Produced Water Management Lessons from the Ula & Valhall fields

Eugenia Marinou-Dahle, BP Norge AS, Norway / Senergy Ltd, UKTorben Lund Skovhus, DTI Oil & Gas, DenmarkJanuary 25, 2012 TEKNA Produced Water Management 2012, Stavanger

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Presentation outline

• Ula: topsides scale management

− Unexpected scale findings in the water injection pump

− Commingled produced water/sea water

− Impact of plant condition/cleanliness on effectiveness of scale inhibitor

• Valhall: PW microbiology

− Problems with microbes in oilfield systems

− State-of-the-art analytical methods for detection of microbes

− Re-cap on Valhall shut-down in 2009 due to MIC

− Increased focus on Microbiological Monitoring and mitigation at Valhall

• Closing remarks and questions

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The Ula field

• Located in the southern Norwegian section of the N.Sea

− Tambar (unmanned platform) ties back to Ula

− Talisman’s Blane field also ties back; on production since late 2007

• Field producing since 1986

• 3-bridge connected steel platforms for production, drilling, accommodation

• Sandstone reservoir, supported by means of SW, PW and gas injection

• In terms of scaling risk:

− Barium sulphate (BaSO4)

− Calcium carbonate (CaCO3)

− Zinc/lead sulphide (ZnS and PbS)

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Ula Process Overview

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Essentially…

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Solids at water injection pump

• Reports from the asset of significant solids accumulation in the water

injection pump

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The identity of the solids

• First thoughts were it must be sand...

• A large water producing well was shut-in (ca. 25000 bbls of water/day)

• Quite a bit of scale inhibitor injected around the plant in the PW stream:

- 200 ppm on Tambar, as part of a field trial to inhibit sulphide scales

• Lab testing showed that 25 ppm of the chemical would be

sufficient to protect against BaSO4 and CaCO3 scales

- 10-20 ppm U/S the DHSV of a number of producing wells

• In addition to scale inhibitor carryover from SISQ treatments,

minimum inhibitor concentration typically 2-3 ppm

- 50 ppm U/S the PW degasser

• Scale inhibitor injected in the PW well in excess of what would be required

on the basis of scaling tendency for the plant

• Analysis showed solids to consist of primarily barite, sand and iron

oxides (rust)

• “Cauliflower”-type structures seen under the microscope,

characteristic of poor in situ crystallisation

• Sand grains coated with oil

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Analysis results

• Sand findings in PW coolers earlier on the same year

• Also thermography showed degasser to have significant solids deposition

• During shutdown around 15 m3 of sand recovered

• Desanding unit present but had never been operational

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Where is the scale inhibitor?

• Separate findings from internal visual inspection of the PW degassing

vessel

• 5 areas of localised corrosion found on metal surface; max depth of

attack at 55% of wall thickness

• Attributed to microbiologically-influenced corrosion (accompanied

by unusually high H2S readings, 140 ppmv)

• Normally degasser temperature at 100 oC, but because of so much

sand down to 50 oC ideal for bacterial activity

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Further impact of solids accumulation

• Impact of unplanned changes to plant operation not fully appreciated

• Having a large water producing well shut-in, the PW:SW injected ratio

changed

• No effective mechanism in place to capture changes in scaling risk

− Presence of significant amounts of solids in system

− Depleting the scale inhibitor from the produced water

− Surface-active chemicals, adsorption on sand, scale etc, particles

• By the time PW and SW commingled, insufficient chemical present in

the water to inhibit BaSO4 formation

• Stress tests now done regularly to make sure adjustments are prompt

• System cleanliness is key in maintaining a successful topsides scale

management strategy

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Lessons learned

Valhall bacteria management

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The Valhall field

• Located in the Norwegian section of the North Sea

• Field on stream since 1982

• 5-bridge connected steel platforms, 2 unmanned flank platforms

− Recently completed PH platform

• Chalk reservoir, supported by means of SW injection

• Main production chemistry issues:

− Barium sulphate scale

− Bacteria management

• 2009 shutdown related to MIC findings

• Importance of improving understanding

and control of parameters that promote

undesirable bacterial growth

Source: Petroleum Microbiology

Photos: DTI Oil & Gas

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Want control of…

To avoid:

- Product spoilage

- Safety issues

- Loss of integrity

- Production down time

- Loss of reserves

MIC Souring

Fouling Separation

MO

• Flow rates

• Water content

• O2

• CO2

• H2S

• Cl2

• Sulfate

• Solids

• Nutrients

• Temperature

• pH

• Microbes!

Factors affecting biofilms, bacterial growth, MIC and corrosivity

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MPN - Most Probable Number(NACE Standard TM0194)

Amann et al. (1995)

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xxx

MPN

FISH

DAPI

qPCR

Microbial sample

Active

Inactive

Dead

K. Sørensen, J. Larsen and T. L. Skovhus

In Applied Microbiology and Molecular

Biology in Oil Field Systems (Springer, 2010)

Enumeration of microorganisms – what is included?

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Origin of Troublesome Microbes Causing Souring and MIC

Archaeoglobus

Sulfate ReducingBacteria (SRB)

Sulfate ReducingArchaea (SRA)

Methanogens

FermentativeSulfide Producing

Prokaryotes

Net Reactions:

Sulfate Reduction (blue) 4Fe0 + 3H2S + SO42- + 2H

+ 4FeS + 4H2O

Methane Production (red) 4Fe0 + 4H2S + CO2 4FeS + 2H2O + CH4

S2-

Fe0

Fe2+

SO42-

H2S

e-CH4

CO2

H+

H2

FeS

SRP

Methanogens

Larsen et al. NACE Corrosion 2010, Paper No. 10252

MIC Model: Activity of SRP (SRB & SRA) and Methanogens

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MIC at Valhall discovered during spring 2009

• Spring 2009

• Down time: 10 weeks

• Root cause: MIC

• 44 anomalies identified

- 23 MIC Related

- 21 Non-MIC-related

• Several spools replaced

or repaired

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Valhall Microbial Monitoring Database based on MMM

• WI sampling points // PW sampling points // Pipeline sampling

points

• Focus on Water // Solids // Coupons

• Analytical Technologies applied today:

− MPN (as a reference to historic data)

− qPCR (Bacteria/Archaea, SRA/SRB, Methanogens, NUB)

− X-Ray Analysis of corrosion coupons

− Total Weight Loss of corrosion coupons [NACE standard]

− Pitting Corrosion Analysis via surface scanning of coupons

− Soxhlet Distillation of solid samples to analyse for FeSx

Microbiology in the Valhall Produced Water System (WATER)

Molecular Microbiology Monitoring data point to the following conclusions (2011):

• The corrosion mechanism in the PW system is mainly MIC (High levels of SRB +

Methanogens)

• The highest numbers of total cells (DAPI) and summarized total Bacteria and

Archaea (qPCR) were found in the sample collected D/S of the degassing and

slurryfying drum. It is recommended to focus on especially this part of the PW

system in relation to MIC mitigation.

• Total cell numbers and numbers of summarized Bacteria and Archaea at the

different locations in the PW system are in the high end when compared to empiric

data collected by DTI from other studies on PW systems in the North Sea.

Moreover, the number of the specific MIC-related subgroups SRB and

methanogens are considered to be relatively high. It is recommended to keep

focus on how biocide programs and mitigation strategies can be optimized

in terms of inhibiting the abundance of both SRB and methanogens.

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Microbiology in the Valhall Produced Water System (COUPONS)

• In the sample material retrieved from the coupon in the oil export

pipeline SRB represented the vast majority of the total Bacteria.

The percentages of SRB out of the total number of Bacteria in samples

from the coupon collected from the produced water and the stud

collected from D/S X-370 were 5% and 33%, respectively.

• In all samples, the total number of Archaea could be ascribed to

Methanogens.

• Although the corrosion rates were found to be low in the PW system,

iron oxides or iron carbonates and possibly iron sulfides were present in

the samples retrieved from the coupons in the PW system. Scale

products such as BaSO4 and SrSO4 were also present.

• Samples from coupons collected from the PW system (produced water

and oil export pipeline) contained relatively high amounts of barium (Ba)

and strontium (Sr) suggesting that the main part of sulfur in the PW

system was bound in scales (BaSO4, SrSO4).

• It is recommended to keep focus on how biocide programs and

mitigation strategies can be optimized in terms of inhibiting the

abundance of both SRB and methanogens.

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What has changed since 2009?

• Increased focus on microbiology as a threat towards asset and reservoir integrity

• Q-meetings on microbiology with data presentation and follow-up on actions

• Changed location of chemical injection points in the PW system

• Focus on good house keeping of vessels/tanks (frequent inspection and

cleaning)

• Focus on Well Integrity and how the Reservoir can be affected by

biomass/particles/bugs

• Focus on biocide dosing

• Focus on potential MIC in pipelines: Wax samples now analysed with qPCR

• Focus on how to interpret / act upon microbiology numbers is on-going

• Keep the focus on above points – as microbes rarely sleep!

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Interdisciplinary collaboration

• Key improvement: bacterial management is a team effort:

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Goal to get closer to MIC Risk Assessment (MICRA) Approach

Risk Assessment

MICRA

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Closing remarks

• Two assets with separate set of conditions and challenges

• Despite differences, some common elements in these learnings

• Plant cleanliness is decisive factor in minimising solids deposition:

− Affect chemical effectiveness (scale inhibitors, biocides, etc)

− Allow bacteria to grow under deposits

− Impact operation of processing equipment

• Management of change an essential part in adapting to new operating

envelopes

− Requires vigilant monitoring of data and trends

− Requires the best quality data that can be obtained

• Team-wide perspective necessary to have full picture of issues/mitigations

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Acknowledgements

We would like to thank the following for their support in preparing this

presentation:

• Christian Rott (BP)

• Christina Markoff (BP)

• Svein Gunnar Hellevik (BP)

• Reidun Vold (BP)

• Michelle Lison Rebsdorf (DTI)

• Frode Bjoernaas (Force Technology)

• And TEKNA for allowing us to share our experiences

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Questions