zet t litzer

Produced Water Cleaning and Re-InjectionExperience - Zero Discharge to Water

Michael Zettlitzer and Matthias Busch

Wietze E&P Laboratory

RWE Dea Germany

RWE Dea

4th International Conference on Produced Water Management

Stavanger, 31.01. to 01.02.2007


Stavanger, 31.01. to 01.02.2007

2

Outline

� Introduction

� Concept of Water Treatment and Injection

� Water Treatment in RWE Dea’s North German Oilfields

� Long-term Water Injection Profiles

� Conclusions


Stavanger, 31.01. to 01.02.2007

3

Introduction

� RWE Dea founded in 1899

� Water injection since at least 1956, produced water re-injection since at least 1962, including pH-reduction with HCl

� Injection always below frac pressure according to German mining law

Matrix injection

� High-quality water treatment

� Formation water disposal

– disposal into the sea prohibited offshore Germany

– salinity constraints onshore for surface disposal


Stavanger, 31.01. to 01.02.2007

4

Goals of water treatment

� Long-term injection at low and preferably constant wellhead pressure

� Constraints:

– residual oil

– solids (incl. Fe-compounds)

– bacteria

– scale formation

– oxygen (?)

– clay swelling (?)


Stavanger, 31.01. to 01.02.2007

5

Significance of oil removal

� 40 ppm crude in injection water ~ 40 Liter crude/1000 m³

h = 10 m

r = 1 m

Porosity = 20 %

Pore volume = 6.3 m³

157 days of injection ~ 6.3 m³ crude

1000 m³ water/d40 ppm crude


Stavanger, 31.01. to 01.02.2007

6

0.0

0.1

0.2

0.3

0.4

0.5

0 20 40 60 80 100

Water saturation [% pore volume]

Re

lati

ve

pe

rmeab

ilit

y

020406080100

Oil saturation [% pore volume]

0.6

0.7

0.8

0.9

1.0

SorSwi

Effect of oil saturation on relative permeability for water – Water-wet rock

ko

kw(extrapolated)

ko(extrapolated)

kw


Stavanger, 31.01. to 01.02.2007

7

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 20 40 60 80 100

Water saturation [% pore volume]

Re

lati

ve

pe

rmeab

ilit

y

020406080

Oil saturation [% pore volume]

Swi Sor

1.0

100

Effect of oil saturation on relative permeability for water – Oil-wet rock

kw(extrapolated)

ko

ko(extrapolated)

kw


Stavanger, 31.01. to 01.02.2007

8

Effect of solids on injectivity(taken from Pang/Sharma, „A Model for Predicting Injectivity

Decline in Water-Injection Wells“ SPEFE, Sept. 1997)

Internal Filter CakeExternal Filter Cake


Stavanger, 31.01. to 01.02.2007

9

Injectivity decline caused by solids(taken from Pang/Sharma, „A Model for Predicting Injectivity

Decline in Water-Injection Wells“ SPEFE, Sept. 1997)

1Type Curve 1

Invers

eo

f In

jecti

vit

y D

ecli

ne

Pore Volumes Injected

1

Type Curve 2

Invers

eo

f In

jecti

vit

y D

ecli

ne


1Type Curve 3

Invers

eo

f In

jecti

vit

y D

ecli

ne


1

Type Curve 4(S Shaped)

Invers

eo

f In

jecti

vit

y D

ecli

ne


external filter cake

internal filter cake

organic deposits

mixed effects


Stavanger, 31.01. to 01.02.2007

10

0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100 120

Injected volume [pore volumes]

Flo

w r

ate

/dif

f. p

ress

. [c

m³/

(h·b

ar)

]

Constantflow rate(without solids)

Flooding with 10 ppm solids

Core flood test with crude-free brine containing solids, kinit.= 470 md, 105 g/l TDS


Stavanger, 31.01. to 01.02.2007

11

Bacterial activity (SRB)

� Severe mainly

– in low-salinity brine

– at low to moderate temperature

� Regular injection of biocides

– intermittent use of different biocides

– batch treatments with higher concentrations

� Regular checks of total count of bacteria and sulphate reducing bacteria (SRB)

� Regular determination of hydrogen sulphide content in associated gas


Stavanger, 31.01. to 01.02.2007

12

Adverse effects caused by bacteria

� Plugging of filters

� Formation of slimes in injection wells

� Increased risk of pitting corrosion

� Formation of hydrogen sulphide

– HSE aspects

– Risk of FeS-formation

– Stabilisation of emulsions

– Potential removal of hydrogen sulphide from sales gas


Stavanger, 31.01. to 01.02.2007

13

Facilities considerations from a company view

� Low operating cost (chemical dosage, filter replacement, disposal of sludges, …)

� Fully automatic water treatment desired

� Space and weight limitations offshore

� Cost of facilities as low as possible but as high as necessary


Stavanger, 31.01. to 01.02.2007

14

crude

H2O

Demulsifier

ThreePhaseSeparator

Crude Separationand Storage

Pump SupplyTank

BoosterPump

Hydrocyclone

Walnut ShellFilter

Filter Bag(5 µm)

pH Adjustment

Biocide HCl

Injection Wells

Water treatment plant(German onshore and offshore field experience)

Gas

pH = 5

≈ 1 ppm crude

≈ 1 ppm solids

≈ 5 ppm crude

≈ 50 ppm crude

Production Wells

(Defoamer)


Stavanger, 31.01. to 01.02.2007

15

Improvement of water quality duringtreatment process

1. After FWKO

2. After Hydroclone

3. After Walnutshell-Filter

4. After Bagfilter at Wellhead


Stavanger, 31.01. to 01.02.2007

16

Produced Water Quality at Injection Wellhead vs. time

1

0.4

1 1

0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Res

idu

al o

il, so

lid

s [

mg

/l]

2

0.5

1

0.4

1

0.5

1

0.6

Feb 02 Mar 2002 Jul 03 Sep 04 Mai 05 Aug 05 Oct 06

Residual oil [mg/l] Solids [mg/l]


Stavanger, 31.01. to 01.02.2007

17

Crude / water properties andtreatment capacity(German onshore/offshore field experience continued)

System temperatureCrude viscosity (50 °C)Crude densityWater density

Treatment capacity

::::

50 °C20 to 200 mPa·s920 kg/m³ (~19 to 22 °API)1150 kg/m³

2.5 x 106 t/year (~ 51,800 bbl/d)2.0 x 106 t/year (~ 36,200 bbl/d)

- crude- produced water

::


Stavanger, 31.01. to 01.02.2007

18

0

500

1000

1500

2000

2500

3000

Nov-01

Feb-02M

ay-02Sep-02Dec-02

Mar-03

Jun-03

Oct-03

Jan-04

Apr-04

Aug-04Nov-04

Inje

cti

on

ra

te [

m³/

d]

0

25

50

75

100

125

150

We

llh

ea

dp

res

su

re[b

ar]

Formation: Dogger Sandstone Eff. Permeabilityw: 1178 md Perf. interval: 42 m

Injection profile H1 well

additional perforation

Injection rate

Wellheadpressure


Stavanger, 31.01. to 01.02.2007

19

crude

H2O

Demulsifier

ThreePhaseSeparator

Crude Separationand Storage

Pump SupplyTank

BoosterPump

GravelFilter

pH Adjustment

Biocide

HCl

Injection Wells

Water treatment plant (Germany onshore:

Hankensbuettel)

Gas

pH = 5

≈ 1 ppm crude≈ 1 ppm solids

< 20 ppm crude

Production Wells

AnnulusScale

Inhibition


Stavanger, 31.01. to 01.02.2007

20

Crude / water properties andtreatment capacity (Hankensbuettel)

System temperatureCrude viscosity (40 °C)Crude densityWater density

Treatment capacity

::::

40 °C8 to 20 mPa·s880 kg/m³ (~ 27-35 °API)1040 kg/m³

1.65 x 106 t/year (~ 30,000 bbl/d)formation water :

18,000 bbl/d600 bbl/d

Current water productionCurrent oil production

::


Stavanger, 31.01. to 01.02.2007

21

Injection profileHankensbuettel-Sued 3

Formation: Dogger Sandstone Permeability: 800 md Perf. interval: 22 m

0

100

200

300

400

500

600

Jul-86

Apr-89

Dec-91

Sep-94

Jun-97

Mar-00

Dec-02

Sep-05

Inje

cti

on

rate

[m

³/d

]

0

25

50

75

100

125

150

Wellh

ead

pre

ssu

re[b

ar]

Injection rate

Wellheadpressure


Stavanger, 31.01. to 01.02.2007

22

Produced water treatment and/or „polishing“Further field experience

� EPCON with and without flocculant

� Active charcoal

� OILSORB (organoclay)

462810141419BTEX03.03.2005

12:00

7859139266428644OIW03.03.2005

12:00

925295571113Alkanes03.03.2005

10:30

CFU+FU

CFU1+2

CFU+FU

CFU1+2

CFU1In

% removalConcentration (mg/l)Analytical parameter

Date & time


Stavanger, 31.01. to 01.02.2007

23

Conclusions

� Proper water treatment is a prerequisite for produced water re-injection into matrix.

� Water treatment includes

– removal of residual oil, solids (and oxygen)

– supervision of and countermeasures against bacteria

– addition of scale inhibitor, if necessary.

� pH-adjustment has a favourable effect on scale prevention and bacteria reduction in many field applications.

� After reservoir-adapted water treatment, continuous produced water re-injection with minor reductions in injectivity index is usually possible.

zet t litzer

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