Modelling of exposure. Further development of the DREAM …Concentrations/stressors in the sediment:...

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Modelling of exposure.Further development of the DREAM model.

Henrik Rye, SINTEF

DREAM Model

DDose-related RRisk and EEffects AAssessment MModel

• Originally: Doses on biota

• Then: Zero discharge policy

• Response: EIF for produced water

• Follow-up: EIF for drilling discharges

Two compartments involved:Water

columnBottom

sediments

Component specific EIFs

Produced Water

Drilling Operations

Model structure:

DREAM model

Dischargedata

Environmentaldata

Modelparameters/databases

Concentrationfields

Risk calculations

Pie charts and time plots

”Ocean currents used in the DREAM model. ”Snapshot”of the surface currentscalculated with the ECOM-3D model. Geographicalresolution 4 km.

Concept

2. Exposure Modeling (PEC)

1. Hazard identification

4. Risk assessment

3. Effect assessment (PNEC/thresholds)

Exposure Modeling (PEC)

PEC = Predicted Environmental Concentration.Concentrations in the recipient calculated with the DREAM model.Concentrations are calculated as a function of x, y, z and time.

PNEC = Predicted No Effect Concentration(Thresholds). The largest concentration of a product or a chemical expected tocause no measurable environmental effects. For offshore chemicals the PNEC value is determined from acute toxicity testing results values divided by an assessment factor.

EIF = Environment Impact Factor.A measure for potential environmental risk, that is, damage on marine organisms from a discharge to sea. EIF is defined as being proportional to the water volume where PEC/PNEC > 1 (or a joint risk probability > 5 %).

Unit EIF for water column: 100m x 100m x 10m (vol.)Unit EIF for the sediment: 100m x 100m (area)

Calculation of produced water concentrations with the DREAM model.

3D and time variable concentration field

Parameters

WindCurrentsBiodegradationEvaporationAdsorption to particulates

1°30'E

1°45'E

2°00'E

2°15'E

2°30'E

2°45'E

0'N 60°50'N

0'N 61°00'N

0'N 61°10'N

0'N 61°20'N

20 km1°30'E

1°30'E

1°45'E

2°00'E

2°15'E

2°30'E

2°45'E

0'N 60°50'N

0'N 61°00'N

0'N 61°10'N

0'N 61°20'N

5:00:00

Calculation of PEC Concentration field for discharge of produced water, calculated with the DREAM model.

The figure shows the sum of all compounds that contribute to potential risk to the environment:

• added chemicals• dispersed oil• PAH’s• phenols• heavy metals

1°30'E

1°45'E

2°00'E

2°15'E

2°30'E

2°45'E

0'N 60°50'N

0'N 61°00'N

0'N 61°10'N

0'N 61°20'N

20 km1°30'E

1°30'E

1°45'E

2°00'E

2°15'E

2°30'E

2°45'E

0'N 60°50'N

0'N 61°00'N

0'N 61°10'N

0'N 61°20'N

5:00:00

Risk Map Time Series

Calculation of EIF

Example of the calculated risk contributions for the concentration field. Red area/volume indicates the water volume where the concentrationsexceed thePNEC level, that is, PEC/PNEC > 1 (or a joint probability of potentialenvironmental damage > 5 %) for the red area/volume.

DischargeDischarge representedrepresented by by particlesparticles((LagrangianLagrangian approachapproach): ):

21°00'E

21°02'E

21°04'E

21°06'E

21°08'E

21°10'E

21°12'E

21°14'E

71°28'N

71°29'N

71°30'N

21°00'E

21°02'E

21°04'E

21°06'E

21°08'E

21°10'E

21°12'E

21°14'E

71°28'N

71°29'N

71°30'N

0:23:00

Deposition of particles on the sea floor:

1°42'45"E

1°43'00"E

1°43'15"E

1°43'30"E

1°43'45"E

1°44'00"E

58°29'30"N

58°29'40"N

58°29'50"N

58°30'00"N

1°42'45"E

1°43'00"E

1°43'15"E

1°43'30"E

1°43'45"E

1°44'00"E

58°29'30"N

58°29'40"N

58°29'50"N

58°30'00"N

15:12:00

DREAM: Near field plume, dissolving and non-dissolving chemicals, particle behavior:

Concentrations in the water column:

Chemical stress (toxicity):• Concentrations are calculated as for produced water

(dilution, transport and biodegradation, basically)• Near field plume mixing and descent are included

Particles stress: • Concentrations are calculated as for chemicals (no

biodegradation), except that fall-out of particles are included

• Near field plume mixing and descent are included• Chemicals with large partition coefficient (Pow ≥ 1000) are

”attached” to particles

Concentrations/stressors in thesediment:

Thickness of deposited layer (deposition of particle matter)

Oxygen content over the active bioturbation layer is calculated by means of a set of ”partial differential equations” for diffusion and consumption of pore water oxygen in the sediment

Average concentration of chemical compounds in added mud is calculated over the upper 3 cm of the sediment. Toxicity is basedon pore water concentrations deduced from ”equilibrium partitioning” between pore water and sediment concentrations

Average change of grain size (in terms of median grain sizechange) is calculated over the upper 3 cm of the sediment causedby particle deposition, mainly cuttings.

Bottom sediment fate calculations:

CC QCKzCD

+−⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

∂∂

=∂∂

Where ….

Use of the “diagenetic” equations:

Change of property

Diffusion term

Source/sink terms

Z is the vertical co-ordinatet is timeD is a diffusion coefficientC is the property consideredK and Q are reaction constants

Impact on water column:

Water columnSediment

Chemicals with Pow < 1000

Chemicals with Pow ≥ 1000

Heavy metals in barite

Particles in mud

Cuttings

Chemical stress

Particle stress

Discharge compound: Impact:

Impact on sediment: Water column

Sediment

Chemicals with Pow < 1000

Chemicals with Pow ≥ 1000

Heavy metals in barite

Particles in mud

Cuttings

Chemical stress

Grain size changeand burial

Discharge compound: Impact:

Oxygen depletion

Restitution time of the sediment:Toxicant concentrations, oxygen changes, grain size changes and burial all change over time

EIF sediment over time

0 2 4 6 8 10 12 14 16 18

time in months

burial

oxygen

toxicants

grainsize

integrated

Stressors (and corresponding risks) arecalculated for each grid cell:

1°40'E

1°45'E

8'N 58°28'N

0'N 58°30'N

2 km1°40'E

1°40'E

1°45'E

8'N 58°28'N

0'N 58°30'N

1:06:00

Drilling discharges included:

CuttingsParticles in mud (barite, bentonite, other …)Non-particle type chemicals in the mudDifferent types of discharges:• Discharges over “shaker” and batch discharges• Both WBM, SBM and OBM types of mud• Both exploration and production drilling• Top hole sections and deeper well sections

Example calculation:Discharges from an exploration drilling, using Water Based Mud (WBM):• Cuttings• Barite as weight material• Water soluble drilling fluid• Discharges go directly to the sea floor (upper drilling

sections) and from the drilling rig (lower drilling sections)

Deposition on the sea floor:

Risks for the sediment layer due to burial. (PNEC = 6.5 mm)9°52'00"E

9°52'00"E

9°52'20"E

9°52'40"E

9°53'00"E

9°53'20"E

9°53'40"E

66°41'00"N

66°41'10"N

66°41'20"N

66°41'30"N

10:00:00

Sediment Risk Map: Effective thickness

Publications: The use of the diagenetic equations to predict impact on sediment due to discharges of drill cuttings and mud.

Henrik Rye, Mark Reed, Ismail Durgut and May Kristin Ditlevsen, SINTEFPresented at the International Marine Environmental Modeling Seminar, Rio, 9 – 11 October 2006. Also submitted.

Development of a numerical model for calculation of exposure to toxic and non-toxic stressors in water column and sediment from drilling discharges.

Henrik Rye, Mark Reed, Tone Karin Frost (Statoil), Mathijs G.D. Smit(presently IRIS/Statoil), Ismail Durgut, Øistein Johansen and May Kristin Ditlevsen, SINTEF.Accepted for publication in the SETAC – IEAM Integrated EnvironmentalAssessment and Management Journal.

Acknowledgement

The oil companies financing the ERMS program are acknowledged for financial support as well as scientific input during the program.

Contractors in the program have been: Akvaplan-niva, Battelle, MUST, RF-Akvamiljø, SINTEF, TNO and University of Oslo, with SINTEF as the co-ordinator of the program.

Modelling of exposure. Further development of the DREAM …Concentrations/stressors in the sediment:...

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