introduction to produced water treatment

“Introduction to produced water treatment”

Nature Technology Solution

Introduction to produced water treatment 2

TABLE OF CONTENTS

TABLE OF CONTENTS .......................................................................................................2

1 INTRODUCTION................................................................................................................3

1.1 THE ORIGIN OF PRODUCED WATER .................................................................................4 1.2 THE PRODUCED WATER COMPOSITION............................................................................4 1.3 PRODUCED WATER IMPACT ON THE ENVIRONMENT ........................................................5 1.4 PRODUCED WATER MANAGEMENT AND INTERNATIONAL AGREEMENTS.........................6

2 CONVENTIONAL TECHNOLOGIES FOR WATER TREATMENT ........................7

2.1 GRAVITY BASED SEPARATION - FLOTATION....................................................................7 2.3 SEPARATION TECHNIQUES BASED ON FILTRATION ..........................................................8 2.2 CYCLONIC SEPARATION METHODS ..................................................................................8 2.4 NEW CHALLENGES IN HANDLING PRODUCED WATER .....................................................9

3 PRODUCED WATER MANAGEMENT – MINIMIZING PRODUCTION ................9

3.1 SUBSEA SEPARATION .......................................................................................................9 3.2 DOWNHOLE TECHNOLOGY.............................................................................................10 3.3 WATER SHUT-OFF METHODS ........................................................................................11 3.4 SIDETRACKING...............................................................................................................11

4 RECENT PRODUCED WATER TREATMENT DEVELOPMENTS ........................11

4.1 SEPARATION BY FILTRATION .........................................................................................12 4.2 WATER TREATMENT BY EXTRACTION ...........................................................................12 4.3 ENHANCED OIL SEPARATION BY MEANS OF COALESCENCE ..........................................12 4.4 METHODS BASED ON ADSORPTION ................................................................................13

5 THE NATURE TECHNOLOGY SOLUTIONS.............................................................13

5.1 THE NATURE PROCESS FOR PRODUCED WATER TREATMENT ........................................14 5.2 THE NATURE PROCESS – WHY ADVANTAGEOUS? .........................................................14 5.3 NATURE EXPERIENCE WITH PRODUCED WATER ............................................................15

www.naturetechsolution.com



1 INTRODUCTION

Large quantities of water are produced along with hydrocarbons in oil and gas fields all over

the world. Water production quantities continue to increase as the oil and gas fields reach

maturity. Produced water comes as a bi-product of petroleum production and requires to be

managed efficiently.

A great deal of scientific research has been carried out to determine the consequences of

long-term exposure of produced water on the environment. Some of this research has given

alarming results. It is reported that some of the toxic components in produced water may

cause irreversible damage to the surrounding environment. Because of this potential risk

very considerable efforts are being expended by the oil companies operating in the North-

East Atlantic into developing new techniques to better manage produced water. Remaining

oil in treated and discharged produced water is the principal source for hydrocarbon

discharges from the petroleum sector in the North East Atlantic. The produced water and

hydrocarbon production profile for a typical oilfield is illustrated in Figure 1.

Production Profile for a Typical Oil Field

0

10000

20000

30000

40000

50000

60000

1 3 5 7 9 11 13 15 17 19Oil field operating time [yr]

Pro

duct

ion

volu

me

[m3]

Water prod Oil prod

Figure 1 - Typical production profile for an oilfield in the North East Atlantic

The figure demonstrates the significant change in the water/oil ratio when the oilfield reach

maturity, and water by far becomes the biggest fraction of the production.



1.1 The Origin of Produced Water

Water is very often found together with petroleum in the reservoirs where the water, as a

consequence of higher density than oil, lays in vast layers below the hydrocarbons in the

porous reservoir media. This water, which occurs naturally in the reservoir, is commonly

known as formation water. After oil and gas production has been occurring for a time, the

formation water will reach the production wells and water production will initiate. The well

water-cuts will normally increase throughout the whole oil and gas field lifetime, such that

when the oil production from the field is shut down, the oil content can be as low as a couple

of percent with ninety eight percent water.

To maintain the hydraulic pressure in the petroleum reservoir, which is reduced as soon as

production is started, seawater is commonly pumped into the reservoir water layer below the

hydrocarbons (Figure 2).

Figure 2 - Re-injection of separated water from an offshore installation (Ill: Courtesy of BJ Services)

This pressure maintenance due to water injection causes high extensions in recoverable

hydrocarbons but simultaneously contributes to increased water production.

1.2 The Produced Water Composition

The compositions of formation water originally in place vary significantly in characteristics

between the different reservoirs. As field production is initiated, produced water composition



from the production wells may be continuously transformed due to injection of seawater, re-

injection of produced water, reservoir stimulation, bacterial activity, introduction of

production chemicals and more.

Produced water is basically a mixture of formation water and injected water but also contains

smaller quantities of:

o Dissolved organics (included hydrocarbons)

o Traces of heavy metals

o Dissolved minerals

o Suspended oil (non-polar)

o Solids (sand, silt)

o Production chemicals

Dissolved hydrocarbons are found naturally in formation water and can be both toxic and

bio-accumulative. Such water-soluble components, which in produced water are mainly

BTEX (benzene, toluene, ethyl benzene and xylene), polyaromatic hydrocarbons (PAH) and

alkylphenols, are together with heavy metals considered the most harmful contaminants in

produced water.

1.3 Produced Water Impact on the Environment

The most common practice in use in the North East Atlantic for management of produced

water is treatment in gravity based separation equipment and discharge to sea. For a long

time the only governmental regulation for produced water discharges in this petroleum

sector has been concerning concentration of non-polar oil in water (OIW). Little attention

has been given to dissolved organics.

There is now wide agreement within the petroleum industry, governments and scientists that

focus should now be put on dissolved organic components, heavy metals and production



chemicals. The oil in water content shall be as low as possible and the industry shall make

use of best available technology (BAT).

Figure 3 presents history and forecast for the water production on the Norwegian continental

shelf (Norwegian Petroleum Department).

Figure 3 – Forecast of water production on the Norwegian continental shelf (Ill: Courtesy of NPD)

The quantity of produced water in Figure 3 that is not discharged to sea is re-injected into the

reservoir or to another formation suitable for disposal.

The long-term effects of such contaminants on the environment are not fully documented

and understood. Some research programmes are completed and several new studies are

underway to map possible consequences for living organisms. Dilution aspects and

movement of species in the oceans makes definite conclusions hard to make. There are so

many variable that the modelling is extremely complex. Results from recent research show

however that fish exposed to alkyl phenols have disturbances in both organs and fertility.

These results are serious and have triggered further investigations.

1.4 Produced Water Management and International Agreements

A common legislation for produced water discharges to sea from offshore installations has

been 40 mg/l (ppm) OIW. The Oslo Paris Convention (OSPAR) has agreed that the



maximum discharge limit is reduced to 30 ppm OIW for the petroleum companies operating

in the North-East Atlantic and that the overall oil discharges in produced water are reduced

by 15% from 1999 levels. In Norway, the oil operators have agreed to implement a policy of

zero environmental harmful discharges within 2005. There shall be no harmful discharges

from any new installation, and existing installations shall continuously work against a

practically achievable zero environmental discharge.

In Norway the Pollution Control Authority (SFT) together with The Norwegian Oil

Industries Associations (OLF) have developed a produced water management tool, the

Environmental Impact Factor (EIF), to meet the zero-discharge strategy. The EIF is a model

for optimising the activities taken to reduce the most harmful components in produced water

for each offshore installation. Contrary to the existing OIW legislation in place today, the

EIF considers all the contaminants in the produced water.

2 CONVENTIONAL TECHNOLOGIES FOR WATER TREATMENT

During petroleum production, vast volumes of liquids have to be managed each day.

Deferred production causes high economical losses and therefore continuous operations is

always strived for. The capacity, reliability and performance of the produced water

management system is often critical for continuous oil production particularly in mature oil

field where the water production can greatly exceed the oil production. The water production

system needs to be designed to receive continuously increasing quantities of water as oil

production continues.

2.1 Gravity Based Separation - Flotation

Produced water treatment has traditionally taken place in gravity based equipment, where the

difference in the density of the two liquids to be separated is utilized. Such separation is

commonly performed in huge horizontal tanks at different pressures. Flotation of the lighter

components (oil) can be enhanced by means of finely distributed gas bubbles going out of



solution (pressure reduction) and parallel plate packages installed diagonally in the

separation vessel.

2.3 Separation Techniques Based on Filtration

A well known technique for separating non soluble components is by filtration. Several

principles for handling produced water have been considered including microfiltration

membranes and media filters. Such treatment technologies are potentially advantageous

because of very good separation degrees can be achieved. However microfiltrations has

found very limited practical application because of cost and poor operability, very high

energy consumption and degradation of the filters elements with use.

2.2 Cyclonic Separation Methods

The continuous demand for higher treatment capacity in very limited

space has resulted in improved treatment methods. The most commonly

used technology in offshore production since around 1990 is the static

hydro cyclone that utilizes available pressure for enhanced speed in

gravity separation. The advantages for this equipment type are high

reliability (no moving parts), low maintenance, requires very little space,

gives good separation effect and high capacity. The figure to the right

[Ill: Deister] shows the water (red) going out in the underflow, while oil

(blue) is forced into the middle and led out in the cyclone overflow.

Another application for separation of oil and water is high-effect

centrifuges. Because the device is motor driven it is often used for low-

pressure water streams. This kind of equipment has high energy and

higher maintenance requirements.



2.4 New Challenges in Handling Produced Water

Gravity based separation techniques have together with static hydro cyclones been the most

extensive method for treating produced water. Other types of equipment have also been

utilized, mostly in special cases with difficult operating treatment characteristics or small

volumes, though to a less extent. Even if produced water systems more or less have

functioned as intended with respect to the design specifications, the future has brought new

considerations regarding what is sufficient treatment.

A good alternative for disposal of produced water would be to send it back into the reservoir

where it came from as part of the pressure support, or to another suitable formation.

Unfortunately this requires extensive treatment prior to re- injection and due to high costs it

is an economically viable alternative mainly for fields with large water production. Re-

injection could also cause degradation of the reservoir production quality and productivity.

3 PRODUCED WATER MANAGEMENT – MINIMIZING PRODUCTION

Based on the serious uncertainties connected to the long-term environmental effects from

produced water discharges and in order to be preventive of possible environmental damage

legislation is now being tightened. On the Norwegian continental shelf in the North-East

Atlantic, the government and the oil companies have agreed to zero harmful discharge in

produced water by the end of 2005. The petroleum industries operating in the area are

investigating several ways of meeting the new requirements.

3.1 Subsea Separation

In order to reduce the necessary processing capacity in the petroleum treatment plant, it

could be advantageous to separate as much as possible of the water fraction from the well

stream at an early point in production sequence. By placing first stage water/oil separation



process equipment on the sea bottom it will not be necessary to transport all the water to the

platform processing facility. The Platform facility is greatly simplified with significant

weight reduction. The water separated at the seabed can be injected into a shallower well

formation. Figure 4 presents a graphic illustration of the Troll Pilot subsea installation in the

Norwegian continental shelf.

Figure 4 - The Troll pilot subsea unit (Courtesy of Norsk Hydro (Ill: Arctic))

3.2 Downhole Technology

A further step in reducing the water-cut from the production stream is to locate oil/water

separation process equipment down in the production wells. This technique has been

investigated extensively the last years. The produced water is separated from the oil and gas.

It is then pressurised by downhole hydraulic pumps and re- injected into the reservoir. The

technology is still only in pilot design. It is still very expensive. The complexity increases

with reservoir depth. Vertical Downhole Oil/Water Separation (DOWS) systems have been

used to some extent worldwide (< 40) in the last six years. A new more complex horizontal

separation system is under pilot testing pilot testing in Norway.



3.3 Water Shut-Off Methods

In order to reduce the water flow to the well production zones, there are two traditional

methods utilized. During mechanical shut-off, cement or mechanical devices blocks the

water pathway by plugging the perforated production section. The chemical shut-off includes

injection of polymers into the reservoir that increases the water viscosity, forms a stable gel

and thereby restricts the water flow ability.

3.4 Sidetracking

An increase in water production for example as a consequence of water break-through in the

production zone could be stopped by pulling the well internals, closing down the perforated

zone (mechanical shut-down) and drilling to a new section. Figure 5 illustrates several

sidetrack wells drilled off from the old original.

Figure 5 - Illustration of sidetrack wells (Ill: Courtesy BP Exploration Inc.)

4 RECENT PRODUCED WATER TREATMENT DEVELOPMENTS

As there is still no economically practically method for disposal of all the produced water via

re-injection or various recycle methods, a range of innovative wastewater technologies have

been developed or are under development. The different technologies all have their operating



characteristics that make them suitable for only certain produced waters or operating

characteristics. There is a major focus on new technique to remove dissolved components

from produced water.

4.1 Separation by Filtration

Utilization of membranes has been considered for treatment of oily wastewater to reduce

dissolved components. The new systems include the use of nano filtration membranes.

However, although the filtration method has very good separation effect, the high costs and

complexity of these treatment techniques means that applications are only experimental.

4.2 Water Treatment by Extraction

Another technology that has been widely tested on both pilot and full scale on the

Norwegian continental shelf is rooted in the solvent properties of supercritical liquids

(CTour). The process utilizes liquid condensate (NGL) from the gas scrubbers and injects it

into the produced water upstream of the hydro cyclones. The dispersed and dissolved

hydrocarbons, which have higher solubility in the condensate, go into the condensate phase

and are separated in the hydro cyclones. This equipment has undergone extensive pilot

testing and its field tests are imminent. The process is very sensitive to the available

condensate quality.

4.3 Enhanced Oil Separation by Means of Coalescence

Several modern produced water treatment methods are based on the coalescing of dispersed

oil droplets, often prior to cyclonic separation. The devices are installed upstream of the

cyclonic vessels to increase oil droplet diameters which will result in better separation

degree in the hydro cyclones. The process of coalescence could be accelerated by different

means.



One method is to install a special fibre media in the pipelining or the hydro cyclone vessels

that attracts oil droplets and promotes coalescence into larger aggregates. These systems

have no effect on removing dissolved hydrocarbons, but are simple and easily retrofitted.

The fibre media is sensitive to fouling and any abrasive elements (sand) in the water.

Other processes include combinations of chemical injection (coagulation/flocculation) and

mechanical agitation in specially built vessels.

Compact flotation units are hybrid cyclone/degassers that could replace standard degasser

equipment.

4.4 Methods Based on Adsorption

Adsorption has proven a successful area in maintaining compliance with produced water

discharges. Unfortunately most processes involve filters and therefore are restricted in

volume or require advanced regeneration processes which could be both energy demanding

and expensive. The adsorption techniques include activated carbon filters with regeneration

by wet air oxidation and oil-adsorbing media canisters based on resins, polymer and clay

technologies.

The Nature Technology Solution treatment of produced water is also based on adsorption

and will be further described in the following chapter (5).

5 THE NATURE TECHNOLOGY SOLUTIONS

Nature Technology Solution (Nature) provides state of the art treatment and management of

most kinds of contaminated wastewater. Nature is delivering services and equipment for

efficient handling of polluted wastewater from onshore, shipping and the offshore industry

(Figure 6).



Figure 6 - The Shell Draugen Platform in the Norwegian Sea (Photo Courtesy of Shell)

Nature offers a range of physical, chemical and biological treatment methods for industrial

wastewater.

5.1 The Nature Process for Produced Water Treatment

The Nature process for treatment of produced water is based on addition of patented

coagulant/flocculant in existing or partially modified water systems. The agent is injected

into the produced water upstream a static mixer or various process equipment (pumps,

valves etc.) to provide sufficient in-mixing. The agent separates dispersed and dissolved

hydrocarbons and is floated and skimmed off in a flotation vessel downstream the in-mixing

point.

5.2 The Nature Process – Why Advantageous?



The Nature process combines coalescence and adsorption and significantly reduces dissolved

and dispersed hydrocarbons from produced water to less than 5 ppm. The Nature process

utilizes documented non-hazardous agents for professional treatment of oily produced water.

Implementation of new process equipment is usually not needed. The Nature technology

provides excellent water handling at low capital and operating costs. Rapid processing time

promotes small, less heavy and more compact treatment facilities.

5.3 Nature Experience with Produced Water

The Nature technology has achieved good results in separating both polar (dissolved) and

non-polar (OIW) hydrocarbons from several produced water types from the Norwegian

continental shelf.

Produced water from the Shell operated Draugen installation was treated with Nature

coagulant in the spring 2002. The OIW concentration was 93 ppm before treatment with

Nature coagulant. Three different doses were used during fixed in-mixing and flocculation

time of 150 and 120 seconds respectively. Draugen salinity was measured to < 3.4 %.

Produced water temperature was 50 °C. Figure 7 presents reduction of OIW following

treatment with three different doses Nature coagulant CF – 200 (dry solid).

Reduction of OiW vs. Dosing of Nature Coagulant (fixed in-mixing time(150 s), fixed flocculation time(120 s))

93

4914

0

20

40

60

80

100

0 ppm 20 ppm 40 ppm 60 ppm

Dosing of Nature coagulant CF-200 (dry solid)

Oil

in w

ater

[pp

m]

OIW

Figure 7 - Reduction of OIW concentration for the Shell Draugen installation

The Nature technology also achieved good results in OIW reduction in produced water from

the Statoil Statfjord C installation in the North Sea, winter/spring 2002 (Figure 8).



Figure 8 - The Statfjord C installation in the North Sea (Photo Courtesy of Statoil)

The results are presented in Figure 9. In-mixing and flocculation time was fixed to 30

seconds each. The produced water temperature and salinity was 80 °C and 3,6 %

respectively. The OIW concentration in the Statfjord C produced water was 19 ppm before

treatment with Nature coagulant. Three different doses of Nature coagulant CF – 200 (dry

solid) were added to the water.

Reduction in OiW Concentration vs. Dosing (fixed in-mixing and flocculation time, 30 sec. each)

11

19

5 4

0

5

10

15

20

B.T. 5 ppm 10 ppm 15 ppm

Dosing of coagulant CF-200 (dry solid)

Oil

in w

ater

[ppm

]

OIW

Figure 9 - Reduction of OIW concentration for the Statoil Statfjord C installation



Nature has also performed tests on produced water from Kuwait to discover the potential of

the Nature technology on separation of hydrocarbons. The water samples were collected

from the disposal well 501 and the disposal pit.

The produced water trials with the samples from Kuwait revealed that the Nature coagulant

effectively reduced the hydrocarbon concentration in water from the disposal well 501

(Figure 10). The blind test showed an OIW concentration of 18 ppm.

REDUCTION OF OIL IN WATER CONCENTRATION VS. DOSING OF FLOCCULANT - DISPOSAL WELL

18

6

3 3 2

0

5

10

15

20

BT 20 40 60 80

Dosage of Nature CF - 200 [ppm]

Oil

in w

ater

co

nce

ntr

atio

n [

pp

m]

Figure 10 - Reduction of OIW concentration from disposal well water (Kuwait)

Four tests were performed on disposal well water at 50 °C. In-mixing and flocculation

periods were set to 60 and 120 seconds respectively.

The water sample from the disposal pit had such low oil in water concentration (2 ppm) that

further testing was cancelled. The salinity in the Kuwait produced water was quite high,

measured to 10 % salt concentration.

introduction to produced water treatment

Documents

norwegian

produced water

produced water

nature technology

handling produced

produced water

produced water

produced water