drive, a higher recovery can be obtained since

the reservoir is supported by an aquifer. The

presence of gas cap in saturated reservoirs

results in gas cap drive which gives a higher

recovery than expansion drive. It increases the

expulsive drive during primary recovery by

expanding when the reservoir pressure drops.

When a reservoir has an aquifer and a gas cap,

the recovery will also be higher [Fig. 1]. Primary

recovery is production occurring as a natural

process. However, primary recovery alone

produces less than 30% of oil for most

reservoirs, even with many types of drives.

Dake [4] and Craft et al [5] are excellent

references on reservoir behaviour.

EOR, IOR or augmented recovery

Water injection was used initially to

maintain or increase reservoir pressure after

primary production. Areal sweep is improved

when a few wells, in a pattern, are used for

injection to push oil from many directions

towards the production well (Fig 2).This process

is called water flooding. The problem with

water as a displacing fluid is the lower viscosity

when compared with most oils. Water being

more mobile then tends to bypass the oil.

Polymer can be added to the water, giving riseto polymer flooding. Gas injection is another

method to increase the pressure and is usually

used in reservoirs with gas cap. Under primary

production, the gas cap expands pushing the oil

towards the production well. Injection of gas

into the gas cap helps to maintain the drive. A

reservoir is abandoned when the rate of oil

produced becomes uneconomical and the

amounts of gas and water produced are high

compared with oil flow rate.

Enhanced Oil recovery, EOR vs. Improved

Oil recovery, IOR

Secondary recovery was the term applied to

waterflooding, hot water flooding and steam

flooding. Any other injection process after

secondary recovery was called tertiary

recovery. However, it is now a standard practice

for oil companies to institute pressure

maintenance by either water or gas injection

from the beginning of production.

Consequently, the terms secondary and tertiary

often became difficult to differentiate. EOR

now is generally accepted as the processes that

involve injection of fluid or fluids. IOR is any

process that increases production and reserves

(commercially recoverable deposits) which

means it includes among others EOR, fracturing

reservoir rocks to improve flow, cleaning up

wells to increase production rate, drilling more

wells, improving seismic process etc. The term

augmented recovery is sometimes encountered

but it had not taken off in the industry. More

detailed description of EOR processes can be

found in van Poollen [6] and Latil [7].

Rock-fluid attraction and fluid-fluid

attraction

Oil and gas reservoirs are porous media

which contain two or three fluids. The way the

reservoirs were formed resulted in the presence

of water in the pores, known as connate water

or interstitial water in all reservoirs. When a

reservoir is found, the water is assumed to be

present but immobile. The attraction between

fluid and rock surface determines the

wettability of the rocks. If water covers the rocksurface while the oil phase is enclosed or

separated by water from the rock surface, then

the system is water wet. This type of rocks

allows oil to flow easier than water.

Conversely, an oil wet reservoir will attract oil

to its surface instead of flowing to the well.

When fluid is injected to expel oil, the amount

of oil recovered is related to the driving force

as described earlier and also the attraction

between the oil /rock surface and other fluids

i.e. surface tension. Consequently, a propertyof the injected fluid is to reduce surface tension

such as surfactant or to induce miscibility with

oil such as liquid CO2, resulting in zero surface

tension. Other properties include no reaction

with the rocks or minerals in the rocks, ability to

withstand high temperature and pressure and,

as usual, cheap.


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Other important factors in EOR

Other factors that are needed to be

considered in EOR are many. For example, in

Saudi Arabia, Iran and Iraq, the reservoirs can

be 1000 ft thick of clean sand with high

permeability while Malaysian reservoirs areusually in the 30 to 80 feet thick, often

containing shale, and permeabilities usually

ranging from 20-100 mD. Since a major aim of

EOR is to improve sweep the presence of shale

or other barriers such as faults posed a

problem. Dulang field [8] for example is split up

into many compartments; therefore, any

injection strategy must address the issue. The

presence of aquifer increases drive but it may

also cause water to flood wells prematurely.

The advantage of Malaysian crudes is the lowviscosity which is usually less than one

centipoise at reservoir condition. Most oils are

sweet without corrosive sulphur or sulphur

compounds. [9] Many oil reservoirs in Sudan

and Venezuela are heavy oil with viscosities in

500-1000 cP or higher.

Flow behaviour

Unlike geologists who deal with types of

rocks, reservoir structure, deposition and other

similar disciplines, petroleum engineers(especially reservoir engineers) deal mostly with

the fluids. However, some aspects of geology

are important in oil and gas production. Since

reservoirs are porous media, two other

properties are important, namely porosity and

permeability. Permeability studies are a well

established area but with more complex

multiphase flow in EOR, research in subsurface

flow has to deal with more complex systems.

Operational considerations

Sea water is usually used in water injection

for offshore reservoirs. If surfactants are added

to the injection water, then the type of

surfactants used must be resistant to high

pressure and temperature and salinity. Fresh

water can be considered but for reservoirs

containing clay, fresh water may cause the clay

to swell. Some reservoirs may have a high

percentage of heavy alkanes (paraffin-based oil)

or asphalts (asphalt- based oil). Injected fluids

must not cause precipitation that will block flow

paths. Malaysian reservoirs are all offshore

except for one and questions concerning size of

platform, location and space for additional

facilities such as pumps and compressors are

important since large volumes of injected fluids

require large pumping and compressing

machines. The oil produced may also consist of

a high percentage of emulsion of crude oil

water and chemicals injected, consequently,

demulsifiers are needed. Past and current

research papers available in the E-library of the

Society of Petroleum Engineers (SPE) can be

accessed via the online database of IRC. E-

library contains peer reviewed publishedpapers, papers from proceedings and any paper

submitted to SPE.

Research areas

Investigations into improving sweep and

reducing surface tension have been reported

since the 70s but as usual more problems are

encountered in trying to solve an existing

problem, resulting in EOR research to span a

wide range of problem solving. For example,

use of polymer started as a step to improvesweep, but since reservoirs have high pressures

and temperatures and contain brine, research

then focused on formulation of polymers that

can withstand high pressure, temperature and

salinity. Often a polymer does not satisfy all

requirements such as xanthan can withstand

high pressure and temperature, salinity and

shear degradation, but it is prone to

biodegradation. Polyacrylamides, on the other

hand, do not biodegrade but are degraded by

high shearing which occurs at high velocity.Reservoirs also cover large areas in the order of

hundreds of acres. As such, reservoirs are

heterogeneous because rock properties differ

from one point to another. Depending on the

deposition history, the differences may be

significant with large variations in permeability,

porosity and presence of fractures, faults and


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shale beds. Heterogeneity makes it difficult to

model and also to improve sweep.

Reports on gas flooding such as CO2,

hydrocarbon gas and flue gas are substantial in

literature. In 2005, the oil production by CO2-

EOR came to 237,000 BPD in the US. [10] Whilemany problems of waterflooding are not

overcome by gas flooding, the environmental

effects of these gases are of great concern in

many instances. As at January 2001, Malaysia's

gas reserves stood at 97.6 trillion cubic feet

(tcf)[11]. Carbon dioxide that is present in

several major gas fields may be used for

injection. Reinjection of dissolved gas produced

from oil production is necessary in countries

where flaring is not allowed and transportation

of gas to the markets is not possible. Flue gases

are hot and therefore for high viscosity oil, the

reduction in viscosity is an advantage which

water does not have.

One of the ways to improve displacement

efficiencies is to use more than one injection

fluid such as water alternating gas (WAG). As

the name suggests, a slug of water is injected

followed by a slug of gas and the two slugs are

then pushed by water. Although many field

studies on WAG have given positive results,

some reservoirs are not suitable for WAG. [12]Variations of injection methods were

investigated e.g. water and gas are injected

simultaneously or variations of the liquid phase

and the gas phase give rise to other WAG

methods, sometimes referred to as hybrid WAG

or modified WAG. Water may be replaced by

foam and the gas may be air, nitrogen, natural

gas or CO2.

The oil industry spans a range of activities

that require expertise and knowledge in many

disciplines. Research related to EOR is similarlydiverse and, very often, challenging. Apart from

improving sweep and reducing surface tension,

other keys areas that are being and need to be

investigated are:

1) prediction of recovery

Before a process can be implemented, it has

to be modelled in order to predict the amount

of oil recovered. Simulation and modelling of

reservoirs under EOR process is a highly

investigated area. It is related to high speed

computing, rock and fluid properties studies,

economic studies and software development.

2) mechanisms of displacement

In order to formulate a chemical and design

a suitable process, studies are necessary to find

the mechanisms of fluid flow through porous

media at high pressure and temperature and

how the injected fluid displaces fluid in the

pores at micro-scale. Knowing the mechanisms

will also assist in predicting recovery.

3) tracing displacement

The position of the displacement front when

fluid is injected into the reservoir is essential toestimate sweep and to ensure that fluid is not

flowing into areas that do not have oil.

Radioactive tracers are usually used for

monitoring displacement front. Development

of better and more accurate tracers is being

pursued by many companies, such as using

nanofluid.

4) equipment design and optimisation

Almost all of Malaysian reservoirs are

offshore and any EOR projects must be

designed for offshore environment.

Consideration of platform space, size and cost

will affect the economic viability of the project.

Meters, sensors, compressors, pumps and other

equipment have to be redesigned for

multiphase fluids which are commonly found in

EOR processes.

5) injectivity and water quality

Fluids may cause clogging of the pores after

some years of injection. Some chemicals may be

corrosive and in the case of tracers, it may beradioactive. Injection water has to be treated if

salt in sea water is too concentrated. Surfactant

may not perform with high salinity water. In

other words, Injection fluid is an area of

research by itself.

6) Oilfield chemicals


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While EOR improves recovery, the addition

of chemicals can cause formation of emulsion

near the wellbore areas. Methods to break up

emulsion cheaply and effectively to recover

produced oil are a potential research area.

Injected chemicals may also be more corrosive

and anticorrosion chemicals will be needed. The

problem of excessive water production can be

dealt with the addition of water control

chemicals. A challenge will be to produce non-

toxic multifunctional chemicals.

Trends in EOR research

Investigations on EOR have always been in

tandem with the price of oil as illustrated by the

frenetic pace in the seventies in the aftermath

of oil embargoes. When the price of oil shot up

from USD 1-2 per barrel in the sixties to USD40

in the early eighties, oil companies began to

invest seriously in EOR. But when the price

dropped down to below USD20 for much of the

eighties and nineties, R&D in EOR dropped

especially profit-oriented international oil

companies. EOR became important as tax

breaks for companies operating in the USA.

Nevertheless, national oil companies such as

the Chinese and Norwegian oil companies

continued to report EOR investigations. While

guesses on the movement of oil prices arereported regularly, long term forecasts have

seldom been accurate. The USD100+ per barrel

price today hopefully will be a lesson to the oil

industry to continue R&D spending even when

oil price is low.

Given the increasing consumption in Asia,

new commercially viable reservoirs are neededto support the growing demand. Saleri [13]

estimated that 50 years of the world's need can

be sustained by a 10% increase in recovery.

Even though renewable biofuels are gaining

popularity, its production is not without

problems. With today's EOR technologies,

recovery is still at most 50%. New and more

effective EOR technologies are needed to

extract the remaining oil. The industry in

general has taken up the challenge with reports

on groundbreaking application of advanced

telemetry and ultrasonic [14-15].

Conclusions

The main concerns in EOR are to reduce

surface tension and increase sweep. However,

many other problems exist and a wide range of

expertise from other science and engineering

discipline is needed. R&D in improving recovery

is no longer a side effect of high oil price but an

absolute necessity to fuel the world's energy

needs.


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References

[1] History of oil region

http://www.oilheritage.com/history/history.ht

m

[2] Historical Gold Prices/Price 1800-2008

http://www.finfacts.ie/Private/curency/goldma

rketprice.htm

[3] T.M. Okasha, J.J. Funk, and H.N. Al-Rashidi,

Fifty Years of Wettability Measurements in the

Arab-D Carbonate Reservoir, SPE Middle East

Oil and Gas Show and Conference, Kingdom of

Bahrain, 11-14 March 2007

[4] L.P. Dake , The practice of reservoirengineering (revised edition) Elsevier,

Amsterdam,2001

[5] B. C. Craft, M. Hawkins, and Ronald E. Terry,

Applied Petroleum Reservoir Engineering (2nd

Edition), Prentice-Hall, New York, 1991

[6] H.K. Van Poollen, Fundamentals of

enhanced oil recovery , PennWell, Tulsa, 1980

[7] L. Marcel Enhanced oil recovery, Technip,

Paris, 1980

[8] Mohamed Zaini B. Md Noor, Kasim B.Selamat, Abdullah B. Kasim, ,Sharifudin

Salahudin, Revitalizing a Mature Sand-Prone

Field by Installing Enhanced Gravel-Pack

Completions - A Case Study, SPE European

Formation Damage Conference, The Hague,

Netherlands, 13-14 May 2003

[9] M.I. Omar and A.C. Todd, Development of

New Modified Black Oil Correlations forMalaysian Crudes, SPE Asia Pacific Oil and Gas

Conference, Singapore, 8-10 February 1993

[10] Oil and gas Journal, Vl 105.15, April 17

2006 p.40.

[11] GasMalaysia website,

http://www.gasmalaysia.com/about_gas/natur

al_gas_in_malaysia.asp

[12] R. Henson, A. Todd, P. Corbett, Geologically

Based Screening Criteria for Improved Oil

Recovery, SPE/DOE Improved Oil RecoverySymposium, 13-17 April 2002, Tulsa, Oklahoma

2002.

[13]N.G. Saleri , The next trillion: anticipating

and enabling game-changing recoveries,

Technology Tomorrow, JPT , April 2006,58:4

[14] SPE Updates Home, Cableless Telemetry

System achieves world first in reservoir

monitoring, November 1, 2006 in Reservoir

(RDD) [14]

[15] SPE Updates Home, Oil-in-watermonitoring gets ultrasonic boost, December 5,

2006 in HSE, Production (PO)
http://www.oilheritage.com/history/history.htmhttp://www.oilheritage.com/history/history.htmhttp://www.oilheritage.com/history/history.htmhttp://www.finfacts.ie/Private/curency/goldmarketprice.htmhttp://www.finfacts.ie/Private/curency/goldmarketprice.htmhttp://www.gasmalaysia.com/about_gas/natural_gas_in_malaysia.asphttp://www.gasmalaysia.com/about_gas/natural_gas_in_malaysia.asphttp://www.gasmalaysia.com/about_gas/natural_gas_in_malaysia.asphttp://www.gasmalaysia.com/about_gas/natural_gas_in_malaysia.asphttp://www.gasmalaysia.com/about_gas/natural_gas_in_malaysia.asphttp://www.finfacts.ie/Private/curency/goldmarketprice.htmhttp://www.finfacts.ie/Private/curency/goldmarketprice.htmhttp://www.oilheritage.com/history/history.htmhttp://www.oilheritage.com/history/history.htmhttp://www.oilheritage.com/history/history.htm


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water zone (aquifer)

gas zone ( gas cap)

Oil zone (formation)

Sea bed

depth

impermeable

rocks

gas capexpands down

water level moves

up to replace oil

impermeablerocks

To platform

Figure 1: A Schematic of a Reservoir with Gas Cap and Aquifer

Figure 2: Waterflooded Reservoir, Five- spot pattern

injectionwell

production

well

swept zone

unswept zone

a review on research areas in enhanced oil recovery_platform eor

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